TX802 displaying garbage, acting weird (video) bad ram? (resolved)

[part12studios]

Hi everyone, I'm hoping to find some help fixing this almost working TX802. I recently replaced the eprom thinking this might explain why i was getting an error with a factory reset.. but sadly this didn't change anything..

I'm thinking bad ram would explain the funky characters in the patch names and such and if I'm lucky enough that this is what's going on does anyone know a good place to find these particular memory chips? unobtanium or maybe a common part still made?




Thanks,
Caleb

[madtheory]

If it passed the RAM test, that part is fine. First, I would test that with the same MIDI cables, another synth gets its SysEx OK.

The issue seems to be in the MIDI interface. You used the term noise, I think you could be onto something. I would be looking at the sockets for continuity and dry joints, i/o buffer (wherever that is, I don't know) and the UART. Hopefully it will be obvious and you won't have to get the logic analyser out.

[part12studios]

Yea reading the manual a bit, I can see that it does in fact pass the ram test without issue since that's THE first test they do.

I made a second video showing some more stuff.

I am using a roland UM-ONE mk2 midi cable that has sent / received sysex before and honestly gets very little usage except on these occasions.

This is how you're suppose to do a system restore..
https://usa.yamaha.com/support/faq/musi ... /1917.html

However I wonder if maybe there is a sysex file i could load from outside? I haven't found such a file if such a file exists (since it has a factory reset it would make sense this doesn't exist)

I followed this more or less to the T.. i don't think when I did it power off and back on after.. rather let it soft reset..

However one observation that someone shared was that the Cartridge test fails and i do see cartridge stuff popping up in what seems like inappropriate areas.. so i'm wondering if maybe there is some chip that manages the reading /writing to the cartridge that is confused and basically thinks there's a cartridge there when there isn't.

Otherwise I can't explain how the cartridge test (#57) would give me an error! message..

[madtheory]

Yea check the schematic. Other problem is you don't have a known working system to check against. Maybe performances go in a different memory, but I doubt it. Check cartridge port is clean and intact. Break out everything you learned in first year electronics in the mid nineties about UARTs and serial busses.

[part12studios]

i'll see what i can figure out. i'm not a trained electronics repair person. i have a local electronic repair guy I've had do numerous tasks for me but he's trained, but not in deep synth repair like this, so I'm trying to isolate where the issue is and then have him do the repair itself as I would do more harm than good if i get in there with a soldering iron

[upunkt]

I've had issues with different Yamaha gear that turned out to be a broken trace between memory chips.
To check that, get schematics of the Yamaha circuit or data sheets of memory or other ICs involved and check data (and address) lines for continuity, something that could be tested with a standard digital multimeter.
From my understanding name garbage could well be something caused by a bit not being transmitted correctly, if the usual suspects can be excluded (low voltage in memory backup battery, defective RAM/ROM).

[part12studios]

Good thought for sure. I will see what I can dig up.. just interesting that it passes the ram inspection.. but somewhere else when data is getting accessed is not working right. thanks for the great suggestions!

[part12studios]

OK so while it has some kind of issue doing a factory restore for some reason, I WAS able to get it working properly again by finding an actual stand alone sysex factory preset dump.. using sysex librarian I was able to push a full load of patches to it and display is great and instrument is making the kind of sounds its supposed too!

When I go through the self test and ultimately try to restore settings i get an error, but at least an external sysex dump is all it takes to get it right. Thanks for all your help everyone.

[madtheory]

Woot!