Mitsubishi TV vertical hold

B

Boris Mohar

Guest
Hello,

Mitsubishi TV Model CS-27403C over 10 years old

Problem: When TV is first turned on there is no vertical sync. As it warms
up sync gradually returns. Initially the problem was minor since the sync
returned quickly. Now it takes an hour or more. There are no obvious
controls on the back. Not like in the good old days. Where to dig?

--
Boris
 
On modern sets, vertical sync is generated from the horizontal sync. The
chip that handles sync separation is a likely possibility.

It's also possible the bias on the vertical output stage is drifting.
 
Bad caps

"William Sommerwerck" <grizzledgeezer@comcast.net> wrote in message
news:hs48s8$kgg$1@news.eternal-september.org...
On modern sets, vertical sync is generated from the horizontal sync. The
chip that handles sync separation is a likely possibility.

It's also possible the bias on the vertical output stage is drifting.
Click to expand...
 
On May 8, 11:43 am, "Lance Dyer" <nipperchip...@hotmail.com> wrote:
Bad caps

"William Sommerwerck" <grizzledgee...@comcast.net> wrote in message

news:hs48s8$kgg$1@news.eternal-september.org...



On modern sets, vertical sync is generated from the horizontal
sync. The
chip that handles sync separation is a likely possibility.

It's also possible the bias on the vertical output stage is
drifting.
Click to expand...

I second the bad caps suggestion. I put the odds at 98% dried out
cap(s). The 'warm up' description is exactly how 'lytics behave. they
always measure better after unsoldering. I just changed 72 caps in
Sony digital Betacam machines this morning.

The 'vertical from horizontal' description is pretty poor. Vertical
like horizontal is part of the composite sync. First sync is recovered
from the video and then processed to extract the H and V components.
This can be done with counters and PLLs or simple RC networks.

G˛
 
On Sat, 8 May 2010 16:53:58 -0700 (PDT), stratus46@yahoo.com wrote:

On May 8, 11:43 am, "Lance Dyer" <nipperchip...@hotmail.com> wrote:
Bad caps

"William Sommerwerck" <grizzledgee...@comcast.net> wrote in message

news:hs48s8$kgg$1@news.eternal-september.org...



On modern sets, vertical sync is generated from the horizontal
sync. The
chip that handles sync separation is a likely possibility.

It's also possible the bias on the vertical output stage is
drifting.

I second the bad caps suggestion. I put the odds at 98% dried out
cap(s). The 'warm up' description is exactly how 'lytics behave. they
always measure better after unsoldering. I just changed 72 caps in
Sony digital Betacam machines this morning.

The 'vertical from horizontal' description is pretty poor. Vertical
like horizontal is part of the composite sync. First sync is recovered
from the video and then processed to extract the H and V components.
This can be done with counters and PLLs or simple RC networks.

G˛
Click to expand...
It turned out to be a 40pin proprietary chip that decided to fail. I found
this out by waning up the whole board with hot air until vertical sync
stabilized. Selective application of cold spray pinpointed the chip. I wish
that it was the caps. Not having the replacement handy I glued a jacket of
thermal insulation over the chip hoping that it warms up sooner. Seems
shorten the "warmup" time.

--
Boris
 
It turned out to be a 40-pin proprietary chip that decided to fail.
I found this out by warming up the whole board with hot air until
vertical sync stabilized. Selective application of cold spray
pinpointed the chip.
Click to expand...
"Heh, heh, heh", he muttered smugly.

Out of curiosity, what exactly was the chip's function or funtions?
 
On Sun, 9 May 2010 08:22:14 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net> wrote:

It turned out to be a 40-pin proprietary chip that decided to fail.
I found this out by warming up the whole board with hot air until
vertical sync stabilized. Selective application of cold spray
pinpointed the chip.

"Heh, heh, heh", he muttered smugly.

Out of curiosity, what exactly was the chip's function or funtions?
Click to expand...
Right now it is a thermometer;

--
Boris
 
On May 9, 8:22 am, "William Sommerwerck" <grizzledgee...@comcast.net>
wrote:
It turned out to be a 40-pin proprietary chip that decided to fail.
I found this out by warming up the whole board with hot air until
vertical sync stabilized. Selective application of cold spray
pinpointed the chip.

"Heh, heh, heh", he muttered smugly.

