TV62 First Light. - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

Courtney Louise · 23rd Mar 2014, 11:39 am

OK There may be something with this damp theory... I have had the TV on now for 30 mins and by 10 mins is had shrunk and dimmed to almost nothing, now after 30 mins I have maybe 3" width ...

Freya · 23rd Mar 2014, 11:52 am

You could try using a hairdryer aimed at the transformer, it should show you pretty quickly if heat makes the problem better/worse. I had an ekco set that showed a similar problem, focusing the heat from the hairdryer on the lopt coil made this revert to normal viewing after about 2-3 mins.
This was carried out with the set running.

If this does alter the fault then it may be better to either bake the lopt in the oven or dry out for a month or two on the copper cylinder (if you have on) in the airing cupboard.

If you have a scope you could also try a ring test on the lopt. Search "lopt ring test" on search engine.

Courtney Louise · 23rd Mar 2014, 12:19 pm

1hr 20 mins and we have 20cm width. Currently watching Doctor Who on Ch.11 as band 3 seems to be aligned

Courtney Louise · 23rd Mar 2014, 12:39 pm

24 cms width now by just running it

Courtney Louise · 23rd Mar 2014, 12:57 pm

OK this is after 2 hours. I have a gap at the bottom and The brightness wont go down to zero but a vast vast improvement and no smoke or bangs yet!

The Screen resistors have been changed already.

Courtney Louise · 23rd Mar 2014, 1:11 pm

OK This set of pics show the different times in the 2 hours running.

2 mins, 6 mins, 10 mins, 20 mins and 1 hour

PJL · 23rd Mar 2014, 2:04 pm

Interesting how narrow this got and yet it still recovered. Can someone confirm this explanation.

Current is only taken through the scan coil if the boost voltage is greater than HT, it will otherwise pass through the PY81. Damp, probably in the EHT winding, is absorbing nearly all the flyback energy preventing any boost voltage. Perhaps the only surprising thing is the PL81 didn't overheat.

Freya · 23rd Mar 2014, 2:08 pm

I would think the damp must be in the associated windings as well, unless its left on for a few days you will most likely find a similar situation next time its on from cold. There must be a fair amount of damp sealed in to produce that great an effect.

PJL · 24th Mar 2014, 8:42 am

And the reduction in height is because the frame oscillator also makes use of the boost volts.

Courtney Louise · 24th Mar 2014, 3:11 pm

Well I turned it off about 3pm yesterday afternoon and turned it on again just now after 10 mins it's still fine, no narrowing at all.. I have managed to get the picture centred correctly but really need to sort some electrolytics as there is now a hum through the speaker..

Any ideas why I can't get the brightness to go any lower? This is almost at zero...

Freya · 24th Mar 2014, 3:19 pm

Have you checked the brightness track resistance out of circuit ?

Courtney Louise · 24th Mar 2014, 3:54 pm

Yeah, it meters ok. It seems to only be too bright when the screen is supposed to be black, almost like an AGC effect.

PJL · 24th Mar 2014, 4:41 pm

Measure the CRT cathode and grid voltages. If you say that even with the grid at 0V it is still this bright then something is wrong around with the vision amplifier (PCF80).

thermionic · 24th Mar 2014, 8:12 pm

I think your first port of call now, is confirming your HT is up to spec. You mention a hum which could indicate a defective reservoir or smoother section in the main electrolytic .
Failure to remedy this could lead you chasing up blind alleys.

Good work so far..........!

SimonT.

23rd Mar 2014, 11:39 am	#41
Courtney Louise Octode Join Date: Sep 2005 Location: Welshpool, Powys, Wales Posts: 1,327	Re: TV62 First Light. OK There may be something with this damp theory... I have had the TV on now for 30 mins and by 10 mins is had shrunk and dimmed to almost nothing, now after 30 mins I have maybe 3" width ... __________________ *33, 45, 78, around and around they go...*

23rd Mar 2014, 11:52 am	#42
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,990	Re: TV62 First Light. You could try using a hairdryer aimed at the transformer, it should show you pretty quickly if heat makes the problem better/worse. I had an ekco set that showed a similar problem, focusing the heat from the hairdryer on the lopt coil made this revert to normal viewing after about 2-3 mins. This was carried out with the set running. If this does alter the fault then it may be better to either bake the lopt in the oven or dry out for a month or two on the copper cylinder (if you have on) in the airing cupboard. If you have a scope you could also try a ring test on the lopt. Search "lopt ring test" on search engine. __________________ Stephen _________"It`s only an old telly" ___

