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Lose the focus


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#1 Andrea Zoli

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Posted 04 October 2004 - 08:33 AM

Hallo guys,
I'm from Italy and I've two old CP's sleds: a IIIA and a III. Recently on all sleds the monitors loses the focus (unlucky?). I've changed the focus tube but the problem is remain. Anybody knows the problem and can help me?
Please answer me quickly, I've the screwdriver in my hand :o

About the level Mr. Ben Fisher build a nice and cheap electric level for all monitors.
See the site www.unitcine.com


Very best
Andrea Zoli (don't decieve, I'm a boy) :)
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#2 Brad Hruboska

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Posted 04 October 2004 - 08:42 AM

There is a large red plastic pot /knob inside the main housing near your tube... use a plastic tweaker or a sheilded screwdriver and adjust that pot until the image sharpens up.....
I used to find that cold weather and dampness used to affect the focus of the monitor as well.......


Hope this helps...
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#3 Andrea Zoli

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Posted 04 October 2004 - 11:20 AM

Hi Brado,
thanks for your answer.
I've done that (it was the first attempt) but the knob is in the end position. The focus leave after 8/10 minuts, not immediatly when I start the monitor.

Thank you very much.


There is a large red plastic pot /knob inside the main housing  near your tube... use a plastic tweaker or a sheilded screwdriver and adjust that pot until the image sharpens up.....
I used to find that cold weather and dampness used to affect the focus of the monitor as well.......


Hope this helps...

<{POST_SNAPBACK}>


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#4 RobinThwaites

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Posted 05 October 2004 - 04:14 AM

Hi Andrea

It is not unusual for the focus pot to be at one end but if you still can't get focus it may be defective. Since the focus changes as the unit warms up it suggests another problem, possibly the h.v. trippler. With a III there are too many possibilities without seeing it but it is unlikely to be the CRT.

Good luck

Robin Thwaites
OpTex
UK
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#5 Ben Fisher

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Posted 05 October 2004 - 12:36 PM

Hi Andrea,

It could be a faulty HT focus output on the trippler but that is unlikely to have occured on two units together.

Does the focus alter at all (from maybe bad to worse) when the pot is tweaked? If there is no change at all it could be the trippler or the pot; if it does change then it might be the focus valve (tube).

Caution your local technician however - the focus voltage is about 2.8Kv; and the trippler is unlike anything he will have seen before; when we used to fix MK3/A Steadicams last century ;) we had to build a 'vacumn chamber' just for drawing out air bubbles in the clear 'silicon' potting compound used in the trippler....

Thanks also for the order for a 2nd BENZ 5000 system - it will be with you next week.

Kind regards,

Ben
UNITCINE

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#6 RobVanGelder

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Posted 05 October 2004 - 12:53 PM

Just for your information, this tripler or HV-unit can easily be replaced by a solid-state manyfactured tripler from a color-tv, on 24 KV. These units cost at the moment a few euro´s and are about half the size and weight of the original.

I did this on my MK3
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#7 Andrea Zoli

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Posted 05 October 2004 - 05:23 PM

Thanks at all for your answers.
The focus "leave" the monitor after 8/10 minutes, not immediatly. If I turn the pot, the focus change. I've bought a new bulbe for try, but the problem is remain. With the old bulbe (original for the CP factory) when the image is soft, if I knock (light) on the main the focus come back and the image is good too. This is very strange 'cause with new bulbes this don't happen, when the monitor lose the focus I must turn off and restart. I've bought an air cilynder and using the CFC I've spray on some components but nothing, the problem is not in the hot. I've thought it was the batteries voltage (two batts gives 15 volts) so I've done a new try with a supply voltage stabilized and I've seen if I give 12,5 / 12,9 volts, the focus is good and stay still. I've checked the 20 volts too (on the HV circuit) and it was perfect (only on a rig, on the second rig the voltage was 23,1).


Andrea Zoli
Forlì, Italy
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#8 Ben Fisher

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Posted 06 October 2004 - 05:01 AM

Hi Andrea,

This definatley sounds like the focus valve/bulb/tube and it's circuitry - in all probability the trippler is OK.

The III/A heater voltage regulation is quite poor and very dependent on battery voltage, if you are putting more than the correct 12.0V (possibly 12.6V) the tube will heat up gradually and the mu/gain will change and affect the focus voltage. This is what shortens the focus tube's life and changes it's charateristics over time.

You can probably remedy this by feeding the heater with a solid-state voltage regulator (LDO) - we (VFX in '94-'97) used to make a new tube regulator PCB with all this on and a better focus pot.

Good luck,

Ben Fisher
UNITCINE
ben@unitcine.com

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