Hello,
I have a brightness problem which I have heard others complain about.
(bloomed, washed out, green tinge and retrace(?) lines) After probing
through the monitor I found G2 to be somewhere between 700-900V (off-scale
on my scope) where I believe it should be 522V (look below) In fact my probe
can cause the voltage to dip enough to cause the picture to come back to
_perfect_ (it's not probe resistance, only if I touch in intermittently it
makes wild fluctuations in the voltage - which I'm guessing is not right at
all).
I have considered just soldering in a resistor to pull it down to
acceptable levels (as is done in cheaper monitors). But this monitor has
some fancy control circuitry consisting of a transistor pair controlled by
microprocessor and I'd rather bring back into spec than anything (I believe
it compensates for changing image intensity, that would be nice too!).
However this is complicated because some of the SMT parts don't even have
labels (Q406) and I have no schematic to diagnose with.

I'm sure it's some commonly failed part as well, if anyone knows which part
it is and has a part number, it would be great!!! or a schematic, I know the
links to Sony were posted before, but they were taken down


I found this while googling:

QUESTION NO. P51503-7: Sony cpdg500 monitor, brightness too high with all
controls set at lowest possible. Image is stable and in focus, all syncs
and geometry ok. Suspect defective ic in brightness circuit, possible
voltage too high. No adjustments internally, all micro-controlled.

Assuming that this is a circuitry fault, rather than a DAS software issue,
the problem might be, that the CRT cathode voltages are too low, or the G2
voltage is too high. On the CRT board ('A' board), check if the cathode
voltages (CRT pins 7,8,9) are in the 80 to 100 Volt range. If these voltages
are too low, it may indicate a bad IC403 (FA4301). The G2 voltage (CRT pin
10) should be roughly 522 Volts at the CRT. If G2 is much higher, check the
G2 circuit, involving transistor pair Q406 & Q410, run by IC405 (pin 7),
under control from IC404 (pin 14). Otherwise, try a DAS alignment.



My info:
Q410 has
E=4.25V
B=4.85V
C=700+V

Q406 has
(I think these are the pinouts, can only guess)
B=0V !!!
E=E Q410=4.125V
C=4.25V


TIA,
Dave (Remove REMVE to reply by email)