"Martin Riddle" wrote in message ...


"Jim Thompson" wrote
in message ...
On Thu, 19 Jul 2012 16:39:16 -0400, "Martin Riddle"
wrote:


"mike" wrote in message
...
On 7/19/2012 9:45 AM, mike wrote:
On 7/19/2012 7:59 AM, Jim Thompson wrote:
I have a cheapy 19" Philips TV hanging on my office wall.

It's taken to making a popping noise, suspiciously sounding like a
spark gap.

I'm pretty sure this is CFL back-lit.

Anyone knowledgeable of what to do about this... adjustment to look
for, etc ?

...Jim Thompson

Since you didn't mention change in brightness when it pops...
First thing I'd try is to plug in headphones and verify it ain't
coming out the speaker. Zero cost experiment that might save you a
lot
of fiddling around.
I'd also try the brightness at extremes to see if that changes
anything.

Weakest link is the transformer.
There's often a tiny cap in series with the CFL. I've seen those go
open. Might arc across that.
Spider webs cause interesting high voltage symptoms.

Another thing that happens is that the caps in the low voltage ps
go open. The average voltage is the same, but the peak voltage
can go much higher. I've only seen that after the fets in the cfl
supply
short, but I presume that the CFL voltage goes higher before it fails.

I'm betting on a pinched wire. Some Q-dope might be a quick fix.
I had a Samsung CRT that would snap every now and then in warmer
weather, but never outright failed.

Cheers


Do CFL's go that high in voltage?

This quits after a few hours of operation ??


They run somewhere around 1k to 5kv depends upon the cfl.

Cheers

****You can get a definitive answer from the HR (famous for their excellent
pattern flyback transformers) backlight inverter datasheets, the datasheet I
read said 1200V to strike & 600V ionised - if they do a pattern inverter for
the specific TV in question, you can nail it to the spot.