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