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From: Boris Mohar on 8 May 2010 13:45

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
From: William Sommerwerck on 8 May 2010 14:00
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.


From: Lance Dyer on 8 May 2010 14:43
Bad caps

"William Sommerwerck" <grizzledgeezer(a)comcast.net> wrote in message
news:hs48s8$kgg$1(a)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.
>
>


From: stratus46 on 8 May 2010 19:53
On May 8, 11:43 am, "Lance Dyer" <nipperchip...(a)hotmail.com> wrote:
> Bad caps
>
> "William Sommerwerck" <grizzledgee...(a)comcast.net> wrote in message
>
> news:hs48s8$kgg$1(a)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.

G²
From: Boris Mohar on 9 May 2010 11:15
On Sat, 8 May 2010 16:53:58 -0700 (PDT), stratus46(a)yahoo.com wrote:

>On May 8, 11:43�am, "Lance Dyer" <nipperchip...(a)hotmail.com> wrote:
> > Bad caps
> >
> > "William Sommerwerck" <grizzledgee...(a)comcast.net> wrote in message
> >
> > news:hs48s8$kgg$1(a)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
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