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I got one of these to fix for a friend. I sold many in my late teens when working for the Shack. It looks in good shape, no burnt parts, all fuses good although one of the five one amp fuse holders was metal fatigued out so I put a new fuse holder in it. No help.Comes on, lights up, no protection relay click. (L601) All other functions are there; tuners, signal meters etc. Just no protection circuit "click" and therefore no output.
Input welcomed. I found a Sam's that says to look at L601. I didn't check everything but the PS voltages are there and the voltages look right on both amp boards.
Thanks in advanceET
50V @PS caps
no voltage on L-601 coil, looking further at that board
Edits: 09/03/14Follow Ups:
Look for DC on the output of one of the channels.
The outputs on most SS amps will have an airwound inductor in series for oscillation protection. You can measure there.
Just a guess - could the relay be sticking? Check the voltages on it and see if it should be closing. If it's simply stuck, isopropyl alcohol on a thin strip of paper (drawn between the contacts) can dissolve gunk and act as a very gentle abrasive to clean the contacts.
Thanks Jon. There was voltage there but it doesn't move. I took the cover off and manually closed it and it blew its main power fuse. Something amiss in the L channel.
ET
So the proection circuit driving the relay detected high amounts of DC and did it's job - that's good!
I'm assuming the relay simply disconnects the speakers in the face of DC at the output. Did you have a load attached when you closed the relay? If you didn't, I'm trying to figure out how closing the relay would give a path to ground (and draw enough current to blow the power fuse). If you did have a load attached, I hope you didn't take out a woofer in the process.
Charles may be right - look at the output transistors, and keep an eye out for anything earlier in the signal path that might have caused an output transistor failure. Without a schematic or the amp itself to look at, it's hard to give much more guidance.
Good luck, and let us know how you make out.
You can try removing the power to one board at a time an see if the relay engages. That will at least tell you which board, and maybe even what channel.
My money is on the output transistors on the driver board.
post your findings.
charles
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