3 Classic Atari Repair Logs

DarrenF

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Recently three true classics by Atari have crossed my workbench:

ASTEROIDS
Condition: Plays fine, but explosion sounds are just beeps

Analysis: Schematic review reveals that explostions are created by a simple circuit; a noise generator which consist primarily of a pair of shift registers. The problem isn't triggering, because the sounds ARE being triggered... they're just beeps (pure tones) instead of explosions.

Diagnosis: Logic probing showed that the second in the cascading shift registers wasn't working.

Repair: replaced bad LS164 @ P9

LUNAR LANDER
Condition: DOA. Closer inspection (with scope) showed it was resetting repeatedly, with no apparently output (audio or video). Disabling watchdog caused it to hang.

Initial Investigation: Scope showed that the clock is fine, and the CPU is nominally working. I pulled the EPROMs, read & ID'd the data (all OK), and also replaced the bipolar PROMs on the board with EPROMs. Now I got a 2-beep error code, indicating a bad RAM.

Repair 1: Replaced 2111A RAM @ E2. Now get all good beeps in test mode, and some vectors. However, instead of text, all I saw was some vertical lines.

More investigation: The vertical lines pointed to a problem in the X counter section. A little probing found an inverter gate which wasn't inverting. This was causing the counters to never get clocked (which explained why the vector generator could LOAD a position into the counters, but it wouldn't move after that).

Repair 2: Replaced 7404 @ H10. Now I got good text in test mode. It is reporting bad ROMs "8 9 10 11 20 21 22 23" (or something similar, I forget exactly). The 8 9 10 11 is normal (no foreign language ROM installed), but the others indicate a real problem.

More problems: At this point, I began having some intermittent issues... different ROM errors, occational RAM errors, etc., so I...

Repair 3: I replaced all of the EPROM sockets and the CPU socket. Now test mode reports normally, and game mode works as well.

MISSILE COMMAND:
Condition: Dead. In game mode: solid green screen, flashing constantly (due to resetting). In test mode: rumbling, long low beep, short high beep, reset, repeat. WD disable causes game mode to reset less often, but has no effect on test mode.

Futile attempts: Pulled & verified EPROMs (all OK). Repaced EPROM sockets (no change). Swapped out CPU & POKEY (no change). Piggy-backed RAMs (no change). Found very hot glass capacitor & replaced (no change).

Analysis: By following the test-mode code in MAME, I was able to understand just what's
going on during the boot process. I was able to trace the progress thru the "rumble" sounds (just a delay loop waiting for VBLANKs), the long low beep (the RAM testing, which was all good... you get a series of beeps if an error is found), then the high beep. I noticed that ALL of the code up to this point was in two ROMs (N/P1 & R1), but shorly after that, it jumps into some code in another ROM. Looking at the schematics, I saw that there are actually two different data paths for different groups of ROMs: N/P1 & R1 thru the LS244 @ N/P3, and the rest use the LS244 @ B/C1. Eureka!

Long story short: I found two bad LS244s. One @ B/C1 and another @ E2. Board fixed.
 
Still wish you lived closer. Congrats for taking on some Atari vectors. Ready for some more Asteroids boards???
 
Ready for some more Asteroids boards???

Sure. Unless it's a problem I can easily isolate based on the symptoms (like the sound issue was) I don't really have a good way to bench-test them, unless you can send a power block, harness & AR board with it :) Or at least the power block & AR board... or maybe as long as Doug has spare to borrow, we're good... Anyhow, I can use the scope instead of a monitor, but the PITA is the variety of power supplies Asteroids needs, there's no easy way to do it w/o the original power supply.

Thanks for documenting this

Nice work on the repairs :)

Thanks. For some unknown reason, people on KLOV don't really seem to give a shit about repair logs. Maybe it's due to the lack of a dedicated sub-forum for them... (or maybe it's because no one here is actually interested in PCB diagnosis & repair, but just wants to know how to fix all their problems by replacing a "Big Blue" and/or re-seating EPROMS). I don't know. But sometimes I feel like I'm almost the only person that ever posts a repair log. I'm very tempted to make the move to aussiearcade; there's a fairly active repair log forum there.
 
Sure. Unless it's a problem I can easily isolate based on the symptoms (like the sound issue was) I don't really have a good way to bench-test them, unless you can send a power block, harness & AR board with it :) Or at least the power block & AR board... or maybe as long as Doug has spare to borrow, we're good... Anyhow, I can use the scope instead of a monitor, but the PITA is the variety of power supplies Asteroids needs, there's no easy way to do it w/o the original power supply.



Thanks. For some unknown reason, people on KLOV don't really seem to give a shit about repair logs. Maybe it's due to the lack of a dedicated sub-forum for them... (or maybe it's because no one here is actually interested in PCB diagnosis & repair, but just wants to know how to fix all their problems by replacing a "Big Blue" and/or re-seating EPROMS). I don't know. But sometimes I feel like I'm almost the only person that ever posts a repair log. I'm very tempted to make the move to aussiearcade; there's a fairly active repair log forum there.

Well you are most welcome on AA any time

Just trying to get ideas to fix some of my own :)

Once again, cheers Darren
 
I also appreciate them. Thank you for taking the time to post them. I agree that it would be nice to have a dedicated repair log section of the forum.
 
I also enjoy the repair logs. I read them on games that I do not even have. I once found a log for the exact problem my rip off was having, without it my rip off would probably still not be working. I read them in hopes to learn a little something every time.
 
Keep 'm coming, we DO care !!! Got a LL board here that I will need to fix (after reconverting it from Asteroids) so your log may be very helpful in the future. I also always read the others, learning all the time :)
 
now now darren, i post then on the village :p

I like the village for a lot of things... but's it's no hot-bed of repair logs.

i appreciate the repair logs. Thanks for posting
Keep posting Darren. I am certain they are being read, but just not replied to.
I definitely appreciate the logs.
No doubt posts like this are very useful.
I too appreciate them alot.
I also appreciate them.
I also enjoy the repair logs.
Keep 'm coming, we DO care !!!

Thanks, everyone, for taking a moment to express appreciation. My annoyance isn't really that the effort isn't appreciated, or read, or anything like that. It's that hardly anyone else seems to be jumping on the bandwagon, and posting their own repair logs. And the few that are posted... well, they seem to get lost among the other noise in the repair forum.

So I guess the problem is mainly the lack of a dedicated sub-forum; and the draconian restrictions on attachments, which makes it more of a PITA to put photos, screenshots, schematic snips, or whatever in a repair log. (I mean, seriously, 100kB limit? Is it still 1998?)
 
Problem is I very very rarely do PCB repairs. I did do my Centipede though, fixed inputs by replacing the buffer IC, fixed the sound by replacing the LM324 and some other basic thing I fixed I can't remember.....but that's all standard stuff.

I'm lost when it gets too complicated.

Best work I do is on Amplifone's and a bit less on WG6100's but almost all about that is documented too....
 
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