Sharp XM-2001 repair log

ELutz

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Since there's not a lot out there on the inter-webs regarding these Sharp monitors....I thought I'd toss up my notes on the two I just finished up.

Monitor #1--Looked like ass, but was working. Fuzzy picture, shriking image....a cap kit and a tube rejuve...done.


Monitor #2--This one was a mess. It looked as if it had been stored outside for a couple years, and rodents had used it as a toilet. Cleaned it up a bit and did a cap kit....fired it up....dead. B+ was reading approximately 90 volts (it's supposed to be 110 volts). I had no high voltage....stuck my high voltage probe under the anode.....nothing. This I found strange. I would have suspected my high voltage to be low, not zero. I found this nugget Ken Layton uploaded...
http://home.comcast.net/~mtpacifico/_kenskorner/files/Sharp%20Monitor%20TroubleShooting%20Guide.pdf


This monitor operates very different from most monitors I'm familiar with. It uses an initial "start up" voltage from a secondary of the flyback. This voltage goes to a SCR. Once the voltage reaches a certain level, the SCR starts to conduct, this will then "turn on" the regulator circuit, thus allowing the horizontal oscillator and output circuit to operate. Since my voltage wasn't high enough to start the conduction of the SCR, my horizontal curcuits were never starting.....thus......zero high voltage. I don't know of any other monitor that operates like this. I started digging through the power supply/regulator section. Nothing. After more digging (and swapping parts from the previous Sharp I just finished)....It turned out to be IC601. Replacing the X0065CE IC chip brought my B+ up to 110 volts, and I now had high voltage. Now the monitor was very dim, but not a normal dim. I had the screen pot on the flyback all the way down, the brightness pot was down, and the sub-brightness pot was down. I has raster lines, but a dim image. The tube checked out fine with the rejuvenator. It was something on the chassis. I started digging through the brightness/blanking circuit...nothing. All transistors and diodes checked out with my meter (I swapped some into the other working monitor), all resistors were good. I saw this once in a Sanyo monitor, and it was a 12 volt zener in the blanking circuit. This Sharp had a very similiar design. The zener tested good, but I swapped anyway.....no change. I swapped neckboards with the other monitor I fixed....no change. I decided to test the voltages at one of the color driver transistors on the neck board....base was 7+ volts(this is good)....emitter was about the same (this is good)....collector was about the same (this is bad.....it should be approximately 65-150 volts). This voltage is a feed straight off the flyback with only a resistor and a diode before reaching the neckboard. I figured the diode (the resistor visiually looked fine)....the diode was good....as soon as I touched the resistor, it broke in half....bingo. I replaced.....the monitor is now fine.

I reassembled the other working monitor I'd been swapping parts from.....now it's blasting red. It's not a red gun stuck on. I can turn the red up and down, but it's not controlling the specific red colors. It's controlling my background/black level. I have no black....it's red! I started going through the red circuit. It turned out to be one of the pre-drivers on the chassis...Q402 had a leaky base-to-collector. Replaced...all good again.


Long-winded as usual,

Edward
 
good stuff. I have one of these from an r-type and it was really tough to work on. In fact, its the only monitor that I've had to send to arcadecup this far. Mine was clean but sure had a lot of blown parts and broken traces. I couldn't find much online documentation either. Thanks for posting.
 
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