TV repair question

wn513@hotmail.com · electronics forum beginner Joined: 15 Jul 2006 Posts: 3

I have a Sampo color TV from the early 80's which has what may be this
problem from the sci.electronics.repair FAQ:

http://www.repairfaq.org/samnew/tvfaq/tvvbocbar.htm
"Vertical brightness or color bars
These are typically more or less equally spaced possibly more evident
at the left side of the screen. They result only in brightness or color
variations, not deflection speed. Diagonal lines are straight and not
squiggly.
Note that the appearance of these bars differs from those caused by
ringing in the deflection circuits where diagonal lines will show a
squiggling stair-step appearance.
The most likely cause is a dried up electrolytic capacitor in the scan
derived power supply for the video or chroma circuits or video output.
Check for this ripple with a scope or test/replace any suspect
capacitors."

The bars I'm seeing are 1/2 to 1 inch wide, with 1/2 to 1 inch between
them.

I have the schematic and can do my own repair work, but needed some
help with the troubleshooting since I don't have a scope or signal
generator. For a small fee, a local shop marked 10 caps on the
schematic for me to replace. None solved the problem- in fact of the
10, 2 were not even on the board. On the second attempt, their tech
claimed to have tracked a signal from the tuner to the final video
driver and everything seemed fine. Their final answer was "the tube
must be bad".

I'm not ready to give up yet. The colors and picture quality are fine,
except for vertical stripes of increased brightness across the screen.
If I can fix this set I'd really like to, as it is the last piece of
"repairable" electronic gear I will probably ever own. Repair shops
will not fix anything this old, for obvious reasons.

All advice appreciated.

JANA · electronics forum Guru Joined: 30 Apr 2005 Posts: 341

You probably have more bad caps than what commonly goes bad. You will need
some test gear and the knowledge to locate, and change them. If you invest
in an ESR meter to test the caps directly, this would be a start.

When servicing these old sets, it is common to have to change many caps.
Especially if the set was not used, many of the caps probably have to be
changed.

If you need an extra TV set, you would be best off to buy a new low cost
set. At least it should go trouble free for about 3 to 4 years, and it will
have a minimum 1 year warranty with it.

--

JANA
_____

<wn513@hotmail.com> wrote in message
news:1152937801.793165.271660@35g2000cwc.googlegroups.com...
I have a Sampo color TV from the early 80's which has what may be this
problem from the sci.electronics.repair FAQ:

http://www.repairfaq.org/samnew/tvfaq/tvvbocbar.htm
"Vertical brightness or color bars
These are typically more or less equally spaced possibly more evident
at the left side of the screen. They result only in brightness or color
variations, not deflection speed. Diagonal lines are straight and not
squiggly.
Note that the appearance of these bars differs from those caused by
ringing in the deflection circuits where diagonal lines will show a
squiggling stair-step appearance.
The most likely cause is a dried up electrolytic capacitor in the scan
derived power supply for the video or chroma circuits or video output.
Check for this ripple with a scope or test/replace any suspect
capacitors."

The bars I'm seeing are 1/2 to 1 inch wide, with 1/2 to 1 inch between
them.

I have the schematic and can do my own repair work, but needed some
help with the troubleshooting since I don't have a scope or signal
generator. For a small fee, a local shop marked 10 caps on the
schematic for me to replace. None solved the problem- in fact of the
10, 2 were not even on the board. On the second attempt, their tech
claimed to have tracked a signal from the tuner to the final video
driver and everything seemed fine. Their final answer was "the tube
must be bad".

I'm not ready to give up yet. The colors and picture quality are fine,
except for vertical stripes of increased brightness across the screen.
If I can fix this set I'd really like to, as it is the last piece of
"repairable" electronic gear I will probably ever own. Repair shops
will not fix anything this old, for obvious reasons.

All advice appreciated.

wn513@hotmail.com · electronics forum beginner Joined: 15 Jul 2006 Posts: 3

Thanks for your reply. This set has been used almost daily for 23
years. It's been in dorm rooms, living rooms, family rooms, bedrooms.
No remote and a mechanical tuner. I have gotten my money out of it for
sure. If I _can_ fix it cheaply I'd like to, simply "because I can".
If the tube was obviously bad, it would be in the trash tomorrow. But
I think the shop was just giving up on it, and the tube is probably
fine. I can't blame them for not spending a lot of time on it, there
is no repair money to be made.

Replacing every cap on the chassis was my fall back position. It
probably wouldn't cost more than $10. I'll think about getting a meter
too.

JANA wrote:

Matt J. McCullar · electronics forum beginner Joined: 06 May 2005 Posts: 33

If I'm understanding your description properly, the problem is called "jail
bars." Is it like looking through a bunch of fence posts? If so, the
problem is likely caused by one or more bad caps not doing their job
properly, and it's causing some "ringing" where it's not supposed to.

It may not be an electrolytic that's causing the trouble, but more likely a
ceramic or polystyrene low-value cap in the horizontal output transistor
circuitry.

Farmer Giles · electronics forum beginner Joined: 25 Jan 2006 Posts: 6

wn513@hotmail.com wrote:

wn513@hotmail.com · electronics forum beginner Joined: 15 Jul 2006 Posts: 3

Farmer Giles wrote:

Farmer Giles · electronics forum beginner Joined: 25 Jan 2006 Posts: 6

Uncle Fester wrote:

wri · electronics forum beginner Joined: 21 Jul 2006 Posts: 2

Replace the Cap, usually 5 to 10 uf 250 to 350 V from the voltage feeding
the Collectors of the Color Output transistors usually located on the CRT socket sometimes on the main chassi..
Voltage originates most the time off flyback or High voltage Trafo.
approx 200 to 300 Volts
should take care of your problem...good luck .. wri

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