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The diodes fitted to the input of the 102101 A-D cards are 1N4148 or simi=
liar types and are a mod to allow some soft clip to take place.
I have not known these to cause this type of effect.
More likely is the chance of drifting PEC's.
You will need to be more scientific and measure the drift at the cell box=
output over a time duration to note if a particular signal is drifting.
If this is ok then check the system through the chain.
There are lot's of variables such as tempereture and mains voltages also.=
Quite common is drifting Blue PEC and defective PEC base sockets.
Date: 7/12/95 12:53 pm
To: Paul Grace
From: KEN ROBINSON
> The most common causes for color drift that I've seen on Ursas an=
MkIIIs (haven't >worked on Golds) have been temperature and line voltage
variations. You might want to >consider borrowing a chart recorder to che=
temp/humidity (usually a dual unit) and/or line >voltage. Alternatively, =
might have a drifty internal power supply.
> BTW, have you been able to monitor the Gold to isolate what's dri=
Does it show up >on test signal or just a film image? Does one color vary=
> Rich Torpey
Okay, so here are my thoughts.... As the machine is in Mexico, the follo=
applies.... We have to turn the machine off every night as we are subjec=
power disruptions, we do have a UPS, but only good for a few minutes, do =
security to turn things of in the right order?
Anyway, is the Gold any different from the MK3 or URSA at the head end? N=
my knowledge, so I suppose it could be a faulty PEC, therefore I would pr=
get a drift just on one colour. THis I have not assertained yet. Temper=
and Humidity are fairly constant. From what I can glean re the other dri=
Gold, is is something to do with a couple of Diodes placed in the head en=
that the A-D's do not overload. As I understand things, as the diodes co=
line, by say varying temperature the signal changes and this also affects=
shading as the bit mapping that takes place is mathematicaly interpelated=
the mid range that it measures to the high end correction. Unfortunately=
diodes change the linearity of the signal, thus the shading correction as=
I have to do quite a few tests to assertain exactly what is happening, bu=
thanks everyone for your thoughts, I will look specifically for your sugg=
and report back.=20
P.S. If anyone at Rank wants to jump in and comment, please do at any sta=
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