B+K precision 1795 User manual

Instruction Manual
Model 1795 High Current Power Supply
B PRECISION
K

Limited Two Year Warranty
B & K Precision Corp. warrants to the original purchaser that its product and
the component parts therof, will be free from defects in workmanship and
materials for a period of two years from the data of purchase.
B & K Precision Corp. will, without charge, repair or replace, at its' option,
defective product or component parts. Returned product must be
accompanied by proof of the purchase date in the form a sales receipt.
To obtain warranty coverage in the U.S.A., this product must be registered
by completing and mailing the enclosed warranty card to B & K Precision
Corp. 22820 Savi Ranch Parkway Yorba Linda, CA-92887, within fifteen
(15) days from proof of purchase.
Exclusions: This warranty does not apply in the event of misuse or abuse of
the product or as a result of unanthorized alternations or repairs. It is void if
the serial number is alternated, fefaced or removed.
B & K Precision Corp. shall not be liable for any consequential damages,
includingwithoutlimitationdamagesresultingfromlossofuse. Somestates
do not allow limitation of incidental or consequential damages, so the
above limitation or execlusion may not apply to you.
This warranty gives you specific right and you may have other rights, which
vary from state-to-state.
ModelNumber:______________ DatePurchased:__________

TABLE OF CONTENTS
SECTION PARTICULARS PAGE NO.
1GENERAL INFORMATION 1
2SPECIFICATIONS 2
3INSTALLATION 3
4OPERATING INSTRUCTIONS 5
5SERVICE INSTRUCTIONS 10
6PART LIST 16
7SCHEMATICS 21
8CIRCUIT DIAGRAMS 28

1
SECTION - 1
GENERAL INFORMATION
1.1 DESCRIPTION :
The1795HighCurrentRegulatedD.C.PowerSupplyiscompletelysolidand suitable
for bench operation or standard 19" rack operation. It is a well regulated constant
voltage / constant current supply which delivers 0-64V at 0-15Amps and can be
adjusted continuously throughout the output range. When the supply is used as a
constant voltage source the front panel VOLTAGE controls can be used to limit the
output voltage. When the unit is used as a constant current source, the front panel
CURRENTcontrolscanbeusedtolimit the output current.Theunitwillautomatically
cross over from constant voltage to current mode and vice-versa if the output
current or voltage exceeds these limits.
Output voltage and current are continuously monitored on two front panel meters.
The load terminals and remote sense terminals are provided on the front panel.
Eitherthe positive ornegative output terminalmay be groundedor thepower supply
can be operated floating at upto a maximum of ±300VDC above ground.
1.2 OUTPUT ON/OFF SWITCH :
The output voltage and Current can be preset without connecting the power supply
to the load. With the OUTPUT ON/OFF switch in the OFF position, the maximum
voltage and current limits can be set. Pressing the OUTPUT ON switch connects
the output of the power supply to the load.
1.3 LIMIT SETTING :
The voltage and current limits can be set when the output is not connected to the
load. With the OUTPUT ON/OFF switch in the OFF position and the LIMIT switch
pressed, the voltage and current limits can be set with the front panel VOLTAGE
and CURRENT potentiometers.
1.4 REMOTE PROGRAMMING ( With External 5K Pot ) :
The output voltage of the unit can be programmed between 0 to 64V by means
of an external remote programming voltage resistor. An external resistance
programming selector link is provided on the rear panel for this purpose.
1.5 REMOTE SENSING :
The degradation in regulation which occurs at the load due to voltage drop in the
load leads can be eliminated by using the power supply in the remote sensing
mode operation. The remote sensing mode is selected by a push switch on the
front panel.

