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v-un-v
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Joined: May 16, 2005 Posts: 8933 Location: Birmingham, England, UK
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Posted: Sun Aug 06, 2006 4:48 am Post subject:
Fixing a MOSFET power amp |
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I've just been away for the weekend visiting friends and of the things that was sprung on me was a homemade mosfet kit amp that keeps blowing the bridge rectifier.
But I'm stumped because I've never come across this sort of problem before. Anyone here have any clues?
The large electrolytics are showing the right voltages across their tags- and appear to be okay (but I suppose you never know?). Any other pointers??
Tom _________________ ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN. |
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elektro80
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Joined: Mar 25, 2003 Posts: 21959 Location: Norway
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Posted: Sun Aug 06, 2006 5:01 am Post subject:
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Is this something out of Elektor magazine?
Bridge rectifier? You are talking PSU here. This one isn´t intergrated on the main PCB? Any chance you can isolate it and see if it works OK without the amp circuitry? You gotta start somewhere. _________________ A Charity Pantomime in aid of Paranoid Schizophrenics descended into chaos yesterday when someone shouted, "He's behind you!"
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v-un-v
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Joined: May 16, 2005 Posts: 8933 Location: Birmingham, England, UK
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Posted: Sun Aug 06, 2006 5:07 am Post subject:
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elektro80 wrote: | Is this something out of Elektor magazine? |
No. Some awful Maplin job!
elektro80 wrote: |
Bridge rectifier? You are talking PSU here. This one isn´t intergrated on the main PCB? Any chance you can isolate it and see if it works OK without the amp circuitry? You gotta start somewhere. |
Again no. This time it was coddled together with the psu separate from the 2 (yes 2 individual) mono mosfet amp boards. At the back of it there is a sort of 'space wired' psu mess ( ) and a large tordial transformer. _________________ ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN. |
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elektro80
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Joined: Mar 25, 2003 Posts: 21959 Location: Norway
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Posted: Sun Aug 06, 2006 5:11 am Post subject:
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Oh oh...
Lemme think...
Do you have scans of the schematics? _________________ A Charity Pantomime in aid of Paranoid Schizophrenics descended into chaos yesterday when someone shouted, "He's behind you!"
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elektro80
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Posted: Sun Aug 06, 2006 5:12 am Post subject:
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Coddled together? Codpiece style? _________________ A Charity Pantomime in aid of Paranoid Schizophrenics descended into chaos yesterday when someone shouted, "He's behind you!"
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elektro80
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Joined: Mar 25, 2003 Posts: 21959 Location: Norway
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Posted: Sun Aug 06, 2006 5:16 am Post subject:
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Only thing I can think of is figuring out if the PSU can drive both mono blocks. Then isole the PSU and find out if it works as advertised ( or has been built correctly).
As for the amps: Check out the schematics and find out if there are any "idle current" suprises somewhere. _________________ A Charity Pantomime in aid of Paranoid Schizophrenics descended into chaos yesterday when someone shouted, "He's behind you!"
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blue hell
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Joined: Apr 03, 2004 Posts: 24079 Location: The Netherlands, Enschede
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Posted: Sun Aug 06, 2006 6:05 am Post subject:
Re: Fixing a MOSFET power amp |
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v-un-v wrote: | Ia homemade mosfet kit amp that keeps blowing the bridge rectifier. |
When switched on or after a while ? _________________ Jan
also .. could someone please turn down the thermostat a bit.
