Delco radio schematics

autocomman

New Member
So ive got a few GM ETR radios from the early 80's, the ones with the orange LCD display. Each one has a different issue, haha and everyone I get from the junk yard has different problems. One worked ok and popped randomly, but I couldn't find bad solder joints, one has poor tuning, im sure it needs to be adjusted but I dont know which pots inside to turn and one worked great for 5 min and died.

Anyone know where I can find the early ETR radio repair manuals? or have a schematic or something I can refer to?

Mark
 
If these are similar to the Ford radios of that era, I wouldn't be surprised if the capacitors have expired. Look for leakage and crust around the bottoms of the cap leads.
 
Problems I have had with my Delco radios is all capacitor-related. Mine are the FM-AM Stereo 5-band EQ-Cassette models. Manuals are hard to come by. I finally found a genuine Delco manual after several years of saved "followed" searches, one finally showed up.
 
I think I found one on sams, but $25, and no download. Issue is im pretty sure none of my radios have a sticker on em anymore, so no part number. I wanted to hopefully not blow $25 cause I dunno if im gonna be able to fix em. And I can find the 2000 series radios, which cover the 5 band EQ versions, but not so much the 2700, and I think the ETR was a different manual cause the 2700 series covers manual tuning versions too.

Ive read bout cap issues with the 5 band EQ versions, this is an earlier model though with only bass and treble tone controls. I know one definitely has solder joint issues, id push on one of the boards and it would act up...maybe I should just plan on recapping that one and going through the solder joints.
 
I would still suspect bad caps.

When I fixed my 2000 series radio only 4 caps all of a certain mfg and value were all bad, all the others tested OK with an ESR meter and had no visible leakage. So I replaced just those 4 caps and the radio is still performing fine in my '88 S10.
 
Well pulled it apart...there are 4 boards in it...the amp board, what looks like a tuner board, a tape amp board and the logic board for the display and im guessing the tape logic...no caps look like they are leaking. This is the one that would pop randomly and the sound would cut out. Some bad solder joints i see..ill replace the electrolytic on the amp board and go over the solder joints that look funky aaand cross my fingers. Beyond that ill just take one and have it repaired...it was a pain to get it torn down this far, 4 of the screws that hold down 2 of the boards were soldered to the board and these things are just a pain to work on.
 
Biggest problem with those beside cassettte deck parts is the output chips. And they are not quite stand alone amps in alot of those 2000/2700s. With most of them you can't just pick up a preamp output. Moreso with the 2000s with the VF display and EQ, and the type D cassette. That is the one Blaupunkt admitted they built. I suspect they built them all but generically. The type Ds were really good but had a bad failure mode. The belt goes it will not eject. Then people got out the screwdriver and reallty FUBARed it up.

The output chips are the biggest problem with those. If you got one with all four channels working fix it, and never heavy load it. Use ten ohm speakers, not eight lol.

The FM is aligned by just tuning it in. This is from a guy who had factory training on them. He said the alignment was the easiest he has ever seen. It really is just tweak it. Adjust for maximum.

Actually, all the selectivity is in the ceramic filters, and the frequency of the local is PLLed, so all there are are a few coils that were necessary. Like transformers or whatever.

In the automotive setting, I believe the vibration throws it off by making the cores move. The position of those cores is what aligns. They move, not aligned anymore of course.

You MUST have the right tools to tweak those coils. DO NOT risk cracking the core, in fact maybe spray them a day before even trying.

The antenna lead is well insulated, select a very strong station in your area, hopefully a rock station that will stay up near 100 % modulation all the time. You want that. Start out with the wire an inch away and draw it away from the antenna jack. Tweak. When it sounds good again, move the wire further away and again, tweak.

This works for FM, and will for AM but it needs a properly matched antenna for that. FM is not picky. Do AM in the car if you can.

On the Delco, before you even start, find a strong station like say it is 100.1. Go to 99.9 and 100.3 and see if the distorted whatever stuff sounds the same. If it does not you have to align the detector. This is not documented, but you can align the detector by tuning it to where the distorted off channel signal sounds the same when off by exactly one channel. Left or right of thsat station off by one, sounds exactly the same. Thatis whe the detector is right.

The IF bandwidth is set and the local oscillator is set, end of story. You need no other reference.

One of the reasons this is so easy is because this is some kind of enhanced Shotz tuner that Hughes Aircraft and Hafler designed or some shit. It really is the best single antenna tuner out there for a long time. Not REALLY audiophile but damn close.

Of course for driving down the road with too much money, they got radios that have two or even three front ends and they switch dynamically lightning fast to whichever one has the best signal.

The "cheap" ones go by signal strength, the good ones analyze the mutipath.

That's all fine and good, but if you snash the car it is more ikely that the Delco will still work rather than a Cructchfield special.
 
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all 3 that I have have 4 working channels, only one had a tuning issue and it needed to be tweaked slightly...it was ever so slightly off on am channels and even less so on FM..but either way i pulled on apart, the one that had the popping issues...gonna recap the amp board, and sucked the solder from the gang pots on both sides and gonna resolder em back up...also found other bad solder joints ill suck the solder out and resolder em.

What I am concerned about is the output transistors. Im using this headunit cause it fits the Olds I put it in. I have a speaker level to line level converter feeding an EQ and from that I feed 2 amps, one for the 4 speakers and one for the sub. The line level converter is nothing special, and was a pretty cheep one...I would assume it has a load resistor in it, but I dont know of it does. Im worried bout frying the output chips from no load...but i dunno if thats really an issue with this unit. Thoughts? Id love to find where I can just add a few RCA outa for the EQ, that would simplify things

As a side note, i think all 3 of these radios are different inside too...i know 2 of em are defiantly different, the 3rd i dunno, havent pulled it open
 
Well I recapped the amp on the one that worked the best, and resoldered a ton of questionable stuff...and ended up soldering 2 pins of one output chip together and fried it....so ill swap it with a good chip and hopefully ill be good to go, or ill get an NTE 1394 which is supposed to be a drop in replacement...derp!
 
I have to ask, what is your plan for these radios? I remember these being in nearly everyone's car back in the day. Are they any good?
 
Delco DM133, I can pull one from the other 2 I have, but id like to keep them intact i may pull one for now...not sure yet
 
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