I'm working on a sound board out of a Williams Jungle Lord. It's got the Sound Rom 3 on it. I'm testing this in my Blackout cabinet (both use the same sound board) with the W1 jumper in place, the speech board disconnected and both dip switches set to Off and connector J3 on the sound board disconnected.

Both fuses were blown and the bridge rectifier was bad so I replaced those. Tested 5/12/-12 voltages and they were good. When I press the diagnostic button on the sound board, I can JUST barely hear the audio with the volume pot cranked up all the way and my ear right next to the speaker. The Blackout sound board works fine so it's not the volume pot/speaker. I figured the TDA2002 was bad so I replaced that with a new one and I'm getting the same thing. Went thru and tested resistors in the speaker/volume section of the sound board and everything looked good.

What else should I be looking at that would cause there to be no audio amplification? Would a bad IC13 (1408 D/A converter) cause this?

C12 (1uf 50V) had high ESR so I replaced that but no change.

Also replaced C29 (10uv 25v) even tho it tested ok with my ESR meter but still no change.

I tested that 2N4401 with my DMM and it tested good but I replaced it anyways. No change.

What's the likelihood that it's the 1408 at this point? I don't have any so I'll have to order some.

It doesn't seem like a bad 1408 would cause low volume but I just don't know what else it would be. I've replaced two of the caps in that circuit (only 1 had high ESR) and checked all the resistors as well. I even went thru tonight and checked for a bad trace but everything looks good. From the few things I've found with other people experiencing low volume, it was caused by bad header pins, a bad TDA2002 or a bad C29 or C12. All that has been addressed on this board.

I'm at a loss for what else would be causing this.

I replaced the 1 bad cap I found. The others test fine with my ESR meter.

Finally getting back to this. I replaced all the caps to make sure that wasn't the issue (didn't think it was as the rest of them checked fine with my ESR meter) but that still didn't fix it. Using my logic probe, I'm seeing no activity on pins 1 and 2 of the TDA2002. I was getting a weird reading on R25 (3.3M). In one direction it reads fine but if I swap the leads it reads -1.5M. I replaced Q2 (2N4401) in that circuit as well. Would a bad C28 (47pfd 1Kv) cause low volume?

At this point I'm not sure what else to look at. Any ideas?

Sorry to say Chris but you were wrong on this one. I finally got back around to working on this sound board. Using my logic probe I compared the signals with my working board on the MC1408 and I discovered that pin 14 was high (low on the working board) and pin 16 showed nothing (low signal on the working board).

I pulled the MC1408 off my working board and now I've got normal volume again. Problem solved.

That's awesome! Glad to hear my repair helped someone else out.