Troubleshooting Technics receiver

[gkellner]

My brother has a Technics receiver model SA-R277 from the mid-80's.
It no longer delivers any sound from left A or left B speaker outputs.
I've tried swapping speakers and wires with same result. no output from left A or left B. I'm guessing the failure might be at the volume control, since one failure there would seem to cause both of the observed failures.
Does anyone have a circuit diagram for this unit? Without one, any advice on further troubleshooting?
Thanks!

[comfortablycurt]

Have you tried using a different source? Try hooking up a different CD player DVD player etc...

I had the same issue on an old Optimus receiver, and it turned out to be a failed RCA output on the DVD player I was using as a source.

[mmadden28]

...
It no longer delivers any sound from left A or left B speaker outputs.
...

Can I assume that means that it was at least working at some point?

I'm not familiar with that receiver, but some older units have jumpers from the preamp outputs to the amp inputs, check to see that they are present and fully inserted.

And when you said you swapped the wires, did that include your inputs?
What source did you use? Did you try other external sources? **EDIT** looks like I'm slow on the typing again...

[gkellner]

Thanks for your suggestions. I swapped the inputs from the CD and got the same result: still sound output from Right A and Right B. From left-A and Left-B there is just a slight hint of sound, scratchy and faint.

I've tried spraying contact cleaner into the volume control pot and into the left-right balance pot, but with no effect.

This receiver used to work fine but stopped fully working at some point. (It belongs to my brother) I suspect the speaker wires may have been shorted at some time, but that's just speculation. And I was wondering whether the volume control might have worn out internally, but I don't know how to check it without a diagram.

I looked for jumber cables to the amplifier, but can't find any there.
Looked for fuses, but can only find one main 4 amp fuse in the power supply, and that one's not blown.

As each of the four outputs has its own transister, I was wondering whether two of the four might be blown. If so, is there a way to test them with an ohm-meter while in-circuit?
Any advice would be appreciated. Thanks.

[mmadden28]

What about the A/B speaker switch? Have you played with that?

I'm trying to remember my EE classes from way back when-but IIRC you can't accurately measure a Transistor in circuit as other components are also in that circuit and will impact your measurements such as a resistor in parallel with the leads you are measuring will provide a path for current flow even if the transistor junction being measured is completely open thus giving a false reading. However, with the power off, you might be able to do some comparison resistannce measurements between the left 2 and the right 2 to see if they are the same. I would imagine the supporting circuitry should be similar.

You could also use an oscilloscope on a live circuit, but most people don't usually have those hanging around (I have 3 :o) or would dare to dabble in an energized unit. I did dabble quite a bit in CB radio repair and tweaking as a hobby way back when, but I have done very little audio work so all my suggestions are SWAGs based on what I might try if I were in a similar situation.

[JimKellyfan]

I just bought a new Sony receiver and could unload one of my other 2 receivers. I have a Pioneer VSX406 cheap, and another Sony, not as cheap...But still decent priced for either...If interested in either, I could give great detail on either...Have manuals for both, remote for Sony lost, remote for Pioneer good...Ehh, let me know...If you don't want either one, I'll just keep 'em....Just trying to help....sorry about the blowed up Technics...
In fact, if you want, the Sony can come with it's own 5.1 set up ( speakers as well )....Both are 5.1's and the Pioneer has the 5.1 and A and B