23rd Mar 2014, 12:19 pm	#43
Courtney Louise Octode Join Date: Sep 2005 Location: Welshpool, Powys, Wales Posts: 1,327	Re: TV62 First Light. 1hr 20 mins and we have 20cm width. Currently watching Doctor Who on Ch.11 as band 3 seems to be aligned __________________ *33, 45, 78, around and around they go...*

23rd Mar 2014, 12:39 pm	#44
Courtney Louise Octode Join Date: Sep 2005 Location: Welshpool, Powys, Wales Posts: 1,327	Re: TV62 First Light. 24 cms width now by just running it __________________ *33, 45, 78, around and around they go...*

23rd Mar 2014, 12:57 pm	#45
Courtney Louise Octode Join Date: Sep 2005 Location: Welshpool, Powys, Wales Posts: 1,327	Re: TV62 First Light. OK this is after 2 hours. I have a gap at the bottom and The brightness wont go down to zero but a vast vast improvement and no smoke or bangs yet! The Screen resistors have been changed already. Attached Thumbnails __________________ *33, 45, 78, around and around they go...*

23rd Mar 2014, 1:11 pm	#46
Courtney Louise Octode Join Date: Sep 2005 Location: Welshpool, Powys, Wales Posts: 1,327	Re: TV62 First Light. OK This set of pics show the different times in the 2 hours running. 2 mins, 6 mins, 10 mins, 20 mins and 1 hour Attached Thumbnails __________________ *33, 45, 78, around and around they go...*

23rd Mar 2014, 2:04 pm	#47
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: TV62 First Light. Interesting how narrow this got and yet it still recovered. Can someone confirm this explanation. Current is only taken through the scan coil if the boost voltage is greater than HT, it will otherwise pass through the PY81. Damp, probably in the EHT winding, is absorbing nearly all the flyback energy preventing any boost voltage. Perhaps the only surprising thing is the PL81 didn't overheat.

23rd Mar 2014, 2:08 pm	#48
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,990	Re: TV62 First Light. I would think the damp must be in the associated windings as well, unless its left on for a few days you will most likely find a similar situation next time its on from cold. There must be a fair amount of damp sealed in to produce that great an effect. __________________ Stephen _________"It`s only an old telly" ___

24th Mar 2014, 8:42 am	#49
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: TV62 First Light. And the reduction in height is because the frame oscillator also makes use of the boost volts.

24th Mar 2014, 3:11 pm	#50
Courtney Louise Octode Join Date: Sep 2005 Location: Welshpool, Powys, Wales Posts: 1,327	Re: TV62 First Light. Well I turned it off about 3pm yesterday afternoon and turned it on again just now after 10 mins it's still fine, no narrowing at all.. I have managed to get the picture centred correctly but really need to sort some electrolytics as there is now a hum through the speaker.. Any ideas why I can't get the brightness to go any lower? This is almost at zero... Attached Thumbnails __________________ *33, 45, 78, around and around they go...*

24th Mar 2014, 3:19 pm	#51
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,990	Re: TV62 First Light. Have you checked the brightness track resistance out of circuit ? __________________ Stephen _________"It`s only an old telly" ___

24th Mar 2014, 3:54 pm	#52
Courtney Louise Octode Join Date: Sep 2005 Location: Welshpool, Powys, Wales Posts: 1,327	Re: TV62 First Light. Yeah, it meters ok. It seems to only be too bright when the screen is supposed to be black, almost like an AGC effect. __________________ *33, 45, 78, around and around they go...*

24th Mar 2014, 4:41 pm	#53
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: TV62 First Light. Measure the CRT cathode and grid voltages. If you say that even with the grid at 0V it is still this bright then something is wrong around with the vision amplifier (PCF80).

24th Mar 2014, 8:12 pm	#54
thermionic Heptode Join Date: Apr 2003 Location: Cornwall, UK. Posts: 989	Re: TV62 First Light. I think your first port of call now, is confirming your HT is up to spec. You mention a hum which could indicate a defective reservoir or smoother section in the main electrolytic . Failure to remedy this could lead you chasing up blind alleys. Good work so far..........! SimonT. __________________ The honesty of imperfection..........