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Old 22nd Oct 2020, 12:04 pm   #81
murphyv310
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Default Re: PYE R33 Over Voltage.

Sorry Ken.
I can't help here but is it in the UCH81 stage?
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Old 22nd Oct 2020, 12:47 pm   #82
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Default Re: PYE R33 Over Voltage.

Yes it is Trevor. Here's a picture that gives an overview. My concern is that in replacing C7 l may have moved the trimmer and soldered it to the wrong pad on the PCB.

The third picture! I'm having troubles with the thumbnails.

PS. Your continued support is greatly appreciated.
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Old 22nd Oct 2020, 12:52 pm   #83
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Default Re: PYE R33 Over Voltage.

According to the schematic the trimmer is connected to C7 and the oscillator coil etc, shouldn't be too hard to figure out.

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Old 22nd Oct 2020, 2:30 pm   #84
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Default Re: PYE R33 Over Voltage.

You're right Lawrence, but I had to take pictures and mirror-image them to be sure!

Point to point wiring under the chassis always has a diagram showing the location of the components, and a modern PCB diagram gives the track side and the components together, but the trader sheets for this halfway house of fun required a bit of head scratching.

I've replaced C7 ( Mica) and the trimmer in the correct position but the problem remains.

I'm out of time now but I'll change C6 tomorrow.
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Old 23rd Oct 2020, 1:16 pm   #85
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Default Re: PYE R33 Over Voltage.

I've replaced C6, no improvement. On Monday I'm going to measure every component from the plug to the aerial! I've got the bit between my teeth now...
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Old 26th Oct 2020, 1:18 pm   #86
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Default Re: PYE R33 Over Voltage.

One problem of course is repairing or giving advice without having the set in front of you.
The issue could be man made or even a faulty new component.
On a recent thread on another forum an amplifier was being discussed with a hum issue. The thread had gone to a couple of hundred posts and eventually after it could only be a smoothing cap that was new. It turned out to be that very capacitor that was faulty from new.
So as you can see remote fixing isn't easy.
It's difficult now with covid19 but is there a member close by to you that can go over it with you?
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Old 26th Oct 2020, 6:21 pm   #87
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Default Re: PYE R33 Over Voltage.

After an overdose of roast lamb and Yorkshire pudding on Sunday l spent today relaxing!

I know what you mean Trevor, I'm going to investigate the power supply end and work from there as l seem to have exhausted the components around (and including) V1.

Never say die!
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Old 28th Oct 2020, 11:39 am   #88
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Default Re: PYE R33 Over Voltage.

Ok, almost never say die!

I'm putting this into the help requested as it's beyond my skill set.

When it's returned working l will post a (possibly redacted) post script, admitting schoolboy errors!

Thanks to all who have done their best, from a distance, to solve this electrical conundrum.
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Old 28th Oct 2020, 5:33 pm   #89
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Default Re: PYE R33 Over Voltage.

Pity you were not closer and there was no Covid-19.
I'm always happy to help and pass on some tips.
I'd have gladly gone over the radio with you.
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Old 28th Oct 2020, 7:37 pm   #90
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Default Re: PYE R33 Over Voltage.

Ditto myself if it could get to DN17.
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Old 28th Oct 2020, 7:47 pm   #91
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Default Re: PYE R33 Over Voltage.

I know! I could have taken it to Golborne where half a dozen friends would have fought for the honour!

We'll all have a good laugh when it turns out to be something really simple, l might even ask Gabriel to post a utube video of it singing.

Right, what's next? Ah yes it's a Vellemann signal injector/tracer...
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Old 29th Oct 2020, 10:17 am   #92
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Default Re: PYE R33 Over Voltage.

Once you get the hang of using an oscilloscope you'll discover that it's the most useful piece of test equipment you have.
I honestly can't remember the last time I used a signal injector to fault find.
Remember your radio has signals so injecting signals is irrelevant. Tracing the signals again without the scope is unlikely to be of assistance.
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Old 29th Oct 2020, 7:37 pm   #93
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Default Re: PYE R33 Over Voltage.

Hi Trevor, looking back to post #15 the Pye R33 has an autotransformer and I can't use my Hameg without an isolated transformer, is that correct?

I've also realized that I haven't posted any voltages, which is usually the first measurements l take!

