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Old 8th March 2005, 03:59 PM   #1
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Default capacitor brands & power transistor trouble on hk amp

capacitor brands,

im working on a harman kardon amplifier, seems one of the componenets faulty is a "Koshin" 63v 470uk capacitor, well my question is would i need to replace with the same brand? would i need to get another koshin capacitor? can you use a diffrent brand? would it make a diffrence?

whats happerning is, i kept blowing the main fuse, i replaced the output power transiator, and after 5 mins it is getting red hot to the touch, and then blowing again, and then blowing the fuse, any ideas? or suggestions?

also trying to source a a harman kardon vr 507 or harman kardon avr 4550, service manual, no luck,


thanks
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Old 8th March 2005, 04:09 PM   #2
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Default brands...

Brands of components sound different, but to my uncertain knowledge 'koshin' is not one of the known 'great' sounding capacitors. So if you can't get koshin easily, I'd go with any of the known good brands, nichicon, panasonic.

If you can't get an exact match you must have the same or greater voltage, and if necessary go to the next larger value.

If applicable, you may want to replace the same device in the other channel, whatever difference it makes will then at least be the same side to side...

Good luck

Stuart
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Old 8th March 2005, 05:47 PM   #3
K-amps is offline K-amps  United States
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Default Re: capacitor brands & power transistor trouble on hk amp

Quote:
Originally posted by mrlennon
capacitor brands,

whats happerning is, i kept blowing the main fuse, i replaced the output power transiator, and after 5 mins it is getting red hot to the touch, and then blowing again, and then blowing the fuse, any ideas? or suggestions?
thanks

Transistors getting red hot? Like literally red hot?

If marginally hot, I suspect either an overbiased output stage, bad VBE circuit (no thermal compensation) or the amp's oscillating.

Perhaps you have checked those already?
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Old 10th March 2005, 11:20 AM   #4
buncey is offline buncey  US Virgin Islands
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yes i too have a h/k and in for repair after 2 mins or so after powerup with a new power transistor is getting red hot, so hot if you did try and touch it it would burn your finger,

i used a genuine Sanken transistor too. there must be a overload someware on the channel, im still trying to track my fault, had no luck yet,

must be common on these units.
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Old 10th March 2005, 12:41 PM   #5
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I assume you guys did replace the driver transistors, didn't you... You can almost guarantee that the output transistors will have damaged them even if they measure OK.
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Old 10th March 2005, 12:51 PM   #6
K-amps is offline K-amps  United States
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Quote:
Originally posted by richie00boy
I assume you guys did replace the driver transistors, didn't you... You can almost guarantee that the output transistors will have damaged them even if they measure OK.

Not if he has a bulb in series with the AC, first things first.
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Old 10th March 2005, 01:00 PM   #7
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and what about when the output transistors blew the first time? Using a bulb now will not help if the drivers are damaged from the first blowup, merely save the new outputs.
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Old 10th March 2005, 01:12 PM   #8
K-amps is offline K-amps  United States
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Chicken and egg Richie,

With the bulb, we put a stop to it, but agree, he should check all semiconductors, OP, drivers, emitter resisters of both and then all other components in that order. Oh yes, the DC fuse too.
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Old 10th March 2005, 08:36 PM   #9
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well on the one im working on, im not 100% sure where the driver transistors are located, as theres quite a few on the channel, about 11 transitors on board.
im still trying to get hold of a avr 507 and cant get the scematic or service manual anyware, ive heard this model is very close to the harman kardon avr 330 but i cant even get hold of that.
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Old 11th March 2005, 07:41 AM   #10
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I think changing brands of the component does'nt have a great impact on the problem. Maybe you have no proper heat sink of your component causing it really hot. It is normal in power stages to become very hot. To avoid damage of your component, put a heatsink on it. Or, maybe you have a short circuit on your output side causing the component to become really hot and bursting your fuse.
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