Question about Sony STR-DE845 Receiver
First of all my STR-DE845 started having the protector problem about 6 months ago and I bought this receiver back in 2001. This is what I found wrong with mine. After searching online I found a service manual for the receiver, this came in handy when diagnosing the problem. The first obvious thing was discoloration of the board around the IC 501, 601, and 701 Op-amps. When looking at the receiver from the front these are the three vertical NEC ICs to the right of the main amplifiers. Even with no load these amps get very warm. Sony failed to add any heat sink to these ICs so eventually they can de-solder themselves, specifically the 701 IC which is the one closest to the back of the unit. With mine I was able to slightly push the 701 more vertical, since it was leaning, and I believe it has helped it make a better contact. The protector circuit will kick in if it senses the Op-amps are shorted or not making contact. The best solution is to add some copper heat sink to these ICs, they already have screw slots for a heat sink. If they ever fail you will have to get new op-amps and re-solder them to the board. Hope this helps.
Posted on Apr 18, 2011
I had a mechanical problem with the relay on the 1st power supply board. The relay right next to the small transformer. The blac cover for the relay just comes right off. Make sure that the little black plastic piece is still in position (you'll see what I mean when you open it.) and check the contacts on the relay.
Posted on Jan 24, 2009
Determin if the speakers are at fault first. un-hook them and turn on the unit if it stays on one of the speakers is bad. if it remains in protect, the output transistors are shorted. there are a pair for each output. they are located on the large heatsink in the center of the unit.
Posted on Jan 18, 2008
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Posted on Jan 02, 2017
Tips for a great answer:
It is possible that the amplifier had encountered a fault with a higher current drain which had triggered it to a protection fault condition. The fault can be with your output drivers. Please check for short on the outputs fitted for both the channels. Use a meter after disconnecting to check for short in the drivers. Disconnect the positive and negative voltages to the output and see if the protect changes. Even a fault in the preamp stages that drives in high current into the output can shut the Amplifier. Sometimes this can be a noise which can be a HUM or HISS before the protect works. Faulty capacitors in these circuits also can cause similar issues and needs close observation.You need to confirm and replace the specific stages or outputs. If not there can be issues in the mother board. Maybe the protect circuit by itself is shutting off due to a faulty bias or there is a leak in any voltage/current sensing circuit. Also disconnect the speakers and test, if the amplifier comes out of the protect mode then check for short on the speakers.
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The far left optical connector on the back is an output.
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