Deaf Detrola 10ZM3

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Deaf Detrola 10ZM3

Post by MrFixIt on Tue Nov 14, 2017 9:23 am

Posted this at ARF, but no response yet. Rather stumped here, could use some suggestions. Thanks in advance for any input!

Schematic here: http://americanradiohistory.com/hd2/IDX-Service-&-Sales-IDX/Archive-Rider-IDX/IDX/30s/37/Rider-1937-DEF-OCR-Page-0005.pdf

Could use some more ideas on this one guys, this radio is deaf.
The amp side is alive, I can touch the plate cap on the 6F5 and the speaker responds. I can feed a AF signal from my signal generator and pass the lead near the 6F5 and it picks up the modulation. The tone is adjustable with radio volume and tone controls so those seem to be working okay.
However, it appears the oscillator isn't working. I do the test with the known good radio and there's no response.
No response at all at the antenna connection either.
Radio has been recapped with the exception of 4 micas. I just tested them and found one open so I replaced it, no change. Most resistors were still in tolerance with the exception of one or two that had drifted, changed those previously when I recapped the radio.
When I got the radio I tested the tubes, all were good except the rectifier tested weak so I replaced that.
Problem is, this schematic is so rough, it's hand drawn and doesn't identify components and there is very little on the web about this model. And I'm not familiar enough with tube radios to know right off what I'm looking at without the help of the schematic.
Any help is appreciated. TIA!

-Niles

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Re: Deaf Detrola 10ZM3

Post by Chas on Tue Nov 14, 2017 9:30 am

Check for continuity the oscillator and RF coils as well as band switch. Any open coils must be repaired. Check also that there are no shorts to the coil system.

AFAIK the schematic offered appears legible enough.

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Re: Deaf Detrola 10ZM3

Post by MrFixIt on Tue Nov 14, 2017 9:43 am

Wow, thanks for the quick reply Chas!
What's there is legible enough, it's the lack of data that vexes me. I'm not an old hand at this so I'm relying on data to guide me though. For instance, better schematics show the pin number for each tube in the circuit. This one doesn't so I have to pull up the data sheet for each tube and match the pinout to the schematic. Somewhat laborious, but that part's doable.
But now I have to identify the oscillator coil, and there's a few coils in this radio...
Good thought on that band switch, I'll check that out. I had to dissemble and R&R all the pots on this radio when I got it, they were all stuck. Could be the band selector has issues to.
Thanks again!
-Niles

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Re: Deaf Detrola 10ZM3

Post by Chas on Tue Nov 14, 2017 5:54 pm

To have tube base data in an easy to use format get a RCA Triple Pindex. It has three identical sections in a loose-leaf type binder that lay flat on bench. It will display three or more tube types. Useful when troubleshooting from tube to tube. These should be available on ebay from time to time.

In ARF there is a download hand book for radio repair. It may be useful...

http://antiqueradios.com/archive.shtml

Elements of Radio Servicing.

The schematic can be printed oversize and the tube pin numbers written-in...

FWIW the coils except the output, power transformer and field coil should be less the 20 ohms.

Check the plate and screen voltages, a missing plate or screen voltage is an open component. Usually, coil or resistor, often resistors are taken out by a shorted capacitor.
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Re: Deaf Detrola 10ZM3

Post by willy3486 on Wed Nov 15, 2017 2:32 pm

Have you injected a signal at the antenna connection and followed it with a signal tracer? If you do that you should be able to get it almost to the part bad. I am with Chaz on this, I would check the coils. In the last few years the ones that have me scratching my head have been coil issues. Years ago I didn't see that many coil issues but in the last 5 years since I took up radios again as a hobby it seems I have seen more coil issues. I think what happens a lot now is the wires corrode and break at the solder joints. I usually take a single wire out of stranded power cord then wrap it around the solder tap on the coil and the wire end thats broke. I then heat the tap and let solder flow on it and then to the broke wire. It usually fixes it right up.

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Re: Deaf Detrola 10ZM3

Post by Bill Cahill on Wed Nov 15, 2017 6:52 pm

I assume you did use an antenna wire to receive stations??

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Re: Deaf Detrola 10ZM3

Post by MrFixIt on Wed Nov 15, 2017 10:51 pm

Thanks guys for all of the ideas, you've given me some good ideas to work on. Checking coil(s) continuity now, so far so good.
Unfortunately this schematic doesn't give me voltages, but at ARF a schematic from the same period was provided to me that I should be able to pull some expected voltages.
I haven't tried to signal trace it yet, but that does give me another option.
I looked up that RCA Triple Pindex, looks kind of handy so I purchased a 1959 edition from ebay. Thanks for that steer.
I did try a wire antenna, but no response. There's not even a click or anything from the speaker to acknowledge that I've hooked up anything to the antenna connection.
Thanks again! I'll keep you posted on my progress!

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