Power supply for back light of LCD monitor
 

I have an HP Pavilion f1903 19" LCD monitor that has gone bad. The
symptoms are a blank screen and a flashing power light. Google finds
are pretty consistent that the problem is with the inverter board
supplying the back lights. My DMM shows a few volts on the 4 outputs -
not the "high" voltage warned of.

Google found this page that describes the fix(es):
http://h30434.www3.hp.com/t5/Desktop...een/td-p/12212
or
http://tinyurl.com/95d3xw7

It says first look for cold solder joints. I couldn't find any, but my
eyes aren't what they used to be, even with a magnifier 8-(. Then,
bulging caps (none of those), replace them anyhow. And, "might as well
replace the power transistors while you're at it".

If that's what it takes, it's not so bad (4 caps, 4 transistors, on a
single-sided board). But I'd rather a more methodical approach that
would actually identify the bad part(s), since I don't have the
replacement caps & transistors.

Your advice would be appreciated,
Bob

Power supply for back light of LCD monitor
 

Bob Engelhardt wrote:

I have an HP Pavilion f1903 19" LCD monitor that has gone bad. The
symptoms are a blank screen and a flashing power light. Google finds
are pretty consistent that the problem is with the inverter board
supplying the back lights. My DMM shows a few volts on the 4 outputs -
not the "high" voltage warned of.

Google found this page that describes the fix(es):
http://h30434.www3.hp.com/t5/Desktop...een/td-p/12212
or
http://tinyurl.com/95d3xw7

It says first look for cold solder joints. I couldn't find any, but my
eyes aren't what they used to be, even with a magnifier 8-(. Then,
bulging caps (none of those), replace them anyhow. And, "might as well
replace the power transistors while you're at it".

If that's what it takes, it's not so bad (4 caps, 4 transistors, on a
single-sided board). But I'd rather a more methodical approach that
would actually identify the bad part(s), since I don't have the
replacement caps & transistors.

Your advice would be appreciated,
Bob
bulging caps isn't the only item on the list when inspecting caps.

You need to do a ESR test, if you have a meter that will do it, and
do a capacitor value test. These are mainly the electros you find on the
inverter board.

Next problem. It most likely has a Xformer on the board or maybe even
two of them. Check the windings, especially on the output, to make sure
they are not opened. Also, look for HV caps on the output near the
xformer if it has them.

it also is possible you may have one or more fluorescent tubes out.
Many inverters for the back light will not come on if it detects
insufficient load, this would indicate a bad CLFL unit.

THen there is always that possibility the main part of the system
isn't starting.. .

Jamie

Power supply for back light of LCD monitor
 

"Jamie" t wrote in message
...
Bob Engelhardt wrote:

I have an HP Pavilion f1903 19" LCD monitor that has gone bad. The
symptoms are a blank screen and a flashing power light. Google finds are
pretty consistent that the problem is with the inverter board supplying
the back lights. My DMM shows a few volts on the 4 outputs - not the
"high" voltage warned of.

Google found this page that describes the fix(es):
http://h30434.www3.hp.com/t5/Desktop...een/td-p/12212
or
http://tinyurl.com/95d3xw7

It says first look for cold solder joints. I couldn't find any, but my
eyes aren't what they used to be, even with a magnifier 8-(. Then,
bulging caps (none of those), replace them anyhow. And, "might as well
replace the power transistors while you're at it".

If that's what it takes, it's not so bad (4 caps, 4 transistors, on a
single-sided board). But I'd rather a more methodical approach that
would actually identify the bad part(s), since I don't have the
replacement caps & transistors.

Your advice would be appreciated,
Bob
bulging caps isn't the only item on the list when inspecting caps.

You need to do a ESR test, if you have a meter that will do it, and
do a capacitor value test. These are mainly the electros you find on the
inverter board.

Next problem. It most likely has a Xformer on the board or maybe even
two of them. Check the windings, especially on the output, to make sure
they are not opened. Also, look for HV caps on the output near the xformer
if it has them.

it also is possible you may have one or more fluorescent tubes out.
Many inverters for the back light will not come on if it detects
insufficient load, this would indicate a bad CLFL unit.

THen there is always that possibility the main part of the system isn't
starting.. .

Jamie



Wot 'e said plus you'll often find a surface mount fuse on the board near
where the low voltage connector is located. Check that you have 12v
(typically) appearing at one of the pins of this connector

Arfa