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Apple II Service Notes: Level 2 board repair, disks, and peripherals
- Subject: Apple II Service Notes: Level 2 board repair, disks, and peripherals
- From: dog_cow@macgui.com (D Finnigan)
- Date: Tue, 6 Oct 2009 23:05:29 +0000 (UTC)
- Newsgroups: comp.sys.apple2
- Organization: Mac GUI
- User-agent: Mac GUI City Usenet Posting
- Xref: g2news2.google.com comp.sys.apple2:13967
I want to make sure that this document propogates, so I am posting it here
for posterity too. It should already be at my site, Asimov, and Mike
Willegal's site. Now it is on every site (which carry this group)
Some background of this document: I am the only known source of this
document, or in other words, this document was typed by me. The source was
about 20 hi-res scans of Apple II Service Notes which were type-written back
in the day. The owner of the original, physical document would be my grand
father. There may be other copies of this document around the world. When I
typed from the scans, I tried to retain the essence of the original,
including layout. I have also proof-read the document quite carefully, and
even Mike Willegal helped point out an error which was even on the original.
Therefore, all chip ID's and numbers _should_ be absolutely correct; any
typos in the description text were left there intentionally, as they
appeared on the original type-written document, though I have fixed _some_
misspellings.
Hopefully, the word-wrapping when I post this won't destroy the layout. If
that happens, I will post a follow-up with links to all three known copies
which I mentioned earlier.
Here is an excerpt from email between the two of us which should explain a
little bit of the history.
>>> They are typed notes from an Apple 2 training class.
>>> I did not type them myself.
>>>
>>> I scanned them at a higher resolution but didn't upload
>>> them that way. Let me know if you want a better
>>> resolution for some reason.
>>
>> Also, could I post the text file online? I think it would benefit a lot
of people who are trying to repair their old Apple.
>
>Your idea of posting it would be the best solution for all since there is
no indication of a copywrite or trademark.
> I really don't have a clue to who typed it originally.
Now, on to the real meat of this post. Be sure to save this to a text file
on your computer, because you may need to refer to it, or refer someone else
to it. Maybe some parts could be adapted for the csa2 FAQS.
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Apple II Service Notes
LEVEL 2 SERVICE NOTES
Motherboard Page 1
A no reset condition when there is no cursor, no prompt, and no speaker beep
as obvious symptoms.
Check pin 40 of the 6502 for a high to low transition when the reset key is
pressed. If no
transition occurs check the following: Q5 (2N3904 near A13), 555 timer at
A13, and the
capacitor below Q5 (.1 microfarad). Usually, if Q5 is bad the APPLE will
keyboard reset
(but will not power on reset). If a transition occurs check the following
points with an
oscilloscope: Data Lines D0-D7 (pins 49-42 on I/O slots), Address Lines A0
to A15 (pins 2-17
on I/O slots), Read/Write (the write signal is active low) at pin 34 of the
6502, pin 5 of H5
(8T97), pin 9 (R/W in) of C14, pin 8 (R/W out) at C14. Look for low logic
levels and missing
(except AD7 and AD9 which are normally low) signals. The following IC's
could be at fault.
Symptoms Probable Cause
-------- --------------
Low Data levels B6,7-74LS257
H10,11-8T28
Bad ROM's
Bad Address levels H3,4,5-8T97
Bad ROM's
6502
No R/W signal H5-8T97
C14-74LS32
A2-74LS00
6502
With an oscilloscope check for the 1 MHz clock on pin 37 of the 6502. Also
check B11 pin 1 (74LS08)
for the 1 MHz clock. Check B11 pin 1 for a +5 volt level, C11 pin 13
(74LS04) for a +5 volt level,
and C11 pin 12 for a low level. See schematic for further details. Check the
following IC's.
Symptoms Cause
-------- -----
No 1 MHz at 6502 C11-74LS04
B11-74LS08
RA01 (resistor pak)
Motherboard Page 2
Check the following signals to make sure there is proper RAM addressing.
