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Old 25th Sep 2018, 7:46 pm   #81
Heatercathodeshort
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Default Re: Help needed restoring a Murphy V310

If the EHT is low and we can only confirm this by measurement. It is almost certainly caused by the oil that the whole assembly is immersed in. It has probably absorbed moisture over decades similar to the overwinds in conventional open transformers.

Murphy transformers were not hermetically sealed relying on just a tight fitting, clamped rubber top with the connecting leads passing through extended rubber 'bushed holes' in the top.

Over the years, oil seeped out and air seeped in!

The problem is most of this is calculated guess work. A few hands on moments would confirm this one way or the other. John.
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Old 25th Sep 2018, 7:48 pm   #82
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Default Re: Help needed restoring a Murphy V310

I've just had a good look with the lights out and I can't see anything. I did find out that the noise stopped if I turn up the "ITA Sensitivity" control. I don't know if that helps?

I forgot to mention earlier that the boost voltage isn't stable. It varies around +/- 10V. Again I don't know if this means anything?

I also discovered today the one of the width coils reads 4.5ohm instead of 3.5ohm and while I'm clutching at straws there's no cover over the 30P4 and U191.

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David
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Old 25th Sep 2018, 8:02 pm   #83
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Default Re: Help needed restoring a Murphy V310

If I remember rightly the oil could leak out back in the day, it's a shame it took so long for the snot pot and tripler to arrive.

Lawrence.
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Old 26th Sep 2018, 7:55 pm   #84
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Default Re: Help needed restoring a Murphy V310

Turning up the 'ITA' sensitivity [Your BBC coils are still in the ITA position?] will increase the brightness and hence draw more current from the EHT system which is probably a bit below par.

By what you say this is probably enough to lower the potential enough to prevent flash over/corona or maybe very minor sparking from within the LOPT.

The other items you mention will not effect the operation of the line output stage.

Direct TV Replacements and BRW [British Relay Wireless] used to produce an open type transformer for replacement purposes but I can't remember seeing one. J.
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Old 27th Sep 2018, 9:36 pm   #85
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Default Re: Help needed restoring a Murphy V310

A lot of Murphy V310 models were modified to the line timebase circuit as employed in the model V330 which was one of a group of receivers with FM radio.
This was a Murphy Radio approved modification for troublesome V310 models that had the self oscillating line output stage.

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Old 27th Sep 2018, 9:53 pm   #86
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Default Re: Help needed restoring a Murphy V310

Was the 30P4MR Line output valve specially selected for use in the Murphy self oscillating line time base?
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Old 27th Sep 2018, 9:56 pm   #87
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Default Re: Help needed restoring a Murphy V310

Hi Frank,
That's right the 30P4MR was made for the Murphy V310. Was still available long after the 30P19 was introduced.
DFWB.
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Old 27th Sep 2018, 10:04 pm   #88
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Default Re: Help needed restoring a Murphy V310

Thanks for the information David, that was at the back of my mind but so long ago I couldn’t be sure.
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Old 27th Sep 2018, 10:19 pm   #89
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Default Re: Help needed restoring a Murphy V310

Hi Frank,
as I remember it,many Murphy V310s with the self oscillating line timebase gave absolutely no line frequency drift whatsoever and yet many others were just a servicing nuisance. Adding the separate line oscillator cured the problem. The correct oscillator valve should be the Mazda 6/30L2 although I've seen sets equipped with the very similar ECC82. Worked just as well.

DFWB.
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Old 1st Oct 2018, 5:21 pm   #90
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Default Re: Help needed restoring a Murphy V310

I will be getting an EHT meter by the end of the week but I had some time to have a little play today.

I thought I'd try, as suggested, to change the mains selector to 230V. The picture was brighter and the focus was better. Unfortunately the picture "jiggle" was worse and within a very short space of time (probably within a minute) the width collapsed into a thin wobbly white vertical line.

From reading other threads I can tell this is bad news. Is it curtains for my V310?.

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Old 1st Oct 2018, 8:41 pm   #91
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Default Re: Help needed restoring a Murphy V310

It's not looking good for the LOPT, you could try testing all the linearity coils and width coils to see if any have gone open circuit. I guess even the line scan coils could be open.

If your using trader sheet 1361 the coil values are given
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Old 1st Oct 2018, 11:04 pm   #92
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Default Re: Help needed restoring a Murphy V310

Circuit diagram of the self oscillating line timebase.

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Old 2nd Oct 2018, 8:29 am   #93
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Default Re: Help needed restoring a Murphy V310

It is very unusual for the secondary section of a line output transformer to go O/C.

