Technics SA5760

I cannot remember this set in detail, but I recall in many of these sets changing the output devices, protection relay, and a fair amount of caps. There were caps that were going high in ESR causing the set to go in to protect, and also causing some device failures.

Jerry G.

$15.00

$16 download; $17-$19 paper or fiche

Watch out if you unplug the driver board! The molex connector is off by one pin intentionally. If you plug it in the way it "looks" like it should go, virtually every part on both amp channels will be fried. Been there, done that. Later versions had a warning label along the top of the board. The only clue is the small angle iron brace at the top doesn't line up correctly unless the pins are offset by one.

Mark Z.

YIKES!!!

I actually 'have' already pulled that board...no warning label either. I did a test fit of the board with power off and unit unplugged. It will indeed go in wrong if one is not careful--in fact 'looks' right. The key, as you say, is to line up the holes on the hold down tabs; but one can also look at the large molex...line up on that and ignore the small one on the other end (which has one extra pin).

Thanks for the heads up. I really want to hear this one 'sing' again.

Thanks, Ray. I know how to Google. I tried to order a download last evening, but their system wouldn't accept my login or registration...says someone with my email has already registered with a different password. This is impossible for security reasons I won't go into here (not impossible for someone else to have registered, just impossible for it to have been me with a different password). I've emailed them. I was hoping (not in vain, as you can see from the above) that someone might have some personal experience with it.

Then there's the hope of not having to *spend* $16.......

jak

I was hoping it was a little less involved; but will go to a good deal of trouble to get this one running. There are quite a few caps in there, and I don't have an ESR meter. I believe the outputs are okay. The relay could be an issue. Do you recall if it merely disco's the speaker outs, or the B+/B- lines?

So far, in hopes of getting the schematic before doing detailed t'shooting, I've only poked around, half at random. I did measure voltages on the relay, and looked (in vain) for signal there. The only significant voltage there was +/- 72v on two of the pins.

It does exhibit some symptoms of the protection circuit being the main issue. As stated in the OP, there was no DC on the outputs when it was working. AC voltage was even--channel to channel--and linear with increasing input. I measured over 30v using only interstation FM noise for a signal. I never got around to actually hooking up speakers...instead used 100w dummy load, listened through the headphone output. Both sides sounded clean except for the previously mentioned intermittant crackling in the right channel.

Any other recollections of fixing this relic would be helpful...anyone?

jak

If their's only crackling on one side and everything else sounds ok through the output not out of the headphone jack it can be a noisy transistor if you have a scope check the driver of that channel for noise. I don't know the specific receiver but this is a general check for that type of problem.

It's also part of the SAMS MHF-118 book. I have 116 and 119, but somehow missed 117 and 118! So close and yet so far...

Missed the OP, I guess. It blew. No output of any kind now. Initially it acted as detailed...then went completely out. The relay doesn't kick in, but no overload (front LED) indicator lit.

Thanks for the response. I was looking for detailed info on that particular model. I have a scope. When I finally get my shop moved and set back up again, I'll trace the sig through from front to back and do detailed t'shooting. I was hoping for a quick fix....

jak

Thanks anyway. I got an answer, registered, and paid for the d/l. They still need to scan it I guess, as it wasn't immediately available.

jak

There was a voltage regulator transistor, a 2SD313 or some such, that would go bad on these. It was on the tone board, as I recall, but quite accessible. You can see it back in there behind the power switch, right there on the long horizontal board which runs almost the length of the front panel. It's on a small heat sink. Didn't mention it before because it didn't relate to any crackling, but it would explain no sound, and the protect relay not coming on.

Mark Z.

Thanks, Mark. I've just returned from a long weekend, and the Holidays are at hand...but, I've gotten the manual and have begun tracing the signal on paper. I'll stick some probes into it soon. I may have some questions later. The PDF file doesn't show the voltages printed on the circuit board traces very well, but....

jak