JBL GTO 7001

[chrisg4]

Hi all,

I'm working on above mentioned amplifier. Amp doesnt turn on, faint protection light is pulsing. PSU and output fets test ok, no shorts. I did notice the 7812 regulator gets extremely hot, I replaced it and the new one gets extremely hot as well. No signs of visible damage.

 

[Perry Babin]

Which 7812 is getting hot?

 

[chrisg4]

sorry, the one next to the 7912.

 

[chrisg4]

Some pics:

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[NadaD]

Those input filter caps and rail caps doesnt look good.

 

[Perry Babin]

Clamp the 7812 to a heatsink to prevent overheating.

Does it produce 12v out?

If so, do any of the audio op-amps heat up?

 

[chrisg4]

I reinstalled the rectifiers and output fets. Amp now powers up and produces audio. I also noticed the caps, would they need to be replaced?

 

[Perry Babin]

What changed to stop the regulator from overheating?

If the caps vented, they need to be replaced. If they did not vent, they likely still meet spec and don't necessarily need to be replaced.

 

[chrisg4]

Not sure, once I clamped it, heat seems to disappate better.

Ok, one of the rail caps had some residue on it. Will source replacements

 

[chrisg4]

Hi Perry,

i cannot get the 3300uf 100v, can i use 4700uf 100v?

 

[Perry Babin]

Yes, if they will fit.

 

[chrisg4]

can i go lower capacitance but same voltage?

 

[Perry Babin]

If this were a class B or AB, you probably could but some class D rely on the capacitance of the rail caps to prevent bus-pumping so lower value caps may not work.

 

[chrisg4]

The height of the cap is the issue, the correct spec items are too long. I can get 2200uf in the correct dimensions.

 

[Perry Babin]

Have you pulled the caps to see how far out of tolerance they are?

 

[chrisg4]

caps are out, i don't have capacitance meter...

 

[Perry Babin]

Many multimeters can measure capacitance. Do you know someone who has one that can?

 

[chrisg4]

Hi Perry,

I actually had a multi-meter with this function, never noticed it before.

measured two of the caps:

3300uF 100v - 2958 mF (looks like the electrolyte leaked)
3300uF 100v - 3219 mF

is mF the same as uF?

 

[Perry Babin]

I would assume that mF is uF.

This amp has 4 3300uF caps, Install two good 3300uF caps (one per rail) and see if the rail voltage holds steady and remains clean. If one 3300uF per rail is good enough, two 2200s per rail would be good enough.

That said, it would be best to find a source for the correct value caps.

If you use the 2200uF caps, clamp all heatsink mounted components, run the amp hard and monitor the temperature of the caps. Something strange may be happening in the amp. It's common to see the PS side OR the rail caps fail but to have both fail is odd.

For the PS primary caps, you want 'low ESR' and 105C caps.