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 Post subject: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Thu 27, 2020 7:15 pm 
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Location: moreno valley
I've had nothing but trouble with Royal 50s, I'm jinxed with them, always still have problems after recapping but now I want to re-tackle the ones I've gotten stuck on. This one has a 6GT40Z1 chassis even though it's a 50K model that was in a 50K Zenith carton w/ 50K instructions and the inner label shows the 6KT43Z1 chassis like a 50K and the entire radio looks hardly used, if at all. I don't know what's up with that but anyway the transistor #s and everything else match with 6GT40Z1.

- Recapped it but no change, only very slight backgound hiss that goes up with volume (if you put your ear right up to it!), but zero reception.
- No noise or static when tuning the dial.
- All the voltage readings appear a-okay.
- Double checked the elec. caps as per my before photo and marking the old caps. (The C6 is shown backwards on the circuit board layout so that threw me.)
- Both diodes in circuit read about 1000 one way, 280 the other so I guess they seem ok.
- When measuring the voltages I do get audible buzz from the speaker when probing the base of the converter and similar with bringing LED lamp very close to the radio.
- Converter is socketed so I cleaned the leads.
- The four antenna wires are all connected.

Still zero reception. I have parts available from the other ones I got stuck on if need be. Any ideas? Thanks!


Attachments:
zenith 50 reg  - voltages.jpg
zenith 50 reg - voltages.jpg [ 368.25 KiB | Viewed 603 times ]
118286310_827079291030461_1195512577503130562_n.png
118286310_827079291030461_1195512577503130562_n.png [ 619.84 KiB | Viewed 603 times ]
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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Thu 27, 2020 10:10 pm 
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Just to clear the earphone jack, try plugging in a test speaker or earphone. Next I would suggest the second radio test, to clear the osc circuit. Also, double check the four connections from the antenna coils to their PCB solder landings.

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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Fri 28, 2020 12:37 am 
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Location: moreno valley
The antenna wires are solidly connected and the speaker/ear jack seem okay, sounds the same on headphones (pure low volume hiss, tuning dial has no effect whatsoever), and I do get that buzzing noise thru either speaker or the headphones when I put my voltage probe on the base of the converter or bring something like an LED lamp or my soldering iron very close by. I looked up what that second radio test is, so I tried that between two good radios at around 1400kz just to see what it's supposed to sound like and that worked, but using this radio in the test I don't get any of those squeals at all.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Fri 28, 2020 2:58 am 
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Then you need to concentrate on the converter circuit. I would esp check the osc coil for continuity.

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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Fri 28, 2020 10:58 am 
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Location: moreno valley
I measured the windings on T1 & T5 using the board trace diagram, reading continuity between all points on each winding, not reading direct shorts between windings. I'm reading resistances from the transistor B and E traces to ground so the two resistors under the converter seem to be okay, and continuity from collector to T5 pin 1. I tried a 121-145 from another non-working 50 and still no reception. Is the oscillator just the converter and T5 and if that's okay, it should run and I'd hear it in the second radio test regardless of the antenna or tuner cap?


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Fri 28, 2020 2:07 pm 
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Location: moreno valley
Also the antenna/tuner as least seem like they are functioning. If I do the trick of turning if off and putting it right up next to another radio that is turned on, that radio's reception gets stronger or weaker (depending on the radio) as I dial the 50 to the same station. But when 'on' it doesn't pass the 'second radio oscillator test'.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Fri 28, 2020 11:20 pm 
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frenchmarky wrote:
I tried a 121-145 from another non-working 50 and still no reception. Is the oscillator just the converter and T5 and if that's okay, it should run and I'd hear it in the second radio test regardless of the antenna or tuner cap?

No, you need the entire front end functioning in order for the oscillator, downstream from them, to work.
frenchmarky wrote:
Also the antenna/tuner as least seem like they are functioning. If I do the trick of turning if off and putting it right up next to another radio that is turned on, that radio's reception gets stronger or weaker (depending on the radio) as I dial the 50 to the same station. But when 'on' it doesn't pass the 'second radio oscillator test'.

You are doing a poor man's tunable loop, but sadly that won't prove anything, beyond that the antenna and tuner are connected to each other.
Please post the three voltages for each of the converter Transistors, the original and the other that you tried.

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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sat 29, 2020 3:20 am 
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Location: moreno valley
Original 121-145 converter: E= .66 B= .82 C= 2.8. The 121-145 from the other radio in there measures essentially the same. But that radio does receive, it has another issue with a glitchy tuner cap that's been on the back burner so problem doesn't look like it's the converter transistor.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sat 29, 2020 8:30 am 
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Don't want to sound like a cop out, but if it were me, I'd take the tuner out of this one, install it in the other one (assuming that it's also a Royal 50), and put the chassis in the best condition case of the two. This one could then be a parts donor.