SECTION - 2
SPECIFICATIONS
OUTPUT VOLTAGE :0-64V DC continuously variable with coarse
and fine voltage controls.
LOAD CURRENT :0-15 Amp max., continuously variable with
coarse and fine controls.
CONSTANT VOLTAGE MODE
REGULATION
LINE :Less than ± 0.01% ± 2mV for ±10% change in
line voltage.
LOAD :Less than ± 0.01% ± 2mV for load change from
zero to full load.
RIPPLE & NOISE :Less than 1mV rms max.(20 Hz - 20 MHz)
CONSTANT CURRENT MODE
REGULATION
LINE :Less than ± 0.05% ±10mA for ±10% change in
line voltage.
LOAD :Less than ±0.05% ±10mA for change in output
voltage from 0 volts to maximum output voltage.
RIPPLE & NOISE :Less than 6mA rms.
OVERLOAD PROTECTION :Automatic overload and short circuit protection.
TRANSIENT RESPONSE :100µsecs to within 10mV of set output voltage
for load change from 10% to 90%.
STABILITY :
Total drift within 8 hours,after : ± 0.2% ± 10mV in constant voltage mode.
warm up under constant line, : ± 0.5% ± 10mA in constant current mode.
load & temp.
PANEL METERS :Digital panel meters (marked V for voltmeter and
A for ammeter) are provided with an accuracy of
± 3 counts.
MODE INDICATION :Respective LED lights up when the unit is
working in CV or CC mode.
SET LIMIT/ ON-OFF :Push Switches for Limit ( V & A ) and output
CONTROLS ON/OFF setting.
OUTPUT CONTROLS :Single turn coarse and fine voltage and current
controls are provided on the front panel
EXTERNAL PROGRAMMING : Output voltage can be programmed by a variable
resistance of 5K ( Pot )
OPERATING TEMPERATURE :0-40°C.
INPUT VOLTAGE :120/230V AC, ± 10% 47 - 63Hz single phase.
DIMENSIONS :19"(W ) x 15.75"(D) x 5.24"(H).
WEIGHT :46 lbs. Net.
2

SECTION - 3
INSTALLATION
3.1 INITIAL INSPECTION :
As soon as the power supply 1795 unit is unpacked, inspect for any damage that
may have occurred during transit. Save all packing material until inspection is
completed. If any damage is found, notify the carriers immediately. Our authorised
representatives should also be notified.
3.2 PHYSICAL CHECK :
This check should confirm that there are no broken knobs or connectors, that the
cabinet and panel surfaces are free of dents and scratches and the meters are not
scratched and cracked.
3.3 ELECTRICAL CHECK :
The power supply unit 1795 should be checked against electrical specifications.
An in-cabinet performance check will verify proper operation.
3.4 INSTALLATION DATA :
The power supply unit 1795 is shipped ready for bench operation. It is necessary
only to connect the unit to a rated source of power (120V AC) and it is ready for
operation.
3.5 LOCATION :
The power supply 1795 unit is fan cooled. Sufficient space should be kept around
the unit while in operation, so that unit do not remain in confined space or close to
anotherheating source.The ambienttemperature of the area aroundthe unit should
be less than 40°C.
3.6 RACK MOUNTING :
The unit is in rack size and can be rack mounted in a conventional rack using
standard mounting screws and the rack attachments optionally supplied.
3.7 INPUT POWER REQUIREMENTS :
The power supply 1795 unit may be operated continuously from input voltage of
120V or 230V AC 47-63Hz power source. It is factory wired for 120V AC operation.
3

3.8 INPUT TAP SELECTION FOR 230V OPERATION :
Incaseof230VMainsoperationpleaseensurethatshortinglinksontheTap Selector
board is changed to 230V, marked on the PCB for both Mains Transformer &
Auxilary Transformer. as per the following diagram.
TAP SELECTOR BOARD
Please make sure the input varistor is replaced by 20D 361K or equivalent for
230V Mains Operation at the Input of EMI Filter located at bottom side of the unit.
3.9 REPACKAGING FOR SHIPMENT :
To ensure safe shipment of the power supply 1795 unit, it is recommended that the
package designed for the unit be used. The original packaging material is reusable.
Be sure to attach a tag to the unit specifying the owner, and the fault observed with
a brief description.
4

