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Sanwa 20" V21 PW-1545


ataritoobin

Question

I recently picked up a Sega After Burner "Commander" model that has a 20 inch Sanwa V21 PW-1545 monitor and chassis in it.

 

It worked well, and I had the image dialed in for about 30 min, aside from the top of the image being "squiggly." Then the flyback crapped out, audibly, and without tripping any fuses. I quickly unplugged the machine.

 

I replaced the flyback with a new one (MSH1FPU515A) and replaced every electrolytic cap. Upon powering it up, the image wouldn't sync. Using my multimeter, I found the SYNC and GND lines were shorted. I traced it back to the game PCB and found that the fault was on the PCB. So I suspect when the flyback failed something shorted to the SYNC line. :realmad:

 

I found that FLT 41 and an LS32 at IC174 on the game PCB were now faulty. Replacing those got me back to a synced image.

 

The top of the screen was no longer squiggly (probably fixed by the caps), but the image was pretty blurry. Turning the flyback's focus knob all the way to the right gets it "close" to in focus, but not quite there.

 

My first thought was a faulty voltage regulator/low B+ (hoping not a crap flyback :realmad:), but I'm not clear where to check, nor have I found schematics online for this model. I checked the resistor at R804, and got 73VDC and the fuse at F802, and got 67VDC.

 

I would think this ought to be closer to 100V or 125V, but I don't want to go twiddling without knowing for sure where I should be measuring.

 

The image seems to be more in focus when there's a brighter image displayed, and shrinks a bit/gets more out-of-focus with a darker image.

 

Something that leads me to suspect a voltage regulation problem is when the motors kick in, the image shrinks and dims a bit. Checking the AC into the monitor, it only drops by about 2VAC when the motion motors kick in at their highest torque.

 

Any insight would be helpful and appreciated!

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You need to get the B+ stable and correct before doing ANYTHING to the chassis as if the B+ isn't correct nothing else can work properly. After that the following applies:

 

Focus pot turned hard one way and still out of focus points to corrosion INSIDE the tube socket mounted on the neck board. Especially if it is a white coloured one they are notorious for a buildup of green "gunk" inside the socket (you can't see it unless you chop the socket apart).

 

I would replace the socket before doing anything else.

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