Alesis HR-16 User manual

HR-16B
Drum Machine
Drum Machine
SERVICE MANUAL
© 1987 Alesis

HR-16/HR16B Service Manual 1.00 i 03/31/06
HR-16/HR-16B Drum Machines
Service Manual
V1.00
7/27/95

HR-16/HR16B Service Manual 1.00 ii 03/31/06
PREFACE
This document is intended to assist the service technician in the operation, maintenance and repair of the HR-
16 and HR-16B Drum Machines. Together with the HR-16/B Reference Manual, this document provides a
complete description of the functionality and serviceability of these machines. Any comments or suggestions
you may have pertaining to the document are welcome and encouraged.
READ THIS!
In addition to any purchase price that Alesis may charge as consideration for Alesis selling
or otherwise transferring this service manual (“Manual”) to you, if you are not a service and
repair facility (“Service Center”) authorized by Alesis in writing to be an authorized Service
Center, Alesis sells or transfers the Manual to you on the following terms and conditions:
Only Service Centers authorized by Alesis in writing are authorized to perform service and
repairs covered by an Alesis warranty (if any), and transfer of the Manual to you does not
authorize you to be an authorized Service Center. Therefore, if you perform, or if the
Manual is used to perform, any service or repairs on any Alesis product or part
thereof, any and all warranties of Alesis as to that product and any service contract
with Alesis for that product shall be voided and shall no longer apply for such
product, even if your services or repairs were done in accordance with the Manual.
All service or repairs done by you or with reference to the Manual shall be solely your
responsibility, and Alesis shall have no liability for any such repairs or service work. All
such service or repairs are performed at the sole risk of the person performing the
service or repairs. You agree that all such work will be performed in a competent,
professional and safe manner at all times and to indemnify and fully hold Alesis and its
successors and assigns harmless in the event of any failure to so perform.
Your purchase of the Manual shall be for your own ultimate use and shall not be for
purposes of resale or other transfer.
As the owner of the copyright to the Manual, Alesis does not give you the right to copy the
Manual, and you agree not to copy the Manual without the written authorization of Alesis.
Alesis has no obligation to provide to you any correction of, or supplement to, the Manual,
or any new or superseding version thereof.
Alesis shall have the right to refuse to sell or otherwise transfer repair parts or materials to
you in its sole discretion. You shall not use, sell or otherwise transfer spare or replacement
parts supplied by Alesis to you (i) to repair or be used in products manufactured for or by
third parties or (ii) to any third parties for any purpose.
You shall not make any warranties or guarantees with respect to the products of Alesis or
the use thereof on behalf of Alesis or in your own name.
The foregoing describes the entire understanding related to sale or transfer of the Manual
to you, and no other terms shall apply unless in a writing signed by an authorized
representative of Alesis.

HR-16/HR16B Service Manual 1.00 iii 03/31/06
WARNINGS
TO REDUCE THE RISK OF ELECTRIC SHOCK OR FIRE, DO NOT EXPOSE THIS PRODUCT
TO WATER OR MOISTURE.
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
The arrowhead symbol on a lightning flash inside a triangle is intended to alert the user to the
presence of un-insulated "dangerous voltage" within the enclosed product which may be of
sufficient magnitude to constitute a risk of electric shock to persons.
The exclamation point inside a triangle is intended to alert the user to the presence of
important operating, maintenance and servicing instructions in the literature which
accompanies the product.
CAUTION
Danger of explosion if battery is incorrectly replaced.
Replace only with the same type or equivalent type
recommended by the equipment manufacturer.
Battery Manufacturer: Tadiran
Type: TL-5101
Rating 3.6V
REPAIR BY ANY PERSON OR ENTITY OTHER THAN AN AUTHORIZED ALESIS SERVICE
CENTER WILL VOID THE ALESIS WARRANTY.
PROVISION OF THIS MANUAL DOES NOT AUTHORIZE THE RECIPIENT TO COMPETE
WITH ANY ALESIS DISTRIBUTOR OR AUTHORIZED REPAIR SERVICE CENTER IN THE
PROVISION OF REPAIR SERVICES OR TO BE OR MAKE REPAIRS AS AN AUTHORIZED
SERVICE CENTER.
ALL REPAIRS DONE BY ANY ENTITY OTHER THAN AN AUTHORIZED ALESIS SERVICE
CENTER SHALL BE SOLELY THE RESPONSIBILITY OF THAT ENTITY, AND ALESIS SHALL
HAVE NO LIABILITY TO THAT ENTITY OR TO ANY OTHER PARTY FOR ANY REPAIRS BY
THAT ENTITY.

