UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Closed Thread
 
Thread Tools
Old 11th Jan 2017, 2:17 pm   #41
Argus25
Heptode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 783
Default Re: Bush TV22 Mk 1

Quote:
Originally Posted by KeithsTV View Post
Once you have EHT if there is nothing visible on the screen briefly connect the CRT cathode to ground via a resistor of around 10k to 47k. If all is well the screen should light up.
Liam,

The reason for above is that the polarity of the video detector diode drives the video output tube grid positive, that is when the TV station RF carrier is received. This increases the video output tube's plate current and so the plate voltage drops, which takes the CRT's cathode more negative with respect to its grid (as does adding the temporary shunt resistor) This increases the CRT's beam current. So with no RF carrier the CRT beam can be cut off, out of range of the brightness control which takes the grid in the positive direction to get beam current and light up the CRT.

The raster looks compressed at the bottom, usually a sign of poor emission in the vertical output tube, or out of spec R's and C's in that stage. Or it might have a combination of off center beam alignment and low amplitude (height). Check the vertical running frequency.

(I think I mentioned that if the set is powered before the full restoration of componentry R's and C's etc and a set of trial nos tubes, there can be a few faults to chase down).

It is good to see the CRT light up, well done.

Many vintage CRT's have ion spots sometimes called ion burns. This is really ion contamination & de-activation of the phosphor. Non-aluminized phosphor is vulnerable to this effect. The reason the ion spot is in the center is that the negative ions have a higher mass and are deflected less than the electrons in magnetic deflection systems. Ion trap magnets help to minimize ions in the electron stream but they are not 100% effective. Aluminized screens solved this problem.

(In electrostatically deflected tubes ion damage to the phosphor wasn't as noticeable because ions are deflected in that case on the basis of their charge, not mass, so they get deflected the same as electrons).
Argus25 is offline  
Old 11th Jan 2017, 2:55 pm   #42
Voxophone
Hexode
 
Voxophone's Avatar
 
Join Date: Oct 2015
Location: Sunderland, Tyne and Wear, UK.
Posts: 314
Default Re: Bush TV22 Mk 1

wd40addict - Thanks I'll give that a try. I'm not sure what the set is tuned to. The tuning knob at the rear is missing and has been broken off at some stage, although the stump is still there and the core seems to screw in and out. The gauge alongside is numbered 1-5.

Argus25 - I'm fairly sure the compression of the raster is due to my camera. It was mounted on a tripod and I only lit up the screen long enough to take the photo. The exposure was about 1/60 I think. I took a few others and I think they showed the bottom as ok. I'll check through them and make sure.

Regarding the EHT: does the presence of a raster confirm that it is present? So far I can't get a spark from the CRT or PL38 after switch off. I also cant be sure the EY51 is lit as it's fossilised under pitch. I do see a faint glow, but it could be a reflection of the PL38 heater.

Last edited by Voxophone; 11th Jan 2017 at 3:10 pm.
Voxophone is offline  
Old 11th Jan 2017, 4:29 pm   #43
HamishBoxer
Dekatron
 
HamishBoxer's Avatar
 
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 5,304
Default Re: Bush TV22 Mk 1

You certainly have EHT with a raster.EY51 do not glow that bright or should not!
__________________
G8JET
HamishBoxer is online now  
Old 11th Jan 2017, 9:30 pm   #44
Argus25
Heptode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 783
Default Re: Bush TV22 Mk 1

Quote:
Originally Posted by Voxophone View Post
Argus25 - I'm fairly sure the compression of the raster is due to my camera.
That sounds good, sometimes camera shots will give a false impression of the raster or TV image with a grey or dark wide band as part of the raster gets under exposed.

All the light you see from the phosphor comes from the scanning electron beam which gets its energy from the EHT supply. The fact the raster is good in width also indicates the line output stage is fine and normal height means the vertical output is fine and the HT must be good too. So seeing a good raster checks multiple parts of the TV's system (except the radio frequency stages and sync separators).
Argus25 is offline  
Old 13th Jan 2017, 9:49 am   #45
Voxophone
Hexode
 
Voxophone's Avatar
 
Join Date: Oct 2015
Location: Sunderland, Tyne and Wear, UK.
Posts: 314
Default Re: Bush TV22 Mk 1

Quote:
Originally Posted by wd40addict View Post
Most old school service generators had a fixed AM setting of 400Hz at 30% modulation depth. Turn this on and sweep freq around 45MHz and you should see something on the screen.

