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Old 30th Jul 2019, 8:41 pm   #1
Dick Glennon
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Default Pye PJ500 blown resistor.

Hi again, I tried powering up the pj 500 with the lamp limiter , All the valves lit up as well as the dial bulbs but no sound whatsoever. All valves are good. I tried for continuity on the output transformer and I discovered no continunity on one wire coming in. I traced it to a green resistor 1600 ohm 5 percent,looks fairly hefty. I wonder what caused it to go open circuit and if I should be looking out for other causes. I still do not have capacitor /resistor chart to refer to. All help would be appreciated. Regards Dick.
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Old 30th Jul 2019, 8:59 pm   #2
Mike. Watterson
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Default Re: Pj 500 blown resistor

I'd check the capacitors before powering up even with a lamp limiter.

You don't need a chart / schematic for these.

The paper dielectric caps are all 100% faulty in these Irish Pye models.

The Electrolytic caps often reform.
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Old 30th Jul 2019, 9:57 pm   #3
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Default Re: Pye PJ500 blown resistor.

Quote:
Originally Posted by Dick Glennon View Post
I traced it to a green resistor 1600 ohm 5 percent, looks fairly hefty. I wonder what caused it to go open circuit...
The service manual is your friend. That resistor is R34, part of the smoothing circuit. I'd check C65.
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Old 31st Jul 2019, 6:48 am   #4
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Default Re: Pye PJ500 blown resistor.

The Radio Museum has the service details.
https://www.radiomuseum.org/r/pyeirl...ram_pj500.html

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Old 31st Jul 2019, 8:06 am   #5
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Default Re: Pye PJ500 blown resistor.

We've already been there:-

https://www.vintage-radio.net/forum/...d.php?t=157663
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Old 31st Jul 2019, 9:23 am   #6
TrevorG3VLF
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Default Re: Pye PJ500 blown resistor.

The resistor could have failed because of corrosion and hence excessive local high temperature. Presumably it is wire wound.
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Old 1st Aug 2019, 8:21 am   #7
Dick Glennon
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Default Re: Pye PJ500 blown resistor.

What wattage would I need to replace it with. Regards Dick.
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Old 1st Aug 2019, 9:35 am   #8
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Default Re: Pye PJ500 blown resistor.

Why not consult the parts list in the service manual to which you've twice been given links? That's what I'd have to do to answer your question.

Help is freely available on here, but we do expect members them to help themselves where possible.
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Old 10th Sep 2019, 9:36 pm   #9
Dick Glennon
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Default PJ 500 no sound.

Hi again, I have got my circuit diagram, all the valves are good,the mains transformer is ok and the speaker. How would I be sure that the output transformer is working. There is no click on the wave change when it is turned, and all hunts caps have been replaced. Any advice would be very much appreciated. Regards Dick.
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Old 11th Sep 2019, 12:09 am   #10
TrevorG3VLF
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Default Re: Pye PJ500 blown resistor.

Get the DC conditions correct first.

A quick test of the output transformer, is to measure the resistance of the primay with an analog meter. If you hear a click, it is likely that the transformer, the wiring to the speaker and the speaker are all OK

You have 6.3V AC on the heaters, connecting this to the output valve grid through a 100k resistor should give a massive hum, checking the power supply, output valve, output transformer and speaker.
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Old 21st Sep 2019, 7:55 pm   #11
Dick Glennon
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Default Re: Pye PJ500 blown resistor.

Hi again,I. discovered that the o.p.transformer was o.c on the primary. I replaced it with a good one from a P 74.. On switch on I am getting a shrill blast on the speaker. I have stations coming in when the shrill blast abates a little as I turn up the volume. This volume control may not have been worked for some years. Anything else I should check. All help would be appreciated. Thanks again Dick
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Old 21st Sep 2019, 9:06 pm   #12
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Default Re: Pye PJ500 blown resistor.

Are the DC conditions close to the voltages on the service sheet? From the snip of the circuit diagram I can see, it appears that there may be a -ve feedback circuit connected to the secondary of the output TX . Replacing the transformer may have reversed the phase and caused a ve+ feedback loop and instability. You could easily check this by snipping the feedback loop (ie the connection from the secondary which does not go to the speaker)
However guesswork isn't the best way to track down instability (I only suggest the above because the check is easy! If that doesnt work, I would start systematically with voltage checks.
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Old 23rd Sep 2019, 10:25 am   #13
Dick Glennon
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Default Re: Pye PJ500 blown resistor.

Is this the output connection that does not go to earth via the mains transformer? Thanks again Dick.
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Old 23rd Sep 2019, 2:39 pm   #14
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Default Re: Pye PJ500 blown resistor.

Both ends of the output transformer secondary are connected to the speaker. One end is , as you identified, connected to earth.

The other (non-earthy) side shows an additional connection which runs off the top of circuit diagram extract that i can see. I suspect this additional connection of being a negative feedback loop and an easy check would be to temporarily snip it and see if the squack clears.
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Old 23rd Sep 2019, 3:09 pm   #15
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Default Re: Pye PJ500 blown resistor.

From the circuit, it is indeed feedback and is more complex than Philips sets! Do as suggested and if it stops the whistle you could try reversing the secondary connections but you may struggle to get it stable.
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