This is one the TVs that my dad had kept in the loft and I decided to have a proper go at restoring it over the holiday period. It gives a well-proportioned raster, but the video signal was not getting through to the CRT. It has a VHF radio with positions for Home, Third and Light included in the turret tuner.
I started by replacing the video demodulator diode (V5) which did not make any difference. Replacing C24 which is the coupling capacitor to the cathode of the CRT resulted in improved brightness with the raster staying focused with the brightness control fully advanced. Replacement of other suspect waxies and Hunts capacitors in the vision stages also did not solve the issue, but C32 which feeds the grid of V3 which is the first vision IF amp valve (EF80) had clearly failed and split open at some point in the past.
After this capacitor had been replaced, measuring voltages at V3 showed that cathode volts were too high at around 5.5 as opposed to the 1.8 specified in the manufacturer’s service data. The anode volts were also too high at 170v as opposed to 148v. Further investigation in this area showed that R6 which feeds the cathode had badly overheated in the past, resulting in it rising from 150R to in excess of 20M! The other resistor feeding the cathode looked okay but had decreased from 39 to 16 ohms, R4 in the HT feed to G2 was also showing signs of having cooked and had gone low from 150R to 50R and likewise with R7, which had decreased from 3.3 to 2.7k. All these were replaced, with a new R6 restoring the vision signal as per the final picture below. Voltages on V3 are now correct. The two 1000pf ceramic caps situated either side of R6 (see pic of PCB below) also appear heat damaged as there are small blobs of solder at their bases, so these will be replaced too. I’m thinking that the failure of C32 would have led to all this overheating and that was probably when the set got placed in loft…
The grid coupling cap to the audio output pentode section of the PCL82 was replaced, as sound was a bit distorted. Sound quality is now good on the VHF radio. The 0.5uf cap in the anode circuit of the boost diode has also been replaced with the result being that I now even have a faint image on the screen with the brightness control turned to minimum. The CRT seems to have plenty of emission which is promising.
There’s clearly quite a bit more to be done and I’ll be tackling the timebase panel next which has a variety of waxies and black Hunts caps needing replacement… It’s very difficult to achieve a stable image at the moment, and the frame timebase is running too slowly as there is visible flicker.
Laurence
What a nice looking set! You have made very good progress. The tube certainly looks a good one. The late Gerry Wells was not a fan of this chassis with what I believe was the first printed circuit TV chassis that PYE produced. I remember speaking with him at one of the Harpenden meets many years ago when he saw that I had purchased a similar looking console version with a 21" CRT. When I got it home and removed the back I found it was a standard metal chassis version but the same layout and construction as your set so probably an earlier model?
I will follow your progress with interest.
Rich.
I decided to have a proper go at restoring it over the holiday period.
It's what holidays are meant for 😉
But what a good result thus far, plus an interesting description of how you achieved it. 👍
PS, Watch C25 and C26, they see the mains you know and might protest in a loud way when you least expect.
To understand the black art of electronics is to understand witchcraft. Andrew.
I have been making progress - it was suggested that I replaced the capacitors around the M3 interlace diode and replacement of C63 cured the sync fault and this has resulted in a stable image when the hold control R77 is fully advanced. I had a bit of foldover at the top of the picture, but replacement of C69 in the linearity network cured this. A new PCL82 frame oscillator/output valve has also extended the range of R83 (vertical amplitude) considerably.
At present I can't get the picture perfectly proportioned in terms of showing castellations at both the top and bottom - I can only get them at the bottom with a full scan or at both the top and bottom by reducing the height control too much. I will continue replacing those old timebase caps which should improve things.
The picture is 'breathing' quite a bit, so replacements for the power supply electrolytics are in the post. The can containing C27, C28 and C29 does have a bit of a bulge at the bottom, but is running cold at present.
PS, Watch C25 and C26, they see the mains you know and might protest in a loud way when you least expect.
Thanks Andrew - I can't see C25, so this must have been snipped out many years ago. In terms of C26, I have taken this out of circuit. I note it is rated at 1.25kv - would a 0.1uf X2 capacitor rated at 275V be suitable as a replacement here?