SECTION - 4
OPERATING INSTRUCTIONS
4.1 TURN ON SETTING PROCEDURE :
The following procedure describes the use of controls and indicators for
Constant Voltage and Constant Current Mode of Operation.
CONSTANT VOLTAGE (CV) MODE :
a. Set ‘POWER ON’ Switch & keep the OUTPUT ON/OFF switch to OFF
position ( ).
b. Press LIMIT switch and adjust the VOLTAGE controls till the desired voltage is
indicated on Voltmeter ( ).
c. Press OUTPUT switch to ON position and observe that CV LED lights ( )
CONSTANT CURRENT VOLTAGE (CC) MODE :
a. Turn off the suppy. Short circuit the output terminals of the power supply
& turn on the supply.
b. Keep the OUTPUT ON/OFF switch in the OFF position ( ).
c. Press LIMIT switch and adjust the CURRENT controls till the desired current is
indicated on Ammeter ( ).
d. Press OUTPUT switch ON position and observe that CC LED lights ( ).
e. Remove the short circuit.
4.2 SET LIMIT CONTROL (VOLTAGE AND CURRENT) :
To preset the output Voltage and Current, proceed as follows :
a. Set the OUTPUT switch to OFF position ( ) ( Release Position ).
b. Press the LIMIT switch and adjust the desired output voltage with the
VOLTAGE control potentiometers ( ).
c. Release the LIMIT switch, set the OUTPUT switch to ON position and check
the output voltage on the voltmeter ( ).
d. Set the OUTPUT switch to OFF position ( ).
e. Press the LIMIT switch and adjust the desired output current limit with the
CURRENT control potentiometers ( ).
f. Release the LIMIT switch, set the OUTPUT switch to ON position and check
the output current on the ammeter ( ).
g. Set the OUTPUT switch to OFF position ( ).
h. Connect the load to the Output terminals and set the OUTPUT switch to ON
position ( ).
4.3 LOAD CONNECTIONS :
The load should be connected to the power supply output terminals using separate
pairs of connecting wires. This will minimize mutual coupling effects between loads
and will retain full advantage of the low output impedance of the power supply.
Eachpair of connectingwires shouldbe as shortas possible andtwisted or shielded
to reduce noise pick up. (If a shielded pair is used, connect one end of the shield to
ground and leave the other end unconnected).
5

4.4 Positive or negative voltage can be obtained from this supply by grounding either
one of the output terminals or one end of the load. Always use two leads to connect
load to the supply, regardless of where the setup is grounded. This will eliminate
any possibility of the output current return paths through the power source ground
which would damage the line cord plug. This supply can also be operated upto
±300V DC above ground, if neither output terminal is grounded.
4.5 REMOTE SENSING :
Warning : Do not Operate the Unit in 'REMOTE SENSE' mode without
ensuring proper 'REMOTE/ 4 TERMINAL' Connections. Serious
Damage to Unit or Equipment under test could result.
Remote sensing is used to maintain good regulation at the load and reduce the
degradation of regulation which could occur due to the voltage drop in the leads
betweeen the power supply and the load. Remote sensing is accomplished by
connnecting the load to remote sense terminals on the front panel. The leads from
the sensing( +S and -S) terminals to the load will carry much less current than the
load leads and it is not required that these leads be as heavy as the load leads.
However, they must be twisted or shielded to minimize noise pickup.
For reasonable lengths of load leads, remote sensing greatly improves the
performance of the supply. However, if the load is located at a considerable
distance from the supply, added precautions must be observed to obtain
satisfactory operation. Notice that the voltage in the load leads subtracts directly
from the available output voltage and also reduces the amplitude of the feedback
error signals that are developed within the unit. Because of these factors, it is
recommended that the drop in each load lead does not exceed 0.5Volts.
NOTE : Due to the voltage drop in load leads, it may be necessary to
readjust the current limit in the remote sensing mode.
Observance of the precautions in para. 4.8 and 4.9 will result in a low dc output
impedance at the load. However, another factor that must be considered is the
inductance of long leads.This causes a high ac impedance and could affect the
stability of the feed back loop seriously enough to cause oscillations. If this is the
case, it is recommended that the following actions be taken:
a) Adjust R6 to remove oscillations, or to achieve best possible transient
response for given long load lead configuration.
b) If performing adjustment in step (a) above does not remove oscillation,
disconn-ect output capacitor C3 ( L1791-FP-CNT-0603 PCB) and connect
a capacitor having similar characteristics (approximately the same capaci
tance, the same voltage rating or greater, and having good high frequency
characteristics) directly across load using short leads.
Readjust R6 as in step (a) above after making this change.
6

