orion xtr

[goviboo]

Good day folks,
I got in an Orion XTR 2200.1D with blown output filter caps (electrolytics), replaced those with new. Amplifier powers up, good rails and reg LV supplies, passes clean audio.
I've noticed however without audio and a 2-ohm load connected if left connected at idle the heatsink gets hot to touch (after ~15mins). I did some probing around and found some ringing on the output FETs gate drive.
The output section appears to be original, how can I go about to reduce this?

 

[Perry Babin]

Were these with the black probe in the FET source terminals?

 

[goviboo]

Yes sir,
My scope is a fluke 190-204, black probe on the FET source terminal.

 

[Perry Babin]

How clean is the waveform on the emitters of the drivers?

 

[goviboo]

There's little ringing on the emitters. the measurements were taken with the black probe on the source of each respective bank of FETs.

Previous to creating this thread I replaced the driver chip (IR2113) and both caps C155/156 on the driver board. the output FETs (IRFP4868) and gate drive resistors( 5.6-ohm) appear to be original/untouched.

 

[Perry Babin]

Some of the amps of this type have a series RC network across the drain and source of each bank of output FETs. It's typically a 1000pf in series with a 20-something ohm resistor. Does this amp have those?

 

[goviboo]

Yes, this amp has the RC network; D-S, one network for each bank. C371/R371

 

[Perry Babin]

A single 56 ohm resistor is a higher value than any other amp I've seen. Some had 2 56 ohm in parallel. The lowest I've seen was a 10 ohm, 2w in series with the 1000pf capacitor. You could try lowering the value of the resistor to see if that helped.

 

[goviboo]

these are 22-ohm.

 

[Perry Babin]

I looked at the wrong resistor. The same applies. If lowering the value doesn't help, there may be no easy solution.