Scrolling lines on Toshiba 27AF46C CRT TV ? - UK Vintage Radio Repair and Restoration Discussion Forum

cjacek2000 · 3rd Mar 2019, 10:26 am

Hi,
I have here a Toshiba 27 inch CRT TV (which I had for about 5 years and previous owner for 5+ years) which presents with an odd problem. I have uploaded a video for you to see and possibly help diagnose it. Please pay close attention only to the upper portion of the screen (the rest of the screen is fine - despite my camera showing otherwise). These lines only appear when the TV has been OFF for a while and is turned ON -- but then the lines scroll up and disappear and all is OK in a few minutes. I have not changed or plugged in anything else that wasn't there for years and I just noticed these lines a while ago. Not sure if they got any worse or not but they're there. Anyway, any comments would be appreciated. Thank you.
Here's the link:
https://youtu.be/x57i0eyayt8

simpsons · 3rd Mar 2019, 11:07 am

The model number would help as the design will include IC's which may include signal processing just to muddy the waters although looking at the video, the set is a 4:3 format which could make it an easy fix.

Argus25 · 3rd Mar 2019, 11:12 am

Most likely there is an electrically leaky electrolytic capacitor in the vertical retrace blanking circuitry. This circuitry applies a rectangular blanking pulse to the CRT precisely timed with the vertical flyback (and H flyback too), so the CRT beam is blanked at that time. The pulse is developing a tapered trailing edge with a delay, by the look of it, until the offending capacitor, probably feeding the base circuit of a blanking transistor (or the blanking amplifier) alters with less leakage current as it warms up. This is just a theory. It would have to be confirmed with a scope.

To fix this would require that the set was disassembled with the schematic at hand and a scope connected to that section of the circuitry, at the time when the problem was present. At least if you wait it goes away after a while.

Heatercathodeshort · 3rd Mar 2019, 12:43 pm

Probably worth checking the two 2.2uf 63v electrolytic capacitors in the frame circuit. They are usually numbered C303 and C313 on large numbers of Toshiba circuits. Often the aluminium cans are red or green in colour. John.

nigelr2000 · 3rd Mar 2019, 10:00 pm

I was just going to say C313/303 even had it written on the mirror back in the day to remind me, had loads of toshiba's in with that fault

Heatercathodeshort · 4th Mar 2019, 9:49 am

That was about the only fault you encountered with Toshiba receivers. They were incredibly reliable.
If I remember correctly they were described in the service manual as being 'organic capacitors'. All very odd. I used to fit 2.2uf 100V types to complete satisfaction.

One rather odd occurrence when unsoldering the original caps from the circuit board was the reaction of the heat from the soldering iron to the gunge that had seeped from the caps. It would give a flash and loud crack, quite startling if not expected. Some sort of chemical reaction.
John.

Sideband · 4th Mar 2019, 2:53 pm

Yes very common. Use a couple of decent caps rated at 100V and it should work forever.....

cjacek2000 · 5th Mar 2019, 2:24 am

Thank you all very much for the informative replies. And by the way, for the person who asked, the model number of the Toshiba is 27AF46C (manufactured May 2007).

Welsh Anorak · 7th Mar 2019, 11:13 am

That seems very late for a CRT set - is that really the date?
Never understood why they used these odd capacitors, especially as an ordinary capacitor seemed to do the trick.

cjacek2000 · 7th Mar 2019, 1:20 pm

Yes, it says so right on the sticker on the back of the TV set.