4.6 OUTPUT CAPACITANCE :
Internal capacitor C3 ( L1791-FP-CNT-0603 PCB ) connected across the output
terminals of the power supply, helps to supply high current pulses of short duration
during constant voltage operation. Any capacitance added externally will improve
the pulse current capability, but will decrease the safety provided by the constant
current circuit. A high current pulse may damage load components before the
average output current is large enough to cause the constant current circuit to
operate.
The effects of the output capacitor during constant current operation are as follows:
a.The output impedance of the power supply decreases with increasing frequency
b. The recovery time of the output voltage is longer for load resistance changes.
c. A large surge current causing a high power dissipation in the load occurs
when the load resistance is reduced rapidly.
4.7 REVERSE VOLTAGE LOADING :
A diode CR1 is connected across the output terminals. Under normal operation,
thediode is reversebiased(anode connected tothenegative terminal ). Ifareverse
voltage is applied to the output terminals ( positive voltage applied to the negative
terminal),the diodewill conduct, shunting current across the outputterminals tothe
forward voltage drop of the diode. This diode protects the series transistor and the
output electrolytic capacitors.
4.8 REVERSE CURRENT LOADING :
Active loads connected to the power supply may actually deliver a reverse current
to the power supply during a portion of its operating cycle.
An external source cannot be allowed to pump current into the supply without loss
of regulation and possible damage to the output capacitor. To avoid these effects,
it is necessary to preload the supply with a dummy load resistor so that the power
supply delivers current through the entire operation cycle of the load device.
4.9 EXTERNAL PROGRAMMING :
Remote external programming can be achieved changing the external program
link on rear panel and connecting a variable resistor of 5K across the terminals as
shown on the rear panel.
7

OPERATORS SAFETY SUMMARY
The general safety information in this part of the summary is for both operating &
servicing personnel. Specific warnings and cautions will be found throughout the
manual where they apply, but may not appear in this summary.
TERMS IN THIS MANUAL :
CAUTION : Statements identify conditions or practices that could result in
damage to the equipment or other property.
WARNING : Statements identify conditions or practices that could result in
personal injury or loss of life.
TERMS AS MARKED ON EQUIPMENT :
CAUTION : Indicates a personal injury hazards not immediately accessible
as one reads the markings,or a hazard to property, including the
equipment itself.
DANGER : Indicates a personal injury hazard immediately accessible as one
reads the marking.
POWER SOURCE :This product is intended to operate from a power source that
does not apply more than 130V rms between the suply conductors or between
either supply conductor and ground. If the Internal Tap is selected for 230V AC
operation, then the input voltage should not be more than 250V rms.
A protective ground connections by way of the grounding conductor in the
power cord is essential for safe operation.
GROUNDING THE PRODUCT :This product is grounded through the
grounding conductor of the power cord. To avoid electrical shock, plug the
power cord into a properly wired receptacle before connecting to the product
input or output terminals. A protective ground connection by way of the
grounding conductor in the power cord is essential for safe operation.
DANGER ARISING FROM LOSS OF GROUND : Upon loss of the protective
ground connection, all accessible conductive parts (including knobs and controls
that may appear to be insulating) can render an electric shock.
USE THE PROPER POWER CORD :
Use only the power cord and connector specified for your product.
Use only a power cord that is in good condition.
Refer cord and connector changes to qualified service personnel.
8

