JL Audio 900/5

[pippolonia]

Hi guys,

this amps doesn't turn on but the power supply is ok because all voltages are present and correct (+15, -15, +5, -5 +35 and -35) with an idle current about 2,5 A.

I think there is a missing connection because the "big hole" at center of the mother board. Problem is i dont't have any schematics of information about mother board traces

But this amp have a "three slice" board ? Because surface is connect to ground, just a little bit inside the board (if i put a tester plug inside the hole) there is a +12 V ....

Thanks for your help.

Giovanni

 

[Osvaldo de Banfield]

This is called "multilayer" or sandwich PCBs, very classic nowadays, with almost classic defects of insulation between them. I estimate that there is no components missing in the zone. Remove al carbonized material and place some kind of insulation varnish to prevent humidity catching, that will fire the PCB again.

What is the device in the R34 connections? (Too dark in my PC).

 

[pippolonia]

Hi Osvaldo,

i suppose it is a transistor (I don't remember the code, I'll give you more detail tomorrow) with two legs shorted; one pin is in R34 and the other in C15.

It was fixed by some "glue" on the board. I try to attach another photo (i hope a litte bit clear)

So in your opinion amps down is not due to an electrical interruption of traces placed into middle layer ?

Because I don't have more ideas how to make some other tests ...


Giovanni

 

[Perry Babin]

I don't think I'll be able to help here but if you post another photo of the entire other side of the board, I'll see is anything looks familiar.

 

[pippolonia]

Hi Perry,


thanks for your help.



Here two foto of the board. In the power supply you can see only two FET in place, but there are 6 (3+3) in total.


Giovanni

 

[Perry Babin]

I'm sorry. I have nothing on that (or any similar) amp.