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Old 16th January 2013, 04:17 AM   #21
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I replaced all the outputs and drivers in that channel. I powered the amp and it was drawing 40 amps current. 3 of the IRF540 FETS were getting hot. I removed those 3 and re powered the amp and it powered up fine.

I re-installed them and it powered up and blew the fuses for that channel.

I removed the D41D8 and powered the amp and the 10uf 50v cap next to it exploded. I replaced the cap and the driver and repowered the amp.

The 75 ohm resistor next to the D41D8 instantly smoked. I replaced it and repowered the amp. Then the 75 ohm resistor next to the D40D8 instantly smoked.

I am not sure what is going on here. It is hard to follow the schematic, as there is no silk screen markings on the board.

Some of the fuse holders have 14 vdc going to them when just power and ground are hooked up and some dont, is this right? When the amp is powered they have rail obviously.

I am at a stand still, unsure where to go next. I dont want to keep blowing parts.
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Old 16th January 2013, 05:46 AM   #22
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Please read post #21 first.

If I leave the fuses out for that channel the amp powers fine. Whatever fuse I put in for that channel it burns the 75 ohm resistor. 1 fuse burns the 75 ohm resistor by the D40D8 and the other fuse burns the 75 ohm resistor by the D41D8.

Any ideas?
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Old 16th January 2013, 09:07 AM   #23
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If you power it up through a current limiter, does that stop the resistors from burning long enough to measure the DC voltage between the bases of the D40 and D41?

Does it help if you set the bias pot fully counter-clockwise?
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Old 16th January 2013, 05:46 PM   #24
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Quote:
Originally Posted by Perry Babin View Post
If you power it up through a current limiter, does that stop the resistors from burning long enough to measure the DC voltage between the bases of the D40 and D41?

Does it help if you set the bias pot fully counter-clockwise?

The bias pot is fully counter clock wise.

You want me to measure across the bases of the D40 and D41? Red probe on one base and black probe on the other base?
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Old 16th January 2013, 06:55 PM   #25
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The amp will not power up through a current limiter with the fuses installed. If both fuses are in with a current limiter just hooking up power and ground makes the amp draw current and when the remote is applied it will not power.

If I remove the 2 fuses for that channel the amp will power up, but I dont think I can get an accurate reading across the bases of the 2 transistors you need without the fuses installed can I?

Something in that channel has to be shorted or something???
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Old 16th January 2013, 06:59 PM   #26
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If you can't do that, check each of the 4 diodes in the string connected to the output of the op-amp. Do any read more than about 0.6v (no power applied, meter on diode-check)?
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Old 16th January 2013, 07:02 PM   #27
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All 4 read about 0.565v
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Old 16th January 2013, 08:02 PM   #28
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With the bias pot fully counter-clockwise, what resistance do you read between the bases of the D40 and D41?
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Old 17th January 2013, 04:23 AM   #29
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0.450K ohms
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Old 17th January 2013, 09:45 AM   #30
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Solder a jumper between the bases of the D40 and D41. Does that allow the amp to power up through the limiter?

If so, does that channel produce audio?
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