HR-16/HR16B Service Manual 1.00 iv 03/31/06
SAFETY SUGGESTIONS
Carefully read the applicable items of the operating instructions and these safety suggestions before using this
product. Use extra care to follow the warnings written on the product itself and in the operating instructions.
Keep the operating instructions and safety suggestions for reference in the future.
1. Power Source. The product should only be connected to a power supply which is described either in the operating instructions or
in markings on the product.
2. Power Cord Protection. AC power supply cords should be placed such that no one is likely to step on the cords and such that
nothing will be placed on or against them.
3. Grounding the Plug. This product has a 3-wire grounding type of plug (a plug with a grounding pin) for safety purposes. This
plug can only be used in a grounding power outlet. If the plug does not insert into the outlet you are using, the outlet probably is
not a grounding type of power outlet. Contact your electrician to replace the obsolete outlet with a grounding type of outlet instead
of defeating the safety feature of the grounding type of plug.
4. Periods of Non-use. If the product is not used for any significant period of time, the product's AC power supply cord should be
unplugged from the AC outlet.
5. Foreign Objects and Liquids. Take care not to allow liquids to spill or objects to fall into any openings of the product.
6. Water or Moisture. The product should not be used near any water or in moisture.
7. Heat. Do not place the product near heat sources such as stoves, heat registers, radiators or other heat producing equipment.
8. Ventilation. When installing the product, make sure that the product has adequate ventilation. Improperly ventilating the product
may cause overheating, which may damage the product.
9. Mounting. The product should only be used with a rack which the manufacturer recommends. The combination of the product
and rack should be moved carefully. Quick movements, excessive force or uneven surfaces may overturn the combination which
may damage the product and rack combination.
10. Cleaning. The product should only be cleaned as the manufacturer recommends.
11. Service. The user should only attempt the limited service or upkeep specifically described in the operating instructions for the
user. For any other service required, the product should be taken to an authorized service center as described in the operating
instructions.
12. Damage to the Product. Qualified service personnel should service the unit in certain situations including without limitation
when: a. Liquid has spilled or objects have fallen into the product,
b. The product is exposed to water or excessive moisture,
c. The AC power supply plug or cord is damaged,
d. The product shows an inappropriate change in performance or does not operate normally, or
e. The enclosure of the product has been damaged.

HR-16/HR16B Service Manual 1.00 v 03/31/06
General Troubleshooting
While this manual assumes that the reader has a fundamental understanding of electronics and basic
troubleshooting techniques, a review of some of the techniques used by our staff may help.
1. Visual Inspection - A short visual inspection of the unit under test will often yield results without the need
of complex signal analysis (burnt, or loose components are a dead giveaway).
2. Self Test - Alesis products that utilize microprocessor control contain built in test software which
exercises many of the units' primary circuit functions. Self test should always be done following any
repair to ensure basic functionality.
3. Environmental Testing - Applying heat and cold (heat gun/freeze spray) will often reveal thermally
intermittent components (Clock crystals, I.C.s, and capacitors are particularly prone to this type of
failure).
4. Burn in Testing - Leaving a unit running overnight often reveals intermittent failures such as capacitors
that begin to leak excess current after a significant amount of time.
5. Cable Checks - Wiggling cables can reveal intermittent failures such as loose cables or poorly soldered
headers. Remember to check power supply cables as well.
6. Flexing the PC Board - Poor solder joints and broken traces can often be found by pressing the PC Board
in various places.
7. Tapping Componants - Somtimes tapping on a component (particularly crystals) will cause it to fail.
8. Power Down/up - Turning the unit off and back on rapidly several times may reveal odd reset and/or
power supply failures.
9. Reset Threshold - A Variac (variable transformer) can be used to check reset threshold levels. This can be
particularly useful in helping customers with low line problems.
10. Compressors - Using a compressor/limiter is often helpful when attempting to solve low level noise
problems, as well as assisting with DAC adjustments.
11. Sweep Tests - Sweep generators are very useful in checking the frequency response envelopes of anti-
aliasing filters.
12. Piggybacking - Piggybacking I.C.s is particularly useful when troubleshooting large sections of logic.
This is especially true when working with older units.

