Flickering picture on Baird dual standard - UK Vintage Radio Repair and Restoration Discussion Forum

lloydwells · 18th Mar 2023, 8:49 pm

I accidentally bought a dual standard Baird a few weeks back 620/640 series chassis I have it up and running and it works brilliantly except the picture on the tube visibly flickers now.ive tried everything I can think of is this a known issue on this chassis has anyone had it before and cured it ? Pic of set attached but you can't see it on the photo.

williamsunique · 18th Mar 2023, 9:12 pm

Flicker? Could you be a little more specific.
Looking at the wavy verticals of the picture on the screen here. Do you mean this wavy picture. This is caused by the large electrolytic capaciter fixed to the chassis. Smoothing block.
The cathode resistor 330ohm? and it's parralel capaciter 100uF? on both the PCL82 (sound) and PCL85 (frame) were common faults. The switch overs would often require cleaning and their associated bowden cable adjusted. The valves in the UHF tuner PC86 and PC88 would often not function in the Winter, engineers would bodge this by increasing the current to them by altering the position of the jumper on the voltage dropper. LOPT failure was a common fault. Where the volume control was sprayed with Genklene (banned now) the UHF tuner plastic drive underneath the volume pot would break with it's softened plastic. This would require replacing and the two drive chords re-strung. Very nice TVs though.

Paul.

lloydwells · 18th Mar 2023, 9:30 pm

No it's a horizontal flickering almost like the frames running a bit slow

williamsunique · 18th Mar 2023, 9:44 pm

Sorry that's not ringing any bells. The LOPT was known to arc around the DY87. I can't remember how line oscillation was achieved in this chassis maybe it was an ECC81. If it was you could check resistors and electrolytics here, eg: screen grid resistor. It was a long time ago since I worked on one. The PL59 and PY801 if faulty just failed, so it doesn't sound as if they are at fault.
I wish I had hung onto the one I owned many years ago.

Paul

slidertogrid · 18th Mar 2023, 9:48 pm

What a nice looking set! Have you tried attenuating the signal ? Could it be AGC flutter? Just a thought... What standard are you using or is it on both ?
Rich.

lloydwells · 18th Mar 2023, 10:25 pm

Hi Rich I initially couldn't get the UHF tuner to work which is apparently fairly common so I tricked it in to running in VHF 625 I now have the UHF running and it does it on both attenuating the signal makes no odds.

Graham G3ZVT · 18th Mar 2023, 11:05 pm

Quote:

Originally Posted by lloydwells

No it's a horizontal flickering almost like the frames running a bit slow

It's difficult to visualise that, "horizontal" and "frame" are normally a contradiction in a TV context.

Could you upload a short video to Youtube or similar?

I'm aware it's sometimes difficult to capture on camera subtle effects that can be seen by eye.

williamsunique · 18th Mar 2023, 11:23 pm

Quote:

Originally Posted by williamsunique

Sorry that's not ringing any bells. The LOPT was known to arc around the DY87. I can't remember how line oscillation was achieved in this chassis maybe it was an ECC81. If it was you could check resistors and electrolytics here, eg: screen grid resistor. It was a long time ago since I worked on one. The PL59 and PY801 if faulty just failed, so it doesn't sound as if they are at fault.
I wish I had hung onto the one I owned many years ago.

Paul

Oops ECC81 is twin triode no screen grid. Forget that.

Paul

1955APREN · 19th Mar 2023, 9:33 am

Please try the anode load resistor to the line oscillator ECC82 , this must be done by fitting substitute . This resistor might measure ok on a meter but can be noisy
It is possible coloured grey. sorry I cannot remember the value.
If you sets is fitted with transistor IF panel there are two caps ( yellow) in colour
near to the video output valve PFL200 these tend to be broken up due to heat
from the valve.
hope this might help.
Derrick

lloydwells · 23rd Mar 2023, 9:36 pm

The set is entirely valve with no PFL200 what I am noticing is that the picture is locked and no amount of sliding the hold pot will make it roll I'm wondering if this has something to do with the issue

williamsunique · 23rd Mar 2023, 11:45 pm

Quote:

Originally Posted by lloydwells

The set is entirely valve with no PFL200 what I am noticing is that the picture is locked and no amount of sliding the hold pot will make it roll I'm wondering if this has something to do with the issue

Sorry your description originally was misleading. Just to be clear are you saying it is a line fault or a frame fault?

