My Monitor Test Bench

[SirPeale]

The idea isn't mine, I stole it from my old job, and they stole it from Al from New England Coin Op.



I took a piece of plywood and screwed down a Peter Chou power supply.  An old power block from a scrapped game was perfect to house most of the wiring.  It even has an interlock switch - perfect if I have to suddenly cut the power.  And the isolation transformer was already wired in, along with the power outlet.  I'm not sure what game this came out of, but it's handy.

An old JAMMA harness was perfect because, well, that's what I had.  Plugged in an old Tetris board.



Different monitors have different power connectors - what to do, what to do?  Take an old TV power cord, cut off the ends, and solder the ends of my broken multimeter leads to it.  That way, I can just slide the meter ends into the power connector on the monitor. 



Video signal connector.  The sync wire is an alligator clip so it can go where it needs to.  Note that it's on a six position Molex connector - that's so eventually I'll build connectors for different monitors, like the Sanyo EZ.  I'd love to find an isolation transformer that has outputs for 100VAC out as well as 110VAC.  The one that's in there now has 117 out and 110 out.

[qrz]

just in case ur unaware, a common failure in that perticular smps is open resistors in the start up .

there are two 220k - 470k  .5w resistors that bias the xistors on for start. dead supply if either is open 

add a variac to the xformer and can get variable voltage

qrz

 

[SirPeale]

just in case ur unaware, a common failure in that perticular smps is open resistors in the start up .

there are two 220k - 470k  .5w resistors that bias the xistors on for start. dead supply if either is open 

Good to know.  I've fixed a few of them before, but never with that problem.

add a variac to the xformer and can get variable voltage

Ooh, good idea.

[SirPeale]

Variacs are *expensive!*

Could I use a pot to get the same result?

[MonMotha]

http://www.mpja.com/prodinfo.asp?number=15162+TR  <--- Variac, $50, brand new, and more than enough to run most cabinets off of, let alone just a monitor.

[qrz]

hmmm..,  not a bad price , AND it has a meter too !   or a 15A  unit for $110
pd $495 almost 25 yrs ago for my sencore pr57 
then i see what the stuff now goes for on ebay - 

TNX for the link - had never heard of the co

note to Peale,
 a variac or auto-transformer will allow the output voltage to be adjusted above and below the applied input voltage .  a pot would only lower the voltage and would likely be expensive for the needed wattage .....

qrz

[SirPeale]

note to Peale,
 a variac or auto-transformer will allow the output voltage to be adjusted above and below the applied input voltage .  a pot would only lower the voltage and would likely be expensive for the needed wattage .....

All I need to do is lower the voltage to 100VAC.  But noted about the expense for the needed wattage.  Since I'm doing this on a shoestring, for now I'll just use my Donkey Kong for any that need repair.

[Level42]

Better not touch those multi-meter leads when you've got them plugged in. Quite dangerous solution !

But all the different connectors ARE a pain...

[SirPeale]

Better not touch those multi-meter leads when you've got them plugged in. Quite dangerous solution !

That would require operator error, so I'm not worried.  I only plug that in when they're in place.

[SirPeale]

Since I only need just the two voltages, I should be able to pull it down with a resistor.

What's the formula to determine the value of the resistor I need?

[SirPeale]

That was easier than I thought.

http://www.opamplabs.com/eirp.htm

Now I need ~100ohm resistor.  Something beefy.

[MonMotha]

If you're planning on just using a power resistor inserted inline to drop some voltage, that only works if the input current to your monitor is actually constant, which it never is on a monitor (just do a black screen vs. white screen test to see this, let alone startup transients and running the degauss coil).  There are some ways to do this using "really stiff" voltage dividers, but the power dissipated in the divider would be insane (we're talking space heater levels) to get the kind of load regulation you desire.

As an example, say your monitor is rated for 1A, but you're displaying a black screen, degauss is off, etc.  It may only be drawing half an amp.  So if you had a resistor in-line to drop 120V to 100V on the assumption of a 1A draw (a 20 ohm resistor), you'll only be dropping half that, and you'll be applying 110V to the monitor.  You can go the other way, too.  Usually, the rating is "steady state" and won't include startup inrush.  On inrush, some monitors can draw several dozen amps.  Suddenly, that resistor is basically dropping you down to almost 0V (and getting REALLY toasty)!

A variac or transformer is the best approach here.  Note that if you can get your transformer apart somewhat, you can re-wind them to change the turns ratios and get other output voltages.  Getting it apart depends on how the thing is constructed (sometimes it just isn't worth the effort).

[SirPeale]

Well, so much for that idea then.  Thanks for the input.

[SirPeale]

Someone was asking about this the other day, so here's a gentle bump.

[SirPeale]

Here's another bump to announce that I just found an iso transformer that outputs both 100V and 120V.  Going to wire it up and have the voltage switchable.

I love my setup, but I should really pick up a color inverter for when I test inverted monitors.  I've done this for peanuts though, it would be the most expensive part of this tester.