3rd Mar 2019, 10:26 am	#1
cjacek2000 Tetrode Join Date: Mar 2012 Location: British Columbia, Canada. Posts: 54	Scrolling lines on Toshiba 27AF46C CRT TV ? Hi, I have here a Toshiba 27 inch CRT TV (which I had for about 5 years and previous owner for 5+ years) which presents with an odd problem. I have uploaded a video for you to see and possibly help diagnose it. Please pay close attention only to the upper portion of the screen (the rest of the screen is fine - despite my camera showing otherwise). These lines only appear when the TV has been OFF for a while and is turned ON -- but then the lines scroll up and disappear and all is OK in a few minutes. I have not changed or plugged in anything else that wasn't there for years and I just noticed these lines a while ago. Not sure if they got any worse or not but they're there. Anyway, any comments would be appreciated. Thank you. Here's the link: https://youtu.be/x57i0eyayt8

3rd Mar 2019, 11:07 am	#2
simpsons Octode Join Date: Feb 2007 Location: Harrow, London, UK. Posts: 1,493	Re: Scrolling lines on CRT TV ? The model number would help as the design will include IC's which may include signal processing just to muddy the waters although looking at the video, the set is a 4:3 format which could make it an easy fix.

3rd Mar 2019, 11:12 am	#3
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Scrolling lines on CRT TV ? Most likely there is an electrically leaky electrolytic capacitor in the vertical retrace blanking circuitry. This circuitry applies a rectangular blanking pulse to the CRT precisely timed with the vertical flyback (and H flyback too), so the CRT beam is blanked at that time. The pulse is developing a tapered trailing edge with a delay, by the look of it, until the offending capacitor, probably feeding the base circuit of a blanking transistor (or the blanking amplifier) alters with less leakage current as it warms up. This is just a theory. It would have to be confirmed with a scope. To fix this would require that the set was disassembled with the schematic at hand and a scope connected to that section of the circuitry, at the time when the problem was present. At least if you wait it goes away after a while.

3rd Mar 2019, 12:43 pm	#4
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Scrolling lines on CRT TV ? Probably worth checking the two 2.2uf 63v electrolytic capacitors in the frame circuit. They are usually numbered C303 and C313 on large numbers of Toshiba circuits. Often the aluminium cans are red or green in colour. John.

3rd Mar 2019, 10:00 pm	#5
nigelr2000 Heptode Join Date: Nov 2008 Location: North Walsham, Norfolk, UK. Posts: 900	Re: Scrolling lines on CRT TV ? I was just going to say C313/303 even had it written on the mirror back in the day to remind me, had loads of toshiba's in with that fault __________________ https://www.facebook.com/gntrading

4th Mar 2019, 9:49 am	#6
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Scrolling lines on CRT TV ? That was about the only fault you encountered with Toshiba receivers. They were incredibly reliable. If I remember correctly they were described in the service manual as being 'organic capacitors'. All very odd. I used to fit 2.2uf 100V types to complete satisfaction. One rather odd occurrence when unsoldering the original caps from the circuit board was the reaction of the heat from the soldering iron to the gunge that had seeped from the caps. It would give a flash and loud crack, quite startling if not expected. Some sort of chemical reaction. John.

4th Mar 2019, 2:53 pm	#7
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,578	Re: Scrolling lines on CRT TV ? Yes very common. Use a couple of decent caps rated at 100V and it should work forever..... __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

5th Mar 2019, 2:24 am	#8
cjacek2000 Tetrode Join Date: Mar 2012 Location: British Columbia, Canada. Posts: 54	Re: Scrolling lines on CRT TV ? Thank you all very much for the informative replies. And by the way, for the person who asked, the model number of the Toshiba is 27AF46C (manufactured May 2007).

7th Mar 2019, 11:13 am	#9
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,925	Re: Scrolling lines on Toshiba 27AF46C CRT TV ? That seems very late for a CRT set - is that really the date? Never understood why they used these odd capacitors, especially as an ordinary capacitor seemed to do the trick. __________________ Glyn www.gdelectronics.wales

7th Mar 2019, 1:20 pm	#10
cjacek2000 Tetrode Join Date: Mar 2012 Location: British Columbia, Canada. Posts: 54	Re: Scrolling lines on Toshiba 27AF46C CRT TV ? Yes, it says so right on the sticker on the back of the TV set.