TG77 troubleshooting

[stephenbrown]

My trusty TG77 from 1991 has become noisy on every patch. Reverb and delay effects also reverb and delay the noise. I thought one of the modulator effects might have gone wacko, but when I go into Edit and start with an AWM tone from scratch, it's still there, just a slight"chiff" at the beginning that contiunes until the note is released. It's like every tone has a little saw wave attached. At release (decay? aftertouch?), there's sometimes an extra "woosh" (sorry for the technical jargon) that gets louder until it abrubtly stops. If there's a very long decay it just hangs on as long as the note does.

The only troubleshooting posts here and on other snyth sites are about replacing a battery. Since I didn't even know it had a battery or what it does, and this one has 20 years on it, could that be the cause? Or is this something more critical, like shot circuitry? Hate to give it up.

Thanks for any info. Great site.

[acreil]

Does it happen when the effects are disabled? Does it happen on all outputs? I don't remember if there's a DAC MSB adjust....

It's probably not the battery. If it retains user patches, the battery is fine.

[stephenbrown]

Yes, it's there even with effects disabled. I went into voice edit all the way back to choosing a wave in AWM with no effects, and it still can be heard. That's why I'm afraid it's a basic circuitry problem that doesn't have a fix except to replace the component.

Thanks for the info on what the battery does. If I can solve the noise issue, I should probably replace my 20-year-old battery!

[acreil]

Is it present on the AFM sounds too? Have you tried all the outputs? I think there are multiple DACs...

[stephenbrown]

I'll dig into it some more. Not a "build it from the ground up" kind of programmer, but I usually can slowly find my way through those menus - if my old eyes can read that display!

[CoolColJ]

TG77 can sound like that when it's clipping internally

[acreil]

Originally Posted by CoolColJ

TG77 can sound like that when it's clipping internally

Yeah but this is the part that stands out to me:

there's sometimes an extra "woosh" (sorry for the technical jargon) that gets louder until it abrubtly stops. If there's a very long decay it just hangs on as long as the note does.

Sounds like either a mis-adjusted DAC MSB pot (if it has one, and I don't think it does) or a stuck bit on some audio-carrying data bus.

[CoolColJ]

Maybe time for a recap