On Sun, 9 May 2010 11:04:46 -0700 (PDT), lsmartino
wrote:

On 9 mayo, 11:15, Boris Mohar wrote:
On Sat, 8 May 2010 16:53:58 -0700 (PDT), wrote:
On May 8, 11:43*am, "Lance Dyer" wrote:
Bad caps

"William Sommerwerck" wrote in message

...

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

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.

--
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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.


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