Is the frame valve a PCL85/805? If it is change the cathode resistor and electrolytic capaciter. Probably 330 ohm and 100uF in paralell to chassis.

Paul.

18th Mar 2023, 8:49 pm	#1
lloydwells Heptode Join Date: Aug 2016 Location: Dumfries, Scotland, UK. Posts: 536	Flickering picture on Baird dual standard I accidentally bought a dual standard Baird a few weeks back 620/640 series chassis I have it up and running and it works brilliantly except the picture on the tube visibly flickers now.ive tried everything I can think of is this a known issue on this chassis has anyone had it before and cured it ? Pic of set attached but you can't see it on the photo. Attached Thumbnails

18th Mar 2023, 9:12 pm	#2
williamsunique Tetrode Join Date: Feb 2023 Location: Watford, Hertfordshire, UK. Posts: 86	Re: Flickering picture on Baird dual standard Flicker? Could you be a little more specific. Looking at the wavy verticals of the picture on the screen here. Do you mean this wavy picture. This is caused by the large electrolytic capaciter fixed to the chassis. Smoothing block. The cathode resistor 330ohm? and it's parralel capaciter 100uF? on both the PCL82 (sound) and PCL85 (frame) were common faults. The switch overs would often require cleaning and their associated bowden cable adjusted. The valves in the UHF tuner PC86 and PC88 would often not function in the Winter, engineers would bodge this by increasing the current to them by altering the position of the jumper on the voltage dropper. LOPT failure was a common fault. Where the volume control was sprayed with Genklene (banned now) the UHF tuner plastic drive underneath the volume pot would break with it's softened plastic. This would require replacing and the two drive chords re-strung. Very nice TVs though. Paul.

18th Mar 2023, 9:30 pm	#3
lloydwells Heptode Join Date: Aug 2016 Location: Dumfries, Scotland, UK. Posts: 536	Re: Flickering picture on Baird dual standard No it's a horizontal flickering almost like the frames running a bit slow

18th Mar 2023, 9:44 pm	#4
williamsunique Tetrode Join Date: Feb 2023 Location: Watford, Hertfordshire, UK. Posts: 86	Re: Flickering picture on Baird dual standard Sorry that's not ringing any bells. The LOPT was known to arc around the DY87. I can't remember how line oscillation was achieved in this chassis maybe it was an ECC81. If it was you could check resistors and electrolytics here, eg: screen grid resistor. It was a long time ago since I worked on one. The PL59 and PY801 if faulty just failed, so it doesn't sound as if they are at fault. I wish I had hung onto the one I owned many years ago. Paul

18th Mar 2023, 9:48 pm	#5
slidertogrid Octode Join Date: Apr 2005 Location: Peterborough, Cambridgeshire, UK. Posts: 1,842	Re: Flickering picture on Baird dual standard What a nice looking set! Have you tried attenuating the signal ? Could it be AGC flutter? Just a thought... What standard are you using or is it on both ? Rich.

18th Mar 2023, 10:25 pm	#6
lloydwells Heptode Join Date: Aug 2016 Location: Dumfries, Scotland, UK. Posts: 536	Re: Flickering picture on Baird dual standard Hi Rich I initially couldn't get the UHF tuner to work which is apparently fairly common so I tricked it in to running in VHF 625 I now have the UHF running and it does it on both attenuating the signal makes no odds.

19th Mar 2023, 9:33 am	#9
1955APREN Hexode Join Date: Nov 2010 Location: Market Drayton, Shropshire, UK. Posts: 477	Re: Flickering picture on Baird dual standard Please try the anode load resistor to the line oscillator ECC82 , this must be done by fitting substitute . This resistor might measure ok on a meter but can be noisy It is possible coloured grey. sorry I cannot remember the value. If you sets is fitted with transistor IF panel there are two caps ( yellow) in colour near to the video output valve PFL200 these tend to be broken up due to heat from the valve. hope this might help. Derrick

23rd Mar 2023, 9:36 pm	#10
lloydwells Heptode Join Date: Aug 2016 Location: Dumfries, Scotland, UK. Posts: 536	Re: Flickering picture on Baird dual standard The set is entirely valve with no PFL200 what I am noticing is that the picture is locked and no amount of sliding the hold pot will make it roll I'm wondering if this has something to do with the issue