USE THE PROPER FUSE : To avoid fire hazard, use only fuse of the correct type,
voltage rating and current rating as specified in the parts list for your product.
For 115V operation 20A, For 230V operation 10A Slow blow.
Refer fuse replacement to qualified service personnel.
DO NOT OPERATE IN EXPLOSIVE ATMOSPHERES : To avoid explosion, do
not operate this instrument in an explosive atmosphere unless it has been
specifically certified for such operation.
DO NOT OPERATE UNIT WITHOUT COVERS : To avoid personal injury, do
not operate this product without covers or panels installed.
SERVICING SAFETY SUMMARY
FOR QUALIFIED SERVICE PERSONNEL ONLY
Refer also to the Operators Safety Summary
DO NOT SERVICE ALONE :
Do not perform internal service or adjustment of this product unless another person
capable of rendering first aid and resuscitation if present.
USE CARE WHEN SERVICING WITH POWER ON :
Dangerous voltages exist at several points in this product. To avoid personal injury,
do not touch exposed connections or components while power is on.
Disconnect power before removing protective panels, soldering, or replacing
components.
POWER SOURCE :
This product is intended to operate from a power source that does not apply
more than 130V rms between the supply conductors or between either supply
conductor and ground. A protective ground connection by way of the grounding
connector in the power cord is essential for safe operation.
9

SECTION - 5
SERVICE INSTRUCTION
5.1 GENERAL :
The instrument has been tested throughly and then released for dispatch.Normally,
the unit works satisfactorily under all condition. However due to ageing / misuse or
malfunctioning, the unit may become defective. In case, the user wants to carryout
Servicing, the following instructions will be helpful in rectifying the defects.
The Servicing shall be done only by Qualified personnel.
5.2 TROUBLE SHOOTING TECHNIQUES :
5.2.1 INTRODUCTION:Thetroubleshootingprocedureisarrangedinanorderthatchecks
the simple trouble possibilities before proceeding to extensive troubleshooting.
5.2.2 CONTROL SETTINGS : Incorrect control settings can seem like a trouble that
does not actually exist. If there is any question about the correct function or
operation of any control, see the Operating Instructions section.
5.2.3 SYSTEMANDASSOCIATED EQUIPMENT: Before trobleshooting the 1795, check
for proper input fuse as per part list is intac. Check the line voltage at the power
sourcebefore connecting themainscord is ratedfor the correctinputvoltage. Verify
that the front panel controls are kept at minimum position. The output terminals
must be free from any load connecting leads.
5.2.4 VISUAL CHECK : Many troubles can be located by visual clues such
as unsoldered connections, broken wires, damaged circuit board, damaged
components, etc.
5.2.5 INTERNAL ADJUSTMENT :Check the Adjustment of the suspected circuit if the
trouble is obviously in a certain circuit. The trouble may only be a result of
misadjustment and may be corrected by readjustment.
5.2.6 CIRCUIT ISOLATION: Note the trouble symptoms. These often identify the circuit
in which the trouble is located. When trouble symptoms appear in more than one
circuit,check the effected circuits by making waveform and voltage measurements.
5.2.7 COMPONENT CHECKING : If a component cannot be disconnected from its
circuits, then the effects of the associated circuitry must be considered when
evaluating the measurement. Except for soldered-in transistors and integrated
circuits, most components can be lifted at one end from the circuit board.
5.2.8 TRANSISTORSANDIC's : Turn the power switch off before removing or
replacing any semiconductor. A good check of transistor operation is actual
performance under operating conditions. A transistor can most effectively be
10

