Sony STR-DE635 receiver no sound, what's blown?

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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.
 
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Hi jamil5454,

:eek:

:bigeyes:

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?

-Chris
 
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.
 
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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.

-Chris
 
...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.

Steve/BlueWizard
 
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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.

-Chris
 
Just for the record, I wasn't the one who wired the TV amp to the receiver. If I did that I may not have had the courage to post on this board. :p

So, there is no IC1207 on the digital board (contrary to what the schematic says). I did, however find a 5v BA05T (IC1204) and after checking it's three pins none of them are shorted together. I also checked three-pinned transistors I could find and no shorts.

The only places that look like they got hot are:
- PCB around power output transistors (obviously)
- PCB around speaker terminals
- PCB around discrete 5.1 inputs on digital board
- IC501, IC601, IC701

I could be missing something though. Some of the three-pin transistors I measured (e.g. Mitsubishi 7905) were open between two pins; is this normal?

Here are some pics I took:
http://jamilb.googlepages.com/digital_board_4.jpg/digital_board_4-full.jpg
http://jamilb.googlepages.com/digital_board_5.jpg/digital_board_5-full.jpg
http://jamilb.googlepages.com/digital_board_6.jpg/digital_board_6-full.jpg
http://jamilb.googlepages.com/frontcenter_op_trans.jpg/frontcenter_op_trans-full.jpg
http://jamilb.googlepages.com/rear_amp_board.jpg/rear_amp_board-full.jpg
http://jamilb.googlepages.com/rear_amp_board_2.jpg/rear_amp_board_2-full.jpg
http://jamilb.googlepages.com/speaker_board.jpg/speaker_board-full.jpg
http://jamilb.googlepages.com/digital_board_1.jpg/digital_board_1-full.jpg
 
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Hi,
Just as I remembered. uPC2581V and the famous Sony parts MN2488 and MP1620. I don't know if 2SD2488 and 2SB1620 will work properly. They are both darlington types.

Pretty much certain that they are all gone, but you can try just the outputs. The chip may be bad and cause the others to go.

Frequently, the emitter resistors will open up as well.

-Chris
 
Thanks Chris, it looks like I'll go ahead and order 3 uPC2581's, 5 MN2488's, and 5 MP1620's and try my hand at swapping them out. If I can get this thing fixed it's going in my parent's new home, driving a 5.1 setup and 2 outdoor speakers. :p

For future reference, does RadioShack carry this type of stuff? Do they usually have what you need or should I get it online?
 
Forget radio shack.

The MN2488 and MP1620 are just Sony part numbers for Sanken 2SD2488 and 2SB1620. This is what Sony would give you if you ordered parts from them.

uPC2581 - you'll be lucky - they are most likely long obsolete.

With this kind of damage, you are going to be paying more than the reciever is worth to repair it, assuming it can be repaired. That digital board might be worth keeping/selling though ;)
 
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Hi Jaycee,
The MN2488 and MP1620 are just Sony part numbers for Sanken 2SD2488 and 2SB1620. This is what Sony would give you if you ordered parts from them.
That's what I've heard. I have always ordered the Sony part (marked with the MN/MP numbers) because I was seeing a number of the 2S numbers coming in from other shops. Sony shipped the Mxxxxx numbered parts. Those are expensive, the uPC2581V IC's weren't nearly as expensive as I recall.

Anyway, that's why I said you could give them a try. Thank you for confirming that they are direct subs.

With this kind of damage, you are going to be paying more than the reciever is worth to repair it, assuming it can be repaired. That digital board might be worth keeping/selling though
With two or three channels gone, yeah. This will be more expensive than it's worth to repair.

-Chris
 
Well, after checking a few places online it seems the uPC2581V is either hard to find or it's really expensive. I thought I got lucky with electronix.com and ordered parts to fix 5 channels, selected 2-day shipping, and then BAM they call me the next day and reveal they're out of the uPC2581V and MN2488. Since I don't have the proper equipment/skills to check which exact component(s?) failed, it looks like I'll just put it back together for future possible spare parts use.

diy electronics: 1
jamil5454: 0
 
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