Hi;

A quick tip: When refilling the coolant chanber, right when it's almost full,
stop and push the bellows. Do not let the weight of the coolant fill the
bellows, instead, make sure the bellows is deflated when you seal the chamber.
On newer NAPs (i.e.), you need something to poke through the air bleed, but it
MUST not be sharp. Others you can push in with your finger. Realize why the
bellows is there and don't defeat it's purpose by inflating it with the weight
of the coolant.

Now the question: Coolant leaks seem to be more common these days. What methods
do "y'all" use to clean the PCBs ? I've used acetone with a stiff paintbrush,
alcohol, water and then heat. This seems to be the best method I've tried
lately. On stubborn cases sometime I have to repeat, and sometime remove
non-SMD ICs. I have been known to flush it with water.

Thanks for reading and any input is appreciated.

JURB

"John Del" wrote in message
...
Subject: Coolant leaks, a tip and a question
From: (JURB6006)
Date: 10/11/04 10:47 PM Eastern Daylight Time
Message-id: 20041011224726.06333.00001300@mb-.


Now the question: Coolant leaks seem to be more common these days. What
methods
do "y'all" use to clean the PCBs ?

While it's enormously time consuming, I remove any component that could
trap
liquid. I remove all transformers, chokes, tunable cans, etc. I them
remove
all connector sockets which trap liquid underneath. I then soak the board
in
hot water, and clean with a solution of Parson's kitchen cleaner (uses
amonia)
and water, and scrub the board clean. I then dry in a hot box (big
cardboard
box with a hole at one end to push a hair dryer in) and reassemble. Any
component that has trapped the coolant needs to be replaced. While a pain
in
the ass, at least I know that any further problem isn't from coolant
contamination. If it still doesn't work, I just repair as any other
defect.

BTW, it seems that coolant expands as it ages. I've seen lots of RCAs,
Hitachis, Samsungs and Sonys where the expansion bladder is distended,
even
when cold. When they get hot, the pressure is too much for the
gasket\housing
seal.

The coolant draws moisture out of the air and the combination of coolant and
water is more than can be contained and it
leaks out. This happens most often with TV's in the south and with TV's
that are not used during the summer months (snow birds). When a TV is used
for at least several hours a day the coolant gets hot and moisture is driven
out.

Clean with large amounts of 91% alcohol and a flux brush. Dry with a hair
dryer. Make sure it's really dry!

You might have wires corroded thru or corrosion between two low impedance
devices/lines.

Install a drip shield (plastic tray that will catch future coolant).

Excuse my ignorance, I have never worked on a rear projection set, nor have
I seen the internal layout. But why on earth would the mfg put the tubes
with their possible coolant leaks above circuit boards? Sounds like a dumb
design. Seems like you could put the circuitry up on one side and all the
tubes and optics on the bottom with a drip proof liner under the whole tube
array.
I only mention this because I see so many postings about coolant leaks and
their associated headaches for servicers.
Regards, and kudos to all you guys (and gals) who bravely still work on TV
sets,
Tom

" The coolant draws moisture out of the air and the combination of coolant
and
water is more than can be contained and it
leaks out. This happens most often with TV's in the south and with TV's
that are not used during the summer months (snow birds). When a TV is
used
for at least several hours a day the coolant gets hot and moisture is
driven
out.

Clean with large amounts of 91% alcohol and a flux brush. Dry with a hair
dryer. Make sure it's really dry!

You might have wires corroded thru or corrosion between two low impedance
devices/lines.

Install a drip shield (plastic tray that will catch future coolant).

I usually remove the PCB from the cabinet and put it under a hot water stream,
letting it run for several minutes; then blow it off with an air nozzle
(25psi). Then I set it in front of a small protable heater on low heat for
several hours, followed by several hours of cool air...