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Old 13th February 2010, 08:13 PM   #11
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Quote:
Originally Posted by luka View Post
also go to soundpressure.com, since that is DD forum, you might get some extra help you need. I say go for DIY repair, since as you say, all fets are ok(?), so expensive part is intact, now I would say you need to get yourself scope, or you really don't know what is going on in circuit...it would be much more easy to find the problem, but yes, those 7v on SG is WAY low, fets are open, but not with a lot of voltage margin, so good start is there

Yeah I have been looking on soundpressure today .

There was 1 obviously blown PS FET when I checked it out. I replaced it along with another questionable one. I will need to go through it again to see if I can find any more blown ones.

I just found it interesting that It would come out of protect, but just make those weird noises.

I am not pressed for time, so I would like to do it right.

Thank you guys for your help
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Old 13th February 2010, 08:25 PM   #12
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You shouldn't need to trace the circuit to find the transistor that powers the 3525. Remove power from the amp. Set your meter to ohms or diode check. Place one meter probe on the B+ terminal. Touch each leg of each of the transistors on the driver board. Do any read ~0 ohms?

With one probe on pin 13 of the 3525, do you read anything near 0 ohms to any leg of any transistor on the driver board?

With one probe on pin 15 of the 3525, do you read anything near 0 ohms to any leg of any transistor on the driver board?

Does any individual transistor have direct connections to both the B+ terminal and either pin 13 or 15 of the 3525?
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Old 13th February 2010, 08:49 PM   #13
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Originally Posted by Perry Babin View Post
You shouldn't need to trace the circuit to find the transistor that powers the 3525. Remove power from the amp. Set your meter to ohms or diode check. Place one meter probe on the B+ terminal. Touch each leg of each of the transistors on the driver board. Do any read ~0 ohms?

With one probe on pin 13 of the 3525, do you read anything near 0 ohms to any leg of any transistor on the driver board?

With one probe on pin 15 of the 3525, do you read anything near 0 ohms to any leg of any transistor on the driver board?

Does any individual transistor have direct connections to both the B+ terminal and either pin 13 or 15 of the 3525?
well that is certainly a much better way of tracing the circuit haha. Wow I am surprised I didn't just think of that on my own, you can tell I have little experience in regards to circuits.

After checking over the card I found 2 transistors with low resistance B+ connections, however none of the legs led to either of the 2 pins on the IC with little resistance.

Could blown PS FETs be responsible for the weird readings on the IC? I will be checking over them again, and will remove the questionable ones. Is there an easy way to remove them without snipping the legs, Id assume a solder sucker/solder braid would do the trick?
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Old 13th February 2010, 09:01 PM   #14
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Blown PS FETs would only likely lead to low voltage if they were dragging the 12v power supply voltage down.

See if you can trace the circuit from pins 13 and 15 of the 3525 to either of those transistors. If the voltage passes through a diode or a resistor, that could explain why you're not seeing a direct connection. A lighted magnifying glass will make this easier. Of course, there are traces on the bottom of the driver board so visually following traces may not be possible.

Don't try removing the driver board.

Which components were you going to remove (but didn't want to cut the legs)?
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Old 13th February 2010, 09:10 PM   #15
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Quote:
Originally Posted by Perry Babin View Post
Blown PS FETs would only likely lead to low voltage if they were dragging the 12v power supply voltage down.

See if you can trace the circuit from pins 13 and 15 of the 3525 to either of those transistors. If the voltage passes through a diode or a resistor, that could explain why you're not seeing a direct connection. A lighted magnifying glass will make this easier. Of course, there are traces on the bottom of the driver board so visually following traces may not be possible.

Don't try removing the driver board.

Which components were you going to remove (but didn't want to cut the legs)?
I was referring to removing the PS FETs to test them out of the circuit. I removed the blown ones by snipping the legs, but would like to avoid that on FETs that could be good.

Yeah it seems as if the majority of the traces are on the bottom of the card. But I will continue to check them out
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Old 13th February 2010, 09:14 PM   #16
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Apply additional solder to all 3 legs and lay the tip of the soldering iron across all 3 solder connections to heat them all at once. The transistor should essentially fall out of the board when the solder becomes molten on all 3 legs. If there's excessive solder on top of the board (component side of the board), you may have to remove it beforehand to make it easier to get the solder hot enough.
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Old 13th February 2010, 09:17 PM   #17
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Sounds like a plan...I have heard of doing that before, but assumed it might not work i this case because the mosfet legs are kind of far apart
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Old 13th February 2010, 09:24 PM   #18
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A heavy (broad) tip and a hot iron make it easier. Sometimes, you may have to work the iron back and forth (always keeping in contact with 2 of the 3 legs) to get the solder hot enough.

When you desolder the pads, do so from the side of the board that has the most copper.
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Old 13th February 2010, 10:21 PM   #19
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well I pulled all of the questionable PS mosfets and they all checked out OK according to your test on bcae1.com

I will look over the driver cars more tonight
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Old 13th February 2010, 10:52 PM   #20
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Looking over the card I noticed a diode that had a funky looking solder joint. So I hit it with my DMM in diode check and it read 0.041 in both directions, then 80 ohms in each direction, could this be the issue?
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