checked by substituting a new component for it ( or one which has been checked
previously). However, be sure that circuit conditions are not such that a
replacement transistor might also be damaged. If substitute transistors are not
available, use a dynamic tester. Static-type testers are not recommended, since
they do not check operation under simulated operating conditions. An approved
anti-static suction-type desoldering tool must be used to remove soldered-in
transistors.
Integrated circuits can be checked with a voltmeter, test oscilloscope, or by
direct substitution. A good understanding of the theory of operation is essential to
trouble shooting circuits using IC's. Operating waveforms, logic levels, and other
operating information for the IC's are given in the theory of operation. Use care when
checkingvoltagesandwaveformsaroundtheIC'ssothatadjacentleadsarenotshorted
together.A convenient means of clipping a test probe to the 14 pin in-line IC is with an
integrated circuit test clip. This device also doubles as an extraction tool.
5.2.9 DIODES : Do not use an ohmmeter that has a high internal current. High currents
may damage a diode. A diode may be checked for an open or shorted condition by
measuring the resistantce. With an ohmmeter scale having an internal source of
between 800mV and 1.5V, the resistance should be very high in one direction and
very low when the leads are reversed.
5.2.10 RESISTORS : Check the resistors with an ohmmeter. Resistor tolerances are
given in the Electrical Parts List. Resistors do not normally need to be replaced
unless the measured value varies widely from the specified value.
5.2.11 CAPACITORS : A leaky or shorted capacitor can be detected by checking
resistance with an ohmmeter on the voltage rating of the capacitor. The resistance
reading should be high after initial charge of the capacitor. An open capacitor can best
be detected with a capacito meter, or by checking whether it passes ac signals.
5.3 REPAIRS & MAINTENANCE :
5.3.1 Remove the mains cord from the source before removing top cover of the unit.
5.3.2 To open the cover, remove screws from Top & Bottom Covers. Disconnect
Grounding of both covers.
5.3.3 If there is no output, check the input supply Voltage and the Fuse continuity, etc.
Check both Fans are working
5.3.4 If the output is high and unregulated, check for open Voltage adjust potentiometer
or shorted mosfet, etc.
5.3.5 Similarly, if the current is unregulated, check for value change in the Shunt
Resistor. It may get open.
11

5.3.6 If Fuse blows, connect the unit through a variable AC Source with a current meter
and monitor the current at no load. If the current is very high (more than 2 ampere
or so ) load, check for Bridge Rectifier short or shorted Diode, or Secondary
Winding short, etc
5.3.7 If output voltage or current DPM's are not reading, check for loose connections
especially in crimping, soldering, of Connectors.
WARNING
THE FOLLOWING SERVICING INSTRUCTIONS ARE FOR USE BY
QUALIFIED PERSONNEL ONLY.TO AVOID PERSONAL INJURY, DO NOT
PERFORM ANY SERVICING OTHER THAN THAT CONTAINED IN
OPERATING INSTRUCTIONS UNLESS YOU ARE QUALIFIED TO DO SO.
REFER TO OPERATORS SAFETY SUMMARY AND SERVICE SAFETY
SUMMARY PRIOR TO PERFORMING ANY SERVICE.
5.4 VOLTAGE & WAVEFORM CHECK POINTS :
5.4.1 TEST EQUIPMENTS REQUIRED : Generally, Wide-band Oscilloscope
20MHz Dual Trace, a probe 1:10 / 50MHz, and a multimeter 4½ DMM, Rheostats,
Variable Line Source 30A, Test Leads are all that is needed to perform basic
waveform and voltage checks for diagnostic pusposes.
CONNECT THE MAINS CORD OF THE UNIT TO THE RATED I/P SOURCE.
5.4.2 Check the voltage & waveforms at test points TP1 to TP6 on PRSR 0896 PCB
with respect to output positive or at TP7 with the help of 4½ DMM & CRO. Normal
voltages & waveforms are given below :-
Keep output voltage to max. position with front panel control. All readings
are with respect to TP7 as common :-
Test Points on Voltages on AMP/FREQ. WAVEFORM
PRSR PCB DMM Level on CRO on CRO
TP1 +12.01V 26.7V P-P / 99.8Hz
TP2 +1.03V 2V P-P / 99.8Hz
TP3 -12.04V 26.8V P-P / 99.6Hz
TP4 -11.35V 25.3V P-P / 99.6Hz
TP5 +0.101V 3V -P / 99.6Hz
TP6 +15.05V 26.8V P-P / 99.6Hz
12