HR-16/HR16B Service Manual 1.00 vi 03/31/06
TABLE OF CONTENTS
PREFACE.....................................................................................................ii
READ THIS! .................................................................................................ii
WARNINGS..................................................................................................iii
SAFETY SUGGESTIONS............................................................................iv
General Troubleshooting..............................................................................v
1.0 General Description ...............................................................................1
1.1 Main PC Board Revisions .................................................1
2.0 Power Supply.........................................................................................1
2.1 Battery Backup..................................................................2
2.2 PUP Circuit........................................................................2
3.0 The 8031................................................................................................3
3.1 Reset.................................................................................3
3.2 Memory Mapped I/O..........................................................4
3.3 Keypad I/O.........................................................................4
3.4 MIDI I/O.............................................................................4
4.0 DM3AG ASIC.........................................................................................5
4.1 Mask ROMs.......................................................................5
5.0 Analog Signal Paths...............................................................................6
5.1 Drum Signal Output...........................................................6
5.2 Piezo/Data Slider Input......................................................6
5.3 Tape I/O.............................................................................6
5.4 Tape Output.......................................................................7
5.5 Tape Input .........................................................................7
6.0 Test Procedures.....................................................................................7
6.1 General Testing.................................................................8
6.2 Internal Diagnostics and Hidden Keys..............................8
6.3 DAC Adjustments..............................................................8
7.0 Updates and Corrections .......................................................................9
7.1 New SRAM Supply Circuit.................................................9
7.2 Glass Zener (D15).............................................................9
7.3 Dirty Cliff jacks...................................................................10
7.4 Ground CE.........................................................................10
7.5 RF resistor.........................................................................10
7.6 10K MIDI Resistor (R5).....................................................11
7.7 MIDI Pullup........................................................................11
7.8 RF Shields.........................................................................11
7.9 LCD Contrast Adjustments................................................11
7.10 DAC Drift .........................................................................12
7.11 Old Keypad PC Boards...................................................12
7.12 Lifting R41 .......................................................................12
7.13 Reset Capacitor...............................................................12
7.14 Sram Capacitor ...............................................................12
7.15 Tape Capacitors..............................................................13
7.16 RF chokes .......................................................................13
7.17 AQ reset threshold ..........................................................13
7.18 AQ R116..........................................................................13
7.19 Volume Slider Wiring.......................................................13
7.20 PUP Capacitor.................................................................14
8.0 Common Solutions.................................................................................15
9.0 Service Parts List ...................................................................................18
10.0 Software History...................................................................................20
11.0 MIDI Implementation............................................................................23
12.0 Service Manual History........................................................................31
INDEX...........................................................................................................32

HR-16/HR16B Service Manual 1.00 1
1.0 General Description
Diagram 1 provides a simplified
block diagram to show major sub
systems. Note that the schematic
reference designations and pinouts
used in this manual refer to the AQ
revision of both the main PCB, and
schematic.
1.1 Main PC Board Revisions
There are 3 major main PC
Board revisions.
•A-This was the initial release. This
board revision will require the most
extensive updating of the three.
•CA-This version of the board was a
4 layer design. While offering
several advantages over the older
version (improved R.F.
characteristics, smaller size, etc.) it
was found to be extremely difficult to
service (internal shorts can only be
repaired using lifted pins and
jumpers).
•AQ-This was the final revision. This
revision will of course need the
fewest updates, and should be
relatively easy to troubleshoot.
Diagram 2 is provided in order to assist with board revision identification.
2.0 Power Supply
The power supply begins with the 9 Volt A.C., adapter (Alesis P2 [mini plug] or P3 [barrel]
types). Input from J1 is R.F. filtered before on/off switch S1. From there it is split for the +12V, -12V,
and +5V rails. The +12V rail consists of a voltage doubler (C1, C3, and D2, D3), a 7812 regulator
(U8), and a filter capacitor (C6). The -12V rail is a "mirror" of the +12V rail, consisting of voltage
doubler (C2, C4, and D1, D4), a 7912 regulator (U9), and a filter capacitor (C7). The +5V rail
consists of a rectifier diode (D5), a filter capacitor (C5), a 7805 regulator (U10), and a multitude of
0.1µF bypass capacitors. Note that the raw +10V line used by the microprocessor reset, and the
SRAM power supply (when retrofitted), is located at the input to the 7805 regulator. Note that
revision AQ (the latest) boards also incorporate several R.F. suppression chokes and current
limiting resistors. These have resulted in a few unique situations that may need to be dealt with (see
section 7.16 for details)
Diagram 1

HR-16/HR16B Service Manual 1.00 2
2.1 Battery Backup
Battery backup is actually more complicated
than it might first appear, as it depends on a good
system reset (see section 3.1 for details) in order to
function properly. The actual backup circuit consists
of a battery (3V - 3.6V Lithium), a 10K resistor (R97)
for checking standby current (see below), a
"steering" diode (D7), a filter capacitor (C59), and a
transistor/resistor/diode combination that acts as a
steering diode. This combination may be missing on
older board revisions, and must be installed (see
section 7.1) to prevent data corruption due to a
significant difference between Vcc and the amplitude
of the data buss.
SRAM standby current should always be
checked. While the unit is off, check the voltage
across R97. If the voltage is higher than 80mV
(specification, although a 1 to 20mV range is more
normal) then a problem exists. Usually it indicates a
bad (or simply wrong) SRAM, or a short somewhere
along the MEM PWR line. Note that for a short time
Sony 58256-PM (high power) SRAMs were being
installed at the factory, causing batteries to drain in
about 1 year. They should be replaced with low
power versions (58256-LP) when found, in order to
eliminate excess battery drain. We are currently
using Hitachi 62256ALPs as replacements.
CAUTION:Danger of explosion if battery is
incorrectly replaced. Replace only with the same type or
equivalent type recommended by the equipment
manufacturer.
Battery Manufacturer: Tadiran
Type: TL-5101
Rating 3.6V
2.2 PUP Circuit
The PUP (quiet Power UP) circuit is designed
to prevent the unit from making noise during power
up. Note that this circuit will not be present on the
earliest main PC boards. The circuit utilizes the
RESET line (section 3.1) to control the power supply
lines to U20, which is the final active stage before the output jacks. Since both rails operate
similarly, we'll only take the time to explain the operation of the + rail.
During power up, the RESET line is held low until the regulators are fully functioning. At this
point, Q11 is turned off by RESET via R104. This has the affect of turning off Q10 by allowing the
base of Q10 to pull high via R101. As soon as the reset line goes low, Q11 will turn on, pulling the
base of Q10 lower. Q10 is now biased into saturation, allowing roughly +12V to be fed to the op-
amps. C65 is provided for extra filtering. The - rail consists of R99, R100, R105, Q12-Q13, and C64.
Diagram 2