Check the CAS bar signals
at pin 15 of the RAM. The CAS bar signal at pins 4 ($0-$3FFF), 5
($4000-$7FFF), 6 ($8000-$BFFF)
from F2 (74LS139). Check the CS bar signal at pins 13 of the RAM and pin 7
of C1 (74LS153). Check
the RAM SEL bar at pin 4 of the RAM, pin 6 of A2 (74LS00). Check inputs and
outputs of D2 (74LS20)
and pins 10 ($8000-$BFFF), 11 ($4000-$7FFF), and pin 12 ($0-$3FFF). See the
schematic for complete
detail and check the inputs and out puts of the following IC's.
J1-74LS257 H1-74LS08 F2-74LS139
C1-74LS153 C12-74LS257 D2-74LS20
C11-74LS04 C14-74LS32 A2-74LS00
Also check the Memory Select headers for continuity (except REV. 7 and above
boards)
Check RAM pins 5, 6, 7 and 10, 11, 12 for RA0 (pin 10), RA1 (pin 11), RA2
(pin 12), RA3 (pin 7),
RA4 (pin 6), and RA5 (pin 5) These are the RAM refresh, video addressing
signals. Also check pins
7 and 9 of E11, 12, and 13 (74LS153's). Check the address and sync inputs to
the 74LS153's (see
schematic for pinouts).
If the system works with 16K RAM but not with 32K or 48K check RA02 and RA03
resistor paks.
These located between E10 and E11 and D10 and D11. Check these with an ohm
meter from pins
7 and 9 of E11, 12, 14 between ground and +5 volts. There should be a
reading of about 500
ohms between pin 7 of E11 and ground, also, it should read the same for pin
7 of E11 and +5
volt buss (about 500 ohms). The readings should be the same for each of them
(see schematic for more details).
Motherboard Page 3
The following are some miscellaneous reset and reset related failures and
probably causes.
Symptom Failure
------- -------
Intermittent Reset C14-74LS32
A2-74LS00
E8 ROM
Random characters at keybd reset--
B11-74LS08
F1-jumper block
Chars. moving, appearing randomly on screen--
C11-74LS04
Continuous reset B7-74LS257
Works w/16K RAM but not with 32K or 48K-
F2-74LS139
RA02, RA03
No speaker output J13-74LS74
Beep, no prompt or cursor E11-74LS153
E14-74LS283
F14-9334
No prompt/cursor B3-555 timer
Split location cursor/prompt C11-74LS04
No reset w/ROM card SW down RA01
No reset with Disk Cd. H2,H12-74LS138
Motherboard Page 4
No video, no reset- check 14MHz. output from crystal (B2-74S86 pins 8 and
10). Replace crystal
if no signal. If replacing crystal doesn't help change Q1 and Q2 (2N4258's)
below crystal.
If that does not solve the problem try the following IC's.
A2-74LS00 A10-74LS194 A9-74LS151
B1-74LS175 B2-74S86 B10-74LS74
B11-74LS08 C1-74LS153 C2-74LS195
C13-74LS51 C14-74LS32 D2-74LS20
D11-74LS04 D11, 12, 13, 14-74LS161
Symptoms Cause
-------- -----
Blank white screen- A3-74166
B5,8-74LS174
F14,9334
6502
Blank dark grey screen B10-74LS74
Screen goes blank when disk boots B9-74LS194
Video goes blank during RAM test B2-74S86
Videos wavers C11-74LS04
Pulsating data, speaker clicks H1-74LS08
Video distorted, reset OK D2-74LS20
Top of video missing/distorted B14-74LS02
Video pushed down/to right C13-74LS02
Can't write to upper left screen A9-74LS151
Top 3 lines HIRES gone A11-74LS74
Rolling video B14-74LS32, C11-LS04
Video all ????, scrolls E11-74LS153
Inverse video, cursor not flash B2-74S86
Inverse/incorrect prompt F8 ROM
Split video 4 corners B1-74LS175, C1-74LS153
Split location prompt C11-74LS04, E14-74LS283
No prompt/cursor B3-555 timer
Horizontal lines/junk chars. B5-74LS174
Distorted color bars A12-74LS02
Vertical bars/cold start C12-74LS257
D12-74LS161
F14-9334
2513(char gen)
Vertical bars HIRES B4-74LS194
Left magin vertical white bar A3-74166
Graphics/color bars broken up B4,9-74LS194
No page 2 HIRES open trace B11-6 to R1-10
Black squares w/left to right moving chars.