Sweep around 41.5MHz and you should hear the tone.

Note the above frequencies assume your TV22 is set to London Ally Pally frequencies.
I tried the above with the sig gen connected to the aerial terminals on the r.f. deck via a dummy aerial pad I made for radio work. So far I can't get any response from video or audio. There are still about 4 wax capacitors in the r.f. deck so I'm focusing on replacing those and checking the remaining resistors for now.

Once all components have been checked I'll revisit it and do some voltage checks signal tracing. Hopefully the tuner is ok despite the missing knob.
Voxophone is offline  
Old 13th Jan 2017, 10:56 am   #46
KeithsTV
Nonode
 
KeithsTV's Avatar
 
Join Date: Aug 2007
Location: South Bradford, West Yorkshire, UK.
Posts: 2,043
Default Re: Bush TV22 Mk 1

Do you know which region this TV was set up for? If it's from the North West it wouldn't respond to a 41.5MHz signal. Try sweeping the sig gen from 41MHz to around 70MHz. If the RF side is working you should get some response at some frequency in that range.

The sound channels are 48.25MHz (ch2) 53.25MHz (ch3) 58.25MHz (ch4) and 63.25MHz (ch5).

When I did my TV22 I replaced all the wax paper caps plus the 25uF electrolytic on the RF chassis and the two 2uF electrolytics on the main chassis before switching on. I had no raster on the screen until I connected the Aurora. Then it was a case of adjusting the controls to get the correct height, width and linearity and focus. I didn't replace any of the resistors as they appeared to be OK.

The fact that you have a raster, albeit distorted, on the screen is very encouraging as it shows the timebases and tube are OK.

The 16uF electrolytic C25 can cause problems with apparent ghosting and displacement at the top of the screen if it fails. It didn't reform well on mine. I fitted a 10uF cap in its place.

I don't think it will be too long before you have it up and running.

Keith
KeithsTV is offline  
Old 13th Jan 2017, 11:17 am   #47
Voxophone
Hexode
 
Voxophone's Avatar
 
Join Date: Oct 2015
Location: Sunderland, Tyne and Wear, UK.
Posts: 314
Default Re: Bush TV22 Mk 1

Quote:
Originally Posted by KeithsTV View Post
The 16uF electrolytic C25 can cause problems with apparent ghosting and displacement at the top of the screen if it fails. It didn't reform well on mine. I fitted a 10uF cap in its place.
Is that the 16uF smoothing capacitor under the main chassis? My Trader calls this C63 but it's the Mk1 version so the numbering may be different. I haven't checked it yet, though there seems to be almost no hum on the speaker so smoothing should be working fairly well.
Voxophone is offline  
Old 13th Jan 2017, 3:15 pm   #48
KeithsTV
Nonode
 
KeithsTV's Avatar
 
Join Date: Aug 2007
Location: South Bradford, West Yorkshire, UK.
Posts: 2,043
Default Re: Bush TV22 Mk 1

Yes it's C63 on the trader sheet but C25 in the Bush manual. It decouples the supply to the Line oscillator and the RF chassis. If it fails there is interaction between the two causing the problems I mentioned. I'd wait until you get a picture before you check it.

Keith
KeithsTV is offline  
Old 16th Jan 2017, 9:31 am   #49
Voxophone
Hexode
 
Voxophone's Avatar
 
Join Date: Oct 2015
Location: Sunderland, Tyne and Wear, UK.
Posts: 314
Default Re: Bush TV22 Mk 1

I did more testing on the TV22 over the weekend and managed to get a signal through using the method suggested.

The problem which prevented it working initially seems to have been the contrast control on the r.f. deck. When taking voltage measurements I noticed that the cathodes of the first and third EF91s were measuring more than double the Trader voltage. Since the contrast control is in the cathode circuit I tried turning it, and found that at one extremity the correct voltages were restored and interference could be heard from the speaker. I’ll have to examine the contrast pot again to see what the problem may be.

