Repair of old arcade monitor 1979

John: There may be, as with old B&W TV sets a couple of usually black cardboard looking circular pieces with tabs often mounted on and comprising part of the back of the yoke. Those could be rotated (gosh how rusty I am on this!) to magnetically centre the whole raster (picture)? Try that? I guess the 'black things' were somehow magnetic and steered the electron beam? There used to also be an 'Ion trap' that had to also adjusted; if it was way off the picture would show on the screen at all! IIRC the trap was to steer the electron beam/s back towards the screen to avoid ion burn? because the tube gun was manufactured not exactly pointing at the screen. The ion trap looked like a springy open metal clip around the tube neck and contained a small magnet about half the size of postage stamp. Maybe that's missing? If so try a smallish magnet to see if affects the problem. But stand to be corrected on any of this by those more knowledgeable. Terry

Ion traps were a good deal earlier than 1979. You are correct about the tabs at the back of the yolk though - I think they were called 'shuffle magnets' or something like that(but my memory might be no better than yours here) - and they might well be the cause of the problem. Turning them independently of each other should centralise the raster - loosening and turning the yoke itself will only move the scan in the horizontal plane (but make sure the yoke hasn't come loose and moved away from the CRT). All this assumes that it is a monochrome monitor.

On 28 Mar 2006 11:39:54 -0800, snipped-for-privacy@sbcglobal.net put finger to keyboard and composed:

Could it be a horizontal phase or horizontal delay issue somewhere in the sync stripper circuit?

- Franc Zabkar

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If the picture is off centre, there is obviously a component(s) that has failed. It would be best to have the monitor properly serviced, rather than try tweaking it to compensate for an error. I am sure that the monitor originally did not have the fault you are describing. In a monitor that old, it is more than likely that there are a number of high ESR capacitors, and maybe even some resistor values that have drifted out with age, and whatever use the monitor had.

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JANA _____

John

Suggest jumping to the forums at arcadecontrols.org

Depending on the make & model of the monitor there are prepacked "capkits" made for certain monitors. Yours is certainly old enough to have several failed electrolytic capacitors and a failed trimpot or two.

Buy your capkits from Zanen Electronics at (806) 829-2780. Suggest also checking out the Vector monitor FAQ & repair guide at ionpool.net

Those never had enough range to cause what has been described, unless perhaps deliberately totally messed up by someone before him.

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Thank you all for your tips. It's good stuff. I was able to locate the magnet adjustments but clearly there is something wrong with the electronics. Zanen doesn't appear to offer a kit for this board. It's an old Vectorbeam monitor from a "Warrior" game. And due to the rarity and obscurity of this thing I think I'm going to defer to a professional on this one after all. Thank you all for your help though!

That's not always true, these things quite often got fiddled with, or just mechanical vibration would muck up the adjustments, or the monitor may have come from some other game and been swapped in without adjusting it.

Not in a vector monitor, they're essentially audio amplifiers driving the deflection yoke. These particular monitors have onboard DACs.

Go check out rec.games.video.arcade.collecting There are quiet a few knowledgeable people over there. You might even be able to find someone to fix it for you there also..

- Mike