UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV 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 14th Sep 2011, 7:31 pm   #121
murphyv310
Dekatron
 
murphyv310's Avatar
 
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,420
Default Re: Restorers dream part 2 the chassis.

John.
I am ready to be removed to A&E by ambulance as I have as far as I know broken all my ribs with laughter at your post.
Brilliant
__________________
Cheers,
Trevor.
MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member
murphyv310 is offline  
Old 14th Sep 2011, 8:29 pm   #122
Retired
Heptode
 
Retired's Avatar
 
Join Date: Mar 2009
Location: Fenay Bridge, Huddersfield. UK.
Posts: 673
Default Re: Restorers dream part 2 the chassis.

Hi,

Firstly I'd like to say a huge thank you to Jeffrey for the two U25 valves he so generously gave me; they arrived safely at dinner time today; thank you Jeffrey.

Oh dear John I almost fell from my seat with tears in my eyes; many thanks for the surgical gloves offer; I do need medical help though because every time I take a project on I live in virtual reality until it is completed; am I normal?

I did say that I'll be asking silly questions and I'm pleased to receive such cheerful answers. The reason I checked to see if there was any voltage on the ion trap is that it was abutting a metal cover and I know only too well what it feels like to get an high voltage shock; I've had enough whilst working on vehicles and banged my head on a number of bonnets over the years after coming into contact with HT.

Meanwhile now that I can see again back to the plot. I've now fitted a new U25 and can say for certain it is working as it is giving 1" long "lightning" to the screwdriver and is also now glowing red inside the AC end.

I shorted out the cathode and grid1; turned the brightness right up but still no raster and I've just left the workshop where it is now quite dark. I also turned and slid the ion trap without surgical gloves to many positions but it made no difference whatsoever. There is a distinct whistle and lots of noise through the speaker; also turning the channel selector produces noise in the speaker.

I'll continue tomorrow and Mike Phelan has kindly offered to pop over on Friday afternoon so it had better light up tomorrow or I'll set Mike onto it. Thanks John for the laugh.

Kind regards, Col.
Retired is offline  
Old 14th Sep 2011, 9:04 pm   #123
Heatercathodeshort
Dekatron
 
Heatercathodeshort's Avatar
 
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
Default Re: Restorers dream part 2 the chassis.

Hello Colin,
This is rather odd! The Mazda CRM172 is a very good tube and will always give a raster even if a bit low which is rare. You certainly have EHT if the U25 is lighting. Listen very carefully to the line whistle and see if it alters when you adjust the brightness control particularly at near maximum setting. If it changes very slightly the tube is drawing current and must show some sort of illumination on the screen. Remove your cathode / grid short for this test.This is not a foolproof test but is one that is picked up with experience. Try reducing the brightness setting to say 3/4 and adjusting the ion trap again. Too much beam current can overload the EHT supply causing blackout. Very odd. John.
Heatercathodeshort is offline  
Old 14th Sep 2011, 9:34 pm   #124
murphyv310
Dekatron
 
murphyv310's Avatar
 
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,420
Default Re: Restorers dream part 2 the chassis.

Hi Colin.
In addition to HKS's advice, there are two things that come to mind, 1, the Cathode of the CRT is O/C and no amount of shorting grids to cathodes will help.
2, You now need to ascertain the CRT has emission, If you don't have an EHT meter you can insert a microamp meter in series with the cathode, upping the brightness should increase the cathode current, if this increases then you should have a raster and adjusting the ION trap should result in said raster.
No increase in cathode current on upping the brightness would suggest an O/C cathode or very low CRT. shorting grid to cathode of the tube should show some current on the meter but nothing denotes a duff tube.
__________________
Cheers,
Trevor.
MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

Last edited by murphyv310; 14th Sep 2011 at 9:45 pm. Reason: Wrong name, silly me!
murphyv310 is offline  
Old 15th Sep 2011, 12:40 am   #125
AC/HL
Dekatron
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
Default Re: Restorers dream part 2 the chassis.

Once again it's a long time since I worked on an ion trap tube set (no, a very long time!).
Is the magnet still a magnet, and if so, is it on the tube the right way round, ie. bending the beam the right way to clear the trap?
AC/HL is offline  
Old 15th Sep 2011, 5:50 am   #126
Al (astral highway)
Dekatron
 
Al (astral highway)'s Avatar
 
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
Default Re: Restorers dream part 2 the chassis.

Quote:
Originally Posted by ppppenguin View Post
There are folk down south of the Watford Gap who are on tenterhooks
Yes, including some 'lurkers!' Finding this progess fascinating and tantalising and I'm learning a lot without even doing the restoration!
__________________
Al
Al (astral highway) is offline  
Old 15th Sep 2011, 7:01 am   #127
Heatercathodeshort
Dekatron
 
Heatercathodeshort's Avatar
 
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
Default Re: Restorers dream part 2 the chassis.

