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 Radiomobile

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Gary Tayman



Posts : 37
Join date : 2010-10-13

PostSubject: Radiomobile   Wed Oct 13, 2010 7:56 pm

I've got . . . a Radiomobile model 922T, from a 1964 Jaguar XKE. Customer wants it fixed as original.

Foreign set, but actually it looks very straightforward; about the only thing confusing is the fact that it's a 12 volt positve ground car, so my power supply and voltmeter are backwards.

Power it up, it appears rather dead as no sound and seemingly no current draw. However if I stick a signal tracer probe at the volume control, I hear radio reception, albeit very weak.

From the volume control wiper, wiring goes through an electrolytic cap to a transistor -- base I presume. On the other side of that cap I hear nothing.

Soooo, foreign radio, sound at volume is there but very weak, does not pass through the coupling cap into the audio transistor. Cap open? Transistor shorted? Don't suspect shorts as current is minimal. Why is the volume weak?

I suppose the next step is to pull the coupling cap and measure, or replace. Maybe I should pull ALL the electrolytics. See if voltage checks of the transistors might tell me something. But here's what I DON'T have, a schematic. Sams seems to have skipped over Jaguars and all things Radiomobile. Does anyone out there have a source for a schematic to this thing?
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glasdave

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Join date : 2010-10-12
Location : Aurora Colorado

PostSubject: Re: Radiomobile   Thu Oct 14, 2010 12:30 am

I just got the pdf's off the radio museum site. Shoot me an e-mail, and I will forward them to you, David
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Gary Tayman



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PostSubject: Re: Radiomobile   Thu Oct 14, 2010 4:50 pm

galsdave wrote:
I just got the pdf's off the radio museum site. Shoot me an e-mail, and I will forward them to you, David

Did you receive my PM?
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glasdave

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PostSubject: Re: Radiomobile   Fri Oct 15, 2010 1:30 am

Yes, sent them a while ago. Smile
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kim herron



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Join date : 2010-10-15

PostSubject: Re: Radiomobile   Fri Oct 15, 2010 2:59 am

Hi Gary!!

I had a Radiomobile from a '59 Bentley here a while back and found several of the electrolytic caps open. I would shotgun all the electrolytic caps. They all behave the same way when they get old. Don't know if you've gotten the service info for this box yet, but I set up an account with Mauritron in Great Britain to get info from them. Much more complete than what came from radio museum and a very fast download. Let us know what you find. I'm getting request from the antique car crowd here in MI as the last few shops doing this stuff are refusing to work on the car stuff at all.

Kim Herron
W8ZV
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Gary Tayman



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PostSubject: Re: Radiomobile   Fri Oct 15, 2010 5:12 am

I just received the schematic -- thanks!

As for car radio service, indeed I'm offering this. However there are limitations. Remembering that these sets are 50, 60, 70 or more years old, please don't expect me to give you an exact esitmate either of time or price. I'll be up front and tell you what to expect, and we can go from there. As most people here know, parts aren't always easy to find and there are usually multiple problems, some which don't appear until you're almost finished. I just finished a 50 Plymouth that took well over a month to get a part, then had additional problems -- it simply took awhile, but when it left here it was playing great.

There are also radios that just aren't worth fixing, and a great example is a 58 Corvette that I've been dealing with. Actually the original problem was simple -- in a few minutes I had it playing, sounding great. BUT -- the wonderbar was messed up, and the customer specifically said that he has had trouble with the wonderbar. Turns out that the brass cap on the shaft was slipping among other things. I could also see that I'm not exactly the first one inside this radio -- others have preceeded me. Well, to get that shaft out means to disassemble the entire radio around it -- a major mess, and for some reason ALL of these Corvette radios are filthy, rusty pieces of junk. Oh, but being from a Corvette they're valuable! Still junk.

After spending hours trying in vain to get the wonderbar working properly, I called and gave the customer an option: I can continue to try and fix it, but it will get very pricey. I can offer a conversion, or I can just send it back. He opted for the conversion. Good thing, as when I finally disassembled it, there were broken parts in there that I had to repair or replace -- which are inaccessible unless the tuner is totally removed and totally disassembled.

