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 1st May 2011, 6:17 pm   #21
TriMan66
Pentode
 
Join Date: Jun 2009
Location: Royston
Posts: 116
Default Re: Help with a HMV TV

Hi Chris,

So I replaced the heater loop with no change.
I will take your suggestion of hunting through the circuit until I find something.

regards
Craig
TriMan66 is offline  
Old 1st May 2011, 6:26 pm   #22
oldticktock
No Longer a Member
 
Join Date: Nov 2009
Location: Weardale, UK.
Posts: 1,981
Default Re: Help with a HMV TV

The E.H.T. rectifier valve? it maybe low emission, I know you replaced it but was it a good one?

The symptoms sound familiar to a fault condition I read with regards to low emission E.H.T. rectifier

As soon as the brightness level of the picture is increased instead of becoming brighter the picture will increase in size and eventually disappear, I think you satisfied that criteria earlier in your posts. A test will prove that whilst a pulse potential exists at the anode of the e.h.t. rectifier little or no e.h.t. is present at the heater of cathode, I think you have also satisfied that one, have you another good spare?

Might be nothing but worth a go, I would still also verify voltages to know data and look for discrpancies

Chris

A test you can perform for the rectifier heater, is the scale lamp test. it can be temporarily to the heater supply legs to check that winding is getting what it should negligible voltage between the two leads to the lamp and any wire will do run an ordinary MES lamp holder but the whole affair must be supported to avoid touching chassis. It can be attached with removing the rectifier

Last edited by oldticktock; 1st May 2011 at 6:54 pm.
oldticktock is offline  
Old 1st May 2011, 7:09 pm   #23
Boom
Nonode
 
Boom's Avatar
 
Join Date: Jan 2007
Location: Westbury, Wiltshire, UK.
Posts: 2,451
Default Re: Help with a HMV TV

It seems that someone has been there before you which might well be why the cap' was in the wrong place. Such bodges in a desperate attempt to cure a problem were common. Why diagnose a fault when you can change the circuit?

As the HT is more or less correct and there is no EHT 'blooming' which as OTT says would not cause lack of width I'd say you are getting very near suspect the LOPT time.
__________________
Dave
--------------
A lovely childhood. Just me, my mother and the voices.....
Boom is offline  
Old 1st May 2011, 7:18 pm   #24
oldticktock
No Longer a Member
 
Join Date: Nov 2009
Location: Weardale, UK.
Posts: 1,981
Default Re: Help with a HMV TV

Excuse my poor wording in the bottom of the last post, I was editing but ran out of time.

Chris
oldticktock is offline  
Old 6th May 2011, 12:00 am   #25
AndrewM
Pentode
 
Join Date: Apr 2009
Location: Melbourne, Australia
Posts: 115
Default Re: Help with a HMV TV

Reading over this thread again a few thoughts come to mind.
The Line Out stage is trying to operate but seems to have issues with its operating conditions.
As a start, confirm the voltage on the 6CM5 cathode and screen. These will establish that at least this area is operating correctly and the valve isn't overloaded.
Next, have you tried a replacement 6AL3 damper diode?
Check all connections are correct around the width coil and horizontal linearity coils, someone may have messed about with this area. Ensure all components connected to the boost volts supply are tested or confirmed as working. A leaky capacitor or resistor thats gone high can cause issues here.
AndrewM is offline  
Old 9th May 2011, 1:08 pm   #26
TriMan66
Pentode
 
Join Date: Jun 2009
Location: Royston
Posts: 116
Default Re: Help with a HMV TV

Hi All,

I had the picture below and decided to check the width. The internal slug was stuck, so I pulled it apart and fixed it and replaced it. Unfortunatley, I can't get back to picture below after my repairs!!! I've carfully checked and and it all seems in place. So now I have just barely 1mm of spark form the DY86 (1S2).
TriMan66 is offline  
Old 9th May 2011, 1:46 pm   #27
TriMan66
Pentode
 
Join Date: Jun 2009
Location: Royston
Posts: 116
Default Re: Help with a HMV TV

I pushed the send button too early!!!

I have tried three NOS DY86's (1S2) and three EL36's (6CM5). All high value resistors are within 12% of values. All waxies and electrolytics have ben replaced. Externally, I put 1.4V to the DY86 and it does glow with a similar amount as the one in the set. The "boost" vlotage which says it sould be 650V is 450VDC with 150VAC superiposed on it. The 400V line that goes to pin 3 is 280VDC and quite well smoothed with a 0.22uF cap (new), but low of course.

The EL36 (6CM5) has the following voltages:
Screen is 165V, circuit syas 150V
Grid is -33V, circuit says -32V
Cathode says 0.13V, circuit says 0.14V.
This valve gets really really hot!