Quote:
Originally Posted by ppppenguin View Post
There are folk down south of the Watford Gap who are on tenterhooks
I'm thinking of doing the 1936 Jarrow march in reverse! Yes Trevor, must admit the thought of an O/C cathode connection with the CRM172 never entered my head. This was usually reserved for later tubes such as the CME1901 but it is a possibility with this one. Even if the tube is duff I'm sure we can find one that will be suitable but at the moment we can put that on hold until we have exhausted all possibilities. I would imagine the breakdown of the LOPT was the original cause of the receiver being laid up, let's hope so. Regards, John.
Heatercathodeshort is offline  
Old 15th Sep 2011, 8:45 am   #128
Andrewausfa
Octode
 
Andrewausfa's Avatar
 
Join Date: Dec 2010
Location: St Ives, Cambridgeshire, UK.
Posts: 1,180
Default Re: Restorers dream part 2 the chassis.

And b'twixt the Watford Gap and Huddersfield errr...Gap as well. I agree with Mr Astral, this is very educational for even those of us that don't do TVs.

Andrew
__________________
Invisible airwaves crackle with life. Or they should do.
BVWS Member
Andrewausfa is offline  
Old 15th Sep 2011, 9:17 am   #129
ENGLISH VICTOR
Hexode
 
Join Date: Feb 2008
Location: Sydney, Australia
Posts: 356
Default Re: Restorers dream part 2 the chassis.

I am going to follow up on Trevor's idea and suggest you clip your DVM cross the 220K resistor that is in series with the CRT cathode (pin 11) positive lead to the cathode, there is a 0.1uF in parrallel with it. The voltage read will indicate the beam current of the CRT, 10Volts will equate to roughly 44uA enough to produce quite a bright raster. If no voltage can be read with the brightness turned up check the operating voltages on the crt base if they are correct suspect the tube has gone to heaven. Hopefully this is not the case. The only reason I suggest this is because you don't need to remove any leads from the tube socket. I imagine the voltage on A1 is present at around the same voltage as the boost H.T. supply, it is vital, no voltge there will result in no beam current and a black screen.
It is possible of course that the 220K resistor has gone O/C this would produce the same effect if the 0.1uF cap has very low leakage, the tube would be biasing itself to almost cutoff.
All the best Victor.
P.S I suppose if the centering mechanism is way off adjustment it could prevent the ion trap from being able to align the beam, just grasping at straws. At this stage DON'T touch it. I have never come across the problem.
ENGLISH VICTOR is offline  
Old 15th Sep 2011, 9:53 am   #130
Retired
Heptode
 
Retired's Avatar
 
Join Date: Mar 2009
Location: Fenay Bridge, Huddersfield. UK.
Posts: 673
Default Re: Restorers dream part 2 the chassis.

Hi,

Thank you everyone for your comments and information.

I was wide awake in bed at 3.50 this morning and up before 7.0 so this is getting very interesting.

I've very generously been offered the loan of an EHT probe by a member and already replied thanking him hoping that it won't be needed because I have back up tomorrow afternoon as Mike Phelan will be visiting us and Mike like many of you is a top guy having worked on these sets many years ago so I'm sure Mike will either bump start it or declare the CRT is not working.

I've just spent about an hour in the workshop trying out the various suggestions kindly offered.

The ion trap magnet locks onto a screwdriver so retains magnetism? I notice only one end of the holding clip has insulation added the other being bare metal? I've also turned the magnet over wondering if N&S would make any difference.

I tried backing off the brightness control and the line whistle appears strongest about mid way but I've now listened to it for so long all I can hear is line whistle. I did this with and without the short between cathode/g1.

I must confess that when I first heard the term "first light" I actually expected to see snow on the screen as I remember seeing similar sets when they were new as a kid and they always seemed very sensitive to aerial position.

Whilst in the workshop yesterday I remembered the post by Andy explaining that a certain resistor could black a screen out and out of curiosity I was looking at the two 1/4W carbon resistors on the side of the coils fitted to the tube and I think I read something like 117V across them; when I tried to take resistance readings I could only obtain between 8 and 9 ohms each but obviously this is a wrong reading as I didn't snip one end of each. This is what woke me up last night as it was running through my head but following your expert advice I'm now sure that even if these two resistors were out of spec something would have shown up on the screen? I can feel this chassis talking to me saying come on you fool the problem is staring you in the face!!

I even removed the earthing lead from the CRT coating to chassis; if this coating retains a high voltage immediately after switch off I've never seen tiny sparks as I've discharged it through a resistor to the workshop earth?

I don't know if it would help but Dom very kindly sold me an Aurora very cheaply a while ago; its a model SCRF-405A; as yet I don't even know how to connect it but would this determine if the CRT is actually working if I hooked it up?

