My fuses are flashbulbs!

[stoneface9]

Hi everyone! I'm new to this forum and thought I would start my introduction with a question...
I have a relatively simple Harman Kardon PM 645 VXI stereo integrated amplifier that just won't behave. It eats every fuse that I put near it and I can't figure out why. I've been looking the thing over for a while now and there doesn't seem to be anything that sticks out at me as being messed up. I'm pretty sure the transformer is ok in that i have found threads on here already about that. I just checked the caps today and nothing is wrong there either (I think). There's no heat damage or bad soldering or any visually obvious damaged stuff inside...
As far as I know, someone just pushed the switch one day and nothing happened...no abuse.
I hope someone can point me in the right direction with this little project before I just "shove a penny in it" as the saying goes!

If I'm overlooking something obvious...be gentle, I'm a noob here!

[dimitri]

http://manuals.harman.com/hk/Service...45vxi%20sm.pdf

Do you have DMM? scope?

[KP11520]

Stop with the fuses! It won't fix itself just by chance.

Obviously, something (likely major) is wrong. Every time a fuse pops, the damage has another chance to propagate deeper into the I/A.

Could be many things. I don't know just how to trace step by step but I am sure many here can give some ideas!

Good luck, forget the penny idea (might burn the house down) and be patient! (best advice)

Regards//Keith

[djk]

Fried outputs and/or rectifier.

[KBK]

Originally posted by djk
Fried outputs and/or rectifier.

Zactly.

[jaycee]

probably fried everything now with the repeated application of fuses...

[stoneface9]

Hey! thanks for taking the time to respond...
I didn't put in a dozen fuses or anything, it's just that the one or two I tried went off with a real bang, like there was no resistance at all. I did find that manual already but thanks for re-posting it.
I haven't looked into the rectifier yet...thanks. Would regular use really fry the outputs and rectifier or is it kind of a chain reaction type of thing?

[TheMG]

It's sometimes inexplicable but semiconductors do go bad through even normal use sometimes.

I used to have a little amp, forget which chip it was using, but anyway one day I turned it on and it just went POP and puffed a little bit of smoke. The chip had fried itself. Checked polarity, ok. Checked for shorts on output, ok. Conclusion: the chip just decided to crap itself.

In this case the amplifier wasn't fused. If it was I'm sure the fuse would have blown. Somehow the chip got shorted internally.

Anyways, grab your DMM and start measuring until you find the source of the short, that's about the only way to go about it if there isn't anything visually obvious.

[AndrewT]

Hi,
build up a mains light bulb tester.
Plug it into the mains.
Plug your faulty equipment into the tester.
Switch on.
The bulb will light and only pass a low voltage to the mains transformer.
You can now start measuring some voltage inside the amplifier without any serious overheating or risk of anything blowing up.
This is a bit easier than trying to find a damaged component when there are zero volts in the amplifier & PSU.