West Yorkshire hits tier three on Monday...

I'll do some more investigation.
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Old 29th Oct 2020, 9:07 pm   #94
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Default Re: PYE R33 Over Voltage.

Does you Hameg do differential measurements?
Some could: A X10 probe in each channel, select "invert" for one channel and "add".
One probe tip to chassis, t'other used as normal. Both "earth" clips removed or safely taped up out of the way.

Last edited by G8UWM-MildMartin; 29th Oct 2020 at 9:07 pm. Reason: missed X10
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Old 29th Oct 2020, 10:07 pm   #95
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Default Re: PYE R33 Over Voltage.

Quote:
Originally Posted by G8UWM-MildMartin View Post
Does you Hameg do differential measurements?
Some could: A X10 probe in each channel, select "invert" for one channel and "add".
One probe tip to chassis, t'other used as normal. Both "earth" clips removed or safely taped up out of the way.
Hi.
Although that will work I still feel its not the safest approach.
Personally I'd be buying an isolation transformer before other test equipment.
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Old 30th Oct 2020, 10:34 am   #96
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Default Re: PYE R33 Over Voltage.

Aha! Yes, the Hameg 203-7 has a 20 meg bandwidth, two channels and two X1/X10 probes.

I'm going to tidy up a couple of components that are tacked on and post the voltages. I'm using a 16 uf 450 volt electrolytic for C25 (8uf) as it's the nearest I've got - let me know if it's unsuitable.

I might be able to do this over the weekend, if not I'll get onto it on Monday.

I'll obviously need help with the oscilloscope, it was such a bargain and I wouldn't want to break it.

Just seen Trevor's post - I'll take all advice, including not doing what Martin suggested.
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Last edited by Kentode; 30th Oct 2020 at 10:37 am. Reason: Trevor's safety warning.
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Old 30th Oct 2020, 10:58 am   #97
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Default Re: PYE R33 Over Voltage.

Hi Ken.
To be fair Martin's approach will work but it's far from ideal. It can induce hum onto the waveform and distort readings but my main worry is it's potentially unsafe and not the best idea for a beginner.

I'd look out for a used isolation transformer 200 Watts would be fine for radios. I've a 1kw one which came from my old business, far too big IMHO. Re the tracer, they can prove useful but I think in your situation it won't help that much. Sometimes the loading and added capacitance can mask faults or even clear them which can be confusing. I think your radio has some form of instability that even taking meter readings will seem to effect a cure. Sometimes this kind of fault can be quite elusive to cure.
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Old 1st Nov 2020, 4:21 pm   #98
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Default Re: PYE R33 Over Voltage.

I'm happy to say that this radio will be going for a holiday with Trevor in Ayrshire!

Update to follow...
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Old 6th Nov 2020, 11:02 am   #99
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Default Re: PYE R33 Over Voltage.

Hi.
Ken's radio landed here this morning. On first look the PCB is badly discoloured and might be leaky. Too early to be sure though. Hope to get into it on Sunday.
Watch this space.
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Old 6th Nov 2020, 5:24 pm   #100
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Default Re: PYE R33 Over Voltage.

Well I got an unexpected hour this afternoon..
Ken's work is nice and tidy and there is no issues with what he's done.
I did a couple of cold checks first. I didn't like the look of R15 an HT feed it read spot on but drifted badly when warm so I replaced it. Also one of the 1 Meg AGC resistors drifted with pressure on the meter leads, common enough with these PCB resistors so I replaced both. On power up the set worked reasonably well for a couple of minutes. Then the fault appeared, a bit like motorboating. The issue with light was really easy to see. So a poke with the scope revealed the issue. The oscillator waveform was perfect but on Pin 6 of the UCH81 Heptode anode the resultant waveform was full of hum. I suspected a PCB leak from pin 5 to pin 6. After a scrape with a flat screwdriver the fault cleared with a big improvement in sensitivity. The UCH81 valve base was also in a poor state. A new base has been fitted, the scratchy tuning cap sorted out and a good hour run as perfect.
I've cleaned the PCB as best as possible and am happy to sign off the repair.

https://youtu.be/4Jm7Jfk9D_s
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Last edited by murphyv310; 6th Nov 2020 at 5:52 pm.
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