I would test it in a different system first.

Thanks for the suggestion!
In fact I did, with the same result unfortunately.

You said the card was in the attic? Could be the caps are dried out on the LAP-I and it is time to change them out. I've thought about doing this on mine given how old these cards are now.

Can you make a recording of the noise ?

I have repaired one LAPC-I card in past and it turned to have a bad LA32 (the main synthesizer) chip. With luck this card would have a bad memory chip which wouldn't be a problem to replace.

Made two (be careful to turn your audio down a bit, it's really like from hell...)

System turned on, where it builds up: https://badsector.de/download/lapc-startup.mp3
Game sound still barely audible: https://badsector.de/download/lapc-pushover.mp3

Okay, let's assume that has been an electrostatic shock (even though I was really caring to make this not happen): I suspect one of these 3 candidates that could have failed:
1. SRAM
2. LA synthesis
3. Echo handling

I'm not too familiar with the chip-side layout of the synth. Are 2 and 3 separated chip-wise? What of those things could possibly be most prone to an electrostatic shock?

I forgot to check the files. I did so now and this sounds definitely coming from reverb related stuff, due to digital overflow which only will happen if there's data corruption going on. There's the reverb coeffs mask ROM, 4x DRAM chips and the reverb chip itself that can be at fault. I would swap out the memory chips first but if that doesn't cure it the fault is likely in one of the big chips and you only get those from another LA device...

Thanks, Tiido!

Could you point me to the right DRAM chips?
https://crossfire-designs.de/index.php?lang=e … %20LAPC-I&num=3

Possibly those with MN4264-12?

That link gives me 403 Forbidden, but yes, the DRAM chips are the MN4264, 4 of them in a row. You can use any 64Kbit 4bit wide DRAMs there, and even 256KBit ones if you tie one address line to GND or VCC since rest of the pinout is same.

Thanks, man! Will try my luck... would make me sad if it wouldn't work any longer.

So, that was a good guess! The first RAM chip was faulty! Got replacements yesterday and had only to replace the first one (that part was my guess).
I think the LAPC-I stores more than samples on its RAM, maybe some track or synth chip commands as well.
Also interesting that this card in essence can create this kind of quality with just 32K of RAM!

very nice!!! glad to see a great piece of hardware saved!

That 32KB is the reverb buffer which is continuously written with new data from the synth output, processed and later read back and mixed with final output. No samples etc. get stored there.
Congratulations, it is nice to have this thing working again ~

Good to know about that buffer.

Thanks! I'm glad as well. They're hard to come by these days.