sony str de345 reciever dislays protect

[cdjtech]

hello, i have a sony str de345 reciever that displays protect when turned on--
all speakers and inputs are disconnected--
further i have a service manual w/diagrams and a multi-meter--
the power supply is working properly-
i have removed both of the output i.c's one at a time but it still displays protect--will removal of these i.c's affect the protect circuit?
and none of the output transistor pins are shorted to each other--
i am an auto tech that does a lot of electrical troubleshooting/ repairs but an not that experienced w/ electronics diagnostics and the service manual offers nothing as far as diagnostics--
any advice on what is the most likely cause or what to check next---would be greatly appreciated

 

[stepher]

Don't know if you ever fixed this unit but.....

I have a Sony STR-DE835 that's about 13 years old. I recently ran into a similar problem (read elsewhere this is a pretty common problem on Sony units this old). What I discovered (and you may need to look closely) is that over time, the solder joints may turn cold, creating small disconnect points that will activate the protect circuitry. I fixed what I could easily get to (front channels) and it worked for a while. Problem came back. Then I got into the rear, center and subwoofer channel circuit and wondered how the unit was continuing to work. The cracks were much worse in this section than in the front channel circuit.

I would suggest you resolder all the connections for output transistors and for the IC amps that drive them (use the usual heat protection cautions).

Ever since I did the resoldering, it runs great. Also never realized my surround sound had been suffering all this time (I had thought it was the rear speakers

Best of luck...Steph

hello, i have a sony str de345 reciever that displays protect when turned on--
all speakers and inputs are disconnected--
further i have a service manual w/diagrams and a multi-meter--
the power supply is working properly-
i have removed both of the output i.c's one at a time but it still displays protect--will removal of these i.c's affect the protect circuit?
and none of the output transistor pins are shorted to each other--
i am an auto tech that does a lot of electrical troubleshooting/ repairs but an not that experienced w/ electronics diagnostics and the service manual offers nothing as far as diagnostics--
any advice on what is the most likely cause or what to check next---would be greatly appreciated

 

[KeepItSimpleStupid]

I've done a LOT of high power amplifier servicing. First, you have to measure the DC voltage at the speaker output BEFORE the protect relay, That will identify the bad channel assuming the protect circuitry didn't go south. Less than 1V may or may not be OK. It should really be below about 50 mV DC.

The other channel may work, so with a signal check for an AC voltage on the good channel.

Let us know what you find.