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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sat 29, 2020 9:24 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 543
Location: moreno valley
I don't know for sure if the tuner in this one is 100% either. The other 50s reception cuts in and out or changes strength when turning the tuner or with slightest tap of the tuner cap and it might be a short in the fins that I couldn't see, or something else entirely. Not even sure the rest of it is 100% good given the incessant cutting out, and haven't done voltage tests on it yet like I did on this one. If I get totally stuck on this one here, I'd rather set it aside and go back to the glitchy one and take another whack at figuring out the intermittency and measure everything. If I can then I might swap it.
I have a good electrolytic cap supply so today I ordered one of those inexpensive ceramic cap assortment kits on ebay so I can test for bad ceramic caps in toughies like this, tired of hoping I have the right one in my meager parts supply, which I almost never do.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sat 29, 2020 9:44 pm 
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I'd be suspect of a possible factory wiring or bad part. Seems like gifted radios that don't work just get put back in their box and stuffed in a drawer. Explains why it's so pristine and unused looking. Can't return it to a store with no receipt or even know where it was purchased. Hate to just toss it, but not worth it to many to have it repaired. Don't wanna make Aunt Edna feel bad about buying you a "bum" gift. So hide it in the drawer is the "right" answer. ;)

Just a pet theory of mine. :P

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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sun 30, 2020 6:02 am 
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Location: moreno valley
Yes, the few I have that appear brand new or never used, none of them worked. A recap brought them all back except one where I had to replace the dead speaker. Must've also been some Aunt Ednas back then who were gifted a radio but simply were not radio fans and just stuck them in a drawer.
When I get the cap kit I'll start crossing/subbing them into the oscillator circuit in this one and see if I can turn up a bad cap, that worked in one or two other radios I got going where nothing else was turning up. Also will do some comparison resistance measurements between it and the other radio which has a working oscillator.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sun 30, 2020 7:17 am 
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If you have a signal tracer, you could compare incoming signal between the two, to see where it stops in the dead set.

If not, good time to buy or build a simple one.

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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sun 30, 2020 8:17 am 
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Location: moreno valley
Any recommendations on a relatively inexpensive tracer I can buy that would be sufficient for helping diagnose simpler AM or FM transistor radio circuits like this? That's really all I need one for. :)


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sun 30, 2020 8:37 am 
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Radio Shack's Micronta brand pops up on eBay from time to time, and Heathkit also had a solid state unit that comes up occasionally. Either/or.

All they really are is a probe with a Diode, resistor and capacitor, connected to an amplifier. Here's a print of the Micronta;


Attachments:
Micronta Signal Tracer Print a.jpg
Micronta Signal Tracer Print a.jpg [ 307.71 KiB | Viewed 424 times ]

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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sun 30, 2020 4:12 pm 
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Location: moreno valley
Okay thanks, I'll keep an eye out for one. I wonder if it's possible to make a simple tracer for battery-powered AM radios out of another surplus but working AM radio since it's already got the AM circuits, the battery, amp and speaker. Like maybe snip something here or there, then add a couple of testing leads to it...


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sun 30, 2020 8:37 pm 
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frenchmarky wrote:
I wonder if it's possible to make a simple tracer for battery-powered AM radios out of another surplus but working AM radio...


I would think so, but making the changes might be tedious on a small cramped circuit. My Conar 230 combines a wide-IF rf section that works as an AM radio, excellent tone but very poor selectivity. The audio portion just switches that out I presume.

The flip side is a signal injector. Here's one from the June 1960 Electronics Illustrated, starts on page 74. Maybe a transistor AM could be altered to serve both functions.

Either tester is so simple it almost doesn't pay to try the conversion, but then again, why not! :)
-Ed


Attachments:
Conar 230.jpg
Conar 230.jpg [ 209.13 KiB | Viewed 395 times ]
SigInjectorPen1.jpg
SigInjectorPen1.jpg [ 198.79 KiB | Viewed 395 times ]
SigInjectorPen2.jpg
SigInjectorPen2.jpg [ 174.52 KiB | Viewed 395 times ]

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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sun 30, 2020 10:01 pm 
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frenchmarky wrote:
Okay thanks, I'll keep an eye out for one. I wonder if it's possible to make a simple tracer for battery-powered AM radios

I did. Used a simple RF probe circuit I found online, and connect it to a Rat Shack amp. Here's a scan.


Attachments:
signal tracer.JPG
signal tracer.JPG [ 251.76 KiB | Viewed 389 times ]

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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sun 30, 2020 10:20 pm 
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frenchmarky wrote:
- Both diodes in circuit read about 1000 one way, 280 the other so I guess they seem ok.

Any ideas? Thanks!


Ok, NO experience with SS radios here, but having checked a few diodes, I would be suspicious about a diode that showed such a small difference in resistances. I would have expected a much higher reverse resistance than 1000 ohms.

Could someone educate me about whether or not I would be wrong and why?

Or, are these testing poorly?

Second ... what is the intermediate frequency of this radio?

cheers


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sun 30, 2020 10:26 pm 
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1000 ohms might seem low, but it's while in circuit and because- Germanium.

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