Hi all,

I've been attempting to repair my first TV, a Teac CT-M805SV, I've made
the problem better, but its still there so I'm hoping for some pointers.

The problem its exhibiting is a lack of picture width (partial
horizontal collapse?) with a fairly bad pincushion problem, which I
suspect will sort itself out when I fix up the picture width problem.

Anyway, I've replaced a number of caps around the vertical section since
that sounded like a good idea, and also fixed a few cold solder joints
in the PSU and around some diodes near the LOPT/flyback. I've also
tested all transistors in the area (as best I can - a go/no-go type
test), and checked all the diodes on the main board.

So far all my efforts have achieved is to make the problem about 50%
better than it was. I noticed when I was testing it after replacing
caps in the vertical area that the picture was creeping inwards (getting
narrower) within about 5 seconds of turning on the set, so I promptly
turned it back off.

I replaced as a precaution a couple of diodes that were running hot, and
one capacitor that was adjacent to one of those diodes as it had been
scorched by the diode beside it. The diodes were still functional, however.

Here's what I've done to date:

Replaced D403 and C431 (D403 was hot, scorched C431)

Replaced D401 (damper diode) as it had been running hot and had
blackened the PCB underneath it. It also had dry solder joints at both
of its pads.

Replaced C419 (4.7uf 50v Bi-Polar), C401 (1uf 50v), C408 (100uF 35v),
C410 (330uF 50v) and as mentioned above, C431 as well.


I don't know where I should actually be looking for this problem on the
PCB/schematic, so if anyone can point me in the right direction that
would be great! I've been contemplating testing the voltages of the
PSU while its running which will probably be my next step if I don't any
better suggestions.

Thanks.

"Robert Davidson" wrote in message
...

Hi all,

I've been attempting to repair my first TV, a Teac CT-M805SV, I've made
the problem better, but its still there so I'm hoping for some pointers.

The problem its exhibiting is a lack of picture width (partial horizontal
collapse?) with a fairly bad pincushion problem, which I suspect will sort
itself out when I fix up the picture width problem.

Anyway, I've replaced a number of caps around the vertical section since
that sounded like a good idea, and also fixed a few cold solder joints in
the PSU and around some diodes near the LOPT/flyback. I've also tested
all transistors in the area (as best I can - a go/no-go type test), and
checked all the diodes on the main board.

So far all my efforts have achieved is to make the problem about 50%
better than it was. I noticed when I was testing it after replacing caps
in the vertical area that the picture was creeping inwards (getting
narrower) within about 5 seconds of turning on the set, so I promptly
turned it back off.

I replaced as a precaution a couple of diodes that were running hot, and
one capacitor that was adjacent to one of those diodes as it had been
scorched by the diode beside it. The diodes were still functional,
however.

Here's what I've done to date:

Replaced D403 and C431 (D403 was hot, scorched C431)

Replaced D401 (damper diode) as it had been running hot and had blackened
the PCB underneath it. It also had dry solder joints at both of its pads.

Replaced C419 (4.7uf 50v Bi-Polar), C401 (1uf 50v), C408 (100uF 35v), C410
(330uF 50v) and as mentioned above, C431 as well.


I don't know where I should actually be looking for this problem on the
PCB/schematic, so if anyone can point me in the right direction that would
be great! I've been contemplating testing the voltages of the PSU
while its running which will probably be my next step if I don't any
better suggestions.

Thanks.

Sounds like a problem with the E-W modulator. Usually a chunky diode, but
you really need a schematic to find out where it is on that particular
model.

Arfa

On Sun, 24 May 2009 17:17:21 +1000, Robert Davidson
put finger to keyboard and composed:

I've been attempting to repair my first TV, a Teac CT-M805SV, I've made
the problem better, but its still there so I'm hoping for some pointers.

ISTR working on this set several times. IIRC the small electrolytic
capacitors in the PSU should be replaced. Your set may have other
problems, though.

I don't know where I should actually be looking for this problem on the
PCB/schematic, so if anyone can point me in the right direction that
would be great!

Can you upload the schematic to a file sharing site? Alternatively you
could email it me and I'll post it on my web space.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Franc Zabkar wrote:
On Sun, 24 May 2009 17:17:21 +1000, Robert Davidson
put finger to keyboard and composed:

I've been attempting to repair my first TV, a Teac CT-M805SV, I've made
the problem better, but its still there so I'm hoping for some pointers.

