No output on center channel Sony STR-K502P

[Deucalion]

I have a Sony STR-K502P home receiver. While watching a program the other day the center channel stopped working. Prior to that I had recently noticed a clicking noise like a relay switching off and right back on. I am assuming this was one of the blue rectangular relays on the main board. I have taken it apart a couple of times since and resoldered some cold joints but nothing seems to have done the trick. I also placed a non conductive thin layer of foam underneath the main board just in case it was a grounding issue. Should I replace the center channel relay? How do I determine which one is for the center channel and a part number for it. I also read in a forum that my output transistors could be bad. There are 2 for each channel. Again, which ones are for the center channel and how can I get a rating or a part number? I have read numerous threads of similar issues. Maybe somebody here has remidied this??? What little sound that does come through the channel is staticy and/or muffled if at all. Before anybody suggests that it is the speaker, wire, or settings I have exhausted those options already. I have had this unit for quite some time and I know what to expect while it is decoding DTS or Dolby, and my center channel simply ceased right in the middle of a fight I was watching. There seemed to be quite a few broken solders on IC701 and IC702. I resoldered all of the relays, output transistors, and most of the other IC, along with anything else that looked questionable. also placed a thin, non-conductive pad underneath of the main board just in case it was a grounding issue. I have the service manual, but I'm not very good with schematics. I am a surgeon with a soldering iron though. I guess I just need for somebody to tell me in plain English the location of what I need to repaid and how to order it.

[Khron]

Re: No output on center channel Sony STR-K502P

1) Try using paragraphs.

2) Do you have a multimeter? Maybe the center channel's starting to put out DC, and thus tripping the protection. Just to make sure, you'd have to measure "before" the center channel output relay.

Center channel relay = RY501
Output transistors = Q503/Q504
Center amp driver = IC501

[Deucalion]

Re: No output on center channel Sony STR-K502P

Thank you very much for that, and sorry if the original posting seemed to run on without any breaks. No, I do not own a multimeter. Any idea about the part numbers for these or where I would find a cross-reference?

[Th3_uN1Qu3]

Re: No output on center channel Sony STR-K502P

You can't go just blindly swapping parts. Sure, it might work sometimes, but it can be very frustrating when it doesn't. You should get a basic, cheap meter to measure stuff and fix your receiver. I'm sure you're going to find more uses for it.

[Deucalion]

Re: No output on center channel Sony STR-K502P

Really, what good would that do me if I don't know what the appropriate outputs should be? If it's pretty much narrowed down to one of about 4 parts, then it's not exactly "blind swapping".

[Khron]

Re: No output on center channel Sony STR-K502P

I've got a hunch that the cheapest DMM (digital multimeter) is cheaper than, say, "all the possible parts" you might end up having to swap, for one reason or another.

If you said you're "a surgeon with a soldering iron", why not be a "real" surgeon, and get a cheapo meter to know WHAT "transplant" to make, if not even why?

[Deucalion]

Re: No output on center channel Sony STR-K502P

I've got a hunch that the cheapest DMM (digital multimeter) is cheaper than, say, "all the possible parts" you might end up having to swap, for one reason or another.

If you said you're "a surgeon with a soldering iron", why not be a "real" surgeon, and get a cheapo meter to know WHAT "transplant" to make, if not even why?

OK then what should be the outputs on the previously mentioned components?

[Deucalion]

Re: No output on center channel Sony STR-K502P

and specifications of the replacement parts? With all due respect, I didn't sign on to this to be patronized.

[Khron]

Re: No output on center channel Sony STR-K502P

I didn't mean to sound patronizing, but one of my mottos is "if something's worth doing, it's worth doing right" No disrespect or offense intended...

I've found the service manual here:


Now, on page 18, you can see the output stages of all the five amplifiers. The center channel is the last one (bottom of the page). If you look carefully, each transistor leg has a voltage label right next to it (ground-referenced, at idle).

Now, if you had a DMM / voltmeter, you could check and confirm (or not) whether there's any DC present at the output (the middle leg of R516, which ends up at one end of the RY501 relay). And/or you could check if voltages are around the values they should be, also on the two power transistors.

[newbiesat]

Re: No output on center channel Sony STR-K502P

Hi there,
Here is the relay part number that sold on ebay "OSA-SS-224DM5 DC 24V 5A 250V 6PIN Power Relay" for $3.49 and ship from China. Good luck

[budm]

Re: No output on center channel Sony STR-K502P

I would check and see if the relay coil is getting the 24VDC on it, see if the coil is open, see if the contacts are closed when 24V is present on the coil.