With the above problem discovered, I was able to get tones from the speaker and lines from the CRT using the sig-gen, and to confirm the operation of the tuner despite the missing knob. The various picture controls seem to work mostly ok, however I noticed that as the height control is moved towards its upper extremity a low frequency mechanical sound can be heard. At one point I also heard a spark but did not see where it came from. Can anyone shed any light on what might be causing this?

All wax capacitors have now been replaced on both decks. Aside from figuring out the contrast problem and replacing the brightness and volume pots, it seems there is little more I can do now until I can get hold of an Aurora.
Voxophone is offline  
Old 3rd Feb 2017, 10:02 am   #50
Voxophone
Hexode
 
Voxophone's Avatar
 
Join Date: Oct 2015
Location: Sunderland, Tyne and Wear, UK.
Posts: 314
Default Re: Bush TV22 Mk 1

I'm hoping to pick this restoration up again this weekend as I've now received the Aurora! Fingers crossed I can get a good picture.

Regarding connection of the Aurora to the TV22: what method do people generally use? The instructions recommend a balun and an isolation transformer for live chassis sets, but I've read in other threads that some people do not bother with the balun. I also don't have an isolation transformer at the moment.
Voxophone is offline  
Old 3rd Feb 2017, 11:31 am   #51
KeithsTV
Nonode
 
KeithsTV's Avatar
 
Join Date: Aug 2007
Location: South Bradford, West Yorkshire, UK.
Posts: 2,043
Default Re: Bush TV22 Mk 1

While I was working on my TV22 I used an isolation transformer and connected the Aurora directly to the aerial input. As it is a ""live" chassis TV the aerial input is isolated.

Now when I use it I don't bother with an isolation transformer and the Aurora is connected directly to the aerial input.

I'd just ensure that the mains input is connected correctly with neutral to chassis but do check the capacitor between the aerial input and the chassis is not leaky.

Keith
KeithsTV is offline  
Old 4th Feb 2017, 9:57 am   #52
Voxophone
Hexode
 
Voxophone's Avatar
 
Join Date: Oct 2015
Location: Sunderland, Tyne and Wear, UK.
Posts: 314
Default Re: Bush TV22 Mk 1

I've done my first test with the Aurora. I connected it to the aerial terminals via two 0.1 uF capacitors to be safe DC wise.

After some fiddling with the controls I was able to get Test Card C on screen. To me it seemed that the picture was not best quality. I'm also not familiar with the correct way to use the controls for picture adjustments. While I was able to get a symmetrical, centred image, I'm not sure if I compensated for lack of height excessively using the controls.

The signal was on Ch1 and came in at two points on the tuning control: one with better picture quality but no sound except a low hum (even with a video/sound source); the other with half-decent sound but poor picture and heavy 'sound-on-vision' interference.

It's difficult for me to set the tuning control accurately as the knob is missing on this set. At some point I'll have to track down a replacement.

Testing with a video signal proved to be an interesting experience. I hadn't realised how few analogue sources were left in my house nowadays. In the end I had to use an original Xbox! Definately not easy to play a first person shooting game on the little 9" screen, with the gunshots distorting the image due to sound-on-vision

So it seems there are still some problems to sort out: including the contrast knob which cuts off the signal. I'll hopefully do more testing today and this time post some pictures.

Cheers

Liam
Voxophone is offline  
Old 4th Feb 2017, 11:16 am   #53
Freya
Octode
 
Freya's Avatar
 
Join Date: Jan 2009
Location: Falmouth, Cornwall, UK.
Posts: 1,228
Default Re: Bush TV22 Mk 1

You really don't need to worry about the capacitors on the input and these will be attributing to the poor picture and even sync issues, assuming you have the mains plug correctly oriented with neutral to chassis. C2 the 500pF is protecting already.

The tuning control should be completely at one end fully clockwise. There is a little pointer that lines up with the mark on the plate assuming it still there.
__________________
Stephen
________________________

"It`s only an old telly"

Last edited by Freya; 4th Feb 2017 at 11:22 am.
Freya is offline  
Old 4th Feb 2017, 4:29 pm   #54
Voxophone
Hexode
 
Voxophone's Avatar
 
Join Date: Oct 2015
Location: Sunderland, Tyne and Wear, UK.
Posts: 314
Default Re: Bush TV22 Mk 1

Thanks. I've tried removing the 0.1 uF capacitors but unfortunately there's no change. I've attached an image of the test card below, along with a picture of the tuning control.