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v-un-v
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Joined: May 16, 2005 Posts: 8933 Location: Birmingham, England, UK
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Posted: Sun Aug 06, 2006 10:08 am Post subject:
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elektro80 wrote: | Only thing I can think of is figuring out if the PSU can drive both mono blocks. Then isole the PSU and find out if it works as advertised ( or has been built correctly). |
Yes the psu drives both monoblocks and the actual amp has been functioning well for 10 years or more. _________________ ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN. |
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v-un-v
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Joined: May 16, 2005 Posts: 8933 Location: Birmingham, England, UK
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Posted: Sun Aug 06, 2006 10:08 am Post subject:
Re: Fixing a MOSFET power amp |
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When switched on or after a while ?[/quote]
when switched on. _________________ ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN. |
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elektro80
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Joined: Mar 25, 2003 Posts: 21959 Location: Norway
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Posted: Sun Aug 06, 2006 10:12 am Post subject:
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As in:
Power on
...Zap!!!!! _________________ A Charity Pantomime in aid of Paranoid Schizophrenics descended into chaos yesterday when someone shouted, "He's behind you!"
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elektro80
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Posted: Sun Aug 06, 2006 10:13 am Post subject:
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?????
_________________ A Charity Pantomime in aid of Paranoid Schizophrenics descended into chaos yesterday when someone shouted, "He's behind you!"
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v-un-v
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Joined: May 16, 2005 Posts: 8933 Location: Birmingham, England, UK
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Posted: Sun Aug 06, 2006 10:41 am Post subject:
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elektro80 wrote: | ?????
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Indeed
?????! _________________ ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN. |
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elektro80
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Joined: Mar 25, 2003 Posts: 21959 Location: Norway
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Posted: Sun Aug 06, 2006 10:44 am Post subject:
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Like Maggie Thatcher in an electric chair?
_________________ A Charity Pantomime in aid of Paranoid Schizophrenics descended into chaos yesterday when someone shouted, "He's behind you!"
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blue hell
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Joined: Apr 03, 2004 Posts: 24079 Location: The Netherlands, Enschede
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Posted: Sun Aug 06, 2006 10:50 am Post subject:
Re: Fixing a MOSFET power amp |
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v-un-v wrote: |
The large electrolytics |
How large exactly ?
Could be the startup current for the caps is too high maybe (but only when switched on at the "right" moment then, so it shouldn't fry itself not always, just often). Especially as toroids tend to be good transformers (in the sense of being able to supply lots of current). _________________ Jan
also .. could someone please turn down the thermostat a bit.
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Uncle Krunkus
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Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
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Posted: Sun Aug 06, 2006 4:16 pm Post subject:
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Well if it worked fine for 10 years, I'd put new rectifiers in which are rated at a higher current than the old ones. Then see what the quiescent current is, and where it's going. I know this sounds dodgy, but whatever the problem, it blew the rectifiers rather than itself, last time.
Does it have any type of output protection circuitry? The only thing I can think of that could carry enough current to blow the rectifiers without going open itself would be the mosfets. Or the caps?
I just had a thought. Even if they "seem" okay that doesn't mean the caps are okay. And after 10 years they are the thing which will definately be getting "past it".
I don't know how much help that is. I'm just thinking out loud. _________________ What makes a space ours, is what we put there, and what we do there. |
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elektro80
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Joined: Mar 25, 2003 Posts: 21959 Location: Norway
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Posted: Sun Aug 06, 2006 4:33 pm Post subject:
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That is a reasonable suggestion.
Tom, does the amp stage have some sort of relay/soft kick in circuitry on the outout somewhere. Some of these designs can really act up. _________________ A Charity Pantomime in aid of Paranoid Schizophrenics descended into chaos yesterday when someone shouted, "He's behind you!"
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v-un-v
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Posted: Mon Aug 07, 2006 1:44 am Post subject:
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elektro80 wrote: | does the amp stage have some sort of relay/soft kick in circuitry on the outout somewhere. . |
Nope. This is why I asked the question in the 'DIY' section!
Jan- I made a note of what the caps were, but I seem to have misplaced it. But I'll get back to you on that one.
The caps? Yes- I suspected the caps immediately. I also know the man who originally put it together. I would suspect that he'd taken the "Oh that'll do" route !
I don't have the amp here (I'm back at home)- but I'll pass the suggestions on, and report back when something good is happening
Thanks folks! _________________ ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN. |
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