Troubleshooting an old receiver

Try asking >>>/diy/

>>344736
It'd be a pretty shit receiver if it couldn't drive four ohms.

In any case, get you a scope, hook it up to a sine wave coming out your phone, and follow the signal to the place it disappears.

Alternatively, just replace every electrolytic in the amplifier section of that side.

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>>344736
And indeed it can, provided you use only two of them.

>>344736

He's probably blown the final stage output transistor. Too low an impedance, too much current, pop.

The thing to bear in mind is that you will need to replace BOTH output transistors (left and right) as a "matched pair" or your volume will be biased toward one channel. I'm guessing because of all those discrete components that it'll be transistors and not chips, whatever it is will be clamped to that huge heat sink. I can't be arsed to google Harman Kardon A-401.

>>344736
Sounds to me like he most likely hooked up a 4 ohm speaker and an 8 ohm speaker on the same channel, which would give it a 3 ohm load iirc. Doesn't really matter now though, since the amp doesn't work right.

Although he is on the right track with his troubleshooting method, replacing electrolytics like>>344824 said will not help, since this is definitely something up with the output transistors like >>344842 suggested. From your schematic, it looks like the output transistors are 2sc1030c's. Some modern equivalents include NTE280, and the mj15003g from ON Semi. (there are many modern equivalents, but I just posted ones that I know for sure.) I think that the ON semi ones are best to use in this case, since they're cheaper, and I saw them used in the same model amp in a thread on audiokarma. I also know that On semi is reliable.
http://www.mouser.com/ProductDetail/ON-Semiconductor/MJ15003G/?qs=HVbQlW5zcXXkCBgZuWlY4A%3D%3D