Re: Old CNMA monitors

On Fri, 13 Mar 98 11:26:49 -0600, Ray Ghanbari <ray@mayo.edu> wrote:

>You wrote:
>> The Barrier monitor schematic on www.spies.com contains the HV section. It's
>> also one of the .TIF files that is readable by Paint Shop Pro.
>
>Got it! Thanks for the pointer.
>
>While there, I saw the service bulletin regarding arcing on cnma monitors with
>the Sylvania tube. Looks like the recommended action was to use a neo lamp to
>sink the HV field.
>
>Has anyone dealt with this problem with the older Sylvania tubes? Is it a
>serious/common problem?
>
>Using a neon lamp seems to be quite a hack. I'd like to skip it if not
>necessary (of course, we have to get the HV working again first ;-)

Actually neon tubes are pretty commonly used on most monitors. Look on the neck
PCB of most monitors and you see a couple of neon tubes.

They break down at about 90 volts and can handle the momentary HV spikes nicely.

The brightness voltage on the Cinematronics monitors is 90v. By placing 2 neon
bulbs in series from the brightness wiper control to ground, all spikes above
180v will be shorted to ground.

I'd definitely recommend them. An ex-Cinematronics employee said they're a must
and were always added to any monitor returned for repair.

Another fix that is highly recommended is the diode across the LF13331. If the
+/- power supply rails come up (or power down) unevenly it will take out the
LF13331. I can't remember the place to put the diode off hand, but check out a
newer Cinematronics schematic (Star Castle) and place a diode on your monitor in
the same place they show.

-Zonn

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Received on Fri Mar 13 18:44:37 1998