A
Al Savage
- Jan 1, 1970
- 0
I've got a VX700 (FCCID BGBTFV8705K -- Mitsubishi) 17" CRT monitor on
my bench that turns off the HV due to the HV protection circuit. The
"X-Pro" and "HV-Adj" pots are potted
For testing, I've disabled the
HV protection by lifting the gate line of D708 (SCR FOR3G). I'm using a
BK HV probe/meter to measure the HV, and it shows 17kv, which for a 17"
CRT doesn't sound too high to me.
The Screen pot on the FBT still has the factory sealant on it, so I
don't think anybody's been screwing around with this before I got to it.
Other than the shutdown issue, the display looks fine, with no
anomalies. The PS output values are silkscreened on the PCB and look
very clean on the 'scope. 45v and 110v lines are about 5v low, but
otherwise all is good there.
I'm fishing for suggestions.
Bonus Question:
This resistor:
ftp://asavage.dyndns.org/hosting/Resistor_390k.jpg (68k)
measures 394k (Fluke 79). If I decode this correctly, it should be a
390k 1%, so it's a bit high? This thing is in series with a diode, from
the FBT's HV monitoring pin to ground. I'm taking a WAG and thinking
that maybe this thing has drifted a bit high and is not bleeding off
quite as much voltage as it should. I'm tempted to un-pot the X-Pro pot
and tweak it ever so slightly, but I thought I'd ask you folks who still
do this for a living for opinions.
my bench that turns off the HV due to the HV protection circuit. The
"X-Pro" and "HV-Adj" pots are potted
For testing, I've disabled theHV protection by lifting the gate line of D708 (SCR FOR3G). I'm using a
BK HV probe/meter to measure the HV, and it shows 17kv, which for a 17"
CRT doesn't sound too high to me.
The Screen pot on the FBT still has the factory sealant on it, so I
don't think anybody's been screwing around with this before I got to it.
Other than the shutdown issue, the display looks fine, with no
anomalies. The PS output values are silkscreened on the PCB and look
very clean on the 'scope. 45v and 110v lines are about 5v low, but
otherwise all is good there.
I'm fishing for suggestions.
Bonus Question:
This resistor:
ftp://asavage.dyndns.org/hosting/Resistor_390k.jpg (68k)
measures 394k (Fluke 79). If I decode this correctly, it should be a
390k 1%, so it's a bit high? This thing is in series with a diode, from
the FBT's HV monitoring pin to ground. I'm taking a WAG and thinking
that maybe this thing has drifted a bit high and is not bleeding off
quite as much voltage as it should. I'm tempted to un-pot the X-Pro pot
and tweak it ever so slightly, but I thought I'd ask you folks who still
do this for a living for opinions.
