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Author Topic: Yamaha G100II Broken, Help Wanted...  (Read 315 times)

Yamaguy

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Yamaha G100II Broken, Help Wanted...
« on: February 28, 2021, 01:54:03 PM »
Found the forum through several painstaking hours of searching for a fix on my amp. Found some great information here and recognize the the amount of skill and knowledge possessed by many on here. Hoping to find some assistance.

Dusted off the old amp after sitting for 5yrs. Things went fine, racked the knobs to prevent some of the usual snap, crackle and pop the old girl would give out. Played for a few hours, shut it off. Next time around, flipped the switch... light up for split second... no sound.

Tore into it, found both .5 amp fuses blown on MA board, ordered some new fuses, changed fuses, blew fuses.

Found 2 capacitors on said board smelled smoked and tested weird on ohm scale, hey maybe that's it, changed with like value orange drop caps, guess what... blew .5A fuses and 4A fuse on board this time, awesome.

Made a limiter bulb set up, as suggested from one of the discussions then my bulb died, probably old age.

Found the 2 transistors tested bad on MA board, Changed them out with exact replacements, replaced the 3 fuses.  Flick power switch, 4A fuse ok now, both .5 amp fuses instant flare out. excellent.

I am a mechanic/technician by trade, I can chase and fix the worst electrical wiring problems and replace controllers and faulty electrical components as needed, I don't open and repair. Some of the jargon used on here is over my head so please be gentle and type slowly.

I have found a manual in pdf but can't figure out how to share it.

nosaj

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Re: Yamaha G100II Broken, Help Wanted...
« Reply #1 on: February 28, 2021, 02:18:07 PM »
Service Manual attached
nosaj

g1

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Re: Yamaha G100II Broken, Help Wanted...
« Reply #2 on: February 28, 2021, 02:19:54 PM »
Have you checked TR203 & 204 ?
They are being used as regulators for the +/-15V supplies.

Yamaguy

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Re: Yamaha G100II Broken, Help Wanted...
« Reply #3 on: February 28, 2021, 03:56:25 PM »
That manual is different from mine, If only I could attach the manual...

I will check tr203 tr204 on board with my manual and compare to the 112 version.

Thank you

Jazz P Bass

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Re: Yamaha G100II Broken, Help Wanted...
« Reply #4 on: March 01, 2021, 01:56:09 AM »
This may be the correct schematic: