cadwallader

I don't have the logic board out, but I carefully inspected both sides of the step-down transformer. I couldn't find anything visibly wrong, however I find it interesting that the tranformer is switched on the low voltage side and not the 120v mains side. That would explain why some of the wires are a bit stiff, probably from the unit being plugged in all the time (years ago) which caused the transformer wire insulation to heat up. Even with the stiffness and a little bit of deformation everything is still OK. The switch itself has good solder joints and despite jiggling, pushing and pulling the knob I couldn't get the problem to repeat. I also looked the fuse under the cardboard cover. OK as well. However I think you have a point that a weakness in the PS somewhere could be causing the voltage drop which expands the screen. Maybe the transformer wires or actual windings of the tranformer are intermittent in some way. I've been tapping on everything in and around it but no reproducing the symptoms. Moving the power board back and forth can cause and correct the problem. Something is weak somewhere. I guess I'm going to have to take everything out and look at the boards more closely. Sometimes taking things apart and putting them back together magically fix some hard-to-find problem.

I discovered two clues that may be of importance for solving this problem: 1) If the display is exapnded (zoomed, scaled) when the machine is turned off, it will remain that way when its turned back on. This would seem to indicate that its a connection problem, because the opposite is also true (turn off the machine with a normal display and it will be normal when turned back on). 2) The screen problem I described (expanding, zooming, scaling) looks exactly like the display just after the machine is powered off: it scales or expands just before it fades out. This may mean that there is a voltage drop that is the cause of the effect (rather than an increase in voltage as I thought before). Taken together this makes sense because a weak electrical connection somewhere could easily lower the voltage to the CRT causing a weaker (or expanded picture). I'm still wondering if this is happening in the flyback transformer - maybe a slight arcing in the coils. Any further suggestions would be greatly appreciated.

I tried your suggestion but apparently the chips in my unit made good contact with the socket pins. The only areas of oxidation were outside the contact areas where the pins of the chip make a right-angle bend. I'm still thinking that the voltage to the CRT must be bypassing a resistor or circuit that regulates it, so when the component or circuit is bypassed the voltage to the CRT is increases, resulting in a scaled-up image. Maybe its the flyback transformer that's doing this.

I haven't been able to find anyone documenting this specific problem either, but I'll give your suggestion a try. I closely inspected the PCB solder joints and could find none that were cracked or loose, so maybe it is one of the chips having a little oxidation in the socket. I'll find out. Thanks.

I'll definitely take a look at that but I doubt its the problem. If the 120V power was intermittent the effects would be very obvious. In my case the machine is fully powered but has some kind of issue with the picture tube control signals.

Thank you for your reply and suggestion. I removed the wiring harness you mentioned and replaced it several times to ensure the contacts got a good scraping but there was no change in behavior. There must be something else loose that causes the expansion (or zooming as you called it). I tried manipulating some of the other wires while the unit was on and found that there wasn't a specific wire that was responsible, however I was able to reproduce the problem most frequently when pushing and pulling on the power cable grommet underneath the console. Its very unlikely the 120V line has anything to do with the screen behavior though it could be causing another loose connection to move.

I've had a Vectrex for about 20 years now and its always had the same problem, however I never knew about this forum with its many solutions until recently. The problem is that the entire displayed image expands or scales so that the edges of it are outside of the displayable boundaries of the picture tube. This causes some of the text and images normally close to the screen boundaries to disappear. For example, in Mine Storm, the number of remaining ships are normally displayed in the lower right corner. When the display expands or scales up, those ships are no longer visible except for faint glow of their upper edges. The scaling is in both the X & Y axes (horizontal & vertical) and is apparently uniform across the screen. About the conditions that seem to bring on the problem, I've found that it occurs randomly while playing and can be cured by simply banging on the console a bit. This problem does not seem to be heat or time related because it can brought on or cured at any time by a slap to the side of the unit. I disassembled the Vectrex and blew dust off the components, looked for obviously damaged parts and faulty connections but haven't seen any despite a fairly throrugh inspection. The high voltage connection to the picture tube is stiff so I manipulated it but that had no effect at all. What did seem to give the display less susceptabilty to this problem was tightening some of the screws holding in the power PCB. I know enough about electronics to have a general idea where this problem originates but not enough to find the exact cause. Hopefully its nothing more than a weak solder joint in a location well known to the experts here. It doesn't see like it would be a component since I haven't seen any bulging capacitors or burned resistors and getting it cured by slapping the machine seems to indicate a connection problem, though it would be great to know where to look for a bad solder joint or loose wire. Attached are two photos of the screen, one under normal conditions and one with the screen exhibiting the expansion I described. In the photo of the expanded screen its possible to see the faint glow of the mostly off-screen Mine Storm ships remaining. Any advice, suggestions, solutions or recommendations will be greatly appreciated. My Vectrex is like an old friend with a long running ailment and maybe now I can find a cure for him.