Commodore PET 2001 Series User manual

Commodore Business Machines, Inc.
901 California Avenue
Palo Alto . California 94304, USA
Commodore/MOS Technology
Valley Forge Corporate Center
950 Rittenhouse Road
Norristown , Pennsylvania 19401, USA
Commodore Business Machines Limited
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Aginco\Jr( Ontario , Canada M1W2K4
Commodore Business Machines Limited
Eaglescliffe Industrial Estate
Eaglescliffe, Stockton on Tees
Teeside TS
160 PN, England
Commodore Business Machines Limited
360 Euston Road
London NW1 3BL, England
Commodore Biiromaschinen GmbH
Frankfurter Strasse 171- 175
6078 Neu lsenburg
West Germany
Commodore Japan Limited
Taisei-Oenshi Building
8-14 lkue 1- Chome
Asahi - Ku , Osaka 535, Japan
Commodore Electronics (Hong Kong) Ltd .
Watsons Estates
Block C, 11th floor
Hong Kong , Hong Kong
~cornrnodore
Copyright 1978 by Commodore Business Machines Inc .
I

(
Testing the PET Computer
The PET Test includes a cassette tape containing four diagnostic
programs and the diagnostic connector. Let's first look at these two.
The program list includes
the ROM test, the memory poker, the data
checker and screen alignment.
They're recorded redundantly and, in
the case of memory and data, for both the 4K and the 8K units. The
exact sequence can be found below.
The diagnostic connectors,
one connected to the keyboard connec-
tor and the other to the user port, enable you to conduct the diag-
nostic routine resident in the ROM.
You will now be able to check
out:
• all RAM chips
• the parity of ROM
• the keyboard circuit
• the TV display logic
• the read/write of both cassette ports
• the user port
• the I.E.E.E. 488 port
Program List for Diagnostic Test Tape
I.
ROM Test
2.
ROM Test
3.
ROM Test
4. 4K Memory POKER
5. 4K Memory POKER
6. 8K Memory POKER
7. 8K Memory POKER
8. 4K Data Checker
9. 4K Data Checker
I0. 8K Data Checker
11. 8K Data Checker
12. Screen Alignment
13 . Screen Alignment
I. Diagnostic Routine -
Using the Diagnostic Connectors
A. Opening the PET Computer.
1. Press the rocker switch to the "Off" position.
2. Remove the power cord from the wall socket to avoid pos-
sible electrical shock.

3. Remove the two screws located on each side of the unit
und er the lip of the cover.
4. Lift
the cover slowly- a few inches. When you locate the cable
leading
to the cassette, remove the connector at the main
board.
Then li ft the cover a ll the way up and engage the sup-
porting rod located on the l eft side of the cover.
B. The Diagnostic Connectors
1. Remove the keyboard cable from the connector on the main
logic board.
2. Insert the proper diagnostic connector into this connector.
3. Insert the other connector into the user port. Make sure of
power polarity.
ROW A CHARACTER GENERATOR
ROM 6522- VIA
ROW B TIMING CHIPS AND
6520 PIA
ROW C BUFFERS AND TIMING
ROW D BUFFERS AND TIMING
C. The Diagnostic Routine
1. Turn on the PET.
2d CASSETTE PORT
\
A
MEMORY
~_,_r,vvv C EXPANSION
_.~ , .~ , PORT
ROW F MPU
ROW G 6520 PIA AND TIMING
ROW H ROMs
ROW I RAMs
ROW J RAMs
2. The routine will now clear the screen. (The red LED on th e
main
board should not be on.)
3. The c ur sor should now begin to sweep across all locations on
the TV screen.
4. When
the cursor leaves the screen at the bottom right, the
display will fill
with a fu ll character test pattern. Use this
test pattern to check visually for all characte rs; make sure
that no bits are flickering on the screen.
5.
The red LED shou ld now be lit indicating the main logic
board has passed the diagnostic test.
D. Completing the Diagnostic Routine: Extended BASIC Test
I. Turn off the PET. Remove the keyboard diagnostic connec -
tor and reconnect the keyboard cable. Remove the diagnostic
connector from the user port . Close the unit and turn the
PET back on.
2. The TV display should clear and then display the follow in g:

