Topic: Atari Tempest PCB Repair Log  (Read 3663 times)

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Offline EQUITES

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Atari Tempest PCB Repair Log
« on: December 14, 2012, 12:45:11 PM »
I recently took ownership of a Tempest PCB set, I had no information on it's history. This was the first time I have looked at a Tempest, although I did have some experience repairing Asteroids PCBs.

The PCB was initially dead, checking the ROMs against ROMident found three bad ROMs, which included a bad Vector ROM at N/P3.  It may be interesting to note that aside from the Vector ROMs at N/P3 and R3, only ROM R1 is required in order to run test, and the PCB will report up to eight bad ROMs at any one time.

Fresh ROMs were burned and the PCB would then go into TEST mode, which when compared to MAME did not seem 100%.



The following TEST screen reveals a bad ROM and a Mathbox problem which is related to the AUX board;













In-game forced the PCB to reset constantly, as watchdog was barking.  Grounding the watchdog just left the PCB dead.

I had done the following;

Confirmed my test rig is fine with a working Tempest PCB set.
Connected a proven working AUX board (no change).
Used a new (Bob Roberts) Interconnect cable (no change).
Reflowed all Interconnect header pins.
Verified all 8 Vector RAM 2114 ICs as good (no RAM check sound in TEST either).
Checked all voltages on the MAIN board and AUX board.

I'd made some assumptions here, however, these were made by comparing the SELF TEST in MAME to what I had on a real PCB.

Screen 1 of the SELF TEST will only show if the SELF TEST is activated during in-game. Otherwise, if the PCB is powered from SELF TEST active, it will jump straight to Screen 2.

Screen 4 - In MAME this shows a square being scaled down, however, on a real PCB all you see is a static cross. EDIT: I've just realised that I am running Rev.1 ROMs on my PCB. Checking MAME using Rev.1 ROMs indeed shows a static cross on SELF TEST. Only Rev.3 ROMs show a square scaling down in size.

Therefore, it would seem SELF TEST is working 100%.

The only thing to add, is the on the top left hand corner of the screen on Screen 2 SELF TEST, I can see some digits which suggest ROM issues.  The thing was, the re-trace lines on my scope make it hard to make out.

However, I was able to determine that the digit was a '2', which according to the manual is ROM D1.  I had already confirmed that the ROM was fine, so suspected the socket.  This was replaced, but I saw no change.



I was beginning to think this was a ROM addressing issue.  However, I quickly dismissed this as the address lines and data lines are all shared, and the TEST mode was working fine.  

I went back to the multiplexor LS139 at C1, this controls the Output Select on the ROM at C1. I had previously probed this IC, but had made the fatal mistake of leaving the PCB in TEST mode where the pin would not be active anyway. Hence, I never spotted that pin 6 was stuck HI, and therefore it could never select the ROM during game mode.

The Maths box problem was due to a bad ALU and PROM - all working 100% now.



« Last Edit: December 14, 2012, 12:48:20 PM by EQUITES »

Offline porchy

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Re: Atari Tempest PCB Repair Log
« Reply #1 on: December 15, 2012, 07:29:10 PM »
I've never played the arcade version of this but the jaguar version is pretty damn nice.
Nice save, Nad

Offline Elgen

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Re: Atari Tempest PCB Repair Log
« Reply #2 on: December 29, 2012, 08:10:43 PM »
The Jag-version T2K is one of my (if not THE) All Time Favourites };-P

I love Minters all stuff...

Fantastic save.