5.4.3 VOLTAGES AT VARIOUS PINS OF IC LM324 IS AS FOLLOWS ( IC-101 ) :-
IC PIN NO. VOLTAGES & CHECK CONDITIONS
PIN1 -- 0V ( WHEN V POT KEPT AT MIN. POSITION IN CV MODE )
PIN1 -- +5V ( WHEN V POT KEPT AT MAX. POSITION IN CV MODE )
PIN2 & 3-- +4.9V AT V POT MAX. POSITION.
PIN4 -- +12V ALL CONDITION
PIN7 -- 0V AT CC POT MIN. POSITION.
PIN7 -- 0.5V AT CC POT MAX. POSITION.
PIN8 -- +1V TO 3.5V IN CV MODE.
PIN8 -- +10V TO +11V IN CC MODE.
PIN9 -- 0V.
PIN10 -- -6mV.
PIN14 -- +10 TO 11V IN CV MODE.
5.4.4 A. CHECK VOLTAGES AT D3 CATHODE +2V (CV) +10V (CC)
B. CHECK VOLTAGES AT D4 CATHODE +10V (CV) + 2V (CC)
C. CHECK VOLTAGES AT Z101 CATHODE -4.7V
D. CHECK VOLTAGES AT Z102 CATHODE +10V
5.4.5 CHECK ALL REGULATORS OUTPUT WITH RESPECT TO OUTPUT
+VE COMMON.
REF. PCB NO. PART NO. PIN NO. VOLTAGES
U1 IC7812 3 +12V
U2 IC79L05 3 -5.0V
U3 IC7805 3 +5.0V
CHECK WITH RESPECT TO OUTPUT -VE AS COMMON.
U4 IC7812 3 +12.0V
All the above readings are approximate values. The given voltages & waveforms
are refering to a normal working unit. If find any Voltage or Waveform absent at
given points, then trace back to the associated circuits. This complets basic trouble
shooting test points.
5.5 PARTS ORDERING & REPLACING :
5.5.1 OBTAINING REPLACEMENT PARTS : Most electrical parts can be obtained
through your local distributor or representative. However you should be able to
obtain many of the standard components from a local commercial source in
13

your area. Before you purchase check the electrical parts list for the proper value
rating, tolerance and description.
5.5.2 ORDERING PROCEDURE :When ordering replacement parts from B+K Inc.
please include the following minimum information :
1. Power Supply Type ( 1795 B+K ).
2. Power Supply Serial Number ( For example, 03080001 ).
3. A description of the part ( if electrical include the circuit number ).
5.5.3 CIRCUIT BOARDS : If a circuit board is damaged beyond repair, the entire
assembly including all soldered-on components can be replaced. To remove or
replace a board, proceed as follows :-
1. Disconnect all Sockets & leads connected to the board ( both soldered
lead connections and solderless pin connections ).
2. Remove all mounting screws holding the board in the instrument.Remove
any knobs, etc. that would prevent the board from being lifted out of the
instrument.
3. Lift the circuit board out of the unit. Do not force or bend the board.
4. To replace the board, reverse the order of removal. Use care when
replacing pin connectors. If forced into place incorrectly positioned, the
pin connectors may be damaged.
5.5.4 TRANSISTORS AND IC's : Transistors and IC's should not be replaced unless
they are actually defective. If removed from their sockets during routing
maintenance, return them to their original sockets. Unnecessary replacement or
switching of semiconductor devices may affect the calibration of the instruments.
When a transistor is replaced, check the operation of the part of the instrument that
may be affected.
Replacementsemiconductors shouldbe of theoriginal typeora direct replacement.
When removing soldered-in transistors, use an approved anti-static suction-type
desoldering tool to remove the solder from the holes in the circuit board.
An extracting tool should be used to remove the 14 pin integrated circuits to
prevent damage to the pins. If an extracting the pins. Pull slowly and evenly on both
ends of the IC. Avoid having one end of the IC disengage from the socket before
the other end.
14

