Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Hot electrolytics

Anyone idea of the temperature required to make the heatshrink label wrapper
of a small radial electro shrink down the cylinder, requiring stretching the
shrunk end, sliding over the rim, before sliding down the cylinder part. ?


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Default Hot electrolytics

How much is down to conflict between power supply designer and EMC
compliance bod?
Designer: I want convection vent holes here, here and here, through the
shielding
EMC bod: No way, I can let you have a few holes here and thats your lot

Just repaired an LCD monitor, probably started failure with ESR'd caps then
ohmic zener and eventually blown backlight inverter pair of transistors and
blown fuse. Plenty of holes top, side and bottom of the shield on the
digital processing side but only holes at the top on the ps side. So air
comes in on the colder side at bottom rises to the top by about mid board
and little or no air traversing the hottest section, that whole section in a
dead-zone in more ways than one, brilliant


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Default Hot electrolytics

N_Cook wrote:
How much is down to conflict between power supply designer and EMC
compliance bod?
Designer: I want convection vent holes here, here and here, through the
shielding
EMC bod: No way, I can let you have a few holes here and thats your lot

Just repaired an LCD monitor, probably started failure with ESR'd caps then
ohmic zener and eventually blown backlight inverter pair of transistors and
blown fuse. Plenty of holes top, side and bottom of the shield on the
digital processing side but only holes at the top on the ps side. So air
comes in on the colder side at bottom rises to the top by about mid board
and little or no air traversing the hottest section, that whole section in a
dead-zone in more ways than one, brilliant



Any cap with shrinking plastic film is ready to be replaced. Figure out
what circuit it is in and find either a low ESR or low Inductance (or
both) cap to replace the poorer original one.

We put fans on any LCD screens that we install in any sort of cabinet.

It would be nice if tiny fans were installed by the manufacturers...

John :-#(#

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Default Hot electrolytics

John Robertson wrote in message
...
N_Cook wrote:
How much is down to conflict between power supply designer and EMC
compliance bod?
Designer: I want convection vent holes here, here and here, through the
shielding
EMC bod: No way, I can let you have a few holes here and thats your lot

Just repaired an LCD monitor, probably started failure with ESR'd caps

then
ohmic zener and eventually blown backlight inverter pair of transistors

and
blown fuse. Plenty of holes top, side and bottom of the shield on the
digital processing side but only holes at the top on the ps side. So air
comes in on the colder side at bottom rises to the top by about mid

board
and little or no air traversing the hottest section, that whole section

in a
dead-zone in more ways than one, brilliant



Any cap with shrinking plastic film is ready to be replaced. Figure out
what circuit it is in and find either a low ESR or low Inductance (or
both) cap to replace the poorer original one.

We put fans on any LCD screens that we install in any sort of cabinet.

It would be nice if tiny fans were installed by the manufacturers...

John :-#(#

--
(Please post followups or tech enquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."



They would not have to be high revs, just enough to circulate air in or out
of dead zones like between heatsink plates. In this case the hottest as
evidenced by the shrunk sleeves , were from between a U of heatsinkery. I
will try controlled heating of one of the other removed caps of the same
make to see what temp it must reach to axially shrink the wrappers.
Do they make miniature
longitudinal fans say .5 inch diameter x 1 or more inches long ? Failing
that it would be some ducting associated with standard 1 inch fans.

If no fans allowed I would have placed the ps board over the "scaler" board,
assuming the whole monitor is not used horizontally




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Default Hot electrolytics

I had pulled a number of bulging but otherwise looking as original 16V,
470uF of the same date code from this monitor - make HERMEI LT 105 degree C,
purple wrapper
First one took to 190 degree C , wrapper shrank but not fully back over the
rim. Outgassing before that and final colour very dark plum.
Axial shrinkage of the fully shrunk one about 75 percent from edge of open
end at top to the pin end rim , ignoring unaffected other open end at the
pins
Looks as though this shrinkage is a cycling cold/hot effect as the shrunk
one was a plum colour.
Tried another taking the temp only up to the plum colour , about 180 deg C,
also visibly outgassing at that temp
Comparing to additive colour of a pc monitor
Hue/Sat/Lum/R/G/B
unaffected purple of original 200/240/100/215/0/215
180 deg colour 200/240/75 / 165/0/165
190 deg colour 200/240/55/115/0/115


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