Philips G23T210A

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Originally Posted by 1100 man

I've just seen your post above. That's interesting!! There can't be shorted turns on either the primary or the overwind or else you wouldn't get any eht!!
The idea of an interwinding short is interesting.
Could you post the relevant part of the circuit:- I would like to see what the winding arrangement looks like?

Sorry Nick, I overlooked this part of your post. Yes I have now confirmed that it IS an inter-winding short. Attached here should be the line output stage schematic. The sections of the LOPT marked D,E and F should be isolated from the windings GHJK. On my transformer, confirmed by removal to make sure its not something inside the set, these two sets of windings are connected.
Apparently these LOPTs were infamous for this inter-winding short. The test for it in circuit is to remove the PY topcap and to remove the boost cap. Then the line output stage should be dead (no spark at the top of the PL with insolated screwdriver). If there is a short then the line output stage will (partly) work. That's exactly what I get, in fact I got EHT and a raster, although distorted.

[Philips210]

Hi Charles.

I wonder if it's feasible to strip down the primary winding and rewind it. The encapsulation looks to be the stumbling block though.

Regards
Symon.

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Nice thought Symon and yes I have had the same idea. I did try it once for a Philips 17TG100U when I was 15. I stripped down the old one counting the turns and wound my own. back in those days I didn't have the right gauge of wire nor modern ployprop transformer insulation tape. My rewind didn't work back then, but these days I've much more experience, access to materials and ability to measure the gauge of the original wire.
Right now in my "playroom" I'm trying various solvents to see if I can get better access to the windings. Acetone seems to have some effect and I've also got a toluene/xylene solvent that might help. I've also applied current through the coils electrically closest to the short in the hope I might be able to "blow" the short. It gets hot and smells too, suggesting the short may be near the surface Its most probably where the wires come out across the windings to the external pins.

Chas

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I think I may have found a way round the inter winding short. The two coils involved are, it turns out separable electrically. One is actually on the overwind bobbin and is OK. Its the other that is shorting to GHJKL. So, I have measured its resistance and used my digital micrometer to find the wire gauge and disconnected it. It turns out that, given the wire gauge and the resistance I make it 100 turns. So the answer was to wind 100 turns of the wire on top of the existing primary bobbin and just wire it in.

I've cleaned up the LOPT and have re-assembled it with its new coil and the inter-winding one isolated. I'll let you know how big the bang was, assuming I survive.

I'll be back... (I hope)

[1100 man]

Now that (if it works) is a cunningly neat solution to the problem I like it!!
Having studied the circuit you posted earlier, it now becomes clear what the problem is and why it will work with the PY top cap disconnected.
Manufacturers must have really hated the whole dual standard era of sets. LOPT's especially tended to have many more windings than their 405 line forebears! More windings means more trouble

Hope it works
Cheers
Nick

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Well the line output stage no longer holds the HT down so is obviously not drawing the same current as it was but there is only a very tiny spark on the PL anode and no EHT.
Of course I can't rule out there being a shorted turn involved in the inter winding short. That would dump lost of the flyback energy. The LOPT tester would show that up I suppose.

So, I still need a LOPT...

[1100 man]

Originally Posted by space_charged

Of course I can't rule out there being a shorted turn involved in the inter winding short. That would dump lost of the flyback energy. The LOPT tester would show that up I suppose.

Surely by isolating the winding that is shorted to the main winding, and then getting enough energy to light the EHT rectifier, you have proved that there can't be any shorted turns? After all, (I've just done it with the set on the bench to prove the point), just one shorted turn will kill the scan & eht. Granted there was still a very small scan and some eht though. Hmm!
Have you tried reversing the phase of your new winding?
I certainly liked to see a nice decaying 'ring' on the scope when I was testing LOPT's. Any shorted turns would be very obvious.
Cheers
Nick

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Yes Nick, I did carefully check the phase of my new winding. I also tried reversing the phase just in case I had determined it wrongly.

My latest test was to wind two turns of (insulated) solid wire twice round the LOPT core and connect it to a 3V torch bulb. When I run the set, the bulb lights up nicely.

But I don't seem to be getting any EHT and the boost voltage at the boost test point to chassis is only 280 volts, only a bit higher than the HT (which seems correct at about 220V). Its supposed to be 930V.

[Philips210]

Hi Charles.

That's hard luck with the LOPTx, you certainly tried to resurrect it.

As many can testify including Nick, the ring test for a LOPTx is a very good way to check for shorted turns. The LOPTx tester I use was built from Television magazine, September 1993 and it's been extremely useful and I would definitely recommend building it. It requires the use of the oscilloscope to display the damped sinewave.