HR-16/HR16B Service Manual 1.00 3
C62 was added to the analog rails of the op-amp to prevent oscillation during power up, and may
need to be added to some older units (see section 7.20).
3.0 The 8031
The 8031 MPU is the heart of the HR-16's control section. It handles everything from keypad
input and MIDI I/O, to sequencing. Note that the 8031 data buss serves a dual purpose. This buss
multiplexes between low order addresses (1st 8 bits), and data. Latch U7 is used to hold the low
order address half, during 8031 read and write cycles. The EPROM (U11) is used to hold 8031
program information. The SRAM (U12) holds system variables, as well as user sequence data. Z1
provides the 12MHz 8031 clock. MIDI I/O is handled through the 8031's built in RXD (Read Serial
Data), and TXD (Transmit Serial Data) ports. Tape I/O and piezo input is handled through the built
in 8031 I/O ports. DM3AG ASIC control, and LCD output are handled through memory mapped I/O
(see section 3.2). Keypad decoding uses both forms of I/O (see section 3.3).
3.1 Reset
The 8031 reset circuit is perhaps the single most important circuit in the HR-16. When this
circuit is functioning incorrectly, problems ranging from loss of battery backup to a complete lock-up
of the machine can occur. A thorough knowledge of the operation of this circuit will greatly facilitate
troubleshooting this unit.
This circuit uses the differential between raw +10V and regulated +5V to generate the
required signals for system RESET. This is necessary due to fact that the system MUST be in a
reset state while powering down, otherwise random noise on the 8031 data and address busses
could corrupt SRAM data, and destroy any hope that the battery backup will work. R28, R29, and
the 5.1V zener diode (D15) work together as a voltage divider to the base of Q4, and is designed so
that transistor Q4 will turn on when the raw +10V supply is roughly 7V. This is to ensure that
RESET does not occur until after the +5V regulator is fully functioning (i.e. +5V rail is solid). If
RESET occurs too early, noise on the +5V rail can cause data corruption. Before the Q4 turn on
threshold, Q5 remains turned on (the base of the transistor being pulled up by R30). This in turn
holds the voltage across C20 at .3 volts. This is below the threshold (set by R25 and R96)
necessary to turn on the comparator U1 (pins 10, 11 and 13), leaving the reset line high (pulled up
by R10). Once the raw supply has reached a sufficient level to turn on Q4 (roughly 7V), Q4 will pull
the base of Q5 low, turning it off. This allows C20 to begin charging through R24. Once C20 has
charged to roughly 2.5V, the comparator will switch states and hold it low (due to the hysteresis
established by R27). This completes the reset cycle during power up.
During power down, the opposite occurs, ensuring that the 8031 is held in a reset state
during power down as well. This is necessary in order to prevent random data from being written
into the SRAM during shutdown. Be aware that this can cause unusual unit lockups to occur if the
circumstances are just right. For example, if an HR-16 was shut off while in record mode, it's
possible the 8031 was put into reset in the middle of writing a two byte pointer into memory. If only
one of those bytes is written before reset, then it may point to an incorrect location in memory
(battery backup holds the incorrect data). When the unit is powered back up, the incorrect pointer
may send the software into "never never land" where the only way to recover is to reinitialize the
unit.

