Williams R8731 : CMOS error

tmcw

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Got an untested R8731 (Revision B) the other day.

It's pretty much a Rev-B, except that it has the 2G chip taken out, a socket put in, and a little daughterboard inserted into the socket, the daughterboard having a chip (N8T97N 8131) and a SIP resistor package, I presume to make the board similar to the Rev C and D MPU boards?

It originally had 4116's, and when I initially tested the board, I was getting RAM errors, and was able to move the error around, but didn't spend much time on that, as I planned on modding the board to take 4164's.

Did the 4164 mod today, and put the board into the game (Stargate, all other boards and power supply working correctly), get the "all systems go" message, "0" on the ROM board, but the game then displays a message about "adjustment error".

If I press advance at that point, it goes to the game, and I can play, etc., but the high score screen is fully populated with scores of 888,888, and no inititals. When I begin a game, I have more than about 18 ships and smart bombs.

In the game adjustments, the settings for extra men, etc, have values like 98,888, or other ridiculous values like that. One thing I did notice was that with batteries in (giving 4.1V), I was able to set the game to freeplay, and it seems to be retaining that adjustment.

In game diagnostics, it passes the RAM and ROM tests, but I then get a CMOS error message.

Is this definitely pointing to a bad CMOS chip, or is there anything else I need to check first?

I pulled the decoder ROMs and 6809 off the board and tested them in a good board, and they functioned fine. Also checked traces off the CMOS chip to where they should go, and they checked out fine too.
 
Go to the adjustment screen and set the reset to factory settings to yes, the reset high score to yes and the clear bookkeeping to yes. Then press the advance button to exit the adjust screen. You will need to press the adjust button again to start the game. Then go to the adjustment screen and see if the values have been reset to more sane values. If not, then the CMOS chip need to be replaced.

ken
 
Thanks, tried that, but didn't get me anywhere, values are still crazy.

When I go into the game adjustment, the state of the "restore factory settings" and the other 5 below it are all already set to "Yes Press advance to reset". When I press advance, I get the various screens saying the values are being reset, and when I get to the last one (setting some message, IIRC), I need to turn the game off then on; none of the buttons allow me to get past that screen, maybe that's normal?

I did go through the diagnostics procedures again, and when it gets to the CMOS RAM test, I can see "3", then "1", flash twice on the ROM board, which the manual states the game should then display "CMOS interlock failure", but I get "CMOS write error or write protect failure - tabletop must be raised for test".

When I swap this MPU board out for another board, the CMOS test passes fine, so I presume the tabletop interlock switch is ok.

So, it's looking like the chip is bad?

I see the 6114 on GPE is a recommended replacement. Are there others, or is this the best option? Half thinking of going the NVRAM route since the board still has the AA connectors, but it looks tricky to make, and expensive to buy (relative to a replacement CMOS).
 
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