Well once again, i've stumbled over driver transistors.
I have an amp here, with blown mosfets, so i've pulled them all out (12 of them).
Now, the 2 banks of 6 fets are split, there appears to be 1 driver transistor for 6 fets (3 on one side and 3 on another).
Measuring at the pads on the fets I get: 5.4v across 3 of them each bank. (3 each side of the board) On the remaining 6 (2 3's again) I get B+.
So I thought, easy, just a blown driver transistor which is shorting. But here's the tricky part. The transistors are attached to an IC, on both of them at the middle leg, I get milli-volts (very very small). On the leg attached to the IC I get 5.4v (nice). Then on the remaining leg i get 5.4 on the one (nice) and B+ on the other. Now maybe my brain has farted and missed something, or have things really gone mad with this amp?
.
Can anyone give me a starter with this? I'll get a pic up and some model numbers in a while.
Edit:
Driver transistors : A1023's
Ic - TL494 (cn) = http://www.datasheetcatalog.org/datasheet2/a/0a91owp2owcksesx812wr26kdjyy.pdf
The row of 4 components are: 2 resistors in the middle and a diode each end.
I have spare driver transistors to hand (not 1023's, but alternates i've used before)
I have an amp here, with blown mosfets, so i've pulled them all out (12 of them).
Now, the 2 banks of 6 fets are split, there appears to be 1 driver transistor for 6 fets (3 on one side and 3 on another).
Measuring at the pads on the fets I get: 5.4v across 3 of them each bank. (3 each side of the board) On the remaining 6 (2 3's again) I get B+.
So I thought, easy, just a blown driver transistor which is shorting. But here's the tricky part. The transistors are attached to an IC, on both of them at the middle leg, I get milli-volts (very very small). On the leg attached to the IC I get 5.4v (nice). Then on the remaining leg i get 5.4 on the one (nice) and B+ on the other. Now maybe my brain has farted and missed something, or have things really gone mad with this amp?
.Can anyone give me a starter with this? I'll get a pic up and some model numbers in a while.
Edit:
Driver transistors : A1023's
Ic - TL494 (cn) = http://www.datasheetcatalog.org/datasheet2/a/0a91owp2owcksesx812wr26kdjyy.pdf
An externally hosted image should be here but it was not working when we last tested it.
The row of 4 components are: 2 resistors in the middle and a diode each end.
I have spare driver transistors to hand (not 1023's, but alternates i've used before)
Last edited:
Ok, driver transistor removed.
Now I get B+ -2v (B+ =15v now 13v on the gate's of the fets.)
5.6v solid on the end pad and 0v on the middle.
Where this 13v is coming from, i'm stuck. There are a few diodes dotted around, but none seem to be shorted.
Any ideas of how this voltage is getting there? I've followed the traces and there appears to be no shorts?
I'm baffled.
Now I get B+ -2v (B+ =15v now 13v on the gate's of the fets.)
5.6v solid on the end pad and 0v on the middle.
Where this 13v is coming from, i'm stuck. There are a few diodes dotted around, but none seem to be shorted.
Any ideas of how this voltage is getting there? I've followed the traces and there appears to be no shorts?
I'm baffled.
It's probably OK. Clamp all transistors down and let the amp idle for a bout 10 minutes. If the heatsink under the FETs doesn't get warmer than the rest of the heatsink and the amp isn't drawing more than about 1 amp of current, the supply is likely working properly.
I'm assuming that you've checked all of the gate resistors to confirm that none are out of tolerance.
I'm assuming that you've checked all of the gate resistors to confirm that none are out of tolerance.
I checked the gate resistors yes.
Also I let it run for maybe 30 secs. The fets get hot and my supply voltage drops. I have 3a available @15.8v so i'm guessing that it's drawing a lot more power than that?
Should I pop an inline fuse in place?
Or a light bulb?
Then try again?
Also i'm getting perfect conductivity between the outputs (+ve and -ve) on the speaker terminals. Is that normal?
Also I let it run for maybe 30 secs. The fets get hot and my supply voltage drops. I have 3a available @15.8v so i'm guessing that it's drawing a lot more power than that?
Should I pop an inline fuse in place?
Or a light bulb?
Then try again?
Also i'm getting perfect conductivity between the outputs (+ve and -ve) on the speaker terminals. Is that normal?
I've thrown my hat in, i've seen enough of it.
It's a oz audio va 2000.1.
But as I said, it's going off to someone else now, as i've seen enough.
I got 5.6v on every gate +-0.02v
I put the clamp around the supply I got 0.3a for a couple of seconds, then got 15a for about 5 secs till I turned it off.
Thanks for your help anyway PB.
When I have some more patience i'll be back i'm sure
It's a oz audio va 2000.1.
But as I said, it's going off to someone else now, as i've seen enough
.I got 5.6v on every gate +-0.02v
I put the clamp around the supply I got 0.3a for a couple of seconds, then got 15a for about 5 secs till I turned it off.
Thanks for your help anyway PB.
When I have some more patience i'll be back i'm sure
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