Good evening all,
First time poster, long time reader. Please bare with me...
I have found a pretty nice HK PM665vxi. Went back home, plug and wait. couple hours later, tried my turntable. Speakers are JBL L80T. Everything was amazing...for an hour. Then a loud pop was heard and the phono stage stopped working. Everything else was fine. So I changed input and listen to cd's...couple weeks later, Right channel start to work and stop working, then back again...until the fuse blowed.
I decided to took everything a part, clean with deoxit, clean all switch, checked the output transistor, voltage to transistor etc. To my surprise, there is some white residues on some board and some blue marker mark couple of places. Seems someone already open this beast before...
After 24 hours of drying time, I plug the beast. Surprise, no sound, left or right. No even a single hum...Total silence...But On one of the transformer, every 10 seconds or so, I can clearly hear a BIZZ of 1 sec...then nothing...then bizz...the other transformer is ok.
I have followed the signal path from the input to the Pre/separate switch until it went to the protection circuit. There is nothing coming out the protection circuit...no sound.
I assume one of the transformer is bad at this point. With power on, if I check the ouput transistor, I get 65volts for Left channel, 65 volts for right channel but every 10 seconds there is a 10 volts drop.( when I hear the bizz coming from the transfo)
I tried to remove the fuse from the right channel and have the left playing. But it seems the protect circuit is still on and there is nothing anymore.
Sorry for the long post, trying to expalin the best I can.
If the right transformer is bad, can it trigger the protection circuit?
Is the ''bizz'' inside the transformer could be an electric arch?
I'm in a dead end right now and need your input on this to continue.
The transformer that is buzzing gets very hot compare to the other one. It is a Bando 5584-S05. ( this amp is a twin power)
Thanks all for reading...and your help!
First time poster, long time reader. Please bare with me...
I have found a pretty nice HK PM665vxi. Went back home, plug and wait. couple hours later, tried my turntable. Speakers are JBL L80T. Everything was amazing...for an hour. Then a loud pop was heard and the phono stage stopped working. Everything else was fine. So I changed input and listen to cd's...couple weeks later, Right channel start to work and stop working, then back again...until the fuse blowed.
I decided to took everything a part, clean with deoxit, clean all switch, checked the output transistor, voltage to transistor etc. To my surprise, there is some white residues on some board and some blue marker mark couple of places. Seems someone already open this beast before...
After 24 hours of drying time, I plug the beast. Surprise, no sound, left or right. No even a single hum...Total silence...But On one of the transformer, every 10 seconds or so, I can clearly hear a BIZZ of 1 sec...then nothing...then bizz...the other transformer is ok.
I have followed the signal path from the input to the Pre/separate switch until it went to the protection circuit. There is nothing coming out the protection circuit...no sound.
I assume one of the transformer is bad at this point. With power on, if I check the ouput transistor, I get 65volts for Left channel, 65 volts for right channel but every 10 seconds there is a 10 volts drop.( when I hear the bizz coming from the transfo)
I tried to remove the fuse from the right channel and have the left playing. But it seems the protect circuit is still on and there is nothing anymore.
Sorry for the long post, trying to expalin the best I can.
If the right transformer is bad, can it trigger the protection circuit?
Is the ''bizz'' inside the transformer could be an electric arch?
I'm in a dead end right now and need your input on this to continue.
The transformer that is buzzing gets very hot compare to the other one. It is a Bando 5584-S05. ( this amp is a twin power)
Thanks all for reading...and your help!
Transformers very rarely go bad. I would rather suspect that the power amp has an issue and draws a lot of current.
Study service docs, measure current across the emitter resistors on both sides, I'd guess you'll find something decidedly off.
Study service docs, measure current across the emitter resistors on both sides, I'd guess you'll find something decidedly off.
You assumptions are wrong and your method seems also wrong
The procedure you use is also wrong
Problem is that this amplifier even though looks fairly simple actually has a couple of things that can and will give you a hard time .
Help is available by many kind forum members but judging by your post so far it doesn't seem that you are up to it .
Would you like any of us to proceed ?
The procedure you use is also wrong
Problem is that this amplifier even though looks fairly simple actually has a couple of things that can and will give you a hard time .
Help is available by many kind forum members but judging by your post so far it doesn't seem that you are up to it .
Would you like any of us to proceed ?
Sure. I'm hear to learn and I have never assumed anywhere the task was easy. I tried to explain the situation the best I could and no where I have written that I am a certified tech, but I am a simple and humble electronic hobbyist.
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When you say go back to the emitter, you mean the B-E of the output transistor? There is indeed a voltage drop at 2 output transistors from 65 volts to 55 volts when I hear the bizz from the transfo.
I will have a look at power amplifier tonight. The link you sent is for the 655. I have the service manual for the 665, looks almost identical.
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I have done more testing. I have finally found one output transistor bad on the right channel. part Toshiba 2SC3281. To find it, I unsolder the transistor that was way hotter than the other one, et voilà. Anyone has any idea where to get the real ones, not the fake ones? thanks
After more tests( remember, I'm no pro) transistor is good. But after couple hours rechecking all solders, I have found a broken one at D410. Clean, resolder, clean. Put power back on...All is normal again, perfect sound on both channel. Voltage are now stable everywhere, no more bizz in the transformer, heat is stable on all transistors. I'm happy! Now I need to repair the phono stage.
Woke up early this morning, and started to check the phono board. Tested all components, tested voltage, then using my special glasses, checked all solders. Indeed, there was 2 bad solders at the transistor phono amplifier. Unsoldered, cleaned, resoldered, cleaned, test. Wow. Everything is now back and plays like a beauty. I'm so happy now. To me, it does not make sense to sent a vintage integrated amp to a shop since it's value is below the cost of repair. Cheers all.
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