Damaged Bridge Rectifier

[hotscot]

The fuse on my Marantz amp has been blowing. (Just to test I tried new fuses a couple of times.)

I looked at the PCB and there's a big crack on the surface of the Bridge Rectifier. I've attached a jpeg of the circuit.

If the Bridge Rectifier is damaged would/could that be the reason for the blowing fuse?

Regards
Alan

[SY]

Yes indeed, and it may also have taken out the electrolytic capacitors that come right after.

[hotscot]

Yes..the electrolytics were indeed damaged and I have replacements. I'm hoping that nothing further down the line will be damaged. it's just a pet project though.

Thanks
Alan

[d3imlay]

The bridge failed after the electrolytics failed. The bridge may have survived the first blown fuse. But subsequent fuse replacements would blast the bridge.

[Giaime]

If the amp burns a fuse, prior to putting a new fuse I always check power supply components (especially in tube amps). I've learned this the hard way

Don't replace a burned fuse with a new one just to see if the fuse keeps burning.

[davidsrsb]

I would worry about the transformer, if the internal thermal fuse goes you are in trouble, the bridge and ecaps are easy enough to replace.

Always remember that semiconductors usually fail short.

[hotscot]

The fuse no longer blows.
Now the remote works to control the volume.
I don't mean I hear it, I'm still getting no output from the amp but the rotary control moves via the remote.

So..power is going into the main pcb, it's also leaving the main pcb via leads, to supply the remote pcb and the volume pot pcb.

It's been suggested to me that the reason I'm getting no output tp speakers or headphone is because a relay has failed or some kind of protector.
I have the schematic if anyone wants to look.

Alan

[Nigel Goodwin]

Originally posted by hotscot

It's been suggested to me that the reason I'm getting no output tp speakers or headphone is because a relay has failed or some kind of protector.
I have the schematic if anyone wants to look.

I would suggest the most likely cause is that the power amp has failed, resulting in a standing DC voltage on the output - the protection circuits will keep the relay turned off to protect your speakers.

The power amp failing could also easily have killed the bridge rectifier - presumably the emitter resistors will have gone O/C now, which is why it's not blowing the fuse?.

[hotscot]

Can I test the power amp using a meter?

(I'm knew to this but I obtained a meter yesterday and have checked the fusable resistors)


I'd appreciate knowing how to check a poweramp and to test for standing DC.

Thanks
Alan

[Nigel Goodwin]

You simply measure the voltage at it's output (the amplifier side of the relay). Often the easiest place is the emitter resistors, they are usually obvious and easy to get to. The voltage should be zero, or very close to it.