Denon goes to protection mode (flash red) when power on

[plainwater]

I am having problem with my Denon AVR589. Every time when I power it on it goes to protection mode directly. I removed all inputs and outputs and check for shorts and busted components. Every thing looks fine (visually at least). Can anyone please take a look at the schematic and suggest a way to pinpoint the problematic area (used to deals with ICs now back to transistors). Really appreciated.

 

[llwhtt]

Check for DC voltage at pin 3 of all of the test points (TP101, 102, 103, etc.), if more than a few mv there's your reason for Protect mode. Bad output xsistors? Bad/overheated solder joints?

Craig

 

[plainwater]

Am I doing something wrong? I measured 30+ volts for all these test points then discharge to around 0 when the protect mode kicks in. Any possible cause for this?

 

[sajti]

Am I doing something wrong? I measured 30+ volts for all these test points then discharge to around 0 when the protect mode kicks in. Any possible cause for this?

That looks bad... Check the power supply voltage on the filter caapcitors. If all channel is wrong, there must be a common failure somewhere.

Sajti

 

[madtecchy]

No you have a high Dc voltage on the output.. The protection is activating to protec your speakers.. Unless you have any electronics knowlage Now would be the time to find someone to repair this amplifier.. I have repaired a few denons With Dry joints in the power amp section. Some have been caught in time with nothing more than a resolder job .. Mostly i have had to replace output and driver transistors That had been damaged by the effects of the dry joints,, PS the protection circuit shuts down all channels not just the one with a fault on it .. Also as mentioned by sajti the fault does seem common to all channels .. You may be in luck as it could just be a fuse in one of the psu rails

 

[plainwater]

Thanks guys for pointing to the right direction. I took out the power board and check the filter. There were two diodes and one cap showing several ohms either way. I guess this is the problem. I will order components and replace to see if fix the problem.

 

[plainwater]

Anyone knows what the voltage supposed to be on 7915_IN and 7815_IN pins of CN506 (please see attached power board schematic)? Right now I have some diodes and cap busted so I am measuring 0 there.

 

[cihtog]

Those are the unregulated, rectified supply rails from the AC transformer - for the perspective DC regulators, with the same number.

The voltage will be whatever the transformer is rated at.

 

[plainwater]

I just found these two pins are feeding two regulators 7815 and 7915 (+/-15V output). Looks like they supposed to measure +/-24V? I attached a more complete view of the schematic.

 

[plainwater]

Thanks a lot for all the help guys. After replacing the busted rectifier diodes I am back to business.-)