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Old 15th Mar 2018, 3:09 am   #21
space_charged
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Default Re: Philips G23T210A

A couple of photos of the set with the back off. Done a bit of cleaning and checked tube heaters and (approx) emission.
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Old 15th Mar 2018, 9:06 am   #22
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Default Re: Philips G23T210A

Quote:
Originally Posted by space_charged View Post

Sadly I have just noticed a bit of damage in the phosphor right in the centre of the screen. Its a short (looks black) vertical line about 2-3mm long. Could have been caused by un-suppressed switch off burn, or debris falling of the electron gun during storage/transport in the face down position.

So I'm in the market for a good A59-11W or A59-23W. What do you all think my chances of finding one are? I'll post a request in the "items wanted" here of course.
The mark you describe does sound like a phosphor burn due to ineffective switch-off spot suppression. In sets of this vintage, this was usually achieved by a VDR between the low voltage end of the brightness pot and chassis. I'd certainly sort that out before fitting a replacement CRT.
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Old 15th Mar 2018, 3:45 pm   #23
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Default Re: Philips G23T210A

Thanks dazzlevision,

Well the plan now is not to post a request for a CRT now, but to go ahead with the present tube. That way I can find out how many other problems the set has, specifically what caused the burn in the first place.

I did transport the set yesterday face down, so I was really kicking myself when I found the mark on the phosphor. I looked back at the seller's photos and was very relieved to see, when you zoom in, the mark was already there. That got me thinking it would be switch off spot burn.

The set has been repaired in the past, so quite possibly the spot problem has been dealt with. I will be careful, and the already damaged tube gives me a good way to sort that out. Looks like the boost res cap has been replaced in the past and also a section of the dropper has been bridged with a resistor. Both replacements have been "well done" so by a "good" service engineer.

Quick aside; when I had a holiday job as a TV service engineer, the experienced guys in the shop always advised taking a hack-saw to the windings of the bridged section to it couldn't "come back to life" at some time in the future. No sign of that having been done on my set, so I might do something about that.

When and if I get the set to a good working state, I can see how much the mark is noticeable. If the set works well and the spot is really annoying, then I'll ask the good people here about a CRT.

Right now I'd like to ask the guys here for a list of types of sets that used this CRT. Also for known equivalents of it. Probably almost any 23in 110 degree tube with integral implosion screen could be fitted?

Charles

Last edited by space_charged; 15th Mar 2018 at 3:53 pm. Reason: grammer, spelling
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Old 17th Mar 2018, 4:05 pm   #24
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Default Re: Philips G23T210A

Update:
Now got replacement caps for the main HT smoothing.
Also been drying the set out generally, the LOPT in particular and the main PCB with a fan heater at a suitable distance.

Now started drying the LOPT overwind by passing a current through it. Service sheet says it should be 370ohms, and it is. OK, it could have shorted turns and that wouldn't show in a simple resistance check but would drastically affect performance, but lets not be pessimistic. At 370 ohms and a 20 V bench supply that's 1 watt.

Also checked the primary and that is OK too. Not for now passing current through the primary. Because of the difference in resistance that would require a much higher current and another PSU to do it.

More later...

Last edited by space_charged; 17th Mar 2018 at 4:12 pm. Reason: Info added
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Old 3rd Apr 2018, 2:16 am   #25
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Default Re: Philips G23T210A

Finished drying the LOPT overwind. I have replaced the main smoothing electrolytics. Had to use modern ones on a bit o vero board.

I have run up the set on a variac and got some sound when tuning through stations (supplied by a known working UHF modulator). No picture though and the line output valve seems too hot. The anode isn't glowing but looking inside there is an orange glow that isn't just the heater. May be screen grid?

There IS line drive, I see about -25V on the grid (with an AVO 8). The screen grid voltage is a little low if anything at 135V. The HT is about 250V. There is no spark from the anode cap of either LOV or efficiency diode. There is HT on the LOV anode. I have checked the boost capacitor, but not by substitution. I thought I had a spare for it but can't find it. Its supposed to be 0.1uf at 1000V. I do have a 0.47uf at 1000V. Any thoughts as to whether it would do?