FOR 8K MODELS
***COMMODORE BASIC***
7167 BYTES FREE
READY·
•
E. Removing the Logic Board
FOR 4K MODELS
***COMMODORE BASIC***
3067 BYTES FREE
READY
•
In the event that the logic board needs to be replaced, please note
that the board is secured by three (3) screws and three (3) locking
standoffs.
1. Remove all connectors to the board.
2. Remove the three screws.
3. Unlock
the stand-off while pulling the board up off the
standoffs.
NOTE. The following series of four tests will be in conjunction with
the diagnostic program tape.
II. The ROM Test
A. Procedure for Loading
1. Open the cassette drive cover and place the cassette in just
as you would a normal audio cassette.
2.
Type in LOAD, or hold down the !SHIFT! key and touch
and release the IRUN/STOPIkey. (Either way your screen
should
show LOAD.) If you typed in LOAD, now type
in RUN.
3. Press the key labeled "PLAY" on the cassette unit .
4.
Your screen should now show:
LOAD
PRESS PLAY ON TAPE #1
OK
SEARCHING
FOUND PROGRAM (program name)
LOADING
5. Let the program run until the PET is warmed up (approxi-
mately fifteen
minutes) .
B. Verification
This test will verify all ROM chips. If there is a failure, a number will
a ear
to the rioht of the cursor. The number on the screen refers to
the position of the defective ROM (1 to 7) which will always appear
in row H. Now, shut off power, replace the defective ROM, and turn
the power back on.
C. Repeat Test
In the event a ROM has proved to be defective, repeat the test. This
will assure
you that no other ROMs are defective. It's also a safe-
guard: a defective ROM can
make the program invalid; repeating the
test will overcome this.
To repeat the test, repeat steps 1, 2, 3, and 4 in Procedure A above.
(Remember that there are three consecutive ROM Tests on your diag-
nostic program tape. Had there been only one, you would have to
first rewind the cassette and start again).
Ill. The Memory Test (Memory Poker)
A. Procedure for Loading
1. Follow
the general method for loading as outlined previously.
But this time, type LOAD "8K MEMORY POKER" (or 4K
Memory Poker, if you're testing a 4K). This will allow the
PET to skip through ROM TESTS #2 and #3, and the 4K
Memory Poker, if you're testing the 8K. See the program list
on page 1. Then type in RUN.
2. Allow the program to run at least 1000 seconds (approxi-
mately seventeen minutes).
B. Locating Defective RAM
If a failure occurs, the location of the defective RAM will be dis-
played
on the screen in this fashion (as an example):
1
13D2-H
Where the first character (I) is the row, the second (3) is the position
in
the row. Both are printed on a reverse field. The D refers to data
and the next digit indicates the data bit. (The second data bit in this
case.)
The last character (H or L) refers to the failure condition
(High or Low).
C. Replace the Defective RAM
D.
Repeat Test, following the same procedure as in II C.

IV. The Data Checker (Cassette Test)
A. Procedure for Loading and Testing
1. The cassette mechanism shou ld be checked for proper
mechanical operation . Insert a cassette in the player. Test
rewind and fast forward functions. Test play and
stop button.
Listen for any loud rubbing or grinding noise. Finally, test
the eject
function of the cassette mechanism.
Before
you verify the read /w rite capability of the cassette
player, follow
the procedure on "Cleaning and Demagnetiz-
ing Tape Deck
Head" as indicated in "An Introduction to
Your PET" book.
2. Attach the second or external cassette drive to the port in
the rear right
corner of your PET.
3. Following the procedure outlined previously in II A, type in
LOAD "8K DATA CHECKER"
(or 4K, as the case may be).
4. Let program cycle and check for errors.
5. Remove cassette program, insert a
rewound blank tape. Type
SAVE "PET#" IRETURN I
(The# may be any that you choose.) The PET should display
}
PRESS PLAY AND RECORD ON TAPE #1.
Hold REC (record) button down on cassette drive while en-
gaging
the PLAY button. The PET BASIC will save this pro-
gram
on the blank tape under the new name.
6. When cursor
returns to the display, stop the cassette drive
and rewind
the tape.
7.
Type
VERIFY !RETURN!
B. Verification-First (Built-in) Cassette
1. The PET BASIC should find and verify the program just
saved on Tape # 1. Check the name of the verifying program.
It should be the name it was saved under. The "VERIFY"
should finish with an OK.
a. If the screen displays
r? VERIFY ERROR
there could be a tape or memory retention problem.
2.
Type
PEEK (630) ,ST IRETURN I
Two numbers should appear in the display. The first number
represents the amount of drop-out times 2 and should be
less than,
or equa l to , 4. The second number represents the
status word and should be zero.
a. The cassette
read/write capability has been verified with
the external ca~sette application.
C. If First Cassette Malfunctions:
I . Test cassette drive by disconnecting male connector of
cassette on logic board. Substitute a tested cassette drive.
2. To remove
the cassette assembly entirely, remove cassette
connector from main board, loosen the two screws on the
rear bracket, and remove the
two screws located in the
front of the unit.
D. Testing Second (External) Cassette Drive)
I. Remove tape from built-in cassette drive and transfer to the
exte rnal cassette drive.

