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   Home   Help Search  
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Author Topic: Dell monitor and its on/off switch  (Read 1257 times)
KM3K
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Posts: 430




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« on: December 14, 2009, 11:32:43 AM »

I want to use a 3-year old Dell monitor to display HRD/DM780.
My problem is the on/off power-switch is going intermittent (mostly not turning on).
I've taken it apart and see there is a surface-mounted "tactile-switch".
I don't know how the "tactile-switch" is supposed to work.
I could try cleaning the region with alcohol to see what that might do (BTW, this is a non-smoking home).
If nobody can tell me how to fix it, my "plan-B" is to just hard-wire a jumper so it is always ON and just shut it off at a power-strip.
I'm not considering replacing the switch.
73
Jerry KM3K
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KC9HVA
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Posts: 59




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« Reply #1 on: December 14, 2009, 11:47:51 AM »

power strip
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VE6JRU
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Posts: 5




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« Reply #2 on: December 14, 2009, 12:27:23 PM »

Jerry,

You may want to try jumping it without soldering anything on yet; just short the terminals with a piece of wire.

Many "power switches" in modern PCs and monitors are just momentary pushbuttons that activate startup / POST routines.

If a quick short / jump powers it up, it stays running without the jumper, and then another short / jump kills it, you'll know that the switch is just a momentary button, and a permanent bypass with a jumper might not be the best solution.
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W6VPS
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Posts: 369




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« Reply #3 on: December 14, 2009, 12:30:36 PM »

Yet another thought...fiddle with it until the monitor comes on. THEN go to powering it on/off via the power strip.  Less work that way and you can delay soldering a jumper until the switch fails totally.

Paul/W6VPS
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N4NYY
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Posts: 5206




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« Reply #4 on: December 14, 2009, 02:37:47 PM »

Leave it always on, and have it go to sleep, so it powers on when you fire up the tower.
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TANAKASAN
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Posts: 933




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« Reply #5 on: December 15, 2009, 12:12:28 PM »

Wiring a short across a pushbutton switch might not work as this is supposed to be a momentary connection supplying a pulse. If it doesn't work measure the voltage across the contacts and then wire a suitable 0.1uF capacitor across the connections.

Example:
You measure 35v across the contacts so use a 50v rated capacitor.

OR

You measure 5v across the contacts so use any 0.1uF device.

Tanakasan
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KM3K
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Posts: 430




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« Reply #6 on: December 16, 2009, 01:48:32 PM »

Why should I wire a capacitor across the switch?
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KE3WD
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Posts: 5688




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« Reply #7 on: December 16, 2009, 07:17:58 PM »

TANAKASAN is telling you a neat trick to "debounce" the contacts of a dirty or worn/intermittant switch of this type.  

BUT -- in a soft start circuit of this type, it may easily NOT be the switch and its contacts at all.  There are other components in the circuit that may fail, causing it to appear to be a dirty switch contact.  This happens quite a lot in such appliances.  

Permanently jumpering a softstart switch won't work.  The softstart circuit must see a state transition in order to function.  

However, if you can find a schematic or trace back to where the actual AC power is applied, you might find a RELAY that can be jumped and then you can use standard AC mechanical switching method such as that power strip, etc.  

Good luck with it.
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TANAKASAN
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Posts: 933




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« Reply #8 on: December 17, 2009, 05:16:01 AM »

"Why should I wire a capacitor across the switch?"

Some microprocessors in monitors expect to see a pulse from the power switch rather than a steady signal. By wiring a capacitor across the switch this will start at Ov then rise to 5v or 3.3v through the pullup resistor.

Tanakasan
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