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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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31st Aug 2018, 6:36 pm | #21 |
Dekatron
Join Date: Apr 2011
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Re: Help needed restoring a Murphy V310
Ballooning means the picture gets magnified as the brightness is increased, eg: picture over scanned, if it's very bad the raster will disappear with the brightness turned up, it's due to insufficient EHT, the most common cause back in the day used to be the EHT rectifier loosing its umph, the beam's velocity is reduced therefore the scan coils can deflect the beam more than they would if the EHT was normal.
Lawrence. Last edited by ms660; 31st Aug 2018 at 6:41 pm. |
31st Aug 2018, 6:41 pm | #22 | |
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Re: Help needed restoring a Murphy V310
Quote:
"Ballooning" is where the picture expands (gets a lot bigger) when the brightness control is turned up, due to the EHT falling, usually due to a low emission EHT rectifier valve. By getting bigger, I mean less of the usual picture is visible on the screen. This is due to the lower EHT causing a slowing down of the electrons as they pass from the electron gun to the phosphor coated screen. As a consequence, the scanning current in the line scan coils has a greater effect on moving the beam from side to side ("deflection sensitivity"). However, it can also be due to moisture in the LOPT, causing the LOPT to overheat and the Boost HT to fall, the longer it is left on from a "cold" switch on. Boost HT is generated by the LOP stage. As the boost HT voltage falls, so does the EHT. Last edited by dazzlevision; 31st Aug 2018 at 6:53 pm. |
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31st Aug 2018, 6:52 pm | #23 |
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Re: Help needed restoring a Murphy V310
I take it you have also changed C109, the Boost HT reservoir capacitor (0.25uF)?
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31st Aug 2018, 7:35 pm | #24 |
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Location: Warnham, West Sussex. 10 miles south of DORKING.
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Re: Help needed restoring a Murphy V310
The low EHT combined with the flat picture is probably due to the LOPT. The heater winding supplying the U26 used to go O/C hence your fitting of the stick. Perfectly OK by the way.
You may well discover that the transformer seal around the rubber top has allowed moisture to enter and contaminate the oil. It sounds like some oil has escaped by your description of the chassis. Air can also enter via the lead out wires. It's not a very nice design. Other than that everything should be straightforward. It's worth checking that you have replaced the sync coupling capacitor. If leaking it will cause cogging of the test card and difficult sync separator operation. As mentioned the decoupling capacitors in the IF amplifier, especially the ones connected to pin 8 of the 30F5 valves are prone to leakage and going O/C. Some of then look like and are marked similar to resistors. Good luck with it. They are capable of exceptional results. John. |
31st Aug 2018, 8:00 pm | #25 |
Nonode
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Re: Help needed restoring a Murphy V310
Thanks for all the replies,
I can confirm it's not ballooning. The picture shown earlier is with the brightness on full and the contrast set very low. Turning the contrast up distorts the picture and seems to invert it, please see attached picture. There's also a dramatic change of noise. All wax capacitors have been replaced but I will now check the ceramic decoupling caps as per Johns advice. Thanks David
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31st Aug 2018, 8:06 pm | #26 |
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Re: Help needed restoring a Murphy V310
Standard piece of kit in my tool box for those Murphy's was a homebrew instability probe (AKA a 1,000pF on a stick) I reckon those Murphy's were the supergainers of their day.
Lawrence. |
31st Aug 2018, 8:47 pm | #27 |
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Re: Help needed restoring a Murphy V310
Looking at both photos it could be the low EHT or overloading the video but the CRT looks low emission.
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1st Sep 2018, 10:46 am | #28 |
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Re: Help needed restoring a Murphy V310
The CRT may be a bit low but with a bit of use it may reawaken . [CRM172]
The V310 does not have AGC and will overload with the picture turning negative if you advance the contrast too far. Set the contrast mid way then advance the Band 1 gain pot on the back to obtain a point just below the negative picture. It may also be worth checking the setting of the ion trap magnet, on the tube neck under the focus dome. It is less critical compared to Mullard tubes but should be adjusted for MAXIMUM brightness, not focus or picture position. These are separate adjustments. The CRM 172 will take reactivation with care but give it a good test before even thinking about that. John. |
1st Sep 2018, 11:33 am | #29 |
Octode
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Re: Help needed restoring a Murphy V310
Are you using an attenuator with the aurora, without one you may well be swamping the input. Something around 18dB is about right for running a single set.
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1st Sep 2018, 3:48 pm | #30 |
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Re: Help needed restoring a Murphy V310
I cannot turn the contrast knob more than one eighth of a turn before the picture inverts. This problem is not effected at all by the brightness setting.