The marker you mentioned appears to be missing along with the knob. I do have the spring, but with nothing to push against the tuning is very temperamental. The test card comes through in two places with the core almost fully in. It also comes through when the core is screwed all the way out.

The test card doesn't look too bad (not that I'm the best judge), however a white vertical line appears superimposed on video signals. The sound is the main problem at the moment.

Edit - added picture of video signal on screen.
Attached Thumbnails
Click image for larger version

Name:	DSC_0026.JPG
Views:	139
Size:	123.8 KB
ID:	136985   Click image for larger version

Name:	DSC_0029.JPG
Views:	121
Size:	101.7 KB
ID:	136986   Click image for larger version

Name:	DSC_0030.JPG
Views:	128
Size:	113.3 KB
ID:	136988  

Last edited by Voxophone; 4th Feb 2017 at 4:37 pm.
Voxophone is offline  
Old 4th Feb 2017, 6:00 pm   #55
Freya
Octode
 
Freya's Avatar
 
Join Date: Jan 2009
Location: Falmouth, Cornwall, UK.
Posts: 1,228
Default Re: Bush TV22 Mk 1

Looks like your missing some of the shaft and the knob, it could be related to the poor raster you getting. It may be worth asking on the wanted section.
The picture interference limiter must always be fully anticlockwise viewed from rear.
__________________
Stephen
________________________

"It`s only an old telly"
Freya is offline  
Old 4th Feb 2017, 6:19 pm   #56
wd40addict
Heptode
 
wd40addict's Avatar
 
Join Date: May 2009
Location: Stevenage, Herts. UK.
Posts: 503
Default Re: Bush TV22 Mk 1

You may benefit from a bit of attenuation between the Aurora and the TV22.
wd40addict is offline  
Old 4th Feb 2017, 6:57 pm   #57
Voxophone
Hexode
 
Voxophone's Avatar
 
Join Date: Oct 2015
Location: Sunderland, Tyne and Wear, UK.
Posts: 314
Default Re: Bush TV22 Mk 1

A big improvement now. By fiddling with the contrast pot I was able to get rid of the sound-on-vision and display both sound and video clearly. I just watched most of a film on the set and it seemed to perform very well.

The distorted sound turns out to be a loudspeaker problem, as it disappears when the cone is touched. Possibly a loose 'spider' like I had on my DAC90A?
Voxophone is offline  
Old 4th Feb 2017, 7:26 pm   #58
Ian - G4JQT
Heptode
 
Ian - G4JQT's Avatar
 
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 708
Default Re: Bush TV22 Mk 1

Do you have the Trader Sheet, or any TV22 tuning or picture guidance?
Ian - G4JQT is offline  
Old 5th Feb 2017, 4:02 pm   #59
Voxophone
Hexode
 
Voxophone's Avatar
 
Join Date: Oct 2015
Location: Sunderland, Tyne and Wear, UK.
Posts: 314
Default Re: Bush TV22 Mk 1

I have a few manuals for it. Looks like there are some instructions in the Bush one. Now that I've tried the receiver back in its cabinet, the main issue appears to be that the picture is not level in the frame. Looks like I'll need to rotate the CRT. I did notice previously that the scan coils do not lie flat across the chassis deck.

The sound distortion has been largely fixed by re-glueing the speaker spider.

Last edited by Voxophone; 5th Feb 2017 at 4:10 pm.
Voxophone is offline  
Old 5th Feb 2017, 10:39 pm   #60
AC/HL
Moderator
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Idle, Bradford, West Yorkshire, UK.
Posts: 5,643
Default Re: Bush TV22 Mk 1

No point in rotating a round CRT, it's the scan coils that are out of kilter, but they look OK in post 54.
__________________
Bill, BVWS member
AC/HL is online now  
Closed Thread

Thread Tools



All times are GMT. The time now is 11:35 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Copyright ©2002 - 2017, Paul Stenning.