HR-16/HR16B Service Manual 1.00 4
3.2 Memory Mapped I/O
In order to easily control the vast number of hardware functions that the 8031 needs to
access, a system of memory mapped I/O is used. The basic idea is to make hardware functions
appear to the 8031 as unused memory locations. That way all that the software has to do is write to
a memory location in order to send that information to a specific device such as the LCD, or ASIC.
74HC138 (U13) performs the majority of the work in this circuit. Two things are required
before U13 becomes active. 1> A15 must be low (i.e. the 8031 is accessing the lower 32K of
address space). 2> The 8031 WRite line must be active (the 8031 is performing a memory write).
A15 is used to directly control which function (memory or I/O) is active.
Once U13 is enabled, addresses A8-A10 are decoded by it, and the latch corresponding to
the value of the decoded address is strobed. At this point, data on the 8031 data buss is "written"
into the latch.
3.3 Keypad I/O
Keypad I/O is handled through a simple polling process Each row of the keypad matrix is
pulled low one at a time (via U14 which is memory mapped). If any button along the row is pressed,
the corresponding
column input (U22) will
appear high. If no
buttons are pressed, all
column inputs will
appear as a low. D9-
D15 and R42-R47
provide protection for
the outputs of U14. Use
diagram 3 to localize
individual button
failures.
3.4 MIDI I/O
The MIDI
hardware is a standard
implementation. MIDI
out begins at the
8031's TXD port (pin
11) and travels via R6
to the darlington pair
Q1/Q2. Note that the
8031's internal pullup is
not very strong, and
older units (revision A)
may require the addition of an external pullup resistor for the MIDI out to function correctly (see
section 7.7).
MIDI in consists mostly of the opto isolator (U4), protection diode D6, pullup R7, and
threshold resistor R5. Note that the threshold resistor may need to be changed in order to eliminate
false MIDI triggers (see section 7.6).
Diagram 3

HR-16/HR16B Service Manual 1.00 5
4.0 DM3AG ASIC
The DM3AG ASIC is a complex LSI device, specifically designed for the purpose of playing
percussion samples. Obviously, the internal workings of such a device are beyond the scope of this
manual. However, a brief description of some of the important pins follows.
NAME PIN#(s) Function
MD0-MD7 27-34 8031 Data Buss Input.
CLOCK 37 Asic Clock Input (6MHz in HR-16).
DAC0-DAC16 42-51, 53-60 Output to DAC.
A0-A19 3-17, 19-23 Mask Address Buss
D0-D7 61-68 Mask Rom Data Buss
SNH0 39 Output Sample and Hold Control
SNH1 40 " " " " "
SNHIN 41 Output Sample and Hold Inhibit.
STRES 26 Instruction reset strobe.
STB 25 Instruction latch strobe.
4.1 Mask ROMs
The mask ROMs contain the all of the sample information. The 18 bit address buss allows for
2 megabytes per mask ROM. Address line A19 from the ASIC is actually used in conjunction with
Q15 to switch the Mask ROM CE lines (pin 22) such that only one device is enabled at any given
time.
Diagram 5
Diagram 4

HR-16/HR16B Service Manual 1.00 6
5.0 Analog Signal Paths
5.1 Drum Signal Output
The output of the DM3AG ASIC is an 18 bit value. This may seem a little strange at first,
since we are using a 16 bit DAC. R63 and R73-R75 provide the binary weighted resistor network
necessary to achieve a full 18 bit output.
The PCM-54 DAC adjust circuit consists of R52, R53, R54, C34, and trimpot R90 (see
section 6.3 regarding adjustment).
The output of the DAC is sent via R68 to the 4052 analog switch (U19), where the ASIC
controls to which output (out1 left/right or out2 left/right) the final signal will be sent. (Note that
stereo panning is achieved by sending the same signal to the left and right sides separately.)
Each output section (consisting of 1/4 of U20, 1/4 of U21, and misc. resistors and capacitors)
serves the dual purposes of filtering and buffering (with a little gain added in). In the case of output
1, the signal is fed through the volume slider (via J11)(see section 7.19 regarding differences in
wiring) before final output to the 1/4 inch jacks.
5.2 Piezo/Data Slider Input
Successive approximation is the method used to determine the value of the keypad piezo
crystals (keypad velocity), and the data slider. It is a heuristic approach to the process of analog to
digital conversion. The idea is to divide the process into short, manageable sections. Each
significant binary weight (starting with the Most Significant Bit) is taken in turn, thus requiring only 8
comparisons to achieve a final value.
74HC04s U2 and U3 (replaced by a single 74HC540 [U2] in revision AQ PC boards) combine
with the binary weighted resistor network (R16-R20, and SIP R22) to form a simple 8 bit digital to
analog converter. The 8031 sends values to the DAC via it's internal I/O ports. The analog
equivalent of these values is compared to the actual input signals via comparators U1 (pins 2, 4,
and 5 for the data slider) and U1 (pins 8, 9, and 14 for the piezos). The 8031 reads the result of the
comparison through I/O port P3.4 (pin 14) or port P3.5 (pin 15) and proceeds according to that
result. The data slider is read directly via R23 (with C16 acting as a filter to reduce "jitter"). However
the piezos require a little bit of wave shaping and translation before they can be read. First, the
signal is A.C. coupled by C50, and rectified by D19. Q3 is then used to translate the signal into a 0V
to 5V range (the piezos can produce up to about 50V). The signal is now ready for conversion.
5.3 Tape I/O
Tape output is very simple, while tape input is somewhat more complicated. This is due to
the fact that tape backup and tape sync have different requirements. Data transfers need data
integrity which implies guaranteed highs and lows, while tape sync needs tight timing and fast
transistions. It's important to remember that not all tape decks are created equal. Probably the
largest factor involved is the decks input and output capacitances. These can greatly affect the
signals sent to and from the deck, and may cause some decks to be incompatible with the tape I/O
needs of the HR-16. However, these cases should be rare, as the components chosen for the HR-
16 are based on the industry "standards" that most manufacturers adhere to.
While we have heard many complaints regarding tape back up, we have actually found very
few actual tape failures. Most of the complaints arise from user error, so below is a list of successful
backup and tape sync strategies.
1. When attempting to save to a stereo cassette deck, use only the 1 channel (using both channels
may result in odd phase cancellations during playback).
2. Avoid using any noise reduction systems (i.e. Dolby, or DBX) as these can distort the timing of
the pulse train that contains the data.

