jl e6450 repair

[bnae38]

Read the previous posts on this one.

Bought a blown Jl 6 channel to fix up myself.

Found the power transistors were all zorched and their gate resistors were too. After ohming all other 3 pin parts out (none suspicious), I replaced the irfz44n's with irf3205pbf's and the 47ohm 1206 resistors with 49ohm 1206's (that's what i had).


Amp goes into high draw 6A+ and sucks supply down to 8v. I've tried a few times with increased max current hoping it was inrush, but I don't think so.


2-3 of the power transistors get warm. I remember on the hifonics bxi2006d that i repaired, the small transistors that supply switching to the coils were shorted, 15-20ohms. Not so this time.

I cant find a service manual for this guy, so I'm comparing to jbl px300.4/infinity ra6006. Gotta be more or less the same power circuit..


Any thoughts? Am I ok with the irf3205's?

Thanks,
Ben

 

[Perry Babin]

What is the circuit board designation for the transistors that get hot?

I just repaired one of these and used the 3205s.

 

[bnae38]

q49 and q50, the other 6 dont really heat up.

 

[bnae38]

looking to see what they connect to, should have been obvious.. . Likely a problem with the driver transistors i bet.

Ps: you're the man Perry, we all appreciate your help.

 

[Perry Babin]

49, 50, 51 and 53? are all driven by the same transistors. The driver transistors could be the problem but double-check the gate resistors and the connections between the gate resistors and the FETs.

 

[bnae38]

49ohms pins 2-3 on a 2907a driver transistor. Dunno how I missed that..

Hoping to have something i can use. I have bd140's ?

 

[bnae38]

Also have 3906s and 4403 pnps.

 

[Perry Babin]

3906

bd140 has the wrong pin configuration

 

[bnae38]

current rating is way lower though.. 200mA vs 600 hmm

 

[bnae38]

power rating is the same, i'll give it a shot. still have a bunch of them from school years ago lol

 

[Perry Babin]

I thought they were 600ma. Do you have any MPSA56s?

 

[bnae38]

The one that was shorted didn't even go to the two mosfets that got hot.. it was the other pnp next to it causing that. Doing diode drops in circuit, it was open (i forget which pins) when i compared to the one i replaced..


She fires up. Current climbed steadily from 1.5A after 20 sec or so.. all the way to 4A.

Found q416 and q415 are hot, i'll check bias...

 

[bnae38]

q46 and q45 are continuing to get hot after tweaking bias on a couple pairs of output fets..

Thought i read 7mV was ideal. Set that on the two that were off.. I'm getting like 1.5mV occasionally on all sets, something is weird..

 

[Perry Babin]

45 and 46 are the regulators. They're going to get hot.

 

[bnae38]

+/-15? Must be..

Not liking how current kind of climbs on me, something seems wiggy.

Rails appear ok +/-25 and +/-15

 

[Perry Babin]

Are the outputs clamped to the heatsink?

 

[bnae38]

No . Raw pcb on the bench.

I think its good enough.. 2.5A idle.

Gotta play with bias some more, they all seem to be at about 2mV. My dmm batt was dead. Should i be more like 7?

I'll put it back together tomorrow.

ty sir

 

[Perry Babin]

You cannot set the bias unless the outputs and their bias transistors are tightly clamped to the heatsink.

 

[bnae38]

Ok, i wont play with that anymore until I have it back in.

 

[bnae38]

Back in, ch1 and 2 are dead.

Bias voltages all appear to be about 1.5mV, though I don't have a fluke at home.. so I'm not sure how much I trust readings anyway..

Any thoughts on ch1 and 2?

thx