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Old 8th May 2010, 07:19 PM   #1
MihaCro is offline MihaCro  Croatia
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Join Date: Apr 2010
Default Need help, reparing amp. with unknown diode

Need advice.
Repairing Rodek 1kw class D monoblock.

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Two diodes from picture where burned out and it s not possible to recognize model number.

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Looks like some kind of protection of IRFP264, connection is between: diode cathode to drain and diode anode to source

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When replaced with 1N4148 looks that everything else is working fine but they pass away immediately after increasing volume
Please advise what type of diode should I buy to replace.

Thanks,
Greetings from Croatia
Miha
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Old 8th May 2010, 09:43 PM   #2
Andy F is offline Andy F  Spain
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Location: Northwest Spain
Hi:

They are ultrafast diodes, you must measure voltage between drain and source of each mosfet with an scope(dont forget to have your scope unearthed or isolated from mains, after that you can use the right model based on maximum voltage read, if voltage is lower than 200 volts you can use MUR120 or equivalent, if voltage is higher you can use MUR160 (600v) or equivalent. I doubt seriously about the practical effect of any diode in parallel with the intrinsic diode inside the Mosfets without any added circuitry but at least your amp will return to its original status again. Anyway your amp must work exactly the same without those diodes for sure.
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Old 9th May 2010, 09:52 AM   #3
MihaCro is offline MihaCro  Croatia
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Thanks for quick reply Andy.

Maybe any suggestion, why thous two diodes burned out, should I check anything around...
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Old 9th May 2010, 09:59 AM   #4
jej is offline jej  France
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Hi,
You can use UF 5404 (300v 50ns) by Vishay. This diode is required when Mos drive inductive load because intrinsic diode is too slow. It's only a protection and your amp can correctly run without thid diode!
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Old 9th May 2010, 10:40 AM   #5
Andy F is offline Andy F  Spain
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Location: Northwest Spain
Hi again.

Any abnormal behaviour at your load or output filter can kill those diodes as they are small, if your mosfets survived I think that the other components on board must be OK after the diode failure possibly caused by a sudden output voltage rise beyond the rail voltage due to the inductive nature of the filter and load. Clamping seems the main reason for them to be there.
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Old 10th May 2010, 08:26 PM   #6
MihaCro is offline MihaCro  Croatia
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Thanks guys!
I will let you know how it will work (or not) at full load.
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