Technics Su-G50

Chugdog

New Member
Good morning, new member here, thank you and it's a pleasure to be on the forum. I just got my first repair job from a fella with this Su-G50. A little history, I'm a 7th year IBEW trained inside electrician, so I know electricity fundamentals, but not in the way an electronics technician does. I have been studying electronics with passion for about four months, so I'm learning a lot at a fairly fast pace.

So this thing had a blown fuse and one of the rectifier diodes was shorted. When I got it "working" the sound was distorted (clipping?) and only on one channel. I have a somewhat blurry service manual from electrotanya, and I checked the reference voltages for the regulator transistors feeding the big amp transistor IC, as well as the pins on the IC, which on a kind of first cursory inspection all seemed to have the right values. I decided to do it again more thoroughly at the IC and of course I shorted two pins, blew the fuse, and blew the next fuse. The rectifier is ok, I can't see any damage on the board, I'm going to check with a magnifying glass for any cold solder joints. I don't have an lcr or esr meter yet and my cap multimeter only goes up to 100 uf, so don't know how to check the filter caps. There appears to be an similar resistance value on them and takes forever to reach an OL at megohm value, but I'm not familiar enough with that technique and not sure if it's really an accurate diagnosis or if my Ideal meter is designed for those values. In the weeds a bit.

Sorry for the length and triviality, I'm just curious as to what you think might be overloading now. What I also think would be nice is to have an idea how to accurately test the IC with the power off or out of circuit. It's a dodgy proposition to test voltage to the manual specs with those pins so close together. If anyone has an idea about how I should proceed I would appreciate the advice, thanks and much love.
 
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