B12,13-74LS11, 74LS02
No cursor .1uf above 555 B8
Inverse flashes instead of steady inverse
B11-74LS08
Motherboard Page 5
Smallers chars./vertical bars B2-74S86
Moving chars C11-74LS04
Random chars at reset B11-74LS08
Part graphics/part text chars. A11-74LS74
Entire screen !!!!! 2513
Junk chars/ after warmup 27 microhenry choke
Video shows only top halves of letters, you get 2 tops instead of a top and
a bottom
H1-74LS08, char gen 2513 (VC line
to pin 13 2513 held low)
Motherboard Page 6
Miscellaneous Failures
----------------------
Symptom Cause
------- -----
Unable to access disk LED on B5-74LS174
Unable to boot disk H2-74LS138, H3 8T97, H12-74LS138, C1-74LS153
Prompt/no cursor B3-555 timer
Disk boots, screen goes blank B9-74LS194
Goes into monitor, program dies after warm E0 ROM, ROM card, I/O slot 0,
H2,12-74LS138
Keyboard failures (keybd. OK) B6,7-74LS257 B10-74LS74 C11-74LS04
Row D RAM bad, noisy speaker H1-74LS08, J1-74LS257,
D2-74LS20, Jumper blocks (except Rev. 7)
_ Row RAM bad- same as above
Adds chars, and scrolls from bottom B6,7 74LS257, F12-74LS138, B10-74LS74
Peripherals Page 1
ROM CARDS
---------
This will cover both Applesoft and Integer ROM Cards.
Symptoms Cause
-------- -----
Apple won't reset 74LS09 INH bar line held low
74LS11 R/W being held
74S74
74LS244 Data lines being held
Won't go into FP 74S74
D0 ROM
74LS138
Wom't go into INT. see above
ROM fails test even when replaced w/good 74LS09, 74LS138
Apple resets with switch down but not up -Bad Switch
Peripherals Page 2
Serial Card
-----------
Symptoms Cause
-------- -----
Apple won't power up 74LS109
74LS365
P8 Prom
P7 Prom
Proms test bad after replaced Q1,Q2-2N3906 & Q6-MPSU51
Switches test bad 74LS365
Not receiving 74LS125, Q7-2N3904
Not transmitting 74LS109, Q3-2N3906, Q4-2N3904
Peripherals Page 3
Communications Card
-------------------
Symptoms Cause
-------- -----
Apple won't reset Prom P2
DP8304
Prom tests bad when changed Q1,Q2-2N3906
Q3-MPSU51
Card will not respond to PR#/IN# command
MC6850
74C161 (A1 and A2)
74LS74
No RS-232 Output signal Q4,Q5
No RS-232 Input signal Q6
Peripherals Page 4
Parallel Card
Symptoms Cause
-------- -----
Apple won't reset 74LS74
P1 or P9 Prom
Drive won't boot 74LS74
After PR#n command prompt doesn't return Q2-MPSU51
Prom tests bad after replacement Q1-2N3906, Q2-MPSU51
Wrong data being printed 74LS174
74LS298
Not acknowledging data received 74LS74 at B2
Not generating Data ready strobe 74LS74 at B2
Peripherals Page 5
KEYBOARD
--------
Old Style-single board model
----------------------------
Symptoms Cause
-------- -----
Key doesn't work (example-no A) Keyswitch bad
Series of letters don't work (for example "9", "6", "5" or "Q", "ESC",
"A", "Z", "1")
Encoder (331-5740)
bad traces or feed throughs
No control function Keyswitch
U1 (7400)
R1 (4.7K Ohm)
No shift chars. U4 (7400)
No output at all Cable bad
5740 (encoder)
No keyboard strobe encoder
