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Extron 190F power supply issue (DC voltage regulation)


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I was given an Extron 190F sync splitter/combiner by a very nice person a little while ago, and the unit has a small fault. Powered from a wall wart, or other cheap power supply, the picture comes up stable, but with massive black tearing, so bad it's almost flickering. Only a third of the picture is displayed at any instant, and which third moves up and down so fast it's like an instant headache. I was worried it was going to rip into my old sets it was that bad :)

 

I tried 4 different small power supplies, from .3A to 1.5A, wirewound and switching, all at 12V (the unit says 1A at 12V-15V, but will work from a 9V supply happily). Being thorough this one time, i decided that rather than testing all 4 power supplies, i'd try my variable benchtop supply instead and rule them out, and lo and behold it worked perfectly. Figuring this had to do with the quality of DC regulation, and the fact any cheap plug-in AC-to-DC powerpack is going to have a bit of ripple, i thought about it, asked one of the EE's at work, then came home and tried a 5600uF 16V capacitor across the power supply rails (+ve to +ve, -ve to -ve). Problem solved. I'm not sure if this is due to age, of if the Extron devices are really, really picky about the smoothness of the DC power input. But it works now, and i didn't even have to open the unit :)

 

I then tried a 4uH inductor in series with the +ve rail, and the problem returned. Not sure if it's because the power supplies weren't able tp provide enough amperage. The unit was only drawing 0.25A from my benchtop supply.

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... are you masking a problem inside the device perhaps?

 

Almost certainly. The sister unit to this one works normally with the original Extron power supply, I'm told, but not with a cheap replacement (showing the same issue as above). This unit displayed an identical problem with either power supply. Given it ran fine with my variable benchtop supply, i thought i'd try the cap, and it ran for for 4 hours straight without a hiccup.

 

The 190F is a pretty small unit, it can't have much regulation inside, and it's also pretty high quality, so i figure it was meant to have a well-regulated supply. In part because they've used an uncommon power connector, which necessitates people come back to Extron to buy replacements :)

 

I wonder if something inside keeps trying to set a cutoff level, and i hope the smoother power stops degradation of whatever it is.

Edited by buttersoft
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