Williams System 6 (Time Warp) Sound Problem

[pinnies4me]

 

Diagnosing apparent board problems is not my forte! Hoping some of the more technically minded will be able to assist.

We have a sound board that works perfectly in test. I have replaced the PIA (6821).

The game will have normal sounds at start up in most cases. But as soon as any of the special sounds are triggered (by a switch activation) the sound stops altogether. Sometimes it runs for a while before it fails. It will for the most be there when the game is turned off and on, but sometimes not. Mostly it will work on restart though, until the first switch activation triggering a sound.

Painfully, it's at a mate's place, so need to gather as many clues as I don't have immediate access, although I suspect I might need to pack her up and bring it home if this can't be sorted.

Help!

[Strangeways]

Sounds like a dry joint or connector problem - that would be my first guess. Also check for silly things like the wires to the speaker - are they making a good connection ?

[pinnies4me]

Resoldered all connectors, and have checked the speaker connections - wiggled after sound died, also same for the remote volume control etc.

[Retropin]

Its been a while since i worked on a WMS sys game so im a bit hazy to its logic. But, my concern here is that the fault is only present once a switch is activated. Switch inputs are on the driver which then talks to the sound board which has its own CPU yes?
Now sound works OK and board tests fine.. there will be some buffer chips in there to protect the PIA's etc on the sound board - would be 7407 or similar.. check these for correct logic, also check PIA outputs on driver - make sure that the voltages are not 2v as this is not seen as a logic high or low and it will just confuse any other chip down the line.

The board works fine till it has an input - this is the key here i feel

[FirePower]

I realise that given the age of this thread that the problem has most likely been solved, but as I've found reading old threads to be helpful and as I had a similar problem with my Williams sound board I thought I'd document how I fixed mine. Someone may find this useful in the future?
 
Schematics can be found here;
http://www.pinrepair.com/sys37/s67snd.pdf

On mine the test button produced the full compliment of sound and speech, so this proves most of the board is working. ie power supply, pia, dac, amp, speech module.  So the area in question is the sound select inputs from the driver board.

The driver board sees and selects sounds in the same way that physical solenoids are driven ie by grounding an output. The selected sound is achieved by putting the required value into port B of the sound card pia IC10.  IC5 and IC7 buffer the signal from the driver board down to cmos levels and pin 13 of IC6 acts to drive the pia interrupt CB1.

Grounding each of the sound select inputs on J3 and using a logic probe allows the sound select logic to be analysed. Hooking up a speaker and pot to J2 and J4 will allow you to hear any sounds produced.

In my case IC7 had failed and one of the gate outputs had failed to hi impedance. Replacing this chip and using a high quality socket solved my problem.  I also noted that IC5 had been socketed in a previous repair, so perhaps theses chips are susceptible to failure. 

cheers,
David.