Realistic™ "Concertmate" model #12-680 AM/FM stereo tabletop radio schematics

[woodge]

Radio Shack Realistic™ "Concertmate" model # 12-680 AM/FM stereo tabletop radio (approx. 1976): looking for anyone who might have a schematic of said beast, or know where to look.

I've been re-capping one that I found in really very good condition considering its age, but whoever designed the PCB should have been taken out behind the woodshed and given a whoopin'.  It's a dog's breakfast, and has things like 39K resistors tacked onto the foil-side of the board with their leads insulated with old Teflon (?) tape to keep them from shorting out solder bumps/traces; naturally I had to remove them to re-cap that area (don't worry, I took pics first).  Other components are the same.  I guess actually putting everything onto the PCB was too hard, or mebbe they found a flaw in the design and put this stuff on as an afterthought.  Can't imagine what a pain that would've been for the poor assembly-line techs.

In any event, I've done all the usual searches using Google, Bing, DuckDuckGo and the like, and while I can find pics of the unit at places like Radiomuseum.org, I can't even find a schematic or service manual for sale on the 'Bay.  Odd.

Any ideas for unusual sourcing of the schematic/service manual would be appreciated.  Thanks in advance!

Garth

[fzabkar]

Twenty years ago Radioshack used to have a public download area where they kept parts lists, exploded diagrams, user manuals and some circuit diagrams and service manuals. Perhaps it has been archived by the Wayback Machine?

[woodge]

I'd . . . never even known about that!  Thank you!

I'll go see if the Wayback's got anything.  Fingers crossed.  Thanks again.

[woodge]

Fzabkar:

Well, I did find some stuff on the Wayback Machine, but sadly, none of it went anywhere near the mid-1970s.  Thanks again for the idea though, it was worth a try.

Garth

[woodge]

Well, after much cursing, I have finally managed to repair and/or clean everything in this little beast, including the buggered-up dial-cord (re-stringing that involved a lot of guesswork), plus replaced the old dial lamp with a high-brightness warm-white LED plus a small driver circuit I had to shoehorn onto the main PCB. Also replaced all 26 of the electrolytic caps (they were around 45 years old, after all), and paralleled resistors across the stereo volume pot to get something closer to an audio taper.

Remarkable sound from such a plastic beast, and the stereo separation is quite good.

If anyone needs some pointers to repair this unit in the future, hit me up. I still haven't found a schematic (and probably never will), but there are some gotchas inside the case that you might want to be warned about ahead of time. I know I wish I'd been warned. 

Garth

[BrokenYugo]

Did you check Sams? Rare they don't have something for any post WW2 radio/tv.

[woodge]

Did you check Sams? Rare they don't have something for any post WW2 radio/tv.

Yep, sure did (one of the first places I went to); also hit up Norman at analogalley.com, who's come through several times in the past on unusual tuners etc., particularly from that time period (early-to-mid-70s). No joy. It reinforces my belief that this particular model was never designed with servicing in mind, it was truly meant to be disposable. Why go to the expense and effort of creating a service manual if you expect your customers to ultimately trash the device?

[woodge]

Because I'm a nerd with a touch of OCD, and for the sake of completeness, I have managed to find out some additional info about this little unit, so I thought I'd drop it here for public edification/correcting the existing online record (Radiomuseum.org lists this as coming from 1975).

It actually appeared in the U.S. versions of the Radio Shack catalogs for three years, from 1979 through 1981 (pp. 174, 158 and 160, respectively); this makes more sense, because the beast uses an LM1301 chip for most of its FM section, and only has six other transistors onboard.  If it was from the earlier part of the decade, I'd more likely expect to see an all-transistor design.  For its first two years, it sold for $59.95 USD (a whopping equivalence of approx. $229 USD / $290 CDN in 2021 dollars!); by 1981, the price had risen to $69.95 USD (inflation, whattayagonnado?  ).  The whole "Table Radios" index entry in the RS catalogs seemed to have had its heyday from about 1976 through 1982-ish, after which cost cutting could give you an entire cheapish "system" for not much more money, and the table radios slowly faded away.  The early-to-mid 1970s appears to have been a time when RS tried to get away from its "amateur ham radio and experimenter" roots and get into consumer-level entertainment electronics.

My above speculation that this might have been a "disposable" radio is, in my mind, now proven to be utterly wrong, but the non-existence of any service/user manual for it is mebbe a sign that it wasn't a huge seller.  Who knows?  I am aware that RS often bought designs like these from manufacturers in places like Taiwan and simply slapped their own brand names on 'em, so I wouldn't be surprised if, somewhere in this big wide world, there's an identical model with some other brand name on it somewhere, or at least identical guts in another style of case/chassis.