VOGONS


First post, by snorg

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I have an old Samsung LCD monitor that I think the backlight is going bad.
How hard a job is it to replace these? Anyone attempted this before?
Any safety concerns like there are with CRT or is there nothing that would
store a current?

Reply 1 of 4, by retardware

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snorg wrote:

Any safety concerns like there are with CRT or is there nothing that would
store a current?

In case of faults the caps in the PSU can carry up to 400V for long time even after being unplugged.
The backlights inverters create a few hundred volts too.
Definitely sufficient for self-electrocution.

Edit:
When I was at school I repaired and sold abandoned TVs.
One day I slipped and got shocked very well. Not mild like with a cow fence.

There was no insulation transformer from the grid. The chassis was at ground potential.
Curious about the potential that cooler in the convergence unit had, which I touched, I took a measurement...

820V against ground ROCKS 😁

So much that it made me respect enough to obtain an insulation transformer...

Reply 2 of 4, by .legaCy

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ground a flat head screwdriver and short all the caps to ground. that's what i do when i recap PSU

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Reply 3 of 4, by retardware

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.legaCy wrote:

ground a flat head screwdriver and short all the caps to ground. that's what i do when i recap PSU

Actually the recommendation given by manufacturers in their service manuals is to discharge caps using a not-too-low load resistor for about a minute.

There are two reasons for this:
1. There is a phenomenon of charge rebuilding. If shorted only for brief time, the charge does not always disappear completely. On capacitors affected by this phenomenon this can be measured by the slow buildup of voltage after discharging.
2. Shorting damages caps internally.

Reply 4 of 4, by snorg

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retardware wrote:
In case of faults the caps in the PSU can carry up to 400V for long time even after being unplugged. The backlights inverters cr […]
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snorg wrote:

Any safety concerns like there are with CRT or is there nothing that would
store a current?

In case of faults the caps in the PSU can carry up to 400V for long time even after being unplugged.
The backlights inverters create a few hundred volts too.
Definitely sufficient for self-electrocution.

Edit:
When I was at school I repaired and sold abandoned TVs.
One day I slipped and got shocked very well. Not mild like with a cow fence.

There was no insulation transformer from the grid. The chassis was at ground potential.
Curious about the potential that cooler in the convergence unit had, which I touched, I took a measurement...

820V against ground ROCKS 😁

So much that it made me respect enough to obtain an insulation transformer...

Yeah I think I'll take a hard pass on chance of electrocution.