Technics SA-5560K dead channel

[OlleDahl]

Hi,
I have a Technics SA-5560K that I got recently for a very good price. The unit powers up, but the left channel is totally dead.
I have tried all variations when connecting the speakers, but no luck. The radio works fine and so does connected equipment like CD-player.
I haven't opened the unit, but I replaced the fuses on the back to see if that was the problem. It was not.

I am a professional sound engineer, but have absolutely no skills when it comes to anything that is inside any of my equipment. I have the service manual from hifiengine.com.

Is there anything I can do by myself trying to fix the dead channel?
If I try to get someone to fix it for me, maybe someone has some recommendations to make the repair easier?

Well, I hope I don't have to trash it. Got my first one in 1979 and, unfortunately and stupidly, sold it. I have missed every days since, so now that I got a used one I was so happy. Hope to get it fixed someway.

Thanks in advance for any help!

Mr. Olle in Sweden

 

[ryuuoh]

Did you check the speaker fuses?

 

[MacPhantom]

I am a professional sound engineer, but have absolutely no skills when it comes to anything that is inside any of my equipment.

In that case you may want to have the unit serviced by a professional. It usually isn't much that's wrong, but you should have at least some experience in dealing with electronics to not cause, or experience, any harm.
This is not a particularly high-tech unit and the circuit is comparably simple. Hence, finding a culprit should be really straightforward.

I really mean no offence with this post; it's just precaution. Of course, this being a forum and many here being absolute rookies we can give you some advice, so here we go:

1. Check for correct settings of speaker, input and record selectors. Really, such mundane issues have caused problems in the past.
2. Check whether the switches and/or potentiometers are oxidised (crackling). Operate and wiggle them a dozen times, occasionally with careful and sideways movements, and check if sound comes through at least partially. If it does, clean them the correct way.
3. Check whether you get any sound from the headphones jack.

Since you verified the speaker fuses, I guess anything from this point on will be on the electrical side, so here we go:

1. Do you hear the speaker protection relay clicking when powering the machine on (after a delay of around seven seconds)?
2. If not, open up the unit and probe the speaker outputs (before the relay) for DC voltage. If it's in the few (dozen) Volts range you have a blown output transistor.
3. Check those transistors for continuity (the usual tests with bipolar transistors: check for collector-emitter shorts). You'll ideally do that out of circuit. If at least one is blown, replace that side (or both) with a matching replacement. If it's just a pair of transistors per channel (which I'd expect with such a unit), matching isn't super critical.
4. If the output transistors measure fine, use a signal tracer and check for DC voltage along the audio path. There shouldn't be any. As soon as there is, check the respective driver stage transistors (emitter follower, etc.). In the worst case a blow-up in the driver stage can take the output transistors down as well, so blindly replacing blown output transistors without checking the driver stage, or vice versa, might not be a good idea.
5. Once done, re-adjust DC offest and Icq according to the service manual instructions.

That should be the absolute minimum to get the unit to play again. It usually doesn't take much in terms of replacement components, but it requires some skill and knowledge. Whether or not the unit will play according to original specifications is another story.
Also, blindly replacing capacitors is not going to cut it. It never, ever, does, especially not here.

Good luck! If you want you can tell us what you have measured (and where) and we can try to help.

 

[OlleDahl]

Did you check the speaker fuses?

The first thing I did was to replace the fuses on the back of the receiver. 2x250V/4A.

 

[OlleDahl]

In that case you may want to have the unit serviced by a professional. It usually isn't much that's wrong, but you should have at least some experience in dealing with electronics to not cause, or experience, any harm.
Good luck! If you want you can tell us what you have measured (and where) and we can try to help.

Thank you for the input.
Your instructions are very logical and I will try my best to follow them. I do have the equipment to fix it, but no spare parts as of now. It has been some time since I learned how to read schematics, but isn't it like riding a bike - one learned you really never forget? ;-)

I will report on how this proceeds and also document it with photos.

Have a nice weekend!

 

[Snow_]

In that case you may want to have the unit serviced by a professional. It usually isn't much that's wrong, but you should have at least some experience in dealing with electronics to not cause, or experience, any harm.
This is not a particularly high-tech unit and the circuit is comparably simple. Hence, finding a culprit should be really straightforward.

I really mean no offence with this post; it's just precaution. Of course, this being a forum and many here being absolute rookies we can give you some advice, so here we go:

1. Check for correct settings of speaker, input and record selectors. Really, such mundane issues have caused problems in the past.
2. Check whether the switches and/or potentiometers are oxidised (crackling). Operate and wiggle them a dozen times, occasionally with careful and sideways movements, and check if sound comes through at least partially. If it does, clean them the correct way.
3. Check whether you get any sound from the headphones jack.

Since you verified the speaker fuses, I guess anything from this point on will be on the electrical side, so here we go:

1. Do you hear the speaker protection relay clicking when powering the machine on (after a delay of around seven seconds)?
2. If not, open up the unit and probe the speaker outputs (before the relay) for DC voltage. If it's in the few (dozen) Volts range you have a blown output transistor.
3. Check those transistors for continuity (the usual tests with bipolar transistors: check for collector-emitter shorts). You'll ideally do that out of circuit. If at least one is blown, replace that side (or both) with a matching replacement. If it's just a pair of transistors per channel (which I'd expect with such a unit), matching isn't super critical.
4. If the output transistors measure fine, use a signal tracer and check for DC voltage along the audio path. There shouldn't be any. As soon as there is, check the respective driver stage transistors (emitter follower, etc.). In the worst case a blow-up in the driver stage can take the output transistors down as well, so blindly replacing blown output transistors without checking the driver stage, or vice versa, might not be a good idea.
5. Once done, re-adjust DC offest and Icq according to the service manual instructions.

That should be the absolute minimum to get the unit to play again. It usually doesn't take much in terms of replacement components, but it requires some skill and knowledge. Whether or not the unit will play according to original specifications is another story.
Also, blindly replacing capacitors is not going to cut it. It never, ever, does, especially not here.

Good luck! If you want you can tell us what you have measured (and where) and we can try to help.

Hello!

Maybe you might be able to help me.
I also have a technics sa5560 with a left channel that shows no voltage on tp603 and tp602.
The relay clicks and the right channel works just fine.
I am originally at fault, because I shorted between the casing of TR609 (drive transistor) and tp603 when adjusting DC offset.
This blew a couple transitiors and resistors.
Here is a list of what I replaced: (I am confident I used correct parts for replacement)
Transistors: -TR607 -TR609 -all four power transistors -TR606 -TR603
Resistors: -R633 33ohm -R631 47ohm -R637 330ohm

Everything else I have pulled tests fine. (TR601/ TR701/D602/D601/TR618/TR617)

Would you know what my next steps should be? I am completely at a loss, as I see nothing wrong.
I'd appreciate any help so much!
Konrad aka Snow

Edit: Holyshit!!! I didn't solder the connections back for the power transistors (mounted on the heat sink) for the left channel! Oh man, the hours waisted.... I'll do some further testing, but damn I'm happy!