PPI PC21400.2

[Perry Babin]

Confirm that you get no deflection when you touch BOTH probe to 12v at the same time.

 

[caraudioguy2100]

I get no deflection trace stays on reference line when I touch both probes to the 12v

 

[Perry Babin]

For the FETs where you didn't get a traditional square wave, check the drive on those FETs with the two probes on the gate and source. Actually, you can check the drive on all FETs like that.

 

[caraudioguy2100]

When checking the drive Q2,4,6 still have no drive at all the trace remains on the reference line

 

[Perry Babin]

Are those the only 3 with no drive signal?

 

[caraudioguy2100]

Yes

 

[Perry Babin]

What's the resistance between pin 11 of the 4081 and the gate leg of those 3 FETs?

Between pin 11 and the gate of 69, 71 and 73 of the other IC?

 

[caraudioguy2100]

22.1 ohms from pin 11 to Q2,4,6

22.1 ohms from pin 11 to Q69,70,71

 

[Perry Babin]

Swap the ICs if they're in sockets. Does the drive change?

I'm assuming that you no longer have a jumper between the pads that you previously had.

 

[caraudioguy2100]

No jumper between the pads .

And swapped the ic’s and still no drive

 

[Perry Babin]

Do you still have drive on 69, 70 and 71?

 

[caraudioguy2100]

No .

The amp has drive signal on Q2,4,6,69,70,71 when the ic’s are not loaded with a cap


If I put a 0.1uf cap in circuit gate to source legs 1-3 I lose all drive signal on Q2,4,6,69,70,71

 

[Perry Babin]

I asked about 69, 71 and 73.

You are using 69, 70 and 71.

Are 69, 70 and 71 driven by the same drive signal? Measure the resistance between their gates to confirm.

 

[caraudioguy2100]

Sorry my mistake with the locations .

Q69,71,73 have drive until you load the ic’s with a cap same with Q2,4,6

 

[Perry Babin]

Install 4 FETs in locations 1, 2, 7 and 8 (no other loading). Do all have drive?

Does the amp draw excessive current?

 

[caraudioguy2100]

I put fets in locations Q1,2,7,8

I don’t see any drive signal on any of them .

Amp doesn’t draw excessive current and fets remain cold

 

[caraudioguy2100]

Ok I removed the fets again .

I notice something strange on the pads for the fets .

Q2,4,6 have strange voltages on the pads

Leg 1:1.20
Leg 2:13.90
Leg 3:1.20

Q8,10,12

Leg 1:1.20
Leg 2:13.90
Leg 3:1.20

Q73,71,69. Q67,65,63

Have the same voltages 1.22 volts on gate and source legs

I’m wondering if I have a bad 3525 again here’s what I get on the pins

Pin 1:0.00
Pin 2:0.24
Pin 3:0.00
Pin 4:0.00
Pin 5:0.16
Pin 6:0.00
Pin 7.0.00
Pin 8:0.45
Pin 9:0.00
Pin 10:0.00
Pin 11:0.00
Pin 12:0.00
Pin 13:13.06
Pin 14:0.00
Pin 15:13.06
Pin 16:0.47

 

[Perry Babin]

Pin 16 is either being dragged down or the IC is defective.

 

[caraudioguy2100]

Replaced the 3525 .

Still have drive issues .

This is Q1 first pic Q2 second pic .

Scope settings are 5us 5votls/div in both pics

If I put a fet in locations Q7 or Q8 the fets get to hot to touch within 2 secs and amp draws excessive current

 

[Perry Babin]

What is the DC voltage on pin 16 of the 3525?

Are you sure that you had a good connection on both probes when checking the drive?

Were you using differential mode?

What is the DC voltage on terminals 15/16 of the 4081s?