I don't have a Band 1 gain pot, would it be the Sensitivity BBC pot? If so it doesn't seem to do anything. I did catch the iron trap magnet with the soldering iron cable and it pulled it completely off the neck of the tube. Luckily I had photographs so I've replaced it where it looked like it was but I suppose it could be a millimeter or two out, would this matter? I'm not using a attenuator, I'll have to buy one. I've just measured the heater voltage on the tube and its down at 11V. Could this be causing my problems? Thanks David
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1st Sep 2018, 4:17 pm | #31 |
Octode
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Re: Help needed restoring a Murphy V310
The sensitivity control should have an influence on the picture, it will usually be all near one end. Suggest you check this part of the circuit and control.
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1st Sep 2018, 5:03 pm | #32 |
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Re: Help needed restoring a Murphy V310
Agreed and you must set the ion trap on a picture for Maximum brightness manually. It is a critical adjustment.
[Sensitivity = gain] The control should be very active but is probably O/C at one end. That is the reason for the overload. Just a thought. Make sure the BBC coils in the tuner are in the correct positions. If in the Band 3 position you can try the Band 3 sensitivity control as a test. J. |
1st Sep 2018, 5:07 pm | #33 |
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Re: Help needed restoring a Murphy V310
You should realign the iron trap magnet. Loosen it and move it around a little aiming for maximum brightness and no shadow.
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1st Sep 2018, 5:45 pm | #34 |
Nonode
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Re: Help needed restoring a Murphy V310
For clarity the tuning knob is set to BBC and the coils in the tuner are for Channel 5.
So when I set the ion trap movement do I just slide it in and out, no rotating? How much movement should I expect to need? Is it important to keep it square on the tube neck? It's quite a loose fit and was set at a bit of an angle before I knocked it off. Thanks David
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1st Sep 2018, 6:54 pm | #35 |
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Re: Help needed restoring a Murphy V310
Slide it a small amount along the neck 1/4" back and forth and at the same time wiggle [rotate] it from side to side again 1/4" to obtain maximum brightness. Murphy /Mazda ion traps are normally just a friction fit without a securing clamp screw.
It does not matter if it is slightly off centre. Adjust for maximum brightness regardless of focus, picture position etc. With the picture correctly set up [not important at this time] a final adjustment for maximum brightness is normal procedure. A photo will be a great help. Once you have set the on trap investigate the sensitivity control. This will cure the overloaded signal. You can then see what is happening. J. |
1st Sep 2018, 7:55 pm | #36 |
Nonode
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Re: Help needed restoring a Murphy V310
Thanks for all the replies.
I'll have to wait until after the weekend before I can do any more to it. Hopefully I'll report back next week with some good news David
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2nd Sep 2018, 5:31 am | #37 |
Nonode
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Re: Help needed restoring a Murphy V310
Hi!
The CRM tube was 12.6V 300mA nominal heater rating, but unfortunately partial heater short–circuits can occur in these tubes, which gives the effect of low–emission. You might be able to improve matters with a small 12V 6VA transformer added discreetly to the chassis if space permits! Copies of the Mazda Valve & CRT Data Book are in the Internet Archive – one dated 1963 or 1966 will be fine and they're well worth downloading and printing out by anyone doing Murphy radio or TV receivers! I recommend a supply of A5 paper (Rymans, "Office World" or online) for these as these books were only a small page size! Chris Williams
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2nd Sep 2018, 7:34 am | #38 |
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Re: Help needed restoring a Murphy V310
Hello.
From what I've been told it was Mullard tubes that were prone to partial shorts not Mazda tubes. The Mullard tubes normally had a longer life but the Mazda ones gave a brighter picture when new due to aluminizing. As Heatercathodeshort rightly says the ion trap is a critical and important adjustment, slight rotation and in and out movement is the procedure and should be done on a bright picture, not maximum brightness and contrast as high beam current will lower the EHT effecting the beam from the electron gun, even with a displaced ION trap a CRT still pulls beam current. If the picture gets much brighter after adjusting the ION trap back off the brightness a little so it isn't far too bright then recheck. |
2nd Sep 2018, 2:12 pm | #39 |
Nonode
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Re: Help needed restoring a Murphy V310
I had an unexpected few minutes spare so I had a go at the ion trap magnet. Unfortunately it was getting brighter while it was sliding more onto the tube socket than the neck! Then (you guessed it) the socket became unstuck from the neck! I'll have do it all again once I've brought some araldite and reattached it.
I do think I got the magnet in more or less the right position, before the base came unstuck but I must admit the increase in brightness wasn't great. I also found out that I'm on channel 9 not 5 (can somebody explain why there's 13 channels and only 2 stations?) and twiddling the "Sensitivity ITA" knobs has got rid of the inverted picture problem. Regards David
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2nd Sep 2018, 2:31 pm | #40 |
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Re: Help needed restoring a Murphy V310
There were lots of transmitters needed for UK coverage, if the two broadcasters (BBC, ITV) were all trying to share two channels interference would be a big problem.
Lawrence. |