Rotel power amp RMB1075

[busterno1]

i have a rmb 1o75 amp that one day listen then i could smell burning then i

turn it back on half of protected the light 3 out 5 work. i took a local repair he that he repair a blown channel

but now when he fixed the amp but he said that Distortion is in all channels

would anybody have any clues could it be power suppy control unit

 

[busterno1]

coule

 

[rabbitz]

I've discussed this with the OP and it's not known if the original issue was an amp problem or a speaker issue that caused the blown power amp channel. This has been repaired apparently but now all channels are distorting.

This is a 5 channel power amp running off a single transformer giving ± 57V rails. There is a protection mode for temperature and speaker shorts. I've attached schematics for 2 power amp channels for reference (from HIFi Engine).

The only thing I can come up with is the rail voltages have dropped as that's common for all the 5 power amp modules. As far as I can see, all the input signals are separate and do not share any buffer or input components but there's a NJM4558 (part of protection circuit?). What else could be common that could effect all power amp channels?

 

[Old'n'Cranky]

I'd start with the two bridges. D901 D902.
Pull, Meter, Probably just replace with better parts anyway as their cheap enough.

 

[rabbitz]

I better clarify is that I believe this amp is still with the repairer and my comment on the rail voltages should read "could have dropped" as have not seen this amp or know what the rail voltages are.

 

[busterno1]

i have found out that that it is only 1 channel.