Hi all,
I fired up my TV22 yesterday, and it didn't seem too happy, the test card came up, but it looked like the line hold was off a bit, with the picture tearing up, no amount of fiddling with the hold control would sort it, and then the picture broke up completely, even the whistle had changed to more of a quiet hiss and the picture got dimmer, eventually collapsing to a vertical line and disappearing.
I left it for a while and turned it back on and the whole process repeated itself, I managed to get a photo of what was on screen shortly before it collapsed and vanished again. I left it again then tried it and this time no line whistle came up, just a feint ringing noise that could be adjusted with the hold control.
Now prior to all this happening I had been using the set, and I did notice a few times the picture would suddenly loose width, focus and sync, then come back as if nothing had happened!
This is the set that I have in my avatar picture, and had the LOPT in bits a few years ago (thread over on UKVRR). If the LOPT has given up then it looks like my Philips 385U will get it's CRT back!!
Regards,
Lloyd.
I assume you have measure whether there is sync to the line oscillator and the line output and EHT rectifier* are OK? To me, a "faint ringing" adjusted by the horizontal hold suggests to me that the LOPT is still operative in some form.
I'm not familiar with these sets, having not worked on them, but I assume they have EHT rectifiers?*
I assume you have measure whether there is sync to the line oscillator and the line output and EHT rectifier* are OK? To me, a "faint ringing" adjusted by the horizontal hold suggests to me that the LOPT is still operative in some form.
I'm not familiar with these sets, having not worked on them, but I assume they have EHT rectifiers?*
What do you expect them to have if not an EHT rectifier, Aidan?
Hi all,
I fired up my TV22 yesterday, and it didn't seem too happy, the test card came up, but it looked like the line hold was off a bit, with the picture tearing up, no amount of fiddling with the hold control would sort it, and then the picture broke up completely, even the whistle had changed to more of a quiet hiss and the picture got dimmer, eventually collapsing to a vertical line and disappearing.
The picture disappearing to a vertical line does not sound like good news, but could be as simple as a poor connection in the scan coil plug.
As ever in a TV set, a good meter and a 'scope are your best friends.
I'm working from a particularly ratty Issue B diagram, but the line oscillator consists of the triode section of an ECL80 (the pentode section's the sync. sep) and the PL38 itself. I'm assuming you've already changed the electrolytic in series with the scan coils (2uF), and the same value in the boost rail. Then I'd be inclined to disconnect the EY51, run the set up and look for a negative voltage at the grid of the PL38 (pin 5). You'll have the line whistle anyway to guide you, and disconnecting the EY51 will eliminate it from the equation and avoid bitey bits.
Hi,
Yes, there is an EY51, as far as I can tell it's not to blame, the heater has continuity of 13 ohms according to my fluke, and glows nicely when connected to external power (4 AA batteries!). I can also see a tiny blue spark from the EHT winding output when I brush it with a screwdriver, so something's happening, just not as much of something as there should be...
I'll try removing the heater winding from the Lopt, it's on a ceramic former so should come off easily.
Regards,
Lloyd
Actually, looking at it, the 2uf on the scan coils is still the original part, unless I restuffed it! I'll give it a check.
No such luck! Tried a new 2.2uf but no difference. The boost cap has already been changed, but I'll try another just in case.
Also, removing the heater winding from the lopty made no difference, still just the quiet whistle. I'll get the grid voltage checked next.
If the LOPT is duff, consider using a Thorn 950 or 1400 LOPT as a replacement. I've done it and its a very successful mod [...]
Or better still, leave the Thorn transformers for Thorn sets and just send the TV22 LOPT to Mike Barker for a rewind - assuming that's what's faulty?
Some voltage measurements of the triode anode wouldn't go amiss, just to eliminate it from our enquiries.
Right, the PL38 grid is hanging around -13v, it fluctuates up and down by about 1v. I also have a handy frequency counter built into the Fluke, so I pressed the button for it and the line frequency is about right at 10.125khz, and can be varied with the hold control.
I also checked the 820k resistor that Trevor mentioned, it was over 1 meg, so I've tried one from my spare TV22 chassis as I don't have any new ones kicking about, that one read 900k, it made no difference though. The anode voltage for V7b was hovering around 40v.
If the LOPT is duff, consider using a Thorn 950 or 1400 LOPT as a replacement. I've done it and its a very successful mod [...]
Or better still, leave the Thorn transformers for Thorn sets and just send the TV22 LOPT to Mike Barker for a rewind - assuming that's what's faulty?
