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Looking for Delco Sonomatic AM/FM Circuit Schematic


XframeFX

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Last month I was listening to an FM station on my Delco AM/FM radio while troubleshooting numerous electrical issues in my 1963 Riviera. The radio and power antenna were some of the few items that worked and kept my spirits up while testing flakey lights. The radio was powered up for the 1st time in 25 years after I re-installed it. After 30 minutes, it died!

I know the capacitors have long expired and I could've damaged some components powering it up.

So, now I'm looking for a circuit schematic on model: 7283471. The '63 Buick Shop Manual shows circuit schematics for the base AM and Signal Seeking radio. The '64 Manual shows a different circuit for both the AM and Signal Seeking radio. The '64 Manual does mention the AM/FM but no circuit diagram. I do not have a '65 Buick Shop Manual. Can anyone advise if it shows a circuit for an AM/FM radio?

There is a website that sells circuit diagrams but their Delco Model numbers don't come close to what I have.

On the side, I found an interesting website for radio conversions using original chassis. However, I'm repairing mine to original.

http://www.tech-retro.com/Aurora_Design/About.html

Thanks,

John B.

Riviera_AMFM_Radio_.JPG

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If it's like the 50s radios with the wax capacitors, then just open the radio up, make a list of the capacitors you need to buy, and then replace them one by one. Resistors and plastic mica capacitors hardly need to be serviced. If it's the transistors, you might be scratching your head. I think you'll be fine without a schematic if you work through it one by one. 

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Thanks Benjamin, my exact intentions. Can't make a BOM with just the top and bottom removed, have to take it all apart. My bench is a little busy so, later. Was going to blindly change all electrolytic polarized and non polarized capacitors and hope for the best. Circuits in the Shop Manual appear to be similar in the final stage for Delco radios of the era. They show test points which would be a big bonus for trouble-shooting.

If it comes down to a circuit schematic, I may contact https://www.tubesandmore.com/search/schematics/7283471 and see if 7283471 crosses with any of their totally different model numbers.

Thanks, John

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Delco Radio had their own schematic books back then.  They usually existed at the Delco Factory Service Station (warranty repair shops).  In the GM parts books (at least Chevrolet), they had a section on radio "gut" parts.  This was back when many dealers were "away" from metro areas and their larger car electronics "warranty stations".  It was amazing that there were GM part numbers on all of the small parts in the radio!  By about 1966 or so, the parts books didn't have these listings anymore as "modern times" allowed "away" dealers to have greater access to the Delco warranty stations/repair shops.

 

The neat thing about many electronic circuit parts is that they have stampings, markings, and color code stripes to identify their "values", as the type of component can be visually determined.  This can also allow some later components (with the same values) to be substituted and upgraded.

 

Just some thoughts,

NTX5467

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I do not see a 7283471 listed in the Sams index. But if it was, it would be around AR 21  (Auto Radio Photofact Book 21).

 

That DS501 transistor has a resistor used as a fuse that can open when things are not right. Replace the paper caps, electrolytics and check resistance of that resistor. It is a high wattage brown rectangular resistor.

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Thank-you all. This radio is yet another thing to research.

I haven't uninstalled it just yet. I would like to roundup semi conductors 1st. Without a circuit diagram, I'll have to tear it apart and use a magnifier to build a BOM.

Back in '84, I brought it into a retired auto radio guy. It worked but poorly. When I picked it up and asked what was wrong "Aw, I just changed-out the core"! I wasn't happy not to have my original 1963 AM/FM back! What I learned is that Buicks had #980635 for a 6X9 speaker and 980626 for a 4X10 speaker. 1963 Cadillacs had a #7283295, very close to my 7283471. Spec is 9 transistors and 9 diodes. AM radios had 5 transistors.

Yes Frank, there's a fusible resistor in the DS-501 emitter circuit. It will go open if that germanium power transistor goes hot. That might have been the case when I was listening to it in April. So, at least 2 things bad and very likely more. Then there's still a capacitor upgrade for good measure.

Would be nice to have the Service Bulletin in the image!

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  • 2 months later...

Okay, found this free site for downloading schematics for most Delco radios.

http://techpreservation.com/schematics/Delco.htm

Turns-out my radio is a 1964 "core" from my last repair back in the '80s. It bears a tag "980659" and is not found free anywhere, seems to be an oddity. There are sellers on Ebay though for the 980659 service manual.

My original AM/FM core was probably a 980626 in my '63 Riviera. The downloaded schematic appears to be similar but PC board traces are different for the final stage amplifier. Should be enough to go on I hope.

Initial assessment shows the fusible resistor still being good.

Tore apart my dash not just for the radio, one of those famous HVAC levers snapped while testing my blower motor repair last week! Early '63 levers were weaker than late production. Changing them all out!

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If you have a signal tracer, see if you are getting a signal at all on a strong AM station.   If so, try to move forward toward the audio and output section.   This may not be easy without a schematic.  If somebody monkeyed with the speaker wires or power input, the problem may be in the transistors in the output stage.   Also cannot rule out faulty capacitors.

Good luck.

Joe, BCA 33493

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