I think winter is already here as I felt perished leaving the workshop this morning; I was so focussed on this chassis that I forgot to switch the fan heater on. Some-things got to give and it won't be me.

Kind regards, Col.
Retired is offline  
Old 15th Sep 2011, 10:03 am   #131
Retired
Heptode
 
Retired's Avatar
 
Join Date: Mar 2009
Location: Fenay Bridge, Huddersfield. UK.
Posts: 673
Default Re: Restorers dream part 2 the chassis.

Hi,

Many thanks for the information Victor; both the 220K resistor and 0.1cap are new. I will indeed take a reading.

Please bear in mind that I completely removed all the coils from the CRT so "centering mech way off" possibly? How do I check?

I've quickly checked the voltage across the 220K resistor with the brightness set at full and it reads 44V with and without the cathode/g1 shorted.

Kind regards, Col.

Last edited by Retired; 15th Sep 2011 at 10:29 am.
Retired is offline  
Old 15th Sep 2011, 10:55 am   #132
murphyv310
Dekatron
 
murphyv310's Avatar
 
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,420
Default Re: Restorers dream part 2 the chassis.

Hi Colin.
44v across the 220K seems rather on the high side to me and that could well make the CRT conduct far too heavily thus damping the EHT.
Try reading again across the 220k and reduce the brightness level and see if the voltage drops, as Victor says aim for about 10v, If you get this voltage try adjusting the ion trap again and see if you get any brightness on the screen.
__________________
Cheers,
Trevor.
MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member
murphyv310 is offline  
Old 15th Sep 2011, 12:17 pm   #133
Tazman1966
Nonode
 
Tazman1966's Avatar
 
Join Date: May 2006
Location: St Albans, Herts, UK.
Posts: 2,193
Default Re: Restorers dream part 2 the chassis.

Quote:
Originally Posted by ppppenguin View Post
There are folk down south of the Watford Gap who are on tenterhooks
With me being one of them. Surely not far now?
__________________
All the very best,
Tas
Tazman1966 is offline  
Old 15th Sep 2011, 12:21 pm   #134
dominicbeesley
Octode
 
dominicbeesley's Avatar
 
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
Posts: 1,885
Default Re: Restorers dream part 2 the chassis.

Hi Col, don't lose patience we're nearly there...

Sounds like there won't be an o/c cathode if there is that much juice flowing through the 220k resistor unless it is shorted to the heater? Anyway doom and gloom scenarios aside it probably isn't that! Does that voltags go up and down as you vary the brightness. This will tell us if the electron gun is firing and electrons are making it to ir past the grid...

Make sure you reconnect the CRT earthing (and the metrosil while you're at it) they won't hurt... but a bite off the CRT rim band would!

Can you get a spark (same procedure as the DC end of U25) at the anode cap of the CRT....It could be something as daft as an open circuit anode lead...?

The "first light" is not anything as exciting as snow. On these old sets the RF gain is pretty low so you probably won't see snow, if you do it will only be with the sensitivity turned right up and all the RF stages working flat out. What you will see is something akin to a blank screen between scenes on normal TV. So you should be able to see something but it may be faint. Whacking the brightness up will make it brighter but it will still just be a blank grey or white picture.

This is why when adjusting the ion trap you should not be looking at your hands but the screen and give it plenty of wiggle! Starting right at the crt base and forwards and backwards try all the different permutations of angle - the first time you see anything all you might get is a very faint brightening of the screen. If you don't like back and forth round and round you can do round and round back and forth (i.e corkscrew the iontrap) until you find where it wants to be, just be careful doing that as it is all too easy to touch the CRT connections which will make you jump!

Connecting the aurora is dead easy: you connect the RF output (marked on the box) using one of those F-connectors (I think) I gave you via a length of coaxial cable to the aerial input. I don't know what type of connector is on this set but it will be sufficient to get started to just connect the centre of the RF out to the aerial to get something.

Plug in to the mains via a wall wart the little red led will flash on and off letting you know it is playing a test card, if it glows on and off slowly it means it has gone to sleep and you need to turn off and on again to wake it up. You can then try all the different channels on the aurora using the little channel change switch (a rotary blue and white thing) until you get sound or picture. I left the aurora with a narrow Test Card C and 1kHz tone as the test card...At least that will be something like progress while we track down what's up with the picture!

Dom
dominicbeesley is offline  
Old 15th Sep 2011, 12:23 pm   #135
ppppenguin
Retired Dormant Member
 
ppppenguin's Avatar
 
Join Date: Dec 2003
Location: North London, UK.
Posts: 6,168
Default Re: Restorers dream part 2 the chassis.