Some voltage measurements of the triode anode wouldn't go amiss, just to eliminate it from our enquiries.
Hi.
When was the last time you had a duff jellypot tx? I would doubt you ever did! So why not use them eleswhere?
Because it's a Grade-A, chateau-bottled, nuclear-powered bodge.
I've plenty of them so that was the reason I repaired my TV22 with a jellypot.
Good for you. But I, and many others don't, and I'd rather something was kept looking as original as possible.
Didn't someone have a problem recently with Line Drive Trimmer - TC1 (Bush and R&&TS); C25 (Trader 1003); C28 (Trader 1091) - and LLJ points out that the 470pF across the LOPT can cause a number of problems ...
When all else fails, read the instructions
Bodge or not it may come to it yet! I'm going to have a go at ringing the lopty, never tried it before, but it sounds fairly straight forward. At least it will tell us if it is to blame. If it turns out to be the width or linearity coils I have replacements on the other chassis which are hopefully ok.
The 470pf on the Lopt is a new part, I'll check it anyway. The line drive trimmer also seems ok, not shorted.
Cheers,
Lloyd
Bodge or not it may come to it yet! I'm going to have a go at ringing the lopty, never tried it before, but it sounds fairly straight forward. At least it will tell us if it is to blame. If it turns out to be the width or linearity coils I have replacements on the other chassis which are hopefully ok.
The 470pf on the Lopt is a new part, I'll check it anyway. The line drive trimmer also seems ok, not shorted.
Cheers,
Lloyd
It *might* tell you - ringing is not a foolproof test.
Ring test done, here's the results!
I did the test on 2 different scopes, just in case. To my untrained eye, they look ok, what does anyone else think?
It was quite difficult to get a shot of the Hameg as the trace keeps wandering off the screen...
Cheers,
Lloyd.
Could be decaying too quickly. Was the EY51 completely disconnected? If not remove it and test again. Mind the EY heater does damp the "ring" somewhat if still in circuit.
That's what I was thinking.. Not that I've done a live test myself, but thinking back over Chris' article on ringing, it seems to me that the "ring" should have more oscillations, dying out over a longer period.
Would an open circuit heater winding have any effect at all? Obviously, a shorted, or loaded heater winding would have a damping effect.
Marion
If you simulate a shorted turn (a loop of bare wire around the core) you should see the 'ring' disappear completely. I suppose a partial short could cause a damped ring. An open circuit heater winding will have no effect on the ring but a shorted or partially shorted one would.
Hi.
When ringing a lopt everything should be disconnected at the transformer, even long leads can have an effect on the result. Also the use of a X10 probe is mandatory.
Hi Trevor,
That is useful to know, thank you... 
I had a feeling that there was something about open ended wires, somewhere along the lines, but I would guess that for a quick and simple check, wiring could be left in place (but disconnected) then if needs be, removed for a more detailed test?
Marion
Yes, the EY51 was completely removed, as was it's heater winding (it just pulls off!!). I did have an X10 probe, but I'd set it to X1.
Just in case anyone wants a read, here's the history of the LOPTY fitted to this set, and the set's restoration, can't believe it's been 4 years!!
Might have another go at the ring test tomorrow. I have another working TV22, so I might just swap the whole set!! put the duff one back in the workshop! Although, this one did have the better picture..
Regards,
Lloyd.
I've re-done the ring test today with the probe set to X10, I think that if the results are anything to go by then this poor old lopty has gone to meet it's maker 
Just want to check though, are my scope settings right? I have the probe set to X10, timebase 50us, and 50mV. I also used the 2V Cal, I have a choice of that or 0.2V. Scope probe connected to EHT output of the overwind, and the Cal signal connected to the other end of it.
I did try an old Telequipment scope as well, but couldn't get any meaningful results from that, it stated the Cal signal was 50mV on that, but there were other problems with the scope. I should probably clear out some of these old scopes I have lying around! There's more in the loft!
Regards,
Lloyd.
Hi Lloyd.
Sometimes when doing this test on an unknown transformer, you need a reference. Is it possible for you to carry out a ring test on a known good transformer so that you know what to expect from your particular scope and leads?
Maybe you can extract a transformer from a working set if it's not too difficult...pick the easiest one and see what results you get.
I have to say that the last trace doesn't look good at all. What happens if you put a shorted turn around the transformer core? (Just a loop of tinned copper wire will do).
