Greetings AKers,
I come seeking wisdom on G-7700s and their ilk.
I have in my possession a sadly mistreated G-7700. eBay purchase. The seller appears to have tried to disguise an internal fault by doing a completely inadequate job of packing, hoping to then claim shipping damage and insurance.
The thing was shipped in a toilet-tissue-packing box that was about 10 inches too large in every direction, with two pillowcases - not pillows, pillowcases - thrown in, and no other padding. There were pieces of the shattered wood case sticking through the box, and a fair-sized hole ripped through one end of the box, through which some of the trim and knobs apparently leaked during its journey. The aluminum faceplate is dished in in the middle, and the backing plate that carries all of the controls is now shaped kind of like a steel drum.
Miracle of miracles, the thing is /not/ electrically dead. Pried bits of the chassis back away from the boards and made sure that nothing obvious was shorting, figured "what the hell, how much worse can it get", and brought it up on a variac. Who'd have believed it - no smoke. She still starts up, comes out of protection, and lights up her "safe to operate" lamp - so maybe this thing is still worth fixing!
On Aux input, I've got both channels! One is /way/ down compared to the other, but other than static from the dirty controls, doesn't sound horribly distorted. Quite a lot of 60Hz hum bleeding through at zero volume, but it doesn't change with the volume control, so it's getting into the output stage rather than the preamp.
Didn't have the service manual handy when I was poking around in the mangled remains, so I wasn't sure where to check idle (and after reading the SM, and a half-dozen threads that disagree on the topic, I'm still not sure), but I did check DC offset on the speaker terminals. One's "not bad" (everything considered) at 22mV. The other, is showing _negative_ 120mV. Seriously - negative - I know which way to hold the probes…
I'm not even going to screw with trying to adjust things with the original trimmers - will wait until replacements get here from DigiKey - but does this ring any bells for anyone? Any obvious components I ought to be looking at first? I'll probably rebuild a bunch of the F-2980 board anyway - what else is there to do while I wait for the snow to melt - but I'd like to make sure I don't miss any likely suspects.
Thanks for any advice,
Will
I come seeking wisdom on G-7700s and their ilk.
I have in my possession a sadly mistreated G-7700. eBay purchase. The seller appears to have tried to disguise an internal fault by doing a completely inadequate job of packing, hoping to then claim shipping damage and insurance.
The thing was shipped in a toilet-tissue-packing box that was about 10 inches too large in every direction, with two pillowcases - not pillows, pillowcases - thrown in, and no other padding. There were pieces of the shattered wood case sticking through the box, and a fair-sized hole ripped through one end of the box, through which some of the trim and knobs apparently leaked during its journey. The aluminum faceplate is dished in in the middle, and the backing plate that carries all of the controls is now shaped kind of like a steel drum.
Miracle of miracles, the thing is /not/ electrically dead. Pried bits of the chassis back away from the boards and made sure that nothing obvious was shorting, figured "what the hell, how much worse can it get", and brought it up on a variac. Who'd have believed it - no smoke. She still starts up, comes out of protection, and lights up her "safe to operate" lamp - so maybe this thing is still worth fixing!
On Aux input, I've got both channels! One is /way/ down compared to the other, but other than static from the dirty controls, doesn't sound horribly distorted. Quite a lot of 60Hz hum bleeding through at zero volume, but it doesn't change with the volume control, so it's getting into the output stage rather than the preamp.
Didn't have the service manual handy when I was poking around in the mangled remains, so I wasn't sure where to check idle (and after reading the SM, and a half-dozen threads that disagree on the topic, I'm still not sure), but I did check DC offset on the speaker terminals. One's "not bad" (everything considered) at 22mV. The other, is showing _negative_ 120mV. Seriously - negative - I know which way to hold the probes…
I'm not even going to screw with trying to adjust things with the original trimmers - will wait until replacements get here from DigiKey - but does this ring any bells for anyone? Any obvious components I ought to be looking at first? I'll probably rebuild a bunch of the F-2980 board anyway - what else is there to do while I wait for the snow to melt - but I'd like to make sure I don't miss any likely suspects.
Thanks for any advice,
Will
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