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Old 16th Feb 2018, 4:15 pm   #21
Keith
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Default Re: Bush TV22 restoration

Well, I have some progress to report. I managed to successfully rewind both blocking oscillator and frame output transformers using a hand drill clamped in a vice. I even got the oscillator transformer back in the right way round first time (pure luck)! So I now have my first raster. An AM signal generator at 41.5MHz and 45MHz gives me tone and vision bars respectively so the RF deck seems to be working. Time to have a go at producing some video. I was intending first to try producing composite sync using an Arduino (my programming skills have so far only managed to get an LED to flash!). I also read that it might be possible to use a the video card in a PC configured using the "modeline" tool to produce 405 lines. Any advice would be appreciated.
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Old 16th Feb 2018, 6:14 pm   #22
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Default Re: Bush TV22 restoration

Hi Keith,
That looks a very professional job considering the method used! Did you have some form of turns counter rigged up- tell me you didn't count 3000 turns manually You must feel rather pleased with the result!

There have been various references to standards conversion using a PC in the 'standards conversion' thread. This one in particular https://www.vintage-radio.net/forum/...d.php?t=130716. There are a couple of youtube videos as well showing the results.

Seems an interesting idea and if I had better computer skills, I would be keen to have a go at it.

All the best
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Old 17th Feb 2018, 12:18 pm   #23
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Default Re: Bush TV22 restoration

Thanks Nick,

Yes, I was delighted with the result. Luckily, at 50Hz, the winding capacitances don't seem to be critical. No turns counter - I just divided the turns required by 3.75 (gear ratio) and counted handle turns on the drill. Every 100 turns I made a pencil mark on the bench (rather like ticking off the days in a prison cell, I guess!). It really didn't take long to get to 800.

I shall have a play with the PC video card reconfiguration. If it works it would be a very conveniant way to produce programme material.

My more immediate task is to is to find some suitable rubber packing for the CRT clamps. Whatever was there has completely disappeared
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Old 17th Feb 2018, 12:47 pm   #24
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Default Re: Bush TV22 restoration

Inner tube, self amalgamating tape, the antiscratch tabs off double glazing panels are superb, ask a window man.
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Old 8th Mar 2018, 11:35 am   #25
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Default Re: Bush TV22 restoration

Having now managed to produce some 405 line video from an an old PC (albeit without interlace at present) I'm now able to proceed with the TV22. I'm getting a reasonably bright picture, having adjusted the centring and ion trap magnets but am getting a lot of line tearing/breakup. Looking at the anode of the sync separator I can see random fast noise spikes which I'm assuming are the culprits. If I move the scope probe to the other side of the differentiating capacitor (Trader sheet C26) the problem is considerably reduced, presumably due to the probe capacitance. The noise does not correlate with anything and seems to vary with time/temp. I'm wondering if it might be pickup of corona (not visible) from the LOPT which I haven't yet recoated. Anyone come across this before?
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Old 8th Mar 2018, 4:14 pm   #26
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Default Re: Bush TV22 restoration

Hi Keith.
I think I mentioned that I don't get interlace on my PC setup. Peter's TTL circuit should correct it, now I have a scope I will see if I have more luck with it.
Corona discharge interference was very common on Band I. Are you still feeding your set baseband video?
Does the raster look clean with no input?
Go round bridging the decouplers around the sync sep.

Why is that white bar there on the LHS? is it just the way the image is presented to monitor 2?
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Old 8th Mar 2018, 4:53 pm   #27
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Default Re: Bush TV22 restoration

Hi again Graham,

I can manage with the progressive scan video for now although the 25Hz refresh rate would be a bit wearing on the eyes long term. Also I think the vsync timing is chopping off the bottom of the frame. I'm not sure that Peter's logic circuit would help in this case. I thought it was designed to correct the inverted line pulses in the frame blanking period and add in the half line pulses but I may be mistaken. I'd be interested to know the repetition rate of your vsync pulses. Good test for your new scope!

I'm still injecting baseband video into the grid of the video amp so I'm a bit sceptical about the corona interference theory - maybe it's a bit more than corona! I need to look in the LOPT can in the dark. Anyway, I've ordered some RS anti-corona spray from https://www.in-excess.com/products/r...-lacquer-400ml (RS are out of stock). In the meantime I'll have a go at adding a bit of decoupling - it's almost non-existant on the TV22.

You're correct about the white bar - I haven't figured how to get a full screen image on the second monitor yet.
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Old 8th Mar 2018, 8:50 pm   #28
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Default Re: Bush TV22 restoration

The field rate is 50 not 25


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There is no visible interlace on the TV screen, but alternate fields are different, look at the following sequence of four:

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Old 8th Mar 2018, 10:32 pm   #29
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Default Re: Bush TV22 restoration

Thanks Graham,

Interesting - not a true interlaced waveform as I understand it - no half lines of video (unless they've just been left blank). However, at least you've got 50Hz refresh. I think you are now using a different card and driver though.