Laurence
Update: Having continued replacing caps in the frame time base and elsewhere, I have a much improved picture! C65 which is the grid coupling cap to the frame oscillator measured 1.5MO leakage and appeared to have possibly overheated in the past. This was replaced resulting in the hold point being at the middle of the frame hold control rather than at the top.
I initially found that it was difficult to get the test card image centralized, as it was slightly off to the right. Adjusting the ion trap and picture centring magnet improved this, but once the main 200, 100 and 60 uF electrolytics had been replaced, reversing these ion trap and centring magnet adjustments resulted in a perfectly centred picture.
The replacement of these electrolytics did not improve the situation with the ‘breathing’ picture and neither did the replacement of the dual 16uF electrolytic which I noticed had been running rather warm. One of these is part of the power supply smoothing circuit and the other is in the G2 circuit of the frame output valve.
I then replaced C87, which is a 1uF electrolytic with a 2.2uF component as this is all I had to hand. This is situated on the HT rail to the frame oscillator and is also coupled to a tapping on the LOPTX. The replacement of this has pretty much cured the breathing issue and I’m now getting a very nice stable picture.
The EHT overwind is only just warm to the touch after 20 minutes or so operation, but as the set has not yet been used for any extended period of time I’m going to pass DC through the overwind for a day or so to make sure any moisture is expelled and then hopefully it won’t then fail during soak testing.
Laurence
Have you instructions for setting up the ion trap, it’s important, incorrect setting can damage the CRT?
Excellent progress. 👍
Frank
Have you instructions for setting up the ion trap, it’s important, incorrect setting can damage the CRT?
Yes I use the guide at 'thevalvepage' website and also someone has sent me more information on this over on UKVRRR. I re-checked the setup and since I replaced the main power supply electrolytics I've been able to get a properly centred picture with the ion trap set correctly.
I've been passing DC through the EHT overwind, although my DC power supply only goes up to 16.4v and the current passed at this voltage is only 0.28mA and the overwind doesn't get warm, so I don't think this is sufficient.
I have finished replacing the remaining Hunts caps now and I had it running for around two hours last night and the LOPTX was noticeably warm to touch afterwards, but not hot.
Laurence
Correction: I meant 28mA not 0.28mA! I should also have said that some 'breathing' of the picture is still evident and I'm now unsure what might be causing this.
Laurence
I should also have added that I'm having to adjust the line hold regularly during the first 15 minutes or so of viewing, as hold is lost every few minutes or so until it eventually settles down. The line oscillator is the triode section of V21 which is a PCF80, so I will try substituting a new valve to see if this makes any difference.
Laurence
I was pleasantly surprised to find that replacing the PCF80 resulted in a stable picture from switch-on, requiring no subsequent adjustment of the line hold control at all. So the set now seems pretty much sorted and gives a good quality picture, with the only remaining issue being the breathing picture, which isn't that noticeable when watching a programme.
Laurence
I have been continuing to work on this set over the last few weeks, as I had to replace a newly discovered hidden Hunts mouldseal feeding the grid of the triode AF amplifier and replaced the cathode bypass electrolytic for the same valve (PCL82). I purchased some electrolytics for the main power supply with a higher ripple current rating, as some of the ones I had put in originally were not sufficiently rated. Doing this has improved the situation with the breathing picture, although not completely eliminated it.
I have also recently been getting intermittent frame collapse which could be temporarily remedied by wiggling the PCL82 frame oscillator/output valve in its socket. Attempting to clean the base contacts with Deoxit did nothing to help, so I obtained and fitted a new ceramic base and operation is now stable and I’m having trouble free operation. I’ve had to spend quite a bit of time cleaning wax from the surface of the timebase panel from those old wax caps that had become warm and melted everywhere. I’ve also been listening to R4 on the inbuilt FM radio which seems to give very good sound quality.
All in all I’m very pleased with this set, which I will be using on a regular basis.
Laurence