Any ideas? I'm trying not to think LOPT...
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Old 3rd Apr 2018, 12:49 pm   #26
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Default Re: Philips G23T210A

Hmmm. The drive seems a tad low, but it's a long time since I used an Avo!
I'd expect the PY to be glowing if the boost cap's in trouble - they usually short or nothing. If it's O/C (rare) everything would run cool.
The PL is obviously drawing current. I suppose you've tried new valves? Have you removed the DY to see if you get any sort of spark?
I'm thinking the same you're thinking, I'm afraid....
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Old 3rd Apr 2018, 1:27 pm   #27
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Default Re: Philips G23T210A

Thanks Glyn.
Yes tried new valves, not the line oscillator yet though. Yes removed the dy87. I've seen these go gassy and dump the entire eht. Difficult to get to its top cap to see if there is a spark (without encountering the top caps of the line output valves on the way in)!
Interesting you think the drive is maybe low. That could be relevant, but not much info in the service sheet as to what it should be. It has some voltages (not g1 of the LOV though) and no waveforms.
The screen grid voltage is quite a bit too low at 135 instead of 177. Screen feed resistor measures OK. Doesn't seem to run hot but could be the decoupling cap though.

Just switched the set to 405 (its dual standard) and hear a nice line whistle! I can't hear 15.626KHz any more. I'd have thought a shorted turn or two in the LOPT would produce glowing anode syndrome.

I have checked the boost cap and it (measures) OK out of circuit. The boost voltage just reads the same as the HT, which is obviously not right. I'm going to replace the boost cap.

Also going to replace the line drive coupling cap as a leaky and/or low value here will mess up the line drive.

I'll be back...

Last edited by space_charged; 3rd Apr 2018 at 1:41 pm.
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Old 3rd Apr 2018, 2:44 pm   #28
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Default Re: Philips G23T210A

Hi.

It's been quite a long time since I worked on one of these sets and most line output stage problems were unfortunately due to the LOPTx. I remember problems with the high voltage tubular ceramic capacitors though they often show their distress when faulty. The boost capacitor occasionally went s/c. I can't remember for certain what part of the LOPTx was the most troublesome, was it the primary or the EHT overwind, I seem to think the primary failed more often. If the overwind is faulty, the LOPTx can be dismantled to remove it from the core. Disconnecting it is not enough to prove the point. The line output stage should then run without distress. Alternative arrangements will then have to be devised to obtain the EHT.

If dismantling the LOPTx, look out for any core spacers (thin shims) necessary to avoid core saturation.
As with most valve line output stages, if the line output valve is overheating the valve's screen feed resistor can be disconnected to carry out tests like checking the line drive waveform. It's worth checking the components in the line generator including the ECC82 valve itself. I agree the line drive dc voltage is a little low.
On 405 lines it should be -40V and on 625 lines it should be -50V measured at the control grid of the line output valve (PL504) with an Avo 8 or similar 20kΩ/V meter.

The service information for the 210 series appeared in Radio and Television Servicing 1968/69.

Regards
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Old 3rd Apr 2018, 3:36 pm   #29
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Default Re: Philips G23T210A

Hi

There was also a good servicing article in Television magazine, February and March 1970 by Les Lawry-Johns. The issues can be obtained from http://www.americanradiohistory.com/...n_Magazine.htm

Regards
Symon.
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Old 3rd Apr 2018, 3:59 pm   #30
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Default Re: Philips G23T210A

I’d certainly check the anode load resistors in the ECC82 line oscillator circuit.
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Old 3rd Apr 2018, 4:38 pm   #31
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Default Re: Philips G23T210A

Thanks all for your suggestions. Yes, I'll check the oscillator. I've already substituted the valve and will check the anode load resistors.

Still slightly puzzled that the LOV is passing excessive screen current but its anode isn't even slightly red.

I've heard of the LOPTs reputation in this set - sigh. Yes I know that if its the overwind it will have to be removed if its shorting because that will bead buckets of energy out of the system. One might expect it to get hot/warm if its the problem. I do "play" with switch mode supplies so I am aware of the small discs and their significance. The warning is very well advised so thanks for that Now I'm SURE I have a tripler lying around - somewhere!

As to the tubular caps, I assume they are high voltage types, so I don't have any to hand to try. Can they safely be temporarily un-soldered to see if that reduces the overheating problem?

I'd like to put a scope on the line drive and see what's going on. What should it look like and what sort of amplitude should it be?
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Old 3rd Apr 2018, 5:04 pm   #32
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Default Re: Philips G23T210A

Remove top cap from PY if you get spark with insulated screwdriver from top cap of PL then its either lopt or boost cap, remove boost cap ( or caps if 2 in parallel) if a spark is still present then unfortunately it's usually interwinding short on the lopt, this was a very common occurrence.

Steve
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Old 3rd Apr 2018, 5:05 pm   #33
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Default Re: Philips G23T210A

Thanks Symon for the reference to Practical Television. I remember Les very well. I took Practical Television for many years. In fact I probably have the original magazine for these two date. However I have them all on line now, so I'm looking at it now.

Chas
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Old 3rd Apr 2018, 5:29 pm   #34
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Default Re: Philips G23T210A

Hi Chas.

