My beloved Marantz PM-57 released its magic smoke today when I came to turn it on. The cap that's blown is in the voltage amp. (Number 2276 in this schematic should anyone care https://www.dropbox.com/s/lu0tav0zqj44urv/Marantz 74PM47_74PM57 (1).pdf)
Now my question to those with experience of such things is, how often is the cap itself the problem? Or is the cap blowing a symptom of failure further up the line? Very open question I know but I would like to know whether you would replace it in the hope that will fix things or investigate more.
Many thanks, Ollie
Now my question to those with experience of such things is, how often is the cap itself the problem? Or is the cap blowing a symptom of failure further up the line? Very open question I know but I would like to know whether you would replace it in the hope that will fix things or investigate more.
Many thanks, Ollie
If it is truly the one labeled 2276 then something terrible has happened to the vbe multiplier circuit as this capacitors only function is as an ac bypass for it. There would have to be greater than the 25 volts the capacitor is rated for across it to make it smoke. A possibility is that transistor 7256 has gone open circuit or the optocoupler that provides it's bias has shorted. Sadly most likely it has destroyed most if not all of the transistors in the output stage.
Yes that's a very good point, would anyone doing that just take the stereo signal from the point at which it leaves the pre-amp?
Also at what point should one take the power for the gainclone? I willprobably use whatever chinese d-class is flavour of the month.
Without looking at the schematic, I would have to say yes.
Check the power supply voltages. If all is OK, reuse it. I've used old receiver transformers in a couple quick and dirty chip amp builds. I even scavenge the rectifiers sometimes. It works great and saves a lot of money!
I also have a couple of boxes of salvaged transformers at my disposal. It comes in handy when repairing old audio equipment as well as for new circuits; you can often install a transformer out of a completely different unit and restore old equipment to its original (or better
) performance.When you have a transformer and heatsink from the same salvage unit, you usually have a pretty good match. Big transformer = big heatsink.
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