AQ -1200

Perry Babin · 2010-09-29 5:33 am

I could be mistaken but I don't see any driver transistors on the driver board. It's likely that the driver board drives the external driver transistors. The collector of the A1275 would be connected to the 3rd leg of the FETs (ground). No leg of any of the NPN driver transistors would be connected to ground. The emitters of the driver transistors would go the the gates of the power supply FETs. Is that what you have?

mike49504 · 2010-09-29 6:22 am

The A1275's middle leg goes to the 3rd leg of the fets and to ground.

The 1st leg of the 3228's goes to the gate leg of the fet.

Perry Babin · 2010-09-29 6:37 am

Compare the drive signal at the driver IC to the drive signal on the base and emitter of the A1275 driver transistors. The falling side of the waveform should be almost perfectly vertical down to about 2v.

mike49504 · 2010-09-29 6:39 am

Heres what i have now on the gates after replacing a transistor that connects to the driver board. Is this any better?

Perry Babin · 2010-09-29 6:51 am

I can't tell. Manually set the shutter speed on the camera to 1/100. Does that produce a sharper trace?

mike49504 · 2010-09-29 7:07 am

Hope theese pics are a lil better

Perry Babin · 2010-09-29 7:35 am

It may be a bit better. Is the current draw still excessive when you solder the drains to the board?

mike49504 · 2010-09-29 7:43 am

Yes with the drain legs soldered back in it blows the fets still.

Perry Babin · 2010-09-29 7:47 am

Is the falling side of the waveform more vertical on the base of the driver transistors?

mike49504 · 2010-09-29 8:12 am

First pic is the base of the C3228

2nd pic is base of A1275

Perry Babin · 2010-09-29 8:22 am

It should have either 2 PNP transistors or 2 PNP and 2 NPN transistors. If there are only 2 driver transistors, they should both be PNP transistors.

If it has 2 of each, the base of one NPN and one PNP will be directly connected.

mike49504 · 2010-09-29 8:30 am

The amp has 4 driver transistors 2 of the are A1275's and the other 2 C3228's

Thats how it was when i got the amp in for repair . But someone messed with it alot also.

The base of the 1275 is directly connected to the base of the 3228

Perry Babin · 2010-09-29 8:50 am

Do you have any other PNP transistors that you can use in place of the 1275s?

mike49504 · 2010-09-29 11:12 pm

Would the A1023's work in place of the 1275's?

Perry Babin · 2010-09-30 12:06 am

They should. When you initially power up the amp, do so with the drains desoldered.

mike49504 · 2010-09-30 12:32 am

The orginals were C3228's in this amp I switched them over to the C2383's

But the owner said the amp was tosating fets with the orginal drivers in it also.

I put the 1023's in but do i switch the C2383's back to the 3228's or leave them for now to see what i get?

Or switch thoose as well to the 1027's??

Perry Babin · 2010-09-30 12:34 am

The problem is with the PNP drivers, not the NPN drivers. You can leave the NPN drivers as they are.

mike49504 · 2010-09-30 1:13 am

This is what i have now with the 1023's in the amp

Perry Babin · 2010-09-30 1:15 am

That's much better.

mike49504 · 2010-09-30 1:21 am

So should i try soldering the drain legs back in and see what happens?

AQ -1200

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