HT1, HT1A annd HT2 rails are quite close as stated earlier.

All the wiring around the LOPT has been checked and put back the same as the circuit diagram.

I haven't tried another EY88 (6AL3) yet, but this was NOS.

The cathode of V8 ECF82 (6U8), in the AGC\contrast section is 60V and the circuit says 48V. I didn't think this was related to the low EHT and boost though.

The LOPT does not get warm at all. Someone mentioned it might be time to suspect the LOPT. Is there anyway to test it. Its not getting warm, and does work to soem extent.

Any other suggestions on how to proceed from here would be great.

regards
Craig
Attached Thumbnails
Click image for larger version

Name:	HMV_PictureNoWidth.jpg
Views:	264
Size:	62.7 KB
ID:	50791  
TriMan66 is offline  
Old 9th May 2011, 1:54 pm   #28
ppppenguin
Banned
 
ppppenguin's Avatar
 
Join Date: Dec 2003
Location: North London, UK.
Posts: 6,168
Default Re: Help with a HMV TV

I have NOS boxed EL36 and EY88 if these are needed.
ppppenguin is offline  
Old 9th May 2011, 2:23 pm   #29
Steve_P
Dekatron
 
Steve_P's Avatar
 
Join Date: Sep 2003
Location: Bolton, Greater Manchester, UK.
Posts: 6,634
Default Re: Help with a HMV TV

Is the Horizontal Oscillator (their term) OK. There are two caps in the link to the output valve, one to earth and one in series. Swap them both. Check the anode resistances and the valve itself.

Cheers,

Steve P.
__________________
If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?
Steve_P is offline  
Old 9th May 2011, 3:02 pm   #30
TriMan66
Pentode
 
Join Date: Jun 2009
Location: Royston
Posts: 116
Default Re: Help with a HMV TV

Hi Steve,

The drive to EL36 (6CM5) does looks fine. See post #10 (this was shown at the cathode of the 12AU7). The waveform shape looks good into R106, the grid resistor. C87 4.7nF was a waxy and has been replaced. I haven't replaced or checked C86 a 180pF to ground. I will just check the drive into the grid resistor does go to -170V as in the circuit. This I have not yet checked.

regards
Craig
TriMan66 is offline  
Old 9th May 2011, 3:28 pm   #31
Welsh Anorak
Dekatron
 
Welsh Anorak's Avatar
 
Join Date: Apr 2005
Location: North Wales, UK.
Posts: 6,192
Default Re: Help with a HMV TV

Hi
An overheating PL36 with correct control grid drive (assuming you've changed the caps Steve mentions) means excessive damping in the output stage. That might well mean a shorted turn in the LOPT primary, I'm afraid. The width coil could possibly have a shorted turn, and if so might well be getting warm.
Unfortunately a cool LOPT doesn't necessarily mean it's OK, and the only real test is replacement (yes, I know).
Glyn
P.S. C86 will certainly affect the tuning and hence the width so that's the next logical step.
Welsh Anorak is offline  
Old 19th Jul 2011, 2:04 pm   #32
TriMan66
Pentode
 
Join Date: Jun 2009
Location: Royston
Posts: 116
Default Re: Help with a HMV TV

Hi All,
So the story continues...
I obtained a replacement LOPT.
The chap who sent it to me had to bake his in the oven to remove moisture to retore his set.
So I also baked mine slowly for 2 hours in the oven. Although I haven't re-coated mine with anything else just yet and I'm not sure if this is the cause of any of the problems described below.
But at least things are now getting much better.

regards
Craig
Attached Thumbnails
Click image for larger version

Name:	HMV_TV_LOPT_Pic1.jpg
Views:	253
Size:	76.8 KB
ID:	54132   Click image for larger version

Name:	HMV_TV_LOPT_InOven.jpg
Views:	248
Size:	90.3 KB
ID:	54133  
TriMan66 is offline  
Old 19th Jul 2011, 2:15 pm   #33
TriMan66
Pentode
 
Join Date: Jun 2009
Location: Royston
Posts: 116
Default Re: Help with a HMV TV

The previous issue with the EL36 overheating is not present anymore and the HT1 and HT2 lines are stable within a few volts of their correct values.
The current problem is that the boost volts take over an hour to rise from 450V to 650V.
This has now happened three times.
The pictures below show the TV picture with boost volts at 450V, 550V and 650V, and then the test pattern at 670V. The boost volts then remain at 670V after that. The correct value is 650V.
Pin 3 volts to the tube are a little low at 360V instead of 400V.
I thought I might try another slow baking session. The reason I haven't coated the EHT winding yet, is that I didn't want to do something permament just at the moment.
I'd like to ask people's opinion to see how to resolve this slow rising boost volts issue.