U1 (7400) check pin 3
No output/wrong output U2 (7404)
encoder
Encoder not being clocked U4 (7400) pin 3 on encoder
Repeat key does not work U3 (555 timer)
Characters repeat Encoder
Wrong characters Encoder
Characters repeat after unit warm Encoder
New style keyboard (two part)
-----------------------------
Symptoms Cause
-------- -----
No keyboard output Encoder (331-0931)
No Data Strobe (no keybd output) B3 (74LS00)
B4 (74LS00)
C6 (.1 microfarad cap)
Incorrect data out Encoder
B5 (74LS04)
B3 (74LS00)
No output Cable
P, Return, and : keys repeat Change R10 to 3.0K ohm 1/4 watt
resistor. See Apple Service Bulletin #15
Peripherals Page 7
Language Card
-------------
Symptoms Cause
-------- -----
Apple won't reset 74LS09 --> D0 ROM fails
Works w/Pascal but won't load Basics correctly
74LS09 --> will run Integer, but not Applesoft
No reset 74LS175
74LS08
Autostart ROM
RAM Bad
RAM tests bad RAM
Bad cable
74LS09
Not bank switching 74LS86
74LS00
74LS09
74LS08
74LS74
74LS175
74LS20
When repairing Language Cards the most common failure is it just won't work,
won't load
Pascal or Basics. It is difficult to give symptom "X" and say that IC "Z" is
the cause.
Each IC has more than one function and all are interrelated.
Disks Page 1
Disk Drive
----------
Symptom Cause
------- -----
Apple won't power up (dc) 74LS259
74LS323
74LS05
Drive motor on 74LS125 (analog)
74LS174 (controller)
Won't boot P5 (controller)
Q1 (analog)
P6 (controller)
74LS125 (analog)
Q2 (controller)
74LS132 (controller)
74LS259 (controller)
Write current on CA3146 (analog)
74LS125 (analog)
CR3 (IN4148-analog)
74LS05 (controller)
ULN2003 (analog)
P6 (controller)
No drive motor motion motor control bd. (10K pot)
No stepper motion ULN2003 (analog)
cable
No motor speed displayed by test MC3470 (analog)
74LS125 (analog)
74LS174 (controller)
74LS132 (controller)
Motor speed OK, displayed speed high (+1200)
74LS05 (controller)
CA3146 (analog)
Write protect always on Cable
74LS323 (controller)
P6 (controller)
Unable to test (Rd/Wr error) 74LS05 (controller)
ULN2003 (analog)
P5 or P6 (controller)
Disks Page 2
Symptom Cause
------- -----
Diskette not initialized (test#4) P5 (controller)
CA3146 (analog)
Adjust comparator (TP7)
Load button
Data error (checksum) P6 (controller)
Adjust TP7 (comparator)
74LS132 (controller)
Motor spins on pwr. up 74LS125 (analog)
Won't boot (diskette OK) P5 (controller)
Alignment
74LS259 (controller)
Won't boot (wipes diskettes) 74LS125 (analog)
CA3146 (analog)
74LS05 (controller)
Drive does not run at all Q1 (analog)
P5 (controller)
74LS259 (controller)
74LS132 (controller)
Apple does not reset P5 (controller)
74LS259 (controller)
74LS05 (controller)
74LS323 (controller)
NE556 (controller)
Boots, gives I/O error for inside tracks/unable to read/unable to
write when copying
Head alignment
The unchangeable chip on the drive board is an MC3470
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