Technics SA 8500X - looking for pre-amp replacement boards
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quadsearcher
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Technics SA-8500x
Those look like power amp assemblies.
Secondly, complete circuit board assemblies were only available for a short time when new, for warranty servicers, if at all. In that era (as with quality servicers today) component-level service was the norm.
If someone has available replacement assemblies, they would almost certainly be of the same age, likely with similar usage, the same production runs of parts, and prone to similar problems or failures.
Speaking for myself only, If I wanted a working receiver and wanted it to last for a while, I'd have it repaired by someone who knows how to find modern reliable equivalents for failed or failure-prone components. I'd also expect any competent servicer to require the whole unit for service, not just the boards (unless they own the same model for testing). And to warranty the whole unit. Repair of items that age usually is closer to a restoration, in that all aspects of circuit operation must be considered.
Shorter answer: used boards are likely to have the same problem. Is crackling the problem? Are the other two channels OK?
Thanks for your reply. Sorry, I don't know the technicalities of the receiver, Only that I bought it brand new in the 70's and it's now failing. I'm in MT and no one here would touch it, so I took it to Denver while visiting relatives and a Gary Tyler ([email protected]) worked on it. He could not find a parts manual to order the failing components on the boards so he unplugged them and at least for now I can still get it working in two channel stereo. Before it would lock up on a power up. I'm willing to buy a parts/service manual for the guy and take it back to him this summer to repair. Any help and advice will be appreciated. Thanks again.
I went searching on Hi-Fi Engine and got these, the user manual & service guide https://www.hifiengine.com/manual_library/technics/sa-8500x.shtml
Dude you are awesome! I appreciate you posting these! I just got one of these for 150 bucks from marketplace over here in the Midwest and all of the amps have to be turned all the way up just to hear it. But all of the CD4 and the SQ/rm matrix stuff works great piped into another amp from the tape out.
Do you happen to know offhand what kind of matrix decoders they were using in this? Was it similar to the 949A where they went to full logic? Is it similar to lafayette's wave matching logic?
No idea I'm afraid.
I signed up to HiFi Engine years ago when I was after a manual for an old tape machine.
quadsearcher
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I somehow missed your reply. Most likely these power amp sections have shorted transistors etc. causing protection to shut the amp down. There is a limited supply of techs (old or young) who know how to use spec sheets of original parts compared to current production to find equivalent modern parts, but they do exist. An unavailable semiconductor replacement is the rare exception, not the rule. Simply looking up the part number on the devices or part numbers from a manual is often not enough to source replacements. There's got to be a "vintage" ( I use that term reluctantly and prefer "classic" or "old") audio repair shop somewhere around there. Or a TV shop that's been around since the 70's but switched to stereos since TV's are less repairable these days. I looked up Intrinsic and it looks like their main business is (high end) retail.
if you are replacing transistors, make sure that they can handle the the rail voltages...ex....if B+ is +/- 50 volts make sure that the transistors can handle at least 120 volts....and make sure to beef up the current rating ....also watch out for the transiition freq....if it is too high it could cause oscilations......you can find info on this on google and youtube.....good luck.....
barfle
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Excellent advice. While the specifics are lost in the fog of time, I recall that Altec had their own high-voltage version of the 2N2712 they called AL2712. They are not interchangeable!
those are power amp modules and can be repaired/restored....like barfle stated...this unit will need a restoration and not just a repair.....some of the signal transistors from that era have been known to develop noise which causes popping, crackling and hissing sounds.....there is lots on info on youtube and google about that.....you will need to go through all the circuit boards, as there will be lots of poor solder joints.....electrolytic caps will need to be replaced...pretty much all on them....resistors will have to be checked to make sure their values haven't increased, switches will have to be cleaned and if really bad, dis-assembled, cleaned and re-assembled and re- installed...it is what you call a "Labour of Love"......all the power transistors will need new thermal grease and pads......it is a big job but if you can do it yourself can be a very rewarding experience......the only part that I wouldn't fool with would be the tuner section unless you have the alignment gear to do the job...this section is low voltage and low current so I normally don't touch that area...I do not have the equipment needed for an alignment job either.....but I have everything else that I need to do this type of work......good luck with it.....if you need any info let me know...cheers......
they can be repaired unless less the board is burned up and can't be repaired...if you are really serious about replacing them, make them....copy the copper side of the board on a good guality copier and use that as a guide to lay out your tape and pads.....clean the board, etch the board, clean it, again.... drill all the necessary holes and you got it....you can go with 1 oz or 2 oz copper clad boards...
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