HR-16/HR16B Service Manual 1.00 7
3. Avoid using adapters for two reasons. 1> Some adapters contain built in attenuators that can
result in extremely reduced levels, both to and from the tape. 2> Oxidation and "wear and tear"
can cause adapters to become intermittent.
4. Always make several copies of each "save". It's especially smart to make copies on at least 2
different tapes as well. This reduces the chances that tape dropouts will cause loss of data.
5. Always use normal bias tapes, as high bias tapes actually end up recording noise, which could
make it past the wave shaping circuitry and cause false triggers.
6. Always verify tapes after saving them. This helps reduce the chances of bad saves. Note
however that the HR-16 does not compare the tape to the contents of memory. It simply verifies
that the information on the tape is valid HR-16 data.
7. Experimentation with record and playback levels usually lead to better results.
Trouble shooting tape problems should begin with listening to the data tape audibly. This can
help the technician determine if the problem occurs during tape save or load. If unusual dropouts
are heard then the problem is either just a bad tape, bad cable, or the tape save circuit. Normal
sounding tapes usually indicate a tape load problem. Only practice will help you determine what is
"normal".
5.4 Tape Output
The tape output hardware is simply the 8031 output port P3.2 (pin 12), a pullup resistor
(R40), and a voltage divider (R39 and R39) for achieving a line level output. The output during tape
save or type sync out applications will appear as a .5V pulse train, but only if the tape out is NOT
connected to a deck (the decks A.C. coupling will distort the output).
5.5 Tape Input
In it's simplest form the tape input consists of an integrator (under software control of the
8031) and a threshold detector (U1C). Input from J5 is passed through a current limiting resistor
(R112) and on to the integrator (C11, C23, R86). The software controls the integration
characteristics through Q16 via memory mapped I/O latch U14 (see section 3.2). While the unit is in
'TAPE SYNC IN' mode, U14/P12 is held high, turning on Q16 and sinking the majority of current
through the integrator to ground. This provides for faster operation of the detection circuitry. D17 is
used to prevent leakage of the integrator signals through the control circuitry during 'TAPE
LOAD/VERIFY' operations (when U14/P12 is low).
The threshold detection circuitry surround U1C is relatively straight forward. R14 and R15
establish the threshold level with R12 and C9 acting as a filter to stabilize the threshold level and
prevent oscillation. R21 establishes some hysteresis and R13 is a pullup for the open collector
output of the LM339. The output of the '339 is sent directly to the 8031 in the form of an interrupt
line. Forcing the 8031 to respond immediately to tape input is necessary due to the timing
constraints required for I/O (especially in tape sync situations).
6.0 Test Procedures
If possible, user data should always be saved (DataDisk, or equivalent, recommended) prior
to servicing. While this may not be immediately possible (or possible at all), it should be attempted
as soon as possible.

HR-16/HR16B Service Manual 1.00 8
6.1 General Testing
General testing should, at a minimum, consist of self test, and a short audio test (including
testing key response and recording and playing back a pattern). More extensive testing would
include:
♦Checking battery backup
♦Actually sending and receiving MIDI information
♦Saving and loading data from tape
♦Copying full patterns to themselves, then to other patterns so that memory
becomes completely full (this ensures that the 8031 address buss functions
correctly, as the self test does not take addressing into consideration).
6.2 Internal Diagnostics and Hidden Keys
Below is a list of the key presses necessary to activate hidden functions.
Power up while holding "ERASE", "DELETE", and "RECORD"------------Clear memory/Reinitialize system.
Power up while holding "QUANT" and "MIDI UTIL"---------------------------Self test.
Hold "PATT" and press "VOICE"--------------------------------------------------DAC Adjust mode (press "STOP" to exit).
Be aware that the self test will erase all internal memory (equivalent to reinitializing).
To perform the internal diagnostics, connect a MIDI cable between MIDI in and out. Connect
a 1/8 inch cable between Tape in and out. Activate the self test (keys above). the order of items
tested is:
1 ROM Test Tests EPROM for errors
2 RAM Test Tests SRAM for errors
3 MIDI I/O Test Tests MIDI input/output functions
4 TAPE I/O Test Tests Tape input/output functions
5 LED Test Lights each front panel LED for a couple seconds
6 DAC Adjust Enters DAC adjust mode (press stop to exit).
6.3 DAC Adjustments
The only adjustment necessary in the HR-16 is the DAC adjustment. This is normally done at
the end of the HR-16's internal diagnostics, however holding the "PATT" button and pressing the
"VOICE" button simultaneously also starts the DAC adjust routine. While this routine is running,
adjust R90 (the trimpot near the PCM-54 DAC) so that a minimum of noise is heard during each
drum hit. A DAC that is out of adjustment will "buzz", particularly at the end of the sample. Note that
you may have to turn your amplifier up in order to hear this signal. Once the adjustment is complete,
hitting the "STOP" button ends the DAC adjust routine.