No progress today at this end - too much else going on.
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Old 8th Mar 2018, 11:00 pm   #30
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Default Re: Bush TV22 restoration

Quote:
Originally Posted by Keith View Post
I haven't figured how to get a full screen image on the second monitor yet.
Hi Keith,

It depends on your video source. For example I'm using Irfanview for static images and you just need to hit return to switch between full screen and not.
For actual video content I'm using VLC Player and you hit f for full screen mode.

Peter
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Old 8th Mar 2018, 11:08 pm   #31
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Default Re: Bush TV22 restoration

Keith,

It's pretty difficult for you to restore your set without a nice stable known good 405 line signal source.

The three sources I have available are from a Dinosaur standards converter, Richard Russell's programmable testcard generator and The Jon Evans testcard generator (which is a good one to whip up)

I have not tried the Modeline yet, but I intend to.

It might save you some time and a headache if you get or borrow a known good 405 source (preferably with an RF modulator), then get your TV restored, then you can use the TV as a known good 405 line "monitor" to iron out the bugs in the Modeline.

It's hard to tell looking at the screen images what proportion of the problem is coming from the abnormal signal and if any set faults in the TV22 are contributing.

Hugo.
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Old 8th Mar 2018, 11:16 pm   #32
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Default Re: Bush TV22 restoration

Thanks Peter,
I shall have to try Irfanview - currently just using Windows image viewer or whatever it's called. For videos I will try VLC as I'm fairly familiar with it. Also, Graham's suggested Vidblaster X looks interesting.
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Old 9th Mar 2018, 10:30 am   #33
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Default Re: Bush TV22 restoration

You have probably replaced the sync coupling capacitor but your symptoms show one that is typically leaking. Worth a double check.

Failing that it could be your signal that is out of spec. John.
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Old 9th Mar 2018, 11:49 am   #34
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Default Re: Bush TV22 restoration

Thanks for the further replies. I'll check the sync coupling cap, although I've not seen a leaky compression trimmer before. With the extra capacitance of the scope probe after the differentator capacitor, most of the break-up disappears. The remainder at the top is due to the recovery after frame sync which will be the next thing to investigate. The other issue is the loss of the bottom 10% of the frame. I'm guessing that the timing of the vsync is out but I need to use a scope with delayed timebase to have a closer look.

Hugo - I have been offered the loan of a known good test card generator from an amateur radio acquaintance. I shall take this up at the next opportunity.
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Old 9th Mar 2018, 5:17 pm   #35
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Default Re: Bush TV22 restoration

I pleased to report a bit of a breakthough. The random line jitter was not interference due to corona in the LOPT. The cause was actually a wiring error introduced by a previous "repairer". Along with the substitution of the metrosil by a 1N4007, the A1 smoothing capacitor C31 had also been replaced. But instead of connecting it's cold end to 0v, it had been moved two tags along to the junction of C26/C28 i.e. the line sync drive. Correcting this completely removed the random jitter. Next job is sorting out the line tearing/ringing after frame flyback.
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Old 10th Mar 2018, 1:49 pm   #36
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Default Re: Bush TV22 restoration

The picture is looking better all the time. I like your test pattern !
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Old 31st Mar 2018, 7:01 pm   #37
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Default Re: Bush TV22 restoration

I have an interesting "cold" fault on this set. On switch on, after a few days of non-use, I get a low brightness, defocused and offset picture with visible masking (see picture). Refocusing in this condition requires the focus lever to be turned hard clockwise. After about a half hour the problem suddenly disappears, reverting to a bright(ish), centred display again with focus back to normal. The fault remains absent on subsequent switch-ons - even after an overnight period, only returning again after a period of a few days. Is this a low EHT problem (I have no meter), possibly moisture related?
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Old 31st Mar 2018, 8:25 pm   #38
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Default Re: Bush TV22 restoration

Could it be something silly like DC getting into the scan coils from somewhere? That might explain the picture shifting about.
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Old 31st Mar 2018, 8:47 pm   #39
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Default Re: Bush TV22 restoration

Have a good look at the picture centering adjuster. It may be sticking then suddenly releasing. Also check the focus magnet again for any looseness. I would guess it's definitely one or the other. Do not take the focus magnet apart. John.
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Old 31st Mar 2018, 9:30 pm   #40
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Default Re: Bush TV22 restoration

Thanks both,

I don't think it's mechanical - I'm not even touching the set when it suddenly fixes itself although I suppose there could be a change brought about by the CRT heating up (or could it be the CRT gun itself).

DC into the scan coils is worth considering - I should be able to see that on a scope. I've only looked at the line output anode and that doesn't seem to change.
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