Had to look at a couple of Gauntlet II PCB's recently. Both were revision A boards and both had sound issues:
Board 1:
Symptom: Board would start up and play FX and speech but no music, test mode indicates sound CPU and RAM good but no music playing no obvious errors on screen.
On inspection of the board, an LM324N @ 14T was missing meaning everything was leaving the CPU and YM2151 but going nowhere else towards the amplifier side.
Socket installed and fitted an LM324N and sound restored, burn tested and ok.
I regret not taking pictures of the missing chip, I just ploughed on with this one.
Board 2:
Symptom: Board starts, enters test mode ok but sound test reports Sound CPU bad RAM 1 & 2 error. No music, fx or speech heard.
All components present on this one, tested the 2 x 6116's @ 16NP and 16M in rom tester, reports ok, start to debug rest of circuit, 6502 working and resetting fine, ROMs verified ok.
Remembering that part of the eventual resolution to the Pole Position issue was the 6116 NVRAM being bad I decided to pop in 2 6116's I bought a short while ago, suddenly the sound CPU resets ok and the music plays, effects and speech. Ah, fixed I think.......
A trip around the test mode and back to sound test and the music is playing badly, hmmm, change RAM still same issue, consult schematics, requires HM6116, look up datasheets for the AM9128's that someone had put in the board, the MB8128's I have on hand and the HM6116's that the scheme recommends. There seems to be timing differences.
I remember Luke Wells telling me that Atari boards were sometimes put together with voodoo curses and that the chip timings affect the gameplay and other things on some boards so it looks like the HM6116's are 100-120ns and the MB8128's are 150ns and the AM9128's are different too.
Ordered a couple of HM6116P-2's which are 120ns which arrived this morning, popped them in and ta-da the board is fully working. Soak test for a few hours and still good.
Had the strength to do a video on this as well:
[tube]TWVZPWldw5I[/tube]
Now onto board 3 which appears to be a bit on the dead side....
RGP2014-10-22 18:39:15
Board 1:
Symptom: Board would start up and play FX and speech but no music, test mode indicates sound CPU and RAM good but no music playing no obvious errors on screen.
On inspection of the board, an LM324N @ 14T was missing meaning everything was leaving the CPU and YM2151 but going nowhere else towards the amplifier side.
Socket installed and fitted an LM324N and sound restored, burn tested and ok.
I regret not taking pictures of the missing chip, I just ploughed on with this one.
Board 2:
Symptom: Board starts, enters test mode ok but sound test reports Sound CPU bad RAM 1 & 2 error. No music, fx or speech heard.
All components present on this one, tested the 2 x 6116's @ 16NP and 16M in rom tester, reports ok, start to debug rest of circuit, 6502 working and resetting fine, ROMs verified ok.
Remembering that part of the eventual resolution to the Pole Position issue was the 6116 NVRAM being bad I decided to pop in 2 6116's I bought a short while ago, suddenly the sound CPU resets ok and the music plays, effects and speech. Ah, fixed I think.......
A trip around the test mode and back to sound test and the music is playing badly, hmmm, change RAM still same issue, consult schematics, requires HM6116, look up datasheets for the AM9128's that someone had put in the board, the MB8128's I have on hand and the HM6116's that the scheme recommends. There seems to be timing differences.
I remember Luke Wells telling me that Atari boards were sometimes put together with voodoo curses and that the chip timings affect the gameplay and other things on some boards so it looks like the HM6116's are 100-120ns and the MB8128's are 150ns and the AM9128's are different too.
Ordered a couple of HM6116P-2's which are 120ns which arrived this morning, popped them in and ta-da the board is fully working. Soak test for a few hours and still good.
Had the strength to do a video on this as well:
[tube]TWVZPWldw5I[/tube]
Now onto board 3 which appears to be a bit on the dead side....
RGP2014-10-22 18:39:15
