bob urz wrote:
Caesar Valenti wrote:
bob urz wrote:
Any good tips for testing LCD inverters and the CCFL tubes
they hook to?
I am working on more of these and think i need to rig up an external
inverter to test the tubes in a LCD unit in some manner.
When these tubes age and degrade, do they just get weaker like
home units, or do they take more start voltage or current?
How do you really gauge when the bulbs are really bad?
What i am trying to trouble shoot in some cases of units
starting up for a few seconds and shutting down whether its
the inverter, or because the lamps are bad the inverter is
shutting down but otherwise ok.
I have seen some information that its hard to test the inverters
because a slight load on the outputs affects there operation.
Should most scopes have a high enough input z on 10x to do this?
Anyone that has tried some of this please let me know what your
results are.
The gateway i posted about (and got no responses) try's to start up
but shuts down. Caps were OK, and I soldered up what looked bad.
So, short of ordering new bulbs for it i need to know which
part i can eliminate as the problem.
What i thought about is making a external jig or such to power each bulb
up and seeing if they light. Is there a way to sub a dummy load
on the Inverters for the bulbs to test? It would have to have a high
voltage zenar with high z series resistor or such on it to simulate
the CCFL plasma voltage of conduction?
Bob
In my limited experience, most of the time the inverter (or a fuse on
it) is bad. However, on my laptop, when the CCFL would light up for
15-300 seconds and then go out, the problem turned out to be the tube
itself. Once the tube was replaced, it stayed lit.
I usually find bad caps or solder connections. But i don't have enough
spare parts laying around to swap stuff in and out. It seems many of
these inverters have multiple protection systems to shut down the
inverter for over current or over voltage conditions. Short of having
known good replacement lamps, i will have to get the spec sheets on
the controller chip (if it can be ID'd) and see if i can hot wire the
protection to see if the lamps stay lite.
There is going to be a lot more of these units floating around broke,
so i guess need to bone up on how to trouble shoot them. It will be a
little difficult to make a generic test supply, since the lamps
draw different depending on how long they are and such. You almost need
a storage scope or a data logger to see the lamp ramp up voltage, lamp
strike voltage, then the operating voltage. Then how to monitor the
voltage without loading down the power supply.
Maybe sam can add a bit to his site on these issues once researched...
bob
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http://www.dianyuan.com/bbs/u/41/1148120894.pdf
I did find a few links to the inverter controller that were somewhat
helpful(oz960) Now,to figure out how to use that information to trouble
shoot.
It may be possible to hot wire some of the protection circuits to do
some testing. or monitor the controller pins to figure out what
shutdown mode it is in.
bob