HR-16/HR16B Service Manual 1.00 9
7.0 Updates and Corrections
7.1 New SRAM Supply Circuit
•All Revisions.
The new SRAM supply circuit (See diagram
7) supplies a solid 5V to the SRAM, preventing
input data from being higher in amplitude than
the supply voltage, which can cause data
corruption. First, remove the original diode (D8),
then install the new circuit. Diagram 8 shows the
location to install the circuit in Revision A & CA
PC boards, while diagram 6 shows the location
for revision AQ PC boards. The installation of
this circuit is highly recommended, and is
absolutely necessary if a 58257 SRAM is in the
unit. This is because '257s are much more
sensitive to supply voltage the older '256
SRAMs.
7.2 Glass Zener (D15)
•Revisions A & CA.
For a short time, glass package 1N5231B
zener diodes were used instead of the more
familiar metal package. These were found to be
unreliable, and should be replaced with metal
package zeners.
Diagram 6
2N4401
Diagram 7
Diagram 8

HR-16/HR16B Service Manual 1.00 10
7.3 Dirty Cliff jacks
•All Revisions. Occasionally, oxidation will build up on the cliff jack
contacts, causing the jack normaling to fail. When this
happens, some drum sounds will be "lost" when using the
unit in mono. (Only one cable plugged in). The solution is
to thoroughly clean the normaling contacts (See diagram 9
for location).
7.4 Ground CE
•All Revisions.
It was discovered that many units returned
for odd crashes all appeared to have a common
component (National EPROMs). After further
investigation it was revealed that it was not due
to defective components, but due to a minor
"incompatibility". It was determined that using CE (pin 20) to
enable the device took too long, and the 8031 would
occasionally attempt to read it's instructions before the data
was valid. The solution to this effect was to leave the
EPROM permanently enabled, and use OE (pin 22), which
operates much faster, to control it's access to the data buss.
On revision A PC boards, this requires cutting a trace,
scraping the solder mask from the closest ground trace and
adding a jumper (see diagram 11). On revision CA PC
boards, this requires that pin 20 of the EPROM be lifted out
of the socket, and a jumper installed (see diagram 10). On
revision AQ PC boards, pin 22 of the EPROM must also be
lifted, the end (away from the 8031) of R110 is lifted, and a
jumper between the two is added. While non National
EPROMs do not seem exhibit this scenario, it's
recommended that this update be performed on all units.
7.5 RF resistor
•Revision A.
An improvement of R.F. characteristics can be
achieved by installing a 470Ωinto the ASIC clock line. The
best location to accomplish this is between the 74HC04 (U6)
and the nearby feed through. The trace on the solder side of
the PC board can then be cut (see diagram 12 for details).
Diagram 9
Diagram 10
Diagram 11

HR-16/HR16B Service Manual 1.00 11
7.6 10K MIDI Resistor (R5)
•All Revisions.
Since the HR-16 was released,
we have found that a 10K resistor
provides a better signal threshold
level to the opto isolator than the
original 47K specified in the design. If
the older value of 47K is found, then a
12K or 13K resistor soldered in
parallel with R5 will achieve the
desired threshold level.
7.7 MIDI Pullup
•Revision A.
Some early units were prone to sending false or incorrect
data through the MIDI out. This was traced to insufficient pull up
resistance in the 8031's TXD port. This can be solved by installing
a 4.7K resistor between R6 and R7 as shown in diagram 13.
7.8 RF Shields
•Revision A.
In an effort to further reduce the R.F. emissions of the HR-16, a self sticking R.F. shield was
introduced. Care should be taken when installing the shield, as wrinkles in the shield may easily
cause shorts to the main PC board. The tab of the shield should
make a firm mechanical contact to ground when the board is in
place (for a short time revision CA main PC boards were
manufactured with the solder mask covering the ground plane that
will need to be scraped off in order to achieve a proper connection)
If this is not done correctly, this may actually create more R.F. noise
than before (the shield starts acting as a capacitivly coupled
antenna). Also note that some PC board revisions have the DAC
adjust trimpot on the bottom of the board for external access. On
these units, either cutting a out a circle around the trimpot, or the
addition of electrical tape will insulate the trimpot from the shield.
7.9 LCD Contrast Adjustments
•All Revisions.
Normally the LCD contrast is adjusted at the factory.
However, in the event an older LCD is replaced, or the contrast is
not enough to suit the user, it may be necessary to change the
hardware to achieve a suitable contrast level. Diagram 14A shows
the changes needed to convert older revisions so that the trimpot
will function in a more appropriate range. Diagram 14B shows the
latest configuration used on older revisions to achieve a nominal
contrast level. In revision AQ boards, the only way to change
contrast is by adding (or removing, if one is present) a jumper
across D21 (located by J12).
Diagram 12
Diagram 13
Diagram 14