I have the R&TV service info here and there are oscillograms included. I could send you the scanned info via email attachment if required. I will have to first scan the info. PM if needed.
Re the HV tubular caps, I think one was for 3rd harmonic tuning so don't try the set without it or the voltages in the line output stage may well rise to an excessive level and could cause damage to the LOPTx.

Regards
Symon
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Old 3rd Apr 2018, 5:57 pm   #35
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Default Re: Philips G23T210A

Steve,
When I remove the PY topcap (boost diode) then there is a very tiny spark. The boost capacitor has been replaced.
Was the inter-winding short in the primary or the overwind?
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Old 3rd Apr 2018, 6:44 pm   #36
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Default Re: Philips G23T210A

Hi,

I seem to remember it's an interwinding short on the primary of the LOPT, i also seem to remember there are 2x boost caps in parallel (but could be wrong as my memory is now terrible) if so check both, best to just remove them and try the set with the PY top cap removed , you should have nothing at all on anode of PL but don't leave it on too long as screen resistor will overheat.
any volts or spark from PL anode with boost cap (s) removed and its probably the LOPT

other than LOPT troubles these were great set's ,

Steve

Last edited by steve1010uk; 3rd Apr 2018 at 6:46 pm. Reason: old age
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Old 3rd Apr 2018, 8:57 pm   #37
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Default Re: Philips G23T210A

I agree its a nice set, though I confess to being biased! I'm a great fan of Philips stuff and have loads of it. G6 (single standard version) a couple of G11s, two 17TG100s (one restored).

OK, the result of removing the boost capacitor was, to my BIG surprise a HUGE spark on the PL500 anode AND EHT (as in a raster on the screen). OK the raster wasn't the right size or anything.

So, if you are right that means shorted LOPT. Suppose it couldn't be something else shorting part of the LOPT? There are some tubular capacitors...

Maybe something the boost HT supplies is loading if. I know it goes to the frame TB.
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Old 3rd Apr 2018, 9:03 pm   #38
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Default Re: Philips G23T210A

Hi Chas,
It does sound horribly like the LOPT If the heater of the EHT rectifier doesn't light, it's a fair indication that there is not much RF energy in the transformer.
You could knock up a simple tester to test the LOPT out of circuit. I did, and found it really useful. In fact, one LOPT that I was sure had shorted turns proved to be fine when tested!

Have a read through this thread https://www.vintage-radio.net/forum/...d.php?p=950097 The results I got on the scope with good transformers are shown in post 15. Placing a shorted turn round the transformer killed the ringing completely.
Granted, I didn't test any dual standard or 625 only transformers, but I would assume it would work the same.
By increasing the frequency of the applied square wave to 10Khz, you can get an idea whether the overwind will generate any volts!!
If you've got a square wave sig gen, you can even dispense with the 4001 logic chip!!
Hope that might help,
Best of luck
Nick

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?
Cheers
Nick

Last edited by 1100 man; 3rd Apr 2018 at 9:12 pm. Reason: more text added
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Old 3rd Apr 2018, 9:16 pm   #39
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Default Re: Philips G23T210A

Hi.

I own the single standard version G20T306 (300 chassis) that was working very well when last tested about 18 months ago. The line output transformer is the same as in the 210 chassis so I should be able to take a few readings around the line timebase to compare with the 210 chassis set to 625 lines.

Also regarding an interwinding short in the primary winding, then I think it should show up on some cold resistance checks. The service info quotes the resistance readings. I could make some comparitive checks on the windings of my LOPTx if that helps.
I was lucky to find a NOS LOPTx at our local car boot sale which was in a box of old junk, a lucky find but haven't yet had cause to test it. In any case I'd want to make sure it's thoroughly dried before risking it.

Regards
Symon
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Old 3rd Apr 2018, 9:20 pm   #40
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Default Re: Philips G23T210A

Hi Nick,

I'm aware of the various dynamic tests that can be done on a LOPT. I play with switch mode PSUs which have a lot in common with what's going on in a line output stage. I even went as far as designing a SMPS to produce 5V at a couple of amps from the mains! I made a couple of them.

Yes I've got a 50Mhz dual output sig gen so no problems there. The real problem is that I can't really think its anything other than a shorted primary.

Any guidelines as to rewinding it! No, I'm not joking. One of the main reasons I designed my 5V SPMS was because I H A T E winding coils. Now with a switch mode supply the number of turns is seriously small (except for the overwind). Quite easy really to wind - if you can find how many turns each coil is. Now if we know the wire SWG and can measure its resistance, a fair estimate of the number of turns could be made. I'd aim to try to disassemble it and confirm by counting but it looks heavily encapsulated.
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