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Old 21st July 2011, 02:39 PM   #11
Dr Zeus is offline Dr Zeus  United States
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Hey Crash thanks for helping this out.

Any chance you can see what kind of diodes I'm missing in the above photo? There are three small diodes in close proximity to the 18pin IC which on my amp someone clipped as a 'modification'.
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Old 21st July 2011, 06:39 PM   #12
Cr@sh is offline Cr@sh  United States
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Sure can, I have to pull it out from the car. I planned on doing this today so give me a day or two.
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Old 21st July 2011, 07:00 PM   #13
Dr Zeus is offline Dr Zeus  United States
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If you are willing, otherwise I'll just send an email to USAmp. I dont want you going out of your way partner.
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Old 22nd July 2011, 02:05 AM   #14
Cr@sh is offline Cr@sh  United States
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You'll have to contact US Amps. I see no numbers on them. Mine is the green board as well. Shouldn't be any difference but anyway they'll help ya. I just contacted them a month ago about my USA50x and they got back to me within days.
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Old 28th July 2011, 04:08 AM   #15
Dr Zeus is offline Dr Zeus  United States
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I forgot to update, but I heard back from USAmps. They said that once those diodes are clipped, the SAT control unit needs to be re-programmed and is usually not worth it. Beats me why clipping diodes would re-program nvram. Ah well.

I already spoke with this amp's owner and this repair is going to be an as-is but a working repair, if I can find the parts.

I'm trying to source a good place to buy MJE4353 outputs. The complementary MJE4343 Arrow stocks which I also need, but no-where I can find through OctoPart any good non-NTE brand MJE4353.
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Old 28th July 2011, 04:20 AM   #16
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If you can't find them, the FJA4313 and the FJA4213 may be good subs. I have never tried them as a sub for the motorolas.
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Old 29th July 2011, 06:27 PM   #17
Dr Zeus is offline Dr Zeus  United States
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Into re-building the damaged PS section. I replaced a damaged PS driver; MJE15030 and also the two 100ohm 1/2w resistors just next door. Removed all the bad fets and some of the bad 47ohm gate resistors. Replaced some of the gate resistors with 47ohm brand new units, and installed 4 IRF3205 fets; one in each corner of PS section of the board.

I still have all the primary/rail rectifiers removed from circuit.

Power-on heated the fets instantly. Upon inspection, I notice the fets also heat instantly with only Bat+ and ground connected to my power supply. Looknig further, leg 2 of the fets are directly connected to bat+, while leg 3 f the fets are directly connected to ground. Does this sound like there might be a shorted transformer?
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Old 30th July 2011, 05:20 AM   #18
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When you say 'directly connected' do you mean it reads 0 ohms to the B+? That's normal. It's connected via the primary transformer windings.

What's the DC voltage on the gate leg of each of the FETs?
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Old 12th August 2011, 04:13 AM   #19
Dr Zeus is offline Dr Zeus  United States
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I found the other PS driver, an MJE15031 reading OL off the board so I replaced it with a new MJE15031G. I am now able to get this amp to partially power up with the rectifiers removed, but there are two small 25v, 220uf electrolytic caps next to the LM7915CT and LM7815CT regulators which still want to explode as mentioned before. Installed, these caps do not like having 55vDC across them. Once removed, the voltage across them is only 22vDC.

With them both removed, the LM7915 gets hot very quickly, but I am able to measure decent regulated voltage on the opamps.

Last edited by Dr Zeus; 12th August 2011 at 04:17 AM.
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Old 12th August 2011, 04:33 AM   #20
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It may be a regulated power supply that's producing too much output (to the rectifiers for the regulated power supply) with the rectifiers out of the circuit.
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