I have a Viewsonic PS790 monitor with no raster. HV is a solid 25KV, and
the CRT filament lights up. G2 screen voltage is supposed to be 600v, but I
measure about 130v at start up, and within a few seconds it's down to about
75v... same results with socket removed from CRT. I assumed that the HV
divider resistors in the flyback are bad, but someone suggested that the 10
Meg input impedance on my DMM is too low for measuring the screen voltage,
and may be loading it down. Is that true?

(The schematic shows the focus and screen divider resistor chain, but does
not list values for any of the resistors or pots)

TIA,
Paul

He is right. You need the proper high voltage probe. The G2 supply is of
extreme low current.

--

Jerry G.
=====


"Paul" wrote in message
...
I have a Viewsonic PS790 monitor with no raster. HV is a solid 25KV, and
the CRT filament lights up. G2 screen voltage is supposed to be 600v, but I
measure about 130v at start up, and within a few seconds it's down to about
75v... same results with socket removed from CRT. I assumed that the HV
divider resistors in the flyback are bad, but someone suggested that the 10
Meg input impedance on my DMM is too low for measuring the screen voltage,
and may be loading it down. Is that true?

(The schematic shows the focus and screen divider resistor chain, but does
not list values for any of the resistors or pots)

TIA,
Paul

"Paul" bravely wrote to "All" (28 May 04 15:11:49)
--- on the heady topic of "Viewsonic PS790 G2 Voltage Measurement"

Pa From: "Paul"

Pa I have a Viewsonic PS790 monitor with no raster. HV is a solid 25KV,
Pa and the CRT filament lights up. G2 screen voltage is supposed to be
Pa 600v, but I measure about 130v at start up, and within a few seconds
Pa it's down to about 75v... same results with socket removed from CRT. I
Pa assumed that the HV divider resistors in the flyback are bad, but
Pa someone suggested that the 10 Meg input impedance on my DMM is too low
Pa for measuring the screen voltage, and may be loading it down. Is that
Pa true?
Pa (The schematic shows the focus and screen divider resistor chain, but
Pa does not list values for any of the resistors or pots)

Yes, 10M ohm is too small. I'd say at least 250M ohm not to upset the
voltages too much. The focus pot is often between 15 and 50 meg.
However, about the screen dropping, sometimes the pot develops a burn
spot under the wiper and with luck simply rotating it either side of
the pit may restore the contact. Or it may be an oxide film...

A*s*i*m*o*v

.... Letterman of Borg - "Ok, Top 10 reasons why resistance is futile:"