New member. Hope I am posting in the proper thread and thank you for offering this forum.

Device in question is a Paradigm Servo 15a. (schematic of Servo 15 attached)

The unit is a 20 year old subwoofer that I like.

It began to blow fuses when Auto On was ON
Now it blows fuses when just turned on. It does not blow immediately. There is a few seconds of rumbling before this happens.
So far this is what I have done:
1. started her up with a lamp load and no obvious short was found
2. inspected pcb for burnt traces: none found
3. inspected filter capacitors: top slightly spongy on one but no bulging: resistance revs up fine with fluke. Can't check capacitance as fluke has a 10,000 maximum capacitance range and capacitor is 15,000 (removed to check)
4. Used multimeters to check for short in output transistors: none found

Whats next? Thank you
Bill


N

 

Just tested the bridge rectifier and this seems to be working.

 

Welcome to AAC!

Have you checked the MOV to see if it's shorted? Which subcircuits are easily disconnected?

 

If it works with a lamp load but not with a speaker load, have you not checked the speaker?
Regards,
Keith

 

Welcome to AAC!

Have you checked the MOV to see if it's shorted? Which subcircuits are easily disconnected?

The MOV is not shorted. I can disconnect the dc lines from the bridge rectifier to see if it blows fuses.

 

If it works with a lamp load but not with a speaker load, have you not checked the speaker?
Regards,
Keith

I may have said that wrong. I did this:

ie I made current limiting device by plugging the unit into a receptacle that was in series with a lamp. My load was my subwoofer itself.

 

I am continuing to work on this. I am beginning to question if I tested the power transistors as well as I could. Do they need to be removed from the circuit to be tested?

 

Could someone tell me how to test a toroidal transformer for a short for this project? TY