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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Mon 04, 2017 5:44 am 
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al puggy wrote:
I don't have a curve chaser....

In my younger days, I used to be a curve chaser... :wink:

al puggy wrote:
But if the voltage is as schematic reads, would that be enough to verify transistors are good? Thanks AL

Not necessarily.

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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Wed 06, 2017 9:52 pm 
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So I have come to the cross roads....Should I replace all the caps, and transistors, then keep my fingers crossed that she works....or just sell it as is?? If I decide to repair, does anyone know where I can get transistors? All input appreciated
Thanks AL


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Wed 06, 2017 10:54 pm 
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You have had several of us recommending to change the Electrolytic caps. Please do that, and then post the results. Don't be concerned with the Transistors right now. Odds are strong that they're still good.

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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Wed 06, 2017 11:00 pm 
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Just replace the electrolytic capacitors, and then check the speaker for ohmic value. It should be at least 8 ohms, and it's likely marked on the speaker cone. Then get back with us.


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Wed 13, 2017 3:41 am 
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Ok, I changed all electro caps and she is still dead.....but I do get squeals on the second radio test. I also hooked up another speaker across our speaker with out results.....AL


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Wed 13, 2017 4:38 am 
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The fact that the set's oscillator affects another radio displays that the power and converter circuits are apparently working. If you have a signal tracer and the schematic, try tracing from the base of the first audio Transistor, and if you get signal, then it's collector, then the next audio Transistor's base, etc.

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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Wed 13, 2017 4:43 am 
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The transistors are in sockets. Have you tried reseating them as Mark suggested earlier?

Greg.


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Wed 13, 2017 2:05 pm 
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Yes, I reseated transistors and cleaned sockets. I don't have signal generator, but I will try to rig something up. I remember using signal out from stereo to test old tube amp. I will let all know if I find a dead spot....Thanks AL


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Wed 13, 2017 5:08 pm 
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I know that you paralleled another speaker across the Zenith Royal 800 speaker with no results. However, it's possible that the speaker in the Zenith Royal 800 could be shorted so this test would be inconclusive at best. Please try doing what Gregg earlier suggested. With the batteries to the Zenith Royal 800 removed (or with set turned off), and with two lead wires connected to a 1.5VDC AA battery, try tapping the end of those leads across the speaker, and see if you hear a clicking sound. If you do hear the clicking sound, that would definitely eliminate the speaker as the source of the problem. Also check for broken wires to the earphone jack and the speaker itself.


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Wed 13, 2017 6:06 pm 
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Speaker test checks out. I was re-checking voltages at my transistors, and I don't know if its a mis-print on schematic, but on 2N190 AF AMP, The schematic has 1v at collector....I am getting 11v. Do you think this is incorrect? AL


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Wed 13, 2017 7:54 pm 
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al puggy wrote:
I don't have signal generator, but I will try to rig something up. I remember using signal out from stereo to test old tube amp. I will let all know if I find a dead spot....Thanks AL

I had actually suggested using a signal tracer in order to check the audio circuits. If you don't have one, you can use any audio amplifier, since you are tracking AF and not RF frequencies.

An amplifier can be derived from any radio, by simply connecting leads to it's circuit ground and the center wiper of the VC. I would use a battery powered radio in this case, to prevent any chance of excessive voltage travelling from it to the set under test.

al puggy wrote:
Speaker test checks out. I was re-checking voltages at my transistors, and I don't know if its a mis-print on schematic, but on 2N190 AF AMP, The schematic has 1v at collector....I am getting 11v. Do you think this is incorrect? AL

Yes, assuming the print is accurate. I looked at my copy of it, and the 2N190 AF Amp does indeed show 1 volt at the collector, and 11 volts at the emitter. Are you sure you didn't mix them up when taking the reading, and did you re-socket it correctly?

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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Wed 13, 2017 11:49 pm 
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I checked again....getting 12v on E,C and B on the 2N190


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Thu 14, 2017 1:52 am 
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Would I be able to use the 2 wires from ear-phone jack of another battery radio to do signal test? aL


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Thu 14, 2017 2:12 am 
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If you are reading the same voltage on each of the three Transistor elements, that's the problem right there, or at least one of them, if something else is causing it.

Usually the base is one or two tenths of a volt more negative than the emitter, and the print shows that it's supposed to be 10.8 volts.

Please post what you read on each of the elements of the output 2N187A Transistors, so we can determine if the problem is isolated to the 2N190 driver, or more extensive. If they read per the print, then I would check the components connected to the base and emitter of the 2N190.

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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Thu 14, 2017 2:42 am 
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Al,
I have an all-original Zenith Royal 800 and took the following readings this afternoon from 2N190: B - 8.8 volts, C - 0.8 volts, E - 10.8 volts. I've got to clean the transistor sockets as the Zenith 800 stopped working after I removed the chassis from the case, but it started to work again after moving the AF amplifier transistor. I hope you find out what the problem is with your Zenith 800 as it is one of my favorite vintage transistor radios. - Mark


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Thu 14, 2017 3:58 am 
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The 2 2N187'S READ C-.010 B-12.3V E-12.3V


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Thu 14, 2017 4:36 am 
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I think those output Transistor readings are close enough, and we should be able to rule them out as a problem. The driver Transistor OTOH may be the culprit; it or a component in it's circuit.

I would suggest verifying the values of R18, 19, & 20, and if you haven't already, replacing C2, 3, & 4. If those are all good, it would point to the Transistor itself, which sounds like it's shorted.

If you have any small signal PNP Transistors, try some of them in it's socket.

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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Thu 14, 2017 3:11 pm 
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All those resistors check out, and the caps were changed. I have a lot of transistors, but how do I know if they would be in line to replace 2N190? Thanks Mark for checking your voltages! AL


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 Post subject: Re: Zenith Royal 800...Dead
PostPosted: Dec Thu 14, 2017 4:09 pm 
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Al: You would simply need to find a germanium PNP transistor in your inventory, and not a silicon one. I stress the germanium PNP transistor as a silicon PNP will not work. Keep in mind that this substitute GE PNP transistor is only for test purposes only. If the 2N190 GE PNP transistotr is defective, you would likely want to order an original 2N190. Also make sure that all three legs of the substitute germanium PNP transistor correspond exactly with that of the 2N190.


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