2. Type
VERIFY" ",2 (RETURN]
3. When the display reads
(PRESS PLAY ON TAPE #2
do so.
4. Follow same verification procedure
as B, above.
V. Screen Alignment
A. Procedure for Testing
I. Type
LOAD "SCREEN ALIGNMENT"
2. The GET command in BASIC will offer three choices in
display: I, 2, or 3.
a. I is the checker board across the entire screen.
b. 2
is a crisscross pattern across the entire screen ...
for alignment.
c. 3 creates a pattern of @signs and represents 0 in the
binary memory code.
B. Observation and Correction
On the basis of the condition observed, as set forth below, this
is what the correction should be:
1. Vertical size too large (can't see top or bottom lines).
a. Correction: Located to the right and back of the display
assembly
!sa white trimmer pot standing on end with a
slot on it. Turn the slot clockwise
or counterclockwise
until you achieve the proper size.
2. Screen
is slanted.
a. Correction: Loosen the locking screw on the yoke as-
sembly. Rotate the yoke clockwise or counterclockwise
until
you achieve proper alignment.
3. Screen
not centered.
a. Correction: The yoke assembly has 2 metal rings with
taps located in the center
of the yoke. By rotating one
or both rings, move the picture in a circular pattern.
Adjust until screen
is centered.
APPROXIMATE
LOCATION
OF
STANDOFF
/
CRT CONNECTOR
--- --HIGH VOLTAGE
NUTS
CONNECTOR
APPROXIMATE
LOCATION OF
STANDOFF
You have now completed the diagnostic routines using the connec-
tors and the cassette program. You've tested virtually everything,
except the keyboard and the cassette mechanism.

VI. The Display Assembly
CAUTION: THE DISPLAY C IR CUIT GENE RATES 10,000 VOLTS
D. C. EXTREME CARE MUST BE USED.
On the assumption th at the display is faul ty, here's how to remove thb
assembly. We will not discuss how the testing of the assembly per se;
the diagnostics routine should have given us all the needed information.
A. Unplug your PET from any electrical outlet.
B. Remove the three screws from the cover plate on the upper
housing and lift off the plate.
C. Unplug the main board connector .
D. Discharge
the CRT by grounding the high voltage connector :
connect a clip lead from the brightness pot . lead to the shank of a
thin bladed screwdriver (with a well-insulated handle). Then , with
the blade of the screwdriver, reach beneath the plastic cover on the
side of the tube.
E. Unplug the CRT connector by pulling it straight back from the
CRT.
F. Turn
the locking screw on the yoke until it is loose. Pull the yoke
straight back off the picture tube.
G. Unplug the high voltage lead.
H. Remove the two nuts securing the display board.
I. Lift the display board up off the two plastic locking standoffs and
remove
the board from the housing.
VII. The Keyboard
A. Testing.
10
Verify all keys are operational and that each character on the
keyboard corresponds to the display.
2.
Type the following sequence of characters and verify that
they appear on the screen:
! /1 # $%'&/() *-
QWERTYUIOP t
ASDFGHJKL :
ZXCVBNM ,; ?
@ [ ) <>
7 8 9 I 456 * 1 2 3 + o.- =
ISPACE I I RETURNI
PET should respond with
? SYNTAX ERROR
READY .
3. Type this line
? " ICLR HOME I AND I SHIFT I ICURSOR .).I ICURSOR ""* I
IOFFRVS I AAA I RETURNI
Screen should clear and show
r~
READY .
B. Malfunctioning
1. Assuming there is a keyboard fault, replace the keyboard with
one
you're sure of.
a.
The keyboard is secured with eight screws. Remove
these, then press firmly down on the keyboard until
assembly comes loose.
2. If unit still
malf unctions, assume the logic board is at fault.
b.
The board is secured by three screws and three locking
standoffs. Remove alJ connectors to the board. Remove
the three screws. Unlock the standoffs while pulling the
board up off these standoffs.
11

VIII. 1esnng upper ana Lower \Jase
A. Type POKE 59409, 52
1. The TV display should go blank.
B. Reset the PET by turning power switch off then on.
C. Type
+++ZZZ
(+is the shifted Z)
(Use cursor to go down and to the left)
POKE 59468,14 IRETURN I
the row of characters should change to
( zzzZZZ
D. Now type
POKE 59468,12 IRETURN I
The row of characters should once again read
( +++ZZZ
12

ERRATA
Testing The PET C
omputer
Jlage I. Pa rag ra ph 5 should read:
I. ROMTest
1 RO
I\ ·1Test
3. ROM Test
4. 4K Memory POK er
S. 4K Memory POK er
(L 8K Memory POK er
7. 8K Memo ry POK er
8. 4K Data Ch e<.: ker
9. 4K Data Che <.:k er
I0. 8K Data Ch
e<.: ker
II . 8K Data Ch e<.: ker
12. Screen Ali gnment
13. Sn een
Ali gnment
14.
01 9 ROM Test
IS. 019ROMT est
Page 7, Item B2 should re
ad :
Type
? PEEK(630), ST I RETURN I
Page II , Item 3. should re ad :
Typ e this lin e:
? "I SHIFT I AND I clR HOME I IcURSOR I I I cURsoR .... I
IOFF RVS I AAA I RETURN I
Page 5. should be added to Item J B:
Wh en testing with 2114 RAMs
The position in the rows will be rever se d. if th e sn ee n shows
130 2- 11 then the defe div e RAM is in position I(• a nd not in
position 13.
Page 4 II , S:
NOT E: If test shows ROM II I def e div c, you are prob-
ably not us in g the <.:orr ed ROM Test. Lo ad 01 9 ROM
Test in and note if ROM Ill shows dcfe div e again.