The fact that you have a vertical line shows that HT is present on the line output valve etc.
As Stephen has posted, I would make a very careful check of the scan coil connections and their continuity. The mid point is connected to the LOPT so even if one coil was O/C you should get a distorted possibly wedge shaped raster.

Check the continuity of the 3 taps on the transformer feeding the scan coils [with them disconnected]. It is very odd. It appears from the circuit that all three connections from the scan coils must be O/C to produce just a horizontal line. I cannot believe all three would fail at the same time! Careful meter checks ar required. John.
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Old 2nd Oct 2018, 10:00 am   #94
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Default Re: Help needed restoring a Murphy V310

Thanks for the replies,

I should have mentioned earlier the set recovers as soon as I turn it off and on on again (only to collapse again) so I don't think anything is open circuit. However I won't do no harm, so I will check all the coils for resistance.

The only thing which might be worth mentioning is that the line linearity coils have lost their pitch coating, it just crumbled away. The circles on the bottom of my testcard have also grown in height, which I think is a linearity problem?

Regards
David
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Old 2nd Oct 2018, 1:09 pm   #95
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Default Re: Help needed restoring a Murphy V310

Does it collapse instantly or gradually, if instantly then you could try tapping around to try and instigate the fault sooner locating the area, it may also bring it back once collapsed.
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Old 2nd Oct 2018, 8:01 pm   #96
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Default Re: Help needed restoring a Murphy V310

If it collapses instantly it might be worth replacing the 30P4 valve. It may develop a grid cathode short when it gets warm but this would also remove the EHT and you would not be able to see the line collapse.
Don't worry about the line lin coils. Leave them alone and don't pick at them like I do a healing scab!
If your stuck i can send you a 30P4 or maybe a 30P4MR if I can find them. John.
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Old 2nd Oct 2018, 8:17 pm   #97
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Default Re: Help needed restoring a Murphy V310

I get a good picture for a couple of minutes, then it sort of wobbles and within 30 seconds the picture dims, goes out of focus and shrinks to around half size. Then the sides quickly close in until I have a bright, wavy, white vertical line about an inch or two in width. It's hard to see but I think a picture is still there.


The set came to me with an PL36 fitted, so I have already fitted a new 30P4. I've also fitted a new U191 as well.


Regards
David
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Old 2nd Oct 2018, 8:59 pm   #98
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Default Re: Help needed restoring a Murphy V310

I noticed that in my Murphy V410 pin 1 of the 30P4 is used to anchor the 0.01mfd coupling capacitor that is connected to the anode of the oscillator valve. That's OK with the 30P4 currently fitted because there is no internal connection on pin 1 but if there was a design change to the valve and pin 1 was to be used for an internal connection, the correct operation of the circuit will be impaired.
In certain Ekco TVs the vision AGC will not work when a PL36 is fitted instead of a 30P4. Pin 1 of the valveholder was used to anchor certain components in the vision AGC circuit. Pin 1 of the PL36 has an internal connection.
It might be a good idea to check if any components are connected to pin 1 of the 30P4.

DFWB.

Last edited by FERNSEH; 2nd Oct 2018 at 9:05 pm.
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Old 2nd Oct 2018, 9:52 pm   #99
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Default Re: Help needed restoring a Murphy V310

I'm pleased but embarrassed to report that I think I've found the problem.

I did previously (I'm not sure exactly sure when) check the resistances of frame output transformer. To do this I removed all the connections and you've guessed it I've just discovered I failed to connect a small piece of hook up wire which connects one of its windings to the junction of C111, R149 and R151 on the Murphy service manual or C50, R63 and R64 on the Trader sheet.

It's too late to sort it out tonight, hopefully I'll have time tomorrow.

Regards
David
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Old 5th Oct 2018, 10:35 am   #100
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Default Re: Help needed restoring a Murphy V310

Disappointingly reconnecting the wire mentioned above did very little to improve things.

I finally got my hands on an EHT meter and here's the equally disappointing results! The EHT reached a maximum of 11kV then it settled around at 10kV. when the picture started twitching it coincided with the EHT dropping from 10 to 9kV and when the picture collapsed the meter was rapidly heading towards zero, at which time I quickly turned it off! I had a stop watch on and from switching on, from cold, to turning off was just under 5 minutes. The LOPTx feels stone cold but I guess 5 minutes isn't enough time to warm anything!

*Edit* I've just tried again, this time while measuring the HT and this also starts rapidly falling as the picture collapses.

Diagnosis please.

Regards
David

Last edited by Radio_Dave; 5th Oct 2018 at 11:04 am.
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