Boost Regulator fails

[Richard Collins]

Any advise on what might be causing the boost regulator mosfet
switcher to short in my ADI monitor. This mosfet is part of the boost
regulator with 43 volts B+, and feeds the LOT primary with somewhat
higher V. The last replacement lasted about 10 hours, but did
occasionally give a screen image expansion and dimming fault before
ultimate failure.
Thanks.
--
Rich Collins
G4PCE, Debian/Linux rules

 

[JURB6006]

Ten hours ? Look at the feedback ckt., it's probably running full blast all the
time.

JURB

 

[Richard Collins]

Thanks JURB,
I guess it was a total of 10 hours use, split in say 2 hour periods and
occasionally the screen flickered, pointing to stress!!. I'll have a look
at the feedback, unfortunately I don't have a voltage setting, there is a
VR off a LOT secondary for adjusting the input to the TL494.

On Tue, 10 Feb
2004 05:00:22 +0000, JURB6006 wrote:

Ten hours ? Look at the feedback ckt., it's probably running full blast
all the

time.

JURB

--
Rich Collins
G4PCE, Debian/Linux rules

 

[JURB6006]

Determine how it is regulated. If it's a TL494 it's PWM. With a scope you
should see a varying puls width either to the HVOT or a regulating transistor
thereto.

Vary the beam current, you can do this woth the G2 control, but it's better to
somehow change the computer's video. That way you know you're not going too far
out of normal parameters and would assure more conclusive results.

Nokia has a test program at their website, it has tests for this, one function
will go alternately form an almost all black to white screen at about once a
second.

If you have any trouble getting it let me know, I'll email it to you.

JURB

 

[Richard Collins]

On Wed, 11 Feb 2004 01:25:35 +0000, JURB6006 wrote:

Determine how it is regulated. If it's a TL494 it's PWM. With a scope you
should see a varying puls width either to the HVOT or a regulating transistor
thereto.

Vary the beam current, you can do this woth the G2 control, but it's better to
somehow change the computer's video. That way you know you're not going too far
out of normal parameters and would assure more conclusive results.

Nokia has a test program at their website, it has tests for this, one function
will go alternately form an almost all black to white screen at about once a
second.

If you have any trouble getting it let me know, I'll email it to you.

JURB
Jurb,

I was going to forward some info to you, but my mail is bounced.
Rich
--
Rich Collins
G4PCE, Debian/Linux rules