[Tig] PEC limiting MK3

[Steve Roberts - Post Production]

Have you looked at the levels directly out of the cellbox? This sounds
to me like it could be a burn or shading correction problem further down
the chain - the "slow change" business in particular sounds like an AGC
effect. How old is the tube?

Whilst you've got the cellbox open, take the opportunity to replace the
electrolytics on the burn cell head amp. I recently had a problem with
the burn corrector enhancing the edges of phosphor grain, giving that
'dirty window' effect despite the burn corrector lineup being correct.
Eventually I changed this C's (all were o/c with age) and everything was
then fine.

Steve


	Steve Roberts | Senior Engineer | BBC Resources
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-----Original Message-----
From: tig-bounces at tig.colorist.org [mailto:tig-bounces at tig.colorist.org]
On Behalf Of woz
Sent: 26 August 2007 01:00
To: tig at colorist.org
Subject: [Tig] PEC limiting MK3

TIG portal: http://tig.colorist.org/wiki3 thanks to Rick
Schweikert/Frame Set and Match  ====

I have a situation with a mk3 telecine of one of the PECs (blue)
limiting prematurely. This showing as extreme changes of  shading etc.at
the limit,
(slew?) when, with the same light levels, the other PEC's are perfectly
linear.
It (the blue channel) is also behaving too slowly in its response to
change when light levels to the PEC are altered.
If the light to the PEC is reduced it behaves in an acceptable and
linear way, so in the interim I have put an additional filter in the
dichroic box.
I (naturally) changed the PEC for a brand new one and swapped the pec
control board, but to no avail (surprisingly because it looked  to me
almost certain to be the PEC!) I have not yet changed the head amp,
which I will shortly substitute with another.
Power supply voltages etc seem normal.
Anyone else had a similar experience?

Regards
Woz
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