ISTR working on this set several times. IIRC the small electrolytic
capacitors in the PSU should be replaced. Your set may have other
problems, though.

Fair enough. I've checked the power supply voltages (primary supply) as
best I can. There is one output I'm unsure of, since the marking on the
PCB says its a 5v output, but the schematic clearly shows it going to a
2W resistor and then into an LM7805.

+145v is at +143v
+18v is at +22v
+Unknown is at +12v (pin 4 of the PSU connector)

I'm a little concerned about the +18v being at +22v, and I'm currently
looking over the schematic to see what impact that might have on things,
but so far I've only found one area that its used and its going through
a couple more resistors and being clamped to 7.5v by a zener (around the
horizontal drive area of IC201).

I've done some poking around the secondary power supplies derived from
the flyback transformer but still need to do more poking in that area.
There is a +33v output from that area that I've managed to verify is
running at +32.57v, so that seems fine, but there are at least a couple
others I still need to check.

Can you upload the schematic to a file sharing site? Alternatively you
could email it me and I'll post it on my web space.

I've sent it to you via e-mail, if you could post it up on your web
space and provide a link to it for anyone else who is interested that
would be good. I tried to find the original place I downloaded the
service manual from but I didn't have any luck

- Rob.

Robert Davidson wrote:
I've done some poking around the secondary power supplies derived from
the flyback transformer but still need to do more poking in that area.
There is a +33v output from that area that I've managed to verify is
running at +32.57v, so that seems fine, but there are at least a couple
others I still need to check.

Those others checked fine... (+8v, +12v)

I went and found the E/W section of the board, and I found a track there
that was cracked, so I've fixed that and now the width is better, just
too wide now. So whatever caused me to 1/2 fix the width earlier
probably caused that problem.

Apart from that the pincushion problem still seems to be there, the OSD
text is all in italics at the top of the screen, and about right in the
middle (though I can't see the sides of the picture anymore to see how
bad it is).

I guess I'll try to find a way of changing the width now, then to tackle
the pincushion issue.

- Rob.

"Robert Davidson" wrote in message
.au...
Robert Davidson wrote:
I've done some poking around the secondary power supplies derived from
the flyback transformer but still need to do more poking in that area.
There is a +33v output from that area that I've managed to verify is
running at +32.57v, so that seems fine, but there are at least a couple
others I still need to check.

Those others checked fine... (+8v, +12v)

I went and found the E/W section of the board, and I found a track there
that was cracked, so I've fixed that and now the width is better, just too
wide now. So whatever caused me to 1/2 fix the width earlier probably
caused that problem.

Apart from that the pincushion problem still seems to be there, the OSD
text is all in italics at the top of the screen, and about right in the
middle (though I can't see the sides of the picture anymore to see how bad
it is).

I guess I'll try to find a way of changing the width now, then to tackle
the pincushion issue.

- Rob.

There is a limit to the amount of correction that the pincushion modulator
can apply. If the width is now excessive, you may well be beyond that limit,
and not actually seeing a pincushion correction fault per se, at all ...

Arfa

Arfa Daily wrote:

I guess I'll try to find a way of changing the width now, then to tackle
the pincushion issue.

- Rob.

There is a limit to the amount of correction that the pincushion modulator
can apply. If the width is now excessive, you may well be beyond that limit,
and not actually seeing a pincushion correction fault per se, at all ...

No probs, I'll keep that in mind. After I ran the set for about 15-20
mins after I fixed its cracked track, the thing decided to turn itself
off and not come back on.

I'm suspecting a short circuit somewhere as the PSU is just making a
faint ticking noise every 1/2 second or so, so now I've gotta fix that
as well. I don't think it'll be too difficult to track it down.

If you or anyone else wishes to look at the schematic for this thing at
all, Franc Zabkar has put a copy of it up on his web space he

http://www.users.on.net/~fzabkar/Teac-CTM805SV.pdf

- Rob.

Robert Davidson wrote:
I'm suspecting a short circuit somewhere as the PSU is just making a
faint ticking noise every 1/2 second or so, so now I've gotta fix that
as well. I don't think it'll be too difficult to track it down.

