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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Sun 30, 2020 11:41 pm 
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Location: Panama City, FL 32401
If you're testing the diodes in circuit the readings may not be accurate. The only way is to at least cut one lead then measure. Hopefully they're in a place you can do that without having to remove them. You can always solder the leads back together. The reverse biased measurement should show "OL".
The same thing applies if you're using a "diode test" mode on a dmm. High current can cause a diode to fail,but unless something like that happened, it's probably ok. It wouldn't hurt to check the current drain. The forward biased resistance of 280 Ohms is perfectly normal.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Mon 31, 2020 1:00 am 
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Joined: Nov Wed 14, 2007 11:37 pm
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I would check the ground on the tuning cap. Also the traces for hairline cracks.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Mon 31, 2020 7:58 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 881
Location: dayton oh usa
1000 ohms in reverse is a leaker or something in circuit.
did zenith stick those failure prone caps inside coils and transformers?
like smd all over again in miniature.
the issue is the osc is not running.
confines it to a few parts.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Mon 31, 2020 8:49 pm 
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Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
John Bartley wrote:

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

cheers


So, anyone know what the IF number is ??

cheers


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Mon 31, 2020 9:06 pm 
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John Bartley wrote:
John Bartley wrote:

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

cheers


So, anyone know what the IF number is ??

cheers

455 kiloCYCLES, eh eh. This thread got me to work on one of mine, and the generator tone from the set peaks when the cans are set to that freq.

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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Aug Mon 31, 2020 9:27 pm 
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Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
frenchmarky wrote:
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.



Are you sure you did this test correctly?

The "two-radio" test is intended to allow you to "hear" the oscillator from first radio by receiving it on the second.

You know from your radio theory knowledge that the oscillator runs higher then the received frequency by the value of the I.F.

Therefore, if your first radio is set to receive at 1000kc (1mc), and the I.F. is 455kc, then your oscillator in the first radio is running at 1455kc, so that's where you tune your second radio to for a start and then you carefully tune around that frequency until you hear the oscillator of the first set ... in the second set.

Is that what you did?


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Tue 01, 2020 4:06 pm 
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Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
John Bartley wrote:
Are you sure you did this test correctly?

The "two-radio" test is intended to allow you to "hear" the oscillator from first radio by receiving it on the second.

You know from your radio theory knowledge that the oscillator runs higher then the received frequency by the value of the I.F.

Therefore, if your first radio is set to receive at 1000kc (1mc), and the I.F. is 455kc, then your oscillator in the first radio is running at 1455kc, so that's where you tune your second radio to for a start and then you carefully tune around that frequency until you hear the oscillator of the first set ... in the second set.

Is that what you did?


Just wondering ??


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Tue 01, 2020 9:48 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 543
Location: moreno valley
John Bartley wrote:
John Bartley wrote:
Are you sure you did this test correctly?
The "two-radio" test is intended to allow you to "hear" the oscillator from first radio by receiving it on the second.


Yes, first time I ever tried it but pretty sure I did it right, I tested the method with a couple of other radios first including another Royal 50 (the only one I have that works, worked great when I got it which was a nice surprise) and heard the squeal with them but not with this one. Works on the identical one with the iffy tuner too even when the tuner is acting up, which is about 99.9% of the time.

As for the diodes, I know that in circuit the measurements wouldn't be a reliable test but since there are two of them and they both came out very closely the same with high one way and low the other, I figured meh, probably not the problem.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Tue 01, 2020 9:59 pm 
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Posts: 8690
Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
frenchmarky wrote:
John Bartley wrote:
John Bartley wrote:
Are you sure you did this test correctly?
The "two-radio" test is intended to allow you to "hear" the oscillator from first radio by receiving it on the second.


Yes, first time I ever tried it but pretty sure I did it right, I tested the method with a couple of other radios first including another Royal 50 (the only one I have that works, worked great when I got it which was a nice surprise) and heard the squeal with them but not with this one. Works on the identical one with the iffy tuner too even when the tuner is acting up, which is about 99.9% of the time.


Thank you for the confirmation. From your first post I wondered if you had set the defective radio at 1000 and the test radio at 1455 or if you had tuned them both to the same frequency.

cheers !!


