Monitor only showing half of screen

chessfest

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My Asteroids Deluxe is showing only the left half of the screen. The other half is blank although you can see on the dividing line the lines where asteroids are in the y-position. I assume that this has to do with the x-output from the PCB somehow, but how can I fix it? Thanks!
 
First - check the monitor. There are some frame-mounted transistors (2N3716 and 2N3792) that can go bad and cause this. There should be two each, one pair for the X and one pair for the Y. If one goes bad, you'll lose half the picture. If two go bad, you usually lose the entire picture and get the spotkiller light on.

Also, the wires to those transistor sockets can come loose, the connector on the deflection board from the transistors can have cold solder joints underneath, and the connector from the PCB to the monitor can have cold solder and/or loose pins.

I would check that before suspecting the board, especially if it was working prior to this...
 
Well, the easiest way is to get a multimeter, set it to diode test, and measure between the two legs and then each leg and the outside casing. If you get a beep or zero reading, it is bad. Make sure you unplug the the connector to the deflection board before doing so, as you may get a false reading through the board.

If you don't have a meter, you could always swap one 2N3716 with the other 2N3716 and see if the problem changes. If so, replace the bad one (or both if you can't figure out which is bad). If no change, swap the 2N3792's and check again. I usually change out all four if I have a problem with one.

Sometimes, you may find that the transistor that is in there, doesn't have the 3716 or 3792 markings. If that is the case, report back on what you have...
 
All monitors have what they call "lethal voltages" coming from the HV section to the tube. As you will be doing these tests with the power off, you have nothing to worry about, especially since you aren't doing anything with the high voltage cage anyway....
 
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