Could be a poor connection, bad socket, component heating up. Or, something completely different.

Turn the game off and see if any of the socketed ICs are loose. It's possible the sockets have lost tension over the years, and one may need replaced.

Often times, problems like this occur when the game warms up, and a component on the boards expands or contracts and suddenly makes or loses contact.

Turn the game on and make it 'fail' again. Turn the game off, and carefully feel around and see if anything is hot to the touch - you could then make the game 'fail' again, and spray the hot component with freeze spray and see if perhaps it starts working again. If that fixes the problem, replace the component you cooled down.

This is, of course, assuming such a repair is something you are competent to do - if you aren't comfortable doing it, send the board out!

FWIW...I have a BK and your description of the issue sounds like my problem...I troubleshooted mine down to the speech Rom, the legs were a bit corroded on mine. The speech was getting garbled sometimes and other times getting cut-off..I gently shook thing on the boards to see if it was a bad connection somewhere and once I touched the speech rom it started working again...Good luck

To add to what's been said which is all good, you can pull the ROMs from their scokets and check the pins. If there's black corrosion on them they are suspect and should be replaced. Make sure you note the orientation of the ROM as they go in correctly one way only. I had a FP that randomly lost speech. In addition to a bad ROM socket, one of the pins came off after I pulled the ROM because of said corrosion. Replaced ROM and socket and all was well.

viperrwk

I had a similar issue on my BK. I had to replace the sound ROMs. Cleaning/reseating/swapping sockets didn't do it. Replacing the sound ROM chips themselves did.

Did you reflow the solder joints on the sound board and the MPU? Did you repin the connector on both sides?

Nah. The Sys7 sound board is simple. Reflow the headers, swap those sockets if they are the crappy type, and replace the capacitors. That will make it rock solid again for years.

Actually you're looking at about $130 with the sound and speech combo.

New ROMs for the sound and speech board from John Wart will cost you $41.
From GPE:
Cap kit - $7.75
Five 24 pin sockets and a 40 pin socket - $4.20
Two 24 pin friction lock headers - $2.80

Total: $55.75

The other problem is that even if you replace the sound board you could be looking at a connector issue - the harness connector that comes in at 10J1 may be bad and you would have to repin it (about another $1.20.)

I believe it's your connector at 10J1 causing the problem. If you're comfortable doing the work yourself it would be cheaper just to buy all the components and replace them - as Chad said it's a simple board. But if you're not comfortable doing this sort of work, get a quote for a repair or buy a new board, knowing you may still need to repin the connectors.

Oh, and a repaired board will be as good as a new replacement if all the aforementioned components are replaced.

viperrwk

As an aside, Ed lists two cap kits for Williams 6/7 sound board. Chances are your board has the 4700uf cap and he says he's out of stock on that kit. You can ask him to sub a 35v version in there or get the 12000uf version which should work fine as well.

viperrwk

The problem can be on the CPU board. The sound/speech are generated by ground signals to the sound board sound select pins that are originated by a PIA on the CPU board. PIA 5/ IC36 provides the sound signals and display commas. Do the displays still have commas when the problem occurs?

When you have the problem, don't push any buttons, just remove connector 10J3 on the sound board - machine on but with sound problems. With a clip lead, one end to the ground braid, ground pins 2,3,4,5, and 7 while you have the problem. Do you get sounds? Yes, the problem is with the CPU/PIA or connectors 10J3 or CPU connector 1J8.

If you don't get any sounds then the problem is either with the sound board or speech board.

The sound board send sounds to the speech board that are mixed with a pot to control speech/sound balance, op amped on the speech board then returned to the sound board for the main amp that you note is hot on the sound board.

To determine if the problem is on the speech board, temporarily add the option strap W1 on the sound board and disconnect the speech board. This will permit the sound board to operate independently of the speech board.

Operate the game and see if the problem presents itself. If it does not, the problem is on the speech board. Check the sound/speech balance pot and the op amp.

If the problem presents itself the problem is with the sound board and not the speech board. I would suspect any sockets first.

Good point - I read this earlier

as meaning he got sounds when he went into test mode but that may not be the case. Nonetheless since he can sometimes go for hours and have the sound work correctly it points to being more of a connector problem than a logic problem. Still this is a good plan of attack and ruling out the PIA is a good step.

viperrwk

Make sure all the grounding screws are in the boards. I had a blackout that would garble words and was missing screws on a few boards. Replaced missing screws and all was good.

You have isolated the problem to either the sound board or speech board. The next step is to determine if the problem is the sound board or speech board. To do that you need to convert the sound board to be "stand-alone" w/o the speech board. This is controlled by option an strap on the sound board. If you review the sound board picture included, if you look to the bottom right of connector 10J3 on the sound board you will see for the option strap W1 is located.

So by adding strap W1 you can disconnect the speech board and the sound board will function w/o the speech board, and of course there will be no speech during the game but sounds will be present.

If the sounds go away then you have isolated the problem to the sound board.

Sbd.jpg

Assuming you determine the problem is the sound board, eliminating the speech board the next steps to resolve the problem to a root cause on the sound board are next accomplished on the test bench.

Using an old computer power supply you can obtain the +12V and -12V sources. They are DC but it doesn't matter. Then using a logic probe you can examine the processor chip. The best thing to use is Leon's test chip for Williams sound boards. (see link below) This handy chip replaces the sound ROM and will test the PIA. I can't remember if it checks the 6810 RAM or not.

Another possibility is the main amplifier chip may be failing under use as it heats up. As someone else has suggested, you might think about using an upturned can of air to put some cold on the amp and see if it changes the problem.

Great information on working on this sound board is here:

http://www.pinwiki.com/wiki/index.php?title=Williams_System_3_-_7#Useful_Sound_Board_Repair_Links

These sound boards are pretty solid and working examples can be purchased relatively inexpensively compared to the new stuff. You just have to be alert to the sound board having the ribbon cable socket. There are games using the type 2 sound board as used in your Black Knight that do not have the speech board.

All I will say is that a component problem is usually indicated by something not working all the time because a component has failed. A mechanical problem ie connector or socket is usually indicated by an intermittant or inconsistent failure ie bad connector, bad socket, etc. You've narrowed it down to the sound board which works sometimes. The logical thing to do next would be to address the connectors.

viperrwk

On System 3-7 games you should always suspect the connectors first. If you have a problem, and the connectors for that area have not been redone, don't even debug the issue. Redo the connectors and see what happens. More often than not the problem will be an original connector.

I had the same problem with the Black Knight at the museum of pinball, all I did was re-flowed the to wires connected to the speaker and it worked great!