Yamaha DGX640

[Mars_Amp_Repair]

Hello folks,
Just sharing some repair info that might help someone:
I have a Yamaha DGX640 with no sound. I tried a factory reset as usual to eliminate any weird processing glitches. All indications from the display are that everything else seems ok. There is also no sound from the headphone/line out jack (which is derived from the audio output IC201 as is the internal speakers). Running the Self-Test for audio has same result - no sound.
I audio signal traced a very faint signal at the volume pot, but didn't seem high enough level to be correct.
I tried injecting a signal at the input of the power IC201 to no avail. IBTW, injecting a signal at the STBY pin4 did produce a very loud signal at the output jack, which led me to believe IC201 was Ok.
Also BTW, I use a portable signal injector they used to call a 'Mosquito'. It was a kit by Eico from a million years ago. I had purchaced one in the early 70's and after it crapped out, was lucky enough to find one at a place called Fistell's in Denver before they closed down in the mid 20-teens. They built it using what was a very common 'Pen Light' at the time.

Eico Mosquito.jpg

Anyway, I discovered that pin 2 of IC201 that is labelled 'DC', was at 0Vdc. It turned out C207 from that pin2 to ground was shorted. Not uncommon for those small high uf low voltage caps. The cap is a stdrd radial cap & not one of those aluminum SMD varieties.
What threw me off for a minute was how low the level of the signal feeding the power IC was. Upon tracing that back to the op-amp that amplifies (or buffers) the signal from the D/A chip, it appears that the level is correct.
Anyway, just a tidbit of info if anyone happens to come across this problem. Could save some time.
BTW, you do have to remove EVERY silver screw from the bottom of this keyboard to get inside the freaking thing!
Glen

Eico Mosquito.jpg

[Stevem]

Thanks for this info!