Sure enough, it was easy to track down. The HOT blew and went
short-circuit across all pins.

I've replaced the HOT and briefly tested it. The HOT that was in the TV
originally is now back in the TV, the one that went S/C was a
replacement one I bought, not the original. The reason I replaced it
was because a transistor tester said it was dead, but that was rather
misguided.

The HOT that blew did it when I was flicking through channels (about 5
flicks, one every 2 seconds or so). Does that sort of thing likely to
put strain the HOT?

I've also done some reading around the place and it seems that one HOT
is not necessarily equal to another, even if its stamped with the same
number. I've also read that it probably isn't a problem in the drive
circuity for the HOT since problems there don't normally kill HOTs.

I've run the set for about a minute, keeping an infrared thermometer
pointed at the back of the heatsink where the HOT is mounted, it doesn't
seem to be getting hot, luke warm at best. I did a similar thing last
time after the TV shut down due to the HOT going S/C, the max
temperature I read at that time was about 25c (room temperature was
about 18c), however I was a bit slow getting out the thermometer so it
would have cooled down a bit in that time.

What would be the likelyhood that I have a faulty flyback/LOPT?

Could a faulty flyback/LOPT be causing the picture width problems?

- Rob.

Robert Davidson wrote:
I'm suspecting a short circuit somewhere as the PSU is just making a
faint ticking noise every 1/2 second or so, so now I've gotta fix that
as well. I don't think it'll be too difficult to track it down.

Sure enough, it was easy to track down. The HOT blew and went
short-circuit across all pins.

I've replaced the HOT and briefly tested it. The HOT that was in the TV
originally is now back in the TV, the one that went S/C was a
replacement one I bought, not the original. The reason I replaced it
was because a transistor tester said it was dead, but that was rather
misguided.


'Dead' in what way ? It is very very rare for transistors, particularly HOP
transistors, to fail in any obscure way that would lead to any of your width
related problems. Power transistors go short circuit, open circuit, and
leaky. Small signal transistors sometimes go noisy, and occasionally low
gain, as well as the other DC failures. HOP transistors are fussy little
devils. The correct one for the chassis must be used, and you must pay
attention to suffixes, as sometimes, this can mean the difference between
say the transistor having an internal clamper diode, or not.


The HOT that blew did it when I was flicking through channels (about 5
flicks, one every 2 seconds or so). Does that sort of thing likely to
put strain the HOT?

No, not on a normally working TV



I've also done some reading around the place and it seems that one HOT
is not necessarily equal to another, even if its stamped with the same
number. I've also read that it probably isn't a problem in the drive
circuity for the HOT since problems there don't normally kill HOTs.


I would have to dispute that little pearl of wisdom. Some of the commonest
HOP transistor killers, are bad joints on the driver transformer where one
is used, and out of spec base coupling caps, which cause the transistor to
be driven with a distorted waveform, which leads to slow switching,
over-dissipation, and ultimate failure.


I've run the set for about a minute, keeping an infrared thermometer
pointed at the back of the heatsink where the HOT is mounted, it doesn't
seem to be getting hot, luke warm at best. I did a similar thing last
time after the TV shut down due to the HOT going S/C, the max
temperature I read at that time was about 25c (room temperature was
about 18c), however I was a bit slow getting out the thermometer so it
would have cooled down a bit in that time.

What would be the likelyhood that I have a faulty flyback/LOPT?

Could a faulty flyback/LOPT be causing the picture width problems?

I'd say the chances are pretty slim. You need to determine how the width
adjustment on that chassis is supposed to work, and then look into why it
isn't. For instance, do VR402 and VR403 have any influence on the width and
pincushion ? ( see service man pdf page 9)

Arfa


- Rob.

Meat Plow wrote:

Have access to a decent scope where you can look for deformity in
the HOT's output (primary side)?

Possibly, but probably not easily.

Haven't seen a seperate damper in awhile mainly because I don't work
on this stuff now but did enough Teac/GE/Panasonic warranty back in
the day to last a lifetime. These circuits aren't generally too
forgiving where the HOT is concerned. Go astray from the tolerances
too much and you better have a bin full of them.

Hrmph. Fair enough.

So with regard to the excessive width of the picture, could that be
stressing the HOT at all?

- Rob.