regards
Craig
Attached Thumbnails
Click image for larger version

Name:	HMV_TV_Picture_Boost_450V.jpg
Views:	295
Size:	83.3 KB
ID:	54137   Click image for larger version

Name:	HMV_TV_Picture_Boost_550V.jpg
Views:	275
Size:	88.5 KB
ID:	54138   Click image for larger version

Name:	HMV_TV_Picture_Boost_650V.jpg
Views:	277
Size:	61.0 KB
ID:	54139   Click image for larger version

Name:	HMV_TV_TestPattern_Boost_650V.jpg
Views:	354
Size:	79.5 KB
ID:	54140  
TriMan66 is offline  
Old 2nd Aug 2011, 8:22 pm   #34
TriMan66
Pentode
 
Join Date: Jun 2009
Location: Royston
Posts: 116
Default Re: Help with a HMV TV

Hi,
So I took some more measurements whilst the set was in its "warm up phase". It takes 1 hour 5 minutes to get the boost volts up from 450V to 650V. This is consistent over serveral times watching the TV. I'm having great fun watching the original Pink Panther series again!
The grid drive to the EL36 (6CM5) shown in post #1 is rock steady at -150V instead of -170V. Sheild volts are 171V instead of 150V but don't change during the one hour.
Cathode volts should be 0.14V and are 0.15V and don't change.
HT1 should be 240V and is 244V.
HT2 should be 215V and is 221V.
Neither of these change during the hour.
So I assume the drive to the LOPT is OK.
The pin 3 volts to the picture tube should be 400V and does vary from 290V to 350V, but since this is derived from the boost volts this is not surprising.
It is interesting that whilst measuring this, the contrast on the picture significanlty improves.
Since the LOPT was tried and was working previously, although not out of suspission, is unlikely to be the culprit.
I may try a different selection of valves.
I'm also wondering if there is something loading the boost volts, causing this issue.
regards
Craig
TriMan66 is offline  
Old 4th Aug 2011, 6:48 pm   #35
TriMan66
Pentode
 
Join Date: Jun 2009
Location: Royston
Posts: 116
Default Re: Help with a HMV TV

Hello all,
Thanks to everyone who has contributed. I have appreciated the feedback. I was reading back through all the comments to find the problem.
I re-baked the LOPT. I tried yet another set of EHT valves with no change.
Then I finally found the issue. A dry joint on one of the high meg resistors in the boost section driving the picture tube.
I also increased smooting on the boost volts to reduce the ripple.
Now, I have 550V on start up and within 10 minute its settles to 630V. It is very pleasing to turn on the set and be greeted by a full screen picture which is bright and with good contrast.
On this last point, I added a 6.8M resister from pin 3 of the picture tube to gound. I did this since I noticed the contrast got significanlty better each time I used my DMM to measure the pin 3 volts.
I am using direct video input to the video amplifier and the contrast is used to drive the RF section which I am bypassing and so the contrast controls have no effect.
The next issue to move onto is that the vertical hold keeps losing lock. Hopefully not as difficult as the boost volts.

regards
Craig
Attached Thumbnails
Click image for larger version

Name:	HMV_TV_Picture_BoostVoltsOk.jpg
Views:	220
Size:	85.3 KB
ID:	54690  
TriMan66 is offline  
Old 4th Aug 2011, 7:21 pm   #36
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 7,607
Default Re: Help with a HMV TV

Hi Craig, frame TB lock, usually high value resistors gone higher and leaky (even slightly) caps.
Poor linearity is cathode cap (if used) or tired valve.

Ed
Ed_Dinning is online now  
Old 5th Aug 2011, 10:51 am   #37
TriMan66
Pentode
 
Join Date: Jun 2009
Location: Royston
Posts: 116
Default Re: Help with a HMV TV

Hi Ed,
Thanks for the advice.
It turned out to be an easy fix. I was AC coupling the video directly into the video amp valve using a 0.1uF capacitor. The cut-off was approx 200Hz and reducing the level of the frame sync pulses. I increased the coupling to 3uF and all is in lock now.
So, I'm slowly getting there.

regards
Craig
TriMan66 is offline  
Old 10th Aug 2011, 9:21 am   #38
The teleman
Pentode
 
The teleman's Avatar
 
Join Date: Dec 2007
Location: County Durham, UK.
Posts: 227
Default Re: Help with a HMV TV

Hi Craig, Thanks again for your help with the tv. Ive looked long & hard at your problem with this set ; check the line lin coil & c90 / c91 failing that the only thing is as we said it could be a scan coil fault if the insulation is breaking down (disintegrating ) as you said i would try a replacement first ..Chris
The teleman is offline  
Closed Thread

Thread Tools



All times are GMT. The time now is 7:40 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 - 2022, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.