E-MU ESI-2000 submix output question

Hi all, the submix outs on my ESI2k are behaving strangely – they pass audio when voices are routed to them, but it is weak (very low volume) and lacks all bass as though highpass filtered. I know the submix outputs are TRS send-return jacks and I have tried 1/4" TS cables, TS cables inserted halfway, and TRS Y-cables checking both Tip and Ring ends, so I’m sure it’s not a cabling problem.

I’ve also tried “exercising” the jacks in case corrosion is the culprit – but in that case I would expect either no sound or intermittent/noisy sound. This makes me think it is the internal jack detection switching circuitry (Diagnostic menu - submix jack detect always reads “Y” no matter if a cable is plugged in or not). Anyone seen a problem like this before, on ESI or any other E-MU?

I haven’t been able to find ESI2K schematics but the EMAXII schematics I dug up showed it using a 74HCT244 buffer/line driver IC in the submix jack circuitry; I notice this is a part for sale on Syntaur’s ESI-2K page. Could replacing this IC have any effect on the submix audio outs? Machine is 25 years old at this point…

Any help or suggestions would be greatly appreciated!

before you do this check for solder breaks on the jack connectors. mechanical stress could have caused a break.

Good point, I’ll check the solder joints tonight. Although the problem is the same on both jacks… I’ll probe around behind the jacks and see if I can find where the audio goes bad.

use a continuity meter.
next you need to check rails on op amps.
but one step at a time.