Anybody with any experience with this amplifier? I keep blowing a fuse (FU602) in the right channel - the left is ok.
Thanks!
John
Thanks!
John
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If you are replacing fuses, then you have the chance to look closely on the circuit board.
Examine it V closely, inch by inch in a methodical fashion.
Look for brown spots & traces of localized overheating on the board material.
Look closely at each capacitor & resistor for signs of overheating like burn marks on resistors & swelling or bulging caps. -
A bit of history - I think the speaker terminals were shorted during a vacuuming incident.
Both fuses on that sides were blown, replaced, and all was well for about a year.
I lost that channel, checked fuses, and saw the electrolytics were leaking badly. I replaced all of them, assuming an open circuit.
I can put in all the fuses except FU602. If I install FU602, it and FU604 both blow immediately. It has been suggested on another forum that I remove and check all the output transistors for shorts from C to E, which would cause a rail to rail short. Sounds reasonable.
Left channel is still working. I have a copy of the technical manual for reference.
That's where I'm at. Thanks for your help.Comment
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Just a few pointers. If you should find shorted output transistors, be sure to replace all of them with a gain-matched set. You want all the transistors draw equal current as closely as possible, so that no single device is stressed more than the others. The emitter resistors help to enforce current sharing among paralleled outputs, but can't be relied on by themselves. Also check the driver transistors. If you started getting blown fuses after replacing the electrolytics, double-check that you installed them correctly. Last but no least, use a variac or dim-bulb tester (a.k.a. "the poor man's variac") to power up when doing repairs, if you are not already doing so.
Dim Bulb Tester
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Thanks for the tips.
Should I gain-match all the output transistors of the same type? Meaning if I replace any one of the output transistors on a side I should replace all 5?
The electrolytics are triple-checked.
I do have a couple of Variacs in the basement - I forgot about that. I should probably sell one of them.Comment
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