I completely disassembled the tuner (easy with a conversion), cleaned the pieces with acid, repaired and replaced as needed, and now it sparkles -- and works great.

I also don't care for working with 70's AM/FM sets and tape players. I don't work on 91 Hondas. But the older stuff, yes.
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Gary Tayman



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PostSubject: Re: Radiomobile   Mon Oct 18, 2010 6:35 pm

What fun! What Excitement! Whatta waste of time!

I haven't quite decided if I like or hate this radio. Actually it's very neatly made, and most of the components and test points are within easy reach, so it can't be that bad.

But it's giving me fits, for sure.

First off, replaced all the electrolytics. Several were bad, and they had stuff oozing out of them. One of them fixed the audio; another took care of squealing noises while tuning. In fact it appears I've taken care of a number of bugs, but the radio still has a problem -- nearly dead. If I touch a test probe to the base of VT1, radio gives me lots of reception. Let go and it's dead. All tuning coils ohm out correctly. Transistor itself appears to be good. Collector voltage is less than 5 volts (should be 9), emitter is 0.1 base is 0.3 -- should be closer to a volt. If I force cutoff by shorting emitter-base, collector jumps to 11 volts.

So -- been picking through resistors, measuring resistance and checking voltages, figuring sooner or later I'll find something. But it is sure being ornery.
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Tim Tress



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Join date : 2010-10-17

PostSubject: Re: Radiomobile   Mon Oct 18, 2010 8:03 pm

That could be a bad transistor; I had a similar problem with an Oldsmobile radio of the same vintage. If you touched the probe of a meter to the converter transistor, the set would start working, and would keep working for several days; a new transistor did fix the radio.

As old as that one is, it probably uses germanium transistors, as did the Delcos of that era.

Tim KA3JRT
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Gary Tayman



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PostSubject: Re: Radiomobile   Mon Oct 18, 2010 8:15 pm

The bias problem turned out to be a capacitor, C-4 for those of you who might be following along for some reason. Replaced it, voltages are better and the radio plays, but reception is still weak. If I put my hand near the PCB, reception improves. Adjusting antenna trimmer does nothing. So I'm still not done. I'm suspicious of C-3; it is in the AVC circuit and is the same physical type as C-4. But don't have any .1's, gotta run to the store -- gotta go anyway, as I need a dial lamp for this thing and hope they have it.

Unless by some miracle the C-3 gets it, my next step is to check each front end component, one by one until I find something. There's only so many . . .

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Gary Tayman



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PostSubject: Re: Radiomobile   Tue Oct 19, 2010 6:22 pm

Time to slap my forehead with the obvious . . .

Antenna connector (inline type). Replaced, radio is now playing great.

Never before worried much about doing a recap on a solid state set, but this one definitely needed a recap for the electrolytics, and the one ceramic (if it IS ceramic, not sure) was definitely bad.
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glasdave

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PostSubject: Re: Radiomobile   Tue Oct 19, 2010 9:25 pm

Great!
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Gary Tayman



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PostSubject: Re: Radiomobile   Thu Oct 21, 2010 3:00 pm

NO! NOT GREAT!

affraid bounce affraid Mad Evil or Very Mad Crying or Very sad Rolling Eyes affraid

This afternoon the fellow came by to pick it up. I pulled it off the shelf, turned it on, and . . .

DEAD. Dead, dead, dead.

AAAARRRRGGGGHHHHHHHH!!!!!!!!!!

Opened it up, audio OK, no stations at all. Various voltages appear fine. So in desperation, got a diddling stick out and started tapping around. Suddenly the radio came to life.

Long story short, problem appears to be transistor VT-2. Tapping on the leads, or moving them around, particularly the emitter, will make the radio go on and off. Resoldering the PCB traces did nothing. Made sure no leads are touching anything they shouldn't. I suppose the next step is to go out and buy another transistor.

Today's income, same as yesterday -- zero. Can't live on that.
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