I recently had cause to use it on a Ferguson 14M2 (Thorn TX89 chassis). Unloading the line output stage from the power supply and using a 60W lamp to load the power supply seemed to prove it was a line output fault. I couldn't find anything amiss and no shorts or leaky line output transistor etc so condemned the LOPTx. Unfortunately, I couldn't put my hands on the LOPTx tester to confirm. I struggled to find a replacement LOPTx but luckily found a NOS one, and, lo and behold found my LOPTx tester. I didn't like what happened next. I confidently removed the old LOPTx from the chassis and put it on the tester expecting to see a heavily damped waveform. To my surprise it produced a nice healthy damped sinewave. I compared it to the new one and both transformers gave the same display. Without much confidence, I fitted the replacement and as expected, the fault was still present. So it was the wrong diagnosis but if only I had the tester to hand before finally condemning it and buying a replacement. Oh well, these things happen, not too often fortunately.
I eventually found the fault, it was due to a small electrolytic capacitor (blue axial Philips type) in the remote control IC's reset circuit. It reformed itself when testing and the set started up. I believe the excessive leakage current caused problems with the reset circuit.

It's well worth having a ringing tester for transformers though.

Regards
Symon.

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Nice tale Symon about your LOPT. Of course you now have a spare for your transformer which might come in handy one day.

My latest test on my repaired transformer shows that there is EHT, as in nice blue corona when placing the topcap and lead to the EHT rectifier against the chassis.

I suppose it must be a shorted turn (or two) in the LOPT, but it would be good to prove there is. I've got a .pdf of the tester you describe, so I'm going to build one. I have a variety of 'scopes. My best is a 100MHz Rigol 4 channel digital storage 'scope. Though its great, I still hate the feel of a digital 'scope and use my trusty Hameg 20Mhz dual trace "real" one when I don't need storage or high frequency measurements.

One of the members here has a LOPT for a 210 and has offered it to me, so I am no longer stuck. Great lot of people here.

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Originally Posted by Philips210

Is your G6 working? It would be great to see some pics of this set, maybe in another thread.

I don't know if it still works. It has been well stored in a heated room but not used for over 30 years now. It should be OK, but some caps might need attention and main smoothing re-formed of course. The tube was one I fitted, re-gunned of course. re-gunning back then was being very well done so I'd expect the CRT to be OK. I will at some point be "restoring" it and for that, I'll start a new thread.

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Originally Posted by murphymad

Can I just bring up the comment from Dazzlevision about the two 8.2Meg resistors. ... They absolutely MUST be high voltage types. I used Farnell 3Kv rated resistors.

I bought a selection of high value resistors (from Farnell as it happens) a while ago and I always go for 2 watt ones. The ones I've got are all rated at 3Kv. I didn't have 8.2M in the "selection" so have done another order for those.

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Should get the remainder of the high value/high voltage resistors I need on Monday.

Just found a photo of my G6 (working) taken in 1979 after I had fitted the re-gunned tube.
I'll open a thread on this when I start restoration...

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I've got all the high voltage resistors needed for the line timebase, so for now I've done all I can until I can get a LOPT for this beast.

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Thanks to the generosity of Mike, I now have a replacement LOPT for the T210
I will be back, when I have replaced the LOPT...

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I got down to replacing the high value/high voltage resistors in the line timebase today. Then I fitted the replacement line output transformer generously provided by Mike.

As usual I ran the set up slowly on a variac, watching the HT and boost HT. This time the boost HT rose rapidly as oscillation started and a small raster appeared, in fact a picture!
Perhaps optimistically, I had connected the aerial to a UHF modulator. As I turned the variac up, a full picture resulted.

There was very poor line AND frame sync, quite difficult to get a steady picture in fact. The contrast (at maximum) was OK, but maybe should be better. I'm thinking of the ECC82 sync sep, either the valve or more likely anode load resistor or bias.

In the light of the poor contrast I have to suspect the video output stage (PFL200) too.

Anyway, the G23T210 lives

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The video output stage is a FL200 on these sets and this valve has been known to give trouble so a new (NOS) one was tried but there was no improvement.

Attention turned to the rest of the circuit and I next replaced C2047 and C2048. This improved the contrast a lot but there was still no line or frame sync. This pointed to the small pentode section of the PFL200 and its anode resistor R2138 (680K) was found to be o/c. A replacement restored both line and frame sync. The line sync, though "good" as in wide capture ratio, shows line tearing, as though the line sync has a fair amount of (probably picture) noise on it. This fault has yet to be traced. I'll start by checks around V2003 which processes line sync.

On a blank raster with the contrast turned down, there are wide bands of vertical stripes of light and dark. There are about five of these and when not tuned to a signal, they move and change number across the screen with line hold setting. I assume they are some sort of "ringing" from the timebase getting into the video signal. Any ideas anyone?

I'll put up some photos of "first light" on the set shortly.

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Photo of last night's run of the set. The photo shows the light/dark striations.These persist when the contrast is turned down, so probably originate in the video output stage.

Just realized I've overlooked the CRT grid circuitry and in particular the blanking pulses from the LOPT. Will have to check the components in the CRT grid circuits.