Marantz 2245 Protection Circuit Blowing Transistors

[Juanbanzai]

Hoping someone can help. I'm recapping a 2245 and got as far as the protection circuit before developing this problem. I posted something similar about this issue a few weeks back, but now I'm really stuck. After recapping the P800 board and replacing the relay, the first test saw the relay closing immediately. I got audio from the receiver, but that relay closing right away is not what is supposed to happen according to the service manual. While trying to track down the issue, on another test, it got to a point where the relay failed to close at all. That's where I'm at now.

I tested H809 and H8010 and found they were both bad. H808 had tested fine. I replaced 809 and 810 today with a pair of C2383s and that didn't fix anything. In fact, I tested the two new 809 and 810 transistors and they've both blown out. I've followed the circuit and found that both H807 and H804 (diodes) are testing bad in-circuit... but out of circuit they tested fine. I'm going to start voltage tests per the schematic to see if anything is blatantly wrong... but I'm hoping someone can clue me in on what to look for before I blow out any more transistors.

Thanks very much for the help.

Aaron

 

[tranguru]

relay closing immediately... sounds like a shorted cap....
many bad x-tors in that circuit - sounds strange to me?
do you have a power supply issue?
H804 and 7 are Zener diode - 14v - are you using the right test procedure (not sure how experienced you are)?

check incoming voltages -

Just my 2 cents

 

[catrafter]

I'm unsure as to what your problem might be, but I would like to mention that there is a de-spiking diode on the P800 board across the speaker protection relay coil, I think it's labeled H813 in the 2245.
As the relay de-energizes, the collapsing magnetic field induces a large spike that can damage the relay driver transistors (H809 and H810 in the 2245) if this de-spiking diode is bad.

Tom

 

[RayWu]

I'm unsure as to what your problem might be, but I would like to mention that there is a de-spiking diode on the P800 board across the speaker protection relay coil, I think it's labeled H813 in the 2245.
As the relay de-energizes, the collapsing magnetic field induces a large spike that can damage the relay driver transistors (H809 and H810 in the 2245) if this de-spiking diode is bad.

Tom

check your new caps ,you might have replaced some backward.
always mark +and -, cir. boards maybe be wrong.

 

[Steven Tate]

Are you powering up on a DBT? Does it Dim after a few seconds? It would be nice to rule out a short somewhere, in which case the protection circuit is doing its job.

 

[KutzlerTrans]

I'm with Ray Wu.
Are you saying that you created this issue? or did the unit have a problem before you worked on it?
Putting a cap in backwards or a solder joint that shorts across another track could start a chain of burned out parts.
Note::
Make sure when using substitute transistors, that the EBC legs are in the same position before soldering the parts in.

First place to start is to check the base voltage of h808,809,810 and pin j814, to make sure your not feeding some crazy voltage from the amps or another source.