Hi,

Hello group,

I would like to share a troubleshooting story I am in the middle of.

I bought a broken TX802 on the internet. I knew it was broken when I bought it, I felt like taking a chance. The seller said it worked but has "digital noise".

It turns out this TX802 is in pretty good shape. Everything works except that the sounds are wrong. There appears to be something wrong with the output levels of the operators.

If I make an init sound, I am supposed to get a single operator sine wave with an organ envelope. The user interface shows the expected parameters. But when I play it, I get more or less the sound of algorithm 1 with all operators at 99. A harsh overmodulated FM sound. When I then change the algorithm to 32, I get a clean sine wave sound.

It's a fascinating puzzle for me. Almost all the explanations I can come up with would make the TX sound more broken than it actually does. The EGM and OPS2 chips cannot be broken because they can make clean sounds. (I have a DX7II which is my reference.) Data is getting corrupted only in a very specific place, which happens to affect the output levels.

My best guess at the moment is that there is a problem with the chip enable line of the EGM chip that causes it to latch bad output level data when it should not be reading data in the first place. But I have not seen evidence of that yet on my oscilloscope.

I don't know if anyone else finds this interesting, but if there is someone who finds it interesting, they are probably on this list. :)

Cheers, Jacob