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Tue 01, 2020 10:05 pm 
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I have found that sometimes the receiving radio will oscillate at various points on the dial, as the set under test's dial sweeps across the band. I suggested 1000 Kc simply because either a + or - 455 Kc difference would be heard within the band.

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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Tue 01, 2020 10:19 pm 
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Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
fifties wrote:
I have found that sometimes the receiving radio will oscillate at various points on the dial, as the set under test's dial sweeps across the band. I suggested 1000 Kc simply because either a + or - 455 Kc difference would be heard within the band.


Hehehe .... I suggested it because the math was easy .... :)


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Wed 02, 2020 2:55 am 
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Posts: 4
Not sure if this has been mentioned or you have tried this. I have found this with several models of Zeniths, that have cracked or open pc foil. It is now the first step that I take on a near dead set, to use a common ohmmeter and check all pc traces for continuity. Typically find a invisible to the eye open circuit. some have had more than one open (stress fracture) on models 500E x1, 500H x4 500N x1.

Hope this helps, Andrew


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Wed 02, 2020 3:32 am 
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Just finished looking at the foil layout that you have. I would check for a open circuit at the LH corner trace (just above C7 and another spot would be just above C2. The positive ground circuit has only this one source of flow, and these areas are highly expected for a stress crack.

Cheers, Andrew


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Wed 02, 2020 11:04 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 543
Location: moreno valley
DXnorth wrote:
Just finished looking at the foil layout that you have. I would check for a open circuit at the LH corner trace (just above C7 and another spot would be just above C2. The positive ground circuit has only this one source of flow, and these areas are highly expected for a stress crack.


You mean the trace that goes around the edges of the cutout for the tuner cap? Can't find any opens all thru that and spots where it leads to.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Wed 02, 2020 4:43 pm 
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That particular trace is the one I suspected, my error as you had earlier tested the voltages around the oscillator and this would not be the problem. The other set you mentioned with the symptoms of a intermitting tuning cap, was similar to a recent intermittent 500E-1. I did find that the corner of the tuning capacitor must of slowly flexed the pc board, and with some luck found the foil trace being the intermittent culprit.

Lots of good advise here by other members, including a mention of checking the traces that was already mentioned earlier.

Cheers, Andrew


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Wed 02, 2020 5:00 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 543
Location: moreno valley
This is strange, all of a sudden now out of the blue it is *working* And very well! All I was doing this morning was some voltage comparisons with the other radio, and noticed that now it was also totally cutting out intermittently while I was flipping and moving the whole business around. Discovered the wire on the single (+) battery terminal was coming loose in the solder, I reflowed it, that fixed the cutting out. But can't see how that would have caused the original problem since it completely cuts power and I was getting normal voltages (?) I'll keep poking around in there for a crack in a trace I didn't find before, see if I can get it to quit oscillating again. That does seem more likely now... trace crack, bad connection, solder joint maybe. At least it seems the parts are good! :) :) :)

I now notice the radio still does get *some* power if that + battery terminal is open, from the other battery, but then the transistor voltages are halved.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Wed 02, 2020 6:05 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 543
Location: moreno valley
I reflowed the solder along the traces etc. around that area, anyway I can't get it to quit so I put 'er back together. Maybe it WAS that iffy battery connection though if it was I don't understand how it would only kill the oscillator. Calling it done. Thanks everybody!


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Wed 02, 2020 7:13 pm 
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Location: Panama City, FL 32401
There's a black wire on the right side of the battery box,if that contact was corroded could have caused issues too. Glad you got it working. Those are great performers.


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Wed 02, 2020 9:04 pm 
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Yes, glad to hear you fixed it. These are excellent performers, and that big round tuning dial is a real plus!

_________________
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins/////////////////////////


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 Post subject: Re: Zenith Royal 50, no reception (yeah, another one)
PostPosted: Sep Thu 03, 2020 12:47 am 
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Posts: 543
Location: moreno valley
Returned to the 'glitchy' 50, looks like it may indeed be a bad trace or connection there also. Very weak volume but discovered that flexing the board a certain way slightly makes it pop to loud again. Fortunately at rest it is weak so I will go around bypassing the traces with a wire + probes while it is playing and hopefully find it, can't see any breaks. Unless the flexing is really only doing something inside the tuner, but even at weakest I still get a few stations (barely) so that doesn't sound like fins are shorting out completely, but not sure on that yet.


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