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jamil5454 9th July 2007 02:55 PM

Sony STR-DE635 receiver no sound, what's blown?
My friend just gave me his old receiver because it wasn't working. I figured if I can fix it I'll myself a free surround receiver. It's a Sony STR-DE635.

I'm suspecting the amp is blown somewhere, because the unit turns on fine, switches inputs, detects digital signals fine, etc... except I get no sound. I tried all of the speaker terminals and the front headphone jack. I opened it up and checked the visible fuses, and they all appear to check out ok. I don't notice any immediate problems after looking over the circuit boards for a few minutes.

With my headphones plugged in to the front and the volume all the way up (coax source from DVD player) I can hear some white noise coming through. This noise gets noticeably louder if I put on the bass boost.

He said it was working fine until recently, when he moved and tried to hook it up to a 4-speaker system and his TV. He had the wiring all messed up, so let me explain a little:
The front left speaker and rear left speaker cables were twisted together. Same with the front right and rear right. These cables were then connected to front output A, so that each output terminal was driving two speakers. To make matters worse, he ALSO had two cables coming from the built-in TV amp to the receiver, so that there were a total of 3 wires in each terminal of front output A. Now, we were playing music from the TV, and it worked great (the receiver was turned off), but then I noticed his receiver was messed up. I tried to get the cables hooked up correctly but to no avail. The TV amp was turned up quite loudly. I should mention I noticed a little burnt smell coming from the receiver just for a couple seconds. However, I can not find out what is burnt.

As a side note, the TV doesn't work anymore either. It sort of "blips" when you turn it on, making a short blipping noise every half second. You can turn it off, but it won't come on again until you unplug it.

I'm hoping the problem with the receiver is maybe a blown transistor somewhere. I can provide pictures of any component upon request, and if anyone would like the schematic I can post a link to that as well. Otherwise, I appreciate any help anyone is willing to give on this matter and I'll keep you guys updated for others who may be having similar problems. I have a Digital Multimeter and I'm not afraid to do a little soldering.

P.S. -- If it helps, my car stereo behaved exactly the same way after I shorted the speakers wires together with it turned on, so that may be a clue.

anatech 9th July 2007 03:47 PM

Hi jamil5454,



Well, there you go. Both output sections are blown at the very least. Many times, those really good ideas are not. See my sig line.

I would expect IC's to be used in both the TV and the stereo. This has the potential to be expensive. So check on the parts prices. Be aware that there will be any pins to desolder and resolder using small traces. You will need the proper soldering equipment, plus a desoldering tool and solder wick. There are probably heat sinks involved (well, okay. There are for sure). Therefore, you will need new heat sink grease, proper stuff. You will also need a way of cleaning the old grease off. You may run into some other burned resistors.

Did I mention a half decent voltmeter?


jamil5454 9th July 2007 04:18 PM

Thanks for your quick reply.

I'm unfortunately not very well versed in electronics repair. I'm not really sure how to diagnose the problem. I checked for continuity on all the transistors I saw (across all combinations of the three pins) and none seemed to be shorted. They all were either open or had resistances of 10-200 ohms. I looked for blown resistors and caps and didn't see any.

One thing to mention, I'm not sure if this is normal or not, but when I turn the unit on, about five seconds later I hear a "switch" and the display goes off. When I turn the speaker selection dial I can hear the switching as well. Would the output transistors affect the front headphone jack? I figure I should at least get some sort output, but only quiet noise.

I have the thing taken apart and I would really just like to learn from this, even if I don't fix it. My logic is that I can't break what's not already broken. javascript:smilie(';)')

I'll take some pics and post back later.

anatech 9th July 2007 04:27 PM

Hi jamil5454,
The headphone jack normally runs off the output amp through some dropping resistors. So if the amp doesn't work, the headphones won't either.

Measure for shorts and get back to us. I think those used a driver IC and output transistors along with a bias transistor. Blown outputs are common.


Netlist 9th July 2007 04:40 PM

For what it's worth: check IC1207. That would be a BA05T, a 5V voltage regulator.


BlueWizard 9th July 2007 04:44 PM

...when I turn the unit on, about five seconds later I hear a "switch" and the display goes off.

This is likely the internal protection circuits kicking in. These 'protections circuits' are meant to protect against overload on the outputs including shorted speaker wires, and probably thermal overheating protection. But, these protection circuits are not meant to block voltages applied to the speaker output from some external source, because no amp manufacture would expect anyone in their right mind to do this.

Which brings up the question, why on earth DID you do this?

You could have connected either the audio outs (audio, not speaker) of your TV to the audio in (AUX or Tape) of the amp. You could have even connected the headphone jack of the TV to the Aux or Tape of the amp. But why or why would you tie the output of one amplifier (the TV) to the output of another amplifier (the stereo).

Likely the power outputs of the amp are blown in some way, either burned open or shorted. Which would explain why the protection circuit is tripping after you turn it on.

Sadly, all I can say is 'live and learn', just make sure you do.


anatech 9th July 2007 04:58 PM

Hi Hugo,

For what it's worth: check IC1207. That would be a BA05T, a 5V voltage regulator.
Thanks! Good hint. I can only talk in general terms.


Bigred 9th July 2007 05:41 PM

Here is the schematic. I believe those power IC's were expensive.

anatech 9th July 2007 06:19 PM

Hi Bigred,
Your attachment .... didn't. Can you simply send me a high res copy, then try to attach the schematic by reducing the resolution. I can attach it to your post above too if you would rather.

The IC's were pricey way back. Check them now.


Netlist 9th July 2007 07:11 PM


Originally posted by anatech
I can only talk in general terms.

Me too, itís just some scribblings I found. :)
I doubt the output is broken since some noise is still noticed.


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