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Old 27th April 2011, 07:39 AM   #11
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I replaced Q405 and Q305 which are 2AM and that got rid of the dc on the bridging terminals of the rear channels. Is there something else I should be checking? Maybe I have some bad smd resistors?
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Old 27th April 2011, 07:53 AM   #12
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Does it produce clean audio out of those channels?
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Old 27th April 2011, 08:00 AM   #13
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I dont have time to check it something is getting hot and smoking but I cant tell what. Maybe it is the flux around the components I just changed. As these components get hot the dc returns on the bridging terminals.

Both of the IRF9540 in the rear channels have like -2.250 from gate to source and whatever is getting hot increases that voltage as it gets hotter. The IRF540's from the rear have 0.000 vdc from gate to source.
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Old 27th April 2011, 08:04 AM   #14
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Do you have excessive current flow through both rear channels? Measure the DC voltage across the 0.1 ohm source resistors if you don't know if it's one or both channels.
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Old 27th April 2011, 08:07 AM   #15
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Yes it is through both channels. Something starts smoking on both channels. It has to be something close to the 2A's I changed because its got to be getting the flux residue hot to smoke like that.
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Old 27th April 2011, 08:12 AM   #16
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It seems the heat is coming from R423 and R452 on one channel, and R323 and R352 from the other. It takes a second then the amp current draw goes up just a little on my power supply amp meter, then the components start heating making the dc return.
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Old 27th April 2011, 08:16 AM   #17
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Does this amp use the BUZ outputs?

If so, did you check to see if they were shorted gate to source? These transistors commonly short that way instead of drain to source.
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Old 27th April 2011, 08:23 AM   #18
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No it uses the IRF540 and IRF9540. I would probably have to remove them from the circuit to test for short or leakage?

R323 and R423 are directly connected to the emitters of the 2A's I replaced. I have 100's of IRF540 and IRF9540's I could change them out to eliminate them as a fault. The channels were producing audio until the dc came. Maybe they shorted?

I could clip the legs and turn on the amp and see if the heating goes away in the components???

Last edited by seankane; 27th April 2011 at 08:25 AM.
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Old 27th April 2011, 10:00 AM   #19
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I replaced the output fets in the rear channels. I powered up the amp and all seems to be well. I let it idle for 15 min with no heating or smoking. I no longer have voltage from gate to source either. I am going to replace the front channels output fets as well. When I get that done I will set the bias and try for audio again.

I will post my results later.......need sleep.
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Old 27th April 2011, 02:53 PM   #20
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Check the ones you pulled to see if there is any leakage (gate to other legs).
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