Technics SA-600 right channel cutting in and out

DarkAudit

Active Member
Got this off of Craigslist. When it's working right, it's a beast. But it's not working right. The right channel will start to crackle and then diminish to just the bare bass, while the left side will keep on chugging away as if nothing is wrong. Then the right side will come back to life for a few minutes, and then repeat the cycle. You can watch it happen on the output meter. Happens with speakers and headphones.

Suggestions before I take it to the shop?
 
If you have a can of deoxit handy, try cleaning the switches, especially the tape and selector switches. It's not easy to get in there, though.
 
If you have a can of deoxit handy, try cleaning the switches, especially the tape and selector switches. It's not easy to get in there, though.

I'm going to double check the fuses (later... it's time for bed (third shift)), and probably just replace them anyway. I don't see how the monitor and selector switches can cause just the one channel to cut in and out like it is. The white plastic piece on the amplifier circuit looks a little discolored compared to it's twin on the left side.
 
This might not fix it. However, this is pretty much standard advice for this sort of problem, at least as a first stab at it. My first hand experience - on my SA-700 one of the channels would cut out, but not back in. Deoxiting cured it.

If you want to try it, here is a good Technics thread: http://www.audiokarma.org/forums/showthread.php?t=157993

There is also a guide to using deoxit somewhere on the forum.

As I understand it (and please correct me if I am wrong) the signal path travels through all of these switches and pots; if they are corroded, you can end up with the signal dropping or blocked. It might not make intuitive sense at first, but there it is.

Good luck, it's a nice sounding receiver when it's healthy.
 
I didn't fix it yet, but I isolated the problem. It's the fuse. I swapped them, and the issue moved from the right to the left channel. Sow now it just should be a matter of hitting up Lowe's in the morning for replacements.
 
Just wrap it in tin foil, that way you'll never have to worry about failing fuses. ;)

This is why I always replace every fuse in the gear I restore, even if they work. They cannot be trusted.
 
Just wrap it in tin foil, that way you'll never have to worry about failing fuses. ;)

This is why I always replace every fuse in the gear I restore, even if they work. They cannot be trusted.

I should go ahead and replace the fuses on the onboard outlets, then. Even if I never intend to use them. Do most people on here use them at all?
 
Fuses are the very very last thing to be concerned about (unless replaced with tin foil or equivalent), especially in such problems. If they're old, they may blow faster—this way, old fuses are an even better protection, rather than a nuisance!

Crackling, fading sound and these phenomena are ALL caused by dirty switches (only in rare cases by faulty transistors in the first stage). Just clean them all (selector, tone control, loudness, muting, volume, etc.) and you should be ready to go again.
 
I don't buy that, not in this case. Not when I can move the problem at will, and the opposite channel suffers none of the symptoms when the "good" fuse is in place.
 
I didn't fix it yet, but I isolated the problem. It's the fuse. I swapped them, and the issue moved from the right to the left channel. Sow now it just should be a matter of hitting up Lowe's in the morning for replacements.
Hey that's great you found the problem so easily. I wonder, if you haven't done this, if you swap the fuse back to the original positions if the problem still follows it - maybe moving the fuses cleaned some tarnishing or whatever. Or, it's just a flaky fuse.

Still, it's a good idea to do the switch cleaning when and if you feel like it.
 
Flaky fuses are common in vintage gear, and they are rarely something people tend to check thorougly! Never re-use old fuses. Measure them out of circuit with your diode tester. Many times you can measure hundreds of millivolts across them.
 
Hey that's great you found the problem so easily. I wonder, if you haven't done this, if you swap the fuse back to the original positions if the problem still follows it - maybe moving the fuses cleaned some tarnishing or whatever. Or, it's just a flaky fuse.

Still, it's a good idea to do the switch cleaning when and if you feel like it.

I still found the problem easily, but it wasn't the fuse after all. I hadn't switched back before I had to go to work, and put in two brand new fuses once I got home. Left channel was the wonky one still, then it shifted right as I went from fm to aux to run music through the iPad. Yep, it's the same bugaboo that hits most of these. The selector switch. I was hoping I'd be different and wouldn't have to go out right away for the contact cleaner or go any further than removing the top cover. No such luck.

So, yeah. Now I'm buying it.


Sent from my iPad using Tapatalk HD
 
Ok, learnt something new! Sorry about my guess going into the wrong direction above.


Oh, no. You were dead on. I was wrong. And making the sound go wonky by twiddling the selector knob was the clincher. I hit it up with some canned air from the front, and cycled it back and forth. It finally settled down in the aux setting, and I left it playing Camel - Mirage while I went and had a sandwich. :)

Next will be to get the contact cleaner and take care of that switch.
 
Cleaning out switches is always a good thing to do when it comes to vintage gear. The only problem about it is that it can easily be done in a bad way. The best method would be to desolder every switch and potentiometer from the PCB, dismantle them all, thoroughly clean the insides, apply some appropriate lubricant, and putting everything back together.
In my case, deoxit (resp. equivalent) treatment worked fine; in others, it only aggravates the problem.
 
It may be the best, but it's borderline insane given my schedule, budget, and skill level.

I went the other route, and everything now seems to be working okay. Went through sides 2 and 3 of Tommy with no more issues. Now it's time for bed. :)
 
Back
Top Bottom