Out of curiosity, what exactly was the chip's function or funtions?
Click to expand...
OK, you made the 2%. Semiconductor failure are far less frequent
compared to 'lytic caps. Personally I'd change all the lytics around
the chip before changing the chip. They're easier to get, cheaper,
more likely to fail and if more than 5 years old will probably need to
go anyway. You have it open....

G˛
 
On 9 mayo, 11:15, Boris Mohar <borism_vo...@sympatico.ca> wrote:
On Sat, 8 May 2010 16:53:58 -0700 (PDT), stratu...@yahoo.com wrote:
On May 8, 11:43 am, "Lance Dyer" <nipperchip...@hotmail.com> wrote:
Bad caps

"William Sommerwerck" <grizzledgee...@comcast.net> wrote in message

news:hs48s8$kgg$1@news.eternal-september.org...

On modern sets, vertical sync is generated from the horizontal
sync. The
chip that handles sync separation is a likely possibility.

It's also possible the bias on the vertical output stage is
drifting.

I second the bad caps suggestion. I put the odds at 98% dried out
cap(s). The 'warm up' description is exactly how 'lytics behave. they
always measure better after unsoldering. I just changed 72 caps in
Sony digital Betacam machines this morning.

The 'vertical from horizontal' description is pretty poor. Vertical
like horizontal is part of the composite sync. First sync is recovered
from the video and then processed to extract the H and V components.
This can be done with counters and PLLs or simple RC networks.

G˛

It turned out to be a 40pin proprietary chip that decided to fail. I found
this out by waning up the whole board with hot air until vertical sync
stabilized.  Selective application of cold spray pinpointed the chip.  I wish
that it was the caps.  Not having the replacement handy I glued a jacket of
thermal insulation over the chip hoping that it warms up sooner.  Seems
shorten the "warmup" time.

--
Boris- Ocultar texto de la cita -

- Mostrar texto de la cita -
Click to expand...
I don´t know, but I can´t remember a case where a semiconductor
improved after warming. Usually is in reverse: a damaged semiconductor
will work while it´s cold and start to fail as soon as it heats. If
you see any electrolytic capacitors in the vecinity of the chip,
replace them first. Electrolitycs are cheap and easy to replace, and
probaly will solve the fault.
 
On Sun, 9 May 2010 11:04:46 -0700 (PDT), lsmartino
<luismartino76@gmail.com> wrote:

On 9 mayo, 11:15, Boris Mohar <borism_vo...@sympatico.ca> wrote:
On Sat, 8 May 2010 16:53:58 -0700 (PDT), stratu...@yahoo.com wrote:
On May 8, 11:43 am, "Lance Dyer" <nipperchip...@hotmail.com> wrote:
Bad caps

"William Sommerwerck" <grizzledgee...@comcast.net> wrote in message

news:hs48s8$kgg$1@news.eternal-september.org...

On modern sets, vertical sync is generated from the horizontal
sync. The
chip that handles sync separation is a likely possibility.

It's also possible the bias on the vertical output stage is
drifting.

I second the bad caps suggestion. I put the odds at 98% dried out
cap(s). The 'warm up' description is exactly how 'lytics behave. they
always measure better after unsoldering. I just changed 72 caps in
Sony digital Betacam machines this morning.

The 'vertical from horizontal' description is pretty poor. Vertical
like horizontal is part of the composite sync. First sync is recovered
from the video and then processed to extract the H and V components.
This can be done with counters and PLLs or simple RC networks.

G˛

It turned out to be a 40pin proprietary chip that decided to fail. I found
this out by waning up the whole board with hot air until vertical sync
stabilized.  Selective application of cold spray pinpointed the chip.  I wish
that it was the caps.  Not having the replacement handy I glued a jacket of
thermal insulation over the chip hoping that it warms up sooner.  Seems
shorten the "warmup" time.

--
Boris- Ocultar texto de la cita -

- Mostrar texto de la cita -

I don´t know, but I can´t remember a case where a semiconductor
improved after warming. Usually is in reverse: a damaged semiconductor
will work while it´s cold and start to fail as soon as it heats. If
you see any electrolytic capacitors in the vecinity of the chip,
replace them first. Electrolitycs are cheap and easy to replace, and
probaly will solve the fault.
Click to expand...

Once you replace the lytics give the board a good scrub. Fluid which
has leaked from the caps will cause this problem after all the caps
are replaced. The resistance of this liquid will change with the
ambient temperature. Chuck
 
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