What brand of midi cable are you using? Sometimes the cable can be at fault if it’s low enough quality. Have you tried a different sound card? Are you using softmpu or a real hardware mpu?

Inspect the large surface mount chips for shorted pins.
Connect a MIDI cable between the MIDI in and out ports and try the test mode as described in the service manual:
https://www.dosdays.co.uk/media/roland/mt-32/ … vice-manual.pdf

Are you using a polarity correct power plug? MT-32 plug is opposite of most devices. Otherwise, see what others have said. I don't think it's a MIDI cable, though.

@midicollector @Spikey Thanks for your answer. I own another MT-32 that works great in the same setup (I apologize I missed this info).

@Schule04 I'll try that, thank you!

Check the output rca solders, could be in bad shape. Also coud be the rca connectors themselves.

As I reported, I got the audio output directy from PCM54HP chip, bypassing the output stage.

pitchshifter wrote on 2024-03-03, 10:23:

Check the output rca solders, could be in bad shape. Also coud be the rca connectors themselves.

What are the system specs (especially CPU) of the PC you are running MI?
I sometimes have similar issues running certain games, especially when General Midi/MT32 output is selected.
My Pentium MMX 233MHz is too fast for some games.
I have to slow down the CPU. Then the sound output is correct.

Sounds like it is playing the correct instruments and has correct timing; so I doubt anything in the MIDI chain. The samples being produced sound corrupt or clipped - I would have said it was likely to be the DAC, but if you have replaced it, I guess not. Could the rom be corrupt?

Do you have any way of connecting the MT32 up to a keyboard (hardware or software) and playing individual instruments? i.e. is it always the same voices, or is it when 2/3 or more are playing simultaneously?

Likely to be a hardware problem since another mt32 works fine in the same setup. Could be any number of hardware problems: bad caps, cracked solder joints, bad rom. Personally I might start with replacing the caps and reflowing the solder joints. After that it might be bad chips, or possibly a short somewhere. These are just guesses.

I performed MT-32 self test, it passed flawlessy. Also, auto generated sounds are perfect, no rustles that I hear during playback.

Also, with the help of a friend I connected an external piano, and all instruments played are bad as music playback thru PC. Note that it seems that high frequency sounds are not affected by the issue, while mid and low frequencies are.

FYI, issue finally fixed replacing IC37 R15449121.

Andry wrote on 2024-07-14, 08:50:

FYI, issue finally fixed replacing IC37 R15449121.

Well done! May I know where you got the chip from?

zuldan wrote on 2024-07-14, 08:55:

Andry wrote on 2024-07-14, 08:50:

FYI, issue finally fixed replacing IC37 R15449121.

Well done! May I know where you got the chip from?

Initially I ordered a 27C040 IC from Aliexpress but the parcel was lost during the journey. A friend of mine owned some 29040 ICs, so he programmed one and helped me to adapt it fot MT32 (it is a simple mod).

So bit rot on the eeprom? Actual corruption of the samples?