Maybe there are some ideas in this thread. I.e. to fabricate an ISA extension cable so you can have the card you want to inspect laying flat on the table or something. Not sure if these cables come pre-fabricated.

Short on ISA slots? Try this.

Oh, that's awesome. Thanks for pointing me in that direction.
Yeah that is pretty much my tough as well, just slightly different, and with only one slot.

I would say however, no riser or extension is gonna do much except introduce further problems of it's own to complicate troubleshooting... in glitchiness, signal strength, signal integrity, noise, bus reflections...

Ordinarily, yes, I would agree with you. But since the issues I am having, at least from what I can see now, are purely on the audio side. This could be a good way of troubleshooting it.
I am also very aware of the possible signal integrity issues that this may cause.
Thank you for pointing that out to anyone that may be getting crazy ideas from this.
I still want to try it.
I am willing to risk getting issues on the bus to be able to realize my vision of being able to troubleshoot this card on my bench, heck, I even fixed the backlight on one of my digital scopes just for the occasion. 😁

Since I posted this I have been laying out 1 of the 2 PCBs that I would need.
I think I should have all the parts in stock except for a ISA slot, so I will have to order a couple of them (I have a few motherboards with ISA slot damage anyway).
But since it's getting late here, and I need to work tomorrow I should probably call it a day and go to bed.

There, PCBs are done, parts are ordered.

In the meantime, while I wait for delivery, I would like to gather as much information as I can on the card in question the Sound Blaster CT-2940.

Anyone have any knowledge of the architecture and signal path of this card?

I believe from my past session with this card that the signal path from the DAC goes back to the DSP IC. I think this is for volume control/balance etc.
I hope there is nothing wrong internally with the main IC as that is not something I can replace easily (no donor card).
I did take a few measurements like diode, resistance etc, on the inputs of the DSP and nothing stuck out at me.

The quad op-amps and passives should be no problem to replace in case of issues with them.

So my current plan is to wait for my PCBs and parts, build that, test it. Once I know that it works and that there are no signal integrity issues etc I can move on to the next step.
Will probably use some Adlib tracker to produce some tones from the FM DAC and go from there.
Possibly I could write a small program to set the tones up and start that from a boot floppy, just to be able to quickly reboot the machine in case I need to remove the card and solder something etc.

I was just playing around with HSCTracker https://demozoo.org/productions/293837/ and made a simple song file with just one note and some speed control, I can play this with the TSR program hscplay on a boot floppy or something to generate a tone.
That should work for now.

bachler wrote on 2022-03-02, 12:00:

There, PCBs are done, parts are ordered.

Whoo. You're really committed to this 😀

Looks like a fun project. Looking forward to see the assembled cable.

Still waiting for PCBs.

So after a long time I finally picked this project up again.

I had gotten the PCBs and the components delivered quite a while ago, I forget when exactly. And as we all know too well, life (family, work etc.) took priority and the project was put on hold.
It had been nagging me for a while now and after I finished up a few other repair projects I cleared some space on the workbench, gathered all the components and started assembly.
I had a AWE32 laying around so I used that for some mechanical testing

Overview:

After a few mechanical sanity checks I went ahead and cut pin headers, then soldered everything into place.

Assembly completed:

Just to be sure I wouldn't have any troubles with bad cables or anything I connected everything up and beeped it out. I found it's quicker then going back to troubleshoot basic connectivity further down the road.

Beeping it out:

After I was satisfied with the connectivity tests I got the Dolch out and connected everything up.

Now the fun starts, I got my old signal tracer out and went to work.
It took a while but in the end I was able to locate the fault.
It was a quad opamp, one of the TL047s that had one bad amplifier. I removed the bad IC using my hot air station, then started looking through my collection of parts for a replacement.
I am pretty sure that I have some of the them somewhere, but I found TL072s, a lot of them. I also found some pretty nice audio opamps, OP470, ceramic through-hole.
I really wanted to get this done so I opted to glue a DIP socket on top of one of the ICs close by and solder some fly leads to the pads. It works. Gives it some character, some personality.

OP470 soldered in:

After this I was able to test it and it worked great. Also I think, if anything, the OP470 sounds better than the TL047. Or it may just be in my imagination 😜

Overview of the fixed card and the ISA extender hooked up to the Dolch playing a module:

All in all, I think this was a worthwhile approach. I now have another tool that I can use to troubleshoot ISA cards.
I could possibly also hook up my HP 1670D Deep memory logic analyzer to the ISA bus etc.
I now have a few spare sets of PCBs and connectors that I don't really see myself needing, maybe the ISA 16Bit connectors.

Here's the mod I used while testing, really brings back memories: https://modarchive.org/index.php?request=view … eid&query=34216
I also did a quick search for "Classical Module Player" but I couldn't find it anywhere, maybe I need to upload it somewhere.

Link to a short video showing it playing: https://www.youtube.com/watch?v=MohI0rtvzkA

I captured some example of the FM sound from Reality ADlib Tracker showing both channels working after the repair: https://youtu.be/dEV18gwMAkI