PPI PC21400.2

[caraudioguy2100]

In differential mode here is what I get .

Pic 1 is of Q1 Pic 2 is Q2

Pin 16 of the 3525 is 5.09 volts

Pin 15:13.74
Pin 16:13.74

This is for both 4081’s

 

[Perry Babin]

Why didn't you use differential mode in the previous post?

 

[caraudioguy2100]

I was cleaning my bench off at the time and disconnected the probes so I only hooked one up to test this amp .

But to me it appears Q1,Q2 have good drive signal .

Q7,8 now have issues with drive should I go back to a cap in differential mode and post the waveform I get ?

 

[Perry Babin]

The transformer could have shorted windings. Power through a limiter and see if twisting the transformer changes the current draw with 7 and 8 in the circuit.

If you reduce the loading cap to about 1000pf, you may be able to view the drive without the FETs.

 

[caraudioguy2100]

I figured out the problem .

I have problems in the regulator circuit still and is causing the power supply to go crazy .

I will rebuild the regulator circuit again double checking all connections and got from there .

So far I found a shorted diode 1N4744

 

[caraudioguy2100]

I found another diode shorted in the regulator circuit .

1N4004

Can I use a 1N4003 ?

 

[Perry Babin]

Why don't you give circuit board designations?

 

[caraudioguy2100]

Sorry .

CR8 is the board location

 

[Perry Babin]

The diode will work for testing but if someone is paying you to repair this amp or you intend to sell it, order and install the right part before it leaves your shop.

 

[caraudioguy2100]

1 last question before I test for drive again .

Do the 2N6488’s and 6491’s have to be in circuit in order to test the drive for the power supply fets ?

Board locations Q13,14. Q75,76

 

[Perry Babin]

Not as far as I know but I've never needed to remove them for any testing.

If I had to keep them from overheating, I used something like the temporary heatsink in the photo below.

 

[caraudioguy2100]

Ok here is what I get for drive signal they locations are loaded with a 1000pf cap

First pic is Q1
2nd:Q2
3rd:Q7
4th:Q8


Scope is set up in differential mode

 

[Perry Babin]

Do you get the same for Q63 and Q69 as you do for Q2 and Q8?

 

[caraudioguy2100]

Yes

 

[Perry Babin]

Are both channels of your scope set precisely the same?

 

[caraudioguy2100]

Yes

 

[Perry Babin]

If all 4 of the high-side drives (unloaded) look like the low-side drives (the ones with higher amplitude), I'd think that they are OK. There's no way that you could have 4 drive circuits from 2 different ICs that have failed in precisely the same way.

 

[caraudioguy2100]

Put all the fets back in circuit along with the rectifiers and regulators .

I powered the amp up for a couple of secs out of the sink and tested for output everything seems fine right now .

I’m gonna put it back in the heatsink and fully tested it .

I will let you know how it goes

 

[caraudioguy2100]

Amp is finally done .

So wanna say thanks a ton for the help with this amp .

I appreciate your help a lot !!