Here is some information that is not well published regarding Williams Type 1, Version 1 sound boards.

Per a WMS service bulletin, add two 10k resistors to open pads (See my pic) to "reduce susceptibility to noise".

To use a WMS "SOUND 1" labeled ROM or a 2716 EPROM containing the "SOUND 1" rom you need to do some modifications...

1. Change R14 and R23 to 4.7K resistors.

2. Solder pins 39 and 40 together on the 6820/6821 at IC3. If you do not do this, the PIA will not respond to the input connector being grounded yet the diag button will still produce sound. THIS APPLIES TO THE TYPE1 V2 AS WELL.

3. Change jumpers to as seen in my pic. THIS APPLIES TO TYPE 1 V2 AS WELL.

To use a 6821 PIA in place of a 6820, you need to do some jumpering on the V1 board (this is done by the factory on most sound boards except on very early ones). See my pic, it easier.... Blue Jumper wires on the solder side.

The V1 sound board is 100% compatible with V2 games like TimeWarp, Laserball, and probably even the arcade games that used the V2 board. These mods allow the board to be rebuilt more easily. Without knowing some of these tricks you can be left very confused why the board doesnt work right or only with certain components.

Type1 V1 b.jpg
Type1 V1 a.jpg

Hope this helps

Andrew

As always, full release on my pics, text, all info, to do whatever you want with them. I want the tech info to be available to anyone for free (harumph GTB...).

Hi Chris,

I wish I knew / understood the theory. All i got is if you want to use a 6821, the jumpers have to be in place. One is on the RESET line which is a clue. Another looks like it attaches a pullup(down?) resistor that would be otherwise unconnected. Searching on RGP i found a few posts over the years remarking my same findings, yet no theory behind it.

Solder together p39 and p40 of the PIA at ic3 and I bet you are good to go.

Check out the buffers on the signal input. I have seen a bad buffer on the silence input which can cause your same symptom.

This is the only situation where there is compatibility issues with using a 6821 in place of a 6820. I confirmed it on three sound boards.

In all other situations I know of (pinball) 6820\6821 are completely interchangeable.

I was hoping someone knew the theory. I think it is how they program the pia how to operate.

Those input buffers crap out pretty darn often.

hahah... yeah that would do it! That is probably why i find those buffers failed so often, never made that connection. I don think the sound board power connector plug typically has a key in it.