HR-16/HR16B Service Manual 1.00 12
7.10 DAC Drift
•All Revisions.
It has been found that some PCM-54's
linearity tend to drift with time and temperature. In
order to improve the linearity 1 leg of R60, one leg
of C47, and pin 27 of the PCM-54 should be lifted
and soldered together (see diagram 15). This
should only be necessary if the user complains of
noise after the unit warms up.
7.11 Old Keypad PC Boards
•Revision A
The original HR-16 came with standard PCB
type contacts (tinned copper traces), but these
were found to oxidize over time. This was
especially evident when the unit was used in a
moisture rich environment (such as near the
ocean). We have since switched to using PC
Boards with carbon contacts. We recommend
replacing the older type PC Boards with the newer
variety. In the event that the newer board is unavailable (emergency rushes, etc.) it is possible to
clean the old keypad contacts with a pencil eraser. While this will restore operation to the unit, such
a measure is strictly temporary, as the contacts will eventually reoxidize.
7.12 Lifting R41
•Revision A
It was found that the feed through below R41 (located near the battery) would occasionally
short directly to the resistor above it. If this happens then battery backup will not function. The
simplest solution is to lift one or both leads of the resistor slightly with a soldering iron (pushing them
up through from the bottom of the board is probably the easiest). This should prevent any physical
contact of the resistor to the feed through.
7.13 Reset Capacitor
•Revision A & CA
The blue monolithic block RAM capacitors used throughout the board were found to be
unreliable when used in timing critical applications due to excess leakage current. C20 is a prime
example of just such an application. If C20 leaks too much, it acts as a voltage divider with R24, and
never exceeds the threshold voltage required to finish the reset process. A large percentage of
"locked up" units can be repaired by replacing this capacitor with either a ceramic disk or film
(WIMA) type of capacitor. This replacement is recommended regardless of whether the capacitor
seems to be failing or not.
7.14 Sram Capacitor
•Revision A
The blue monolithic block RAM capacitors used throughout the board were found to be
unreliable when used in timing critical applications due to excess leakage current. In this case the
capacitor causes excess battery drain, and is the primary cause of battery failure. These capacitors
should be replaced with either a ceramic disk or film (WIMA) type of capacitor, regardless of
whether the capacitor seems to be failing or not.
Diagram 15

HR-16/HR16B Service Manual 1.00 13
7.15 Tape Capacitors
•Revision A & CA
The blue monolithic block RAM capacitors used throughout the board were found to be
unreliable when used in timing critical applications due to excess leakage current. Here, the
capacitors reside in the tape input path (C11 and C23), and may cause the distortion of incoming
tape signals. Such distortions can cause the loss of tape loading capabilities. These capacitors
should be replaced with either a ceramic disk or film (WIMA) type of capacitor if tape loading failures
occur.
7.16 RF chokes
•Revision CA & AQ
Occasionally the R.F. chokes on these board revisions (located near the power input jacks)
will bust a lead during shipping. When this occurs, it may not be possible to repair the choke. In this
case it is O.K. to remove the choke and add jumpers across its old location. In most cases this
shouldn't be necessary as the units should have had their chokes hot glued to the board at the
factory. Any units that have loose chokes need to be glued (hot glue recommended) to prevent
future damage.
7.17 AQ reset threshold
•Revision AQ During the development of the AQ main PC board,
one of the prime considerations was to reduce R.F.
emissions to virtually 0. Towards this end, a 100 ohm
resistor (R133) was introduced between the raw supply
voltage and the rest of the circuitry to reduce power supply
noise. This had the effect of increasing the threshold of the
RESET circuit, and was found to cause some units to reset
repeatedly in low power situations (i.e. use of lots of lights
in a club could cause fluctuation in the local power by 15V
to 20V, causing the unit to reset over and over again). R28
is part of the threshold circuit for the RESET line. Originally
valued at 3K, the new value is 1.5K (easily obtained by
adding an additional 3K in parallel). This will bring the
threshold into a more reasonable range.
7.18 AQ R116
•Revision AQ
Again an attempt to reduce power supply noise, this
resistor was found to sometimes reduce the power supply
level to the 8031 (and surrounding circuitry) to below the
required 4.75V. It is recommended that a jumper be
soldered across this resistor (located between the 8031
and U6).
7.19 Volume Slider Wiring
Note that the wiring of the volume slider changed
between Revisions CA and AQ. Diagram 16 shows the
correct wiring for each board style.
Diagram 16