Vectrex with half width image and bent vectors

[richud]

Hi,

I have a 3000 UI - UK Vectrex that is only displaying the image at about half its proper width, its height is however fine.
X/Y size control R401/8 are linear and seem to function ok with sensible resistances. (X goes between half size at max and about quarter size at min.)
In Mine Storm the ship on the boot screen looks ok but the star things you shoot seem to have bent lines?? The text looks ok too.

I