The Aurora won't make any difference at this stage. Won't do any harm though and you may get a glimpse of test card at first light if you're very lucky. You may well get test tone now since the sound side is likely to be working. Assuming your Aurora isn't one of the very early ones which didn't have tone
ppppenguin is offline  
Old 15th Sep 2011, 1:57 pm   #136
ENGLISH VICTOR
Hexode
 
Join Date: Feb 2008
Location: Sydney, Australia
Posts: 356
Default Re: Restorers dream part 2 the chassis.

Col, I can't remember what the picture centering arrangements are on your set as I have not seen one for about 45 years. I suspect if you returned the deflection coils etc. to their original positions you wont be far off. I seem to remember a couple of cheese head 2BA or 4BA screws on the rear of the focus assy may have had something to do with picture centering. I am sure there are plenty on this forum who will know.
I changed a few tubes on this model and don't recal a problem. The test with the grid and cathode shorted together is not a valid test to measure tube emission, the voltage with no short circuit should vary with the setting of the brightness control, if it does not perhaps the grid 1 voltage is not varying, it may be the brightness control is faulty or one of the resistors on th low voltage side of it is faulty, G1 pin2 should vary from about 70V to about 140v at maximum brightness. Expect about 14KV of EHT. check the voltage at the slider of the brightness control, it should be as I mentioned for the G1 voltage.
Victor.
ENGLISH VICTOR is offline  
Old 15th Sep 2011, 2:47 pm   #137
Retired
Heptode
 
Retired's Avatar
 
Join Date: Mar 2009
Location: Fenay Bridge, Huddersfield. UK.
Posts: 673
Default Re: Restorers dream part 2 the chassis.

Hi,

I've just come out of the workshop with a running nose and crying because I've laughed until it hurt and I'm even having trouble typing this as I'm seeing double with tears running down my cheeks.

Please; please; anyone with a weak heart kindly sit down whilst I pass on what has happened.

Mike Phelan sent me an email as usual this morning and he casually mentioned that if the CRT was working at all it would make the hairs of my hand stand on end if placed near it; well this CRT was dead to the world regarding EHT.

As you know I've played around with it for hours following your excellent advice to the letter; The electricity company must be sick of me switching it on and off so many times but all to no avail.

I had a spark between my ears during dinner and wondered why I couldn't obtain first light even though everything was screaming at me that it should be lit up like the Blackpool illuminations.

Hands up all those who very wisely informed me that this set would work very well without the Metrosil and that I could remove it. Two leads go into one end of the Metrosil terminated at a solder tag which to a novice like me appeared at first glance to be securely fixed to the Metrosil so I went straight to the top of the dumbest class imaginable and simply removed the Metrosil complete with leads and promptly cut off all EHT to the CRT.

In my defence I'm stupid but I did say right up front than I'm a total novice with TV work and please lead me by the hand. Boy it's ages since I laughed until I cried!!

Only when I went into the workshop and really checked the Metrosil did I find that it was slid into a secure clip or socket and this had been obscured by the plastic cover; I only noticed the soldered joint.

The picture below is taken with the cathode/g1 short in place but I've now removed the short and the screen is still well lit up.

This to me is a miracle because to be honest when I first saw this set I thought even if I can restore the cabinet which looked most unlikely I doubted that I would ever get it working especially when looking at the remains of the LOPT housing which had disintegrated.

Yes I made a mistake but in reality I'm pleased with my progress and gaining first light hasn't really taken too long. I now need to get the test card on display and would again please ask for your continued support and patience in leading me through this procedure.

I'm truly overwhelmed by all the help you have given me and what a result.

Kind regards, Col.
Attached Thumbnails
Click image for larger version

Name:	First light..jpg
Views:	233
Size:	156.0 KB
ID:	56258  
Retired is offline  
Old 15th Sep 2011, 2:53 pm   #138
dominicbeesley
Octode
 
dominicbeesley's Avatar
 
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
Posts: 1,885
Default Re: Restorers dream part 2 the chassis.

Yay, time to connect up that Aurora!

Dom
dominicbeesley is offline  
Old 15th Sep 2011, 3:23 pm   #139
KeithsTV
Nonode
 
KeithsTV's Avatar
 
Join Date: Aug 2007
Location: South Bradford, West Yorkshire, UK.
Posts: 2,571
Default Re: Restorers dream part 2 the chassis.

It's looking good so far. Looks like the scan coils need adjusting but definitely promising. As Dom says connect up the Aurora and lets see a picture.

Keith
KeithsTV is offline  
Old 15th Sep 2011, 3:24 pm   #140
ppppenguin
Retired Dormant Member
 
ppppenguin's Avatar
 
Join Date: Dec 2003
Location: North London, UK.
Posts: 6,168
Default Re: Restorers dream part 2 the chassis.

Did everyone put their hands up as requested?


Why, you might ask.


wait for it.........



Because many hands make light work!

Go and have a to celebrate.

Last edited by ppppenguin; 15th Sep 2011 at 3:34 pm.
ppppenguin is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 8:38 pm.


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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.