CAUTION
Static discharge can damage any semiconductor
component in this instrument.
This instrument contains electrical components that are susceptible to damage
from static discharge. Static voltages of 1KV to 30KV are common in unprotected
environments.
Observe the following precautions to avoid damage :
1. Minimize handling of static-sensitive components.
2. Transport and store static-sensitive components or assemblies in their original
containers, on a metal rail, or on conductive foam. Label any packages that
contains static-sensitive assemblies or components.
3. Discharge the static voltages from your body by wearing a wrist strap while han-
dlingthesecomponents.Servicingstatic-sensitive assemblies or components should
be performed only at a static-free workstation by qualified service personnel.
4. Nothing capable of generating or holding a static charge should be allowed on the
work station surface.
5. Keep the component leads shorted together whenever possible.
6. Pick up components by the body, never by the leads.
7. Do not slide the components over any surface.
8. Avoid handling components in areas that have a floor or work-surface covering
capable of generating a static charge.
9. Use a soldering iron that is connected to earth ground.
10. Use only special anti-static suction-type or wick-type desoldering tools.
15

FAULT FINDING PROCEDURE
( A ) FUSE BLOWS
FUSE BLOWS
Is Line Voltage OK ? Adjust Proper Line Voltage.
Is Fuse Rating OK ? Insert proper rating Fuse.
Is Mains Transformer Tapping OK ? Adjsut the Tap according
to required voltage.
Are Power Diodes Connected
on Heat Sink Short ? Replace the Damaged Diodes.
Is Remote Sense Switch Pressed Release the Remote Switch
in Normal Condition ? in Normal Load Condition.
Is Device Drop setting proper on Load ?
Turn ON the Unit at Rated input Voltage. Load the Unit at
max rated Voltage and Current. Adjust the Voltage between
Output Positive and Capacitor Positive between
4.5V to 5V by using Please VR1 on PREG PCB
1. Check Line Voltage for 230V AC or 115V AC, whichever applicable.
2. Check whether Fuse Present is 20A for 115V AC I/P and 10A for 230VAC I/P.
3. Check the Transformer Tapping, whether it is configured accordingly to I/P
Line Voltage.
4. The Power Diodes connected in Bridge configuration on Heat sink might be
short.
5. If Remote Sense Switch is pressed on Load, in Normal Operation, there is
chance unit may take High Current and Fuse might Blow.
6. If Device Drop measured across O/P Positive and Capacitor Positive is not
between 4.5V to 5V at rated I/P Voltage and rated O/P Voltage and Load
condition, there is a chance of Fuse getting blow in Load Condition.
Note : 4.5V to 5V Device Drop at Full Load.
Y
N
N
N
Y
Y
Y
Y
N
N
N
16

( B ) UNREGULATED O/P VOLTAGE
UNREGULATED O/P VOLTAGE
Is IC LM324 OK ? Replace the IC.
Is Voltage Pot Open OR Replace the Voltage Pot and
Pot Wire is Reaching PCB ? Ensure proper continuity
with the PCB
Are Mosfets OK ? Replace the Damaged
Mosfet.
Is Gate Wire of Mosfet Ensure proper continuity of
Reaching PCB ? Gate Wire and PCB.
Are Diodes D3 and D4 on Replace the Damaged
Front Panel PCB OK ? Diode.
Is INT & COM Terminal on Back Panel Short ?
Short INT COM Terminal when
External Programming
is not in use.
1. Check IC LM324 on Front Panel PCB (L1791-FP-CNT0603).
It might be damaged.
2. Check Voltage Potentiometer (5K Pot), whether it is open or whether the
wiresassociated withVoltage Potentiometer isreachingthe Front PanelPCB.
3. Check the Mosfets and Zener Diodes across Mosfet.
It might be Short.
4. Check Diodes D3 and D4 on Front Panel PCB.
It might be Leaky or Short.
5. EnsurepropercontinuityofGateWire on Front PanelPCBandMosfet module.
6. Ensure INT and COM Terminal at Back Panel are short when External
Programming is not in use.
Y
N
Y
Y
Y
Y
N
N
N
N
N
17