JL Audio 1000/1 No output

[peeby]

So have a 1000/1 had a bad rectifier. Up and running, idles fine, low voltage good everywhere, switching drive looks good on outputs but no audio is reaching outputs.

Tracing out preamp now. Any advice would be welcome.

 

[Perry Babin]

With a speaker and signal source connected, did you operate all pots and switches in all combinations to see if any audio/static/noise ever played through?

 

[peeby]

Yes, no noises or pops.

 

[Perry Babin]

Have you lifted and reset the preamp board?

If you push on various parts of the two boards, does that make any difference?

 

[peeby]

Yes. Resoldered all pins. Removed old solder and resoldered.

 

[peeby]

I noticed in previous thread you mentioned probing this transistor for the same symptoms.

 

[Perry Babin]

What's the DC voltage on all 3 terminals of the transistor in the attached image?

 

[peeby]

-14.3
.137
.136

 

[Perry Babin]

Remove it to see if audio will pass.

 

[peeby]

No audio when removed. Although it checks bad.

 

[Perry Babin]

What is the resistance between legs 1 and 2?

Go back and check the pots and switches with signal and speaker with the transistor out.

 

[peeby]

22 ohms. Its a J fet? J111

OK, audio is fine now. Polarity switch was not passing. Everything is cleaned and working now.

What to replace the J111 with?

 

[Perry Babin]

22 ohms doesn't indicate that it's defective. JFETs read low resistance D-S with no gate voltage.

If it is actually defective, replace with the same.

 

[peeby]

I will put it back in

 

[peeby]

All working.

However, there is a pop on speaker when amp shuts down.

I know output drive remains for 15 seconds. Is there a muting that engages prior to rail going away?

 

[Perry Babin]

When you posted the voltage on the jfet, you posted them in reverse. Leg 3 should have -15v.

 

[peeby]

Any thoughts on the pop on shutdown?

 

[Perry Babin]

Did you confirm that the muting transistor (j111) was installed correctly? The control voltage should be on leg 3, not leg 1.

 

[peeby]

It is in the proper orientation.

I did check it with my MK-328 which does check Jfets and it checked as 2 diodes. It did not id it as a jfet. Don't always trust the MK-328 though.

 

[Perry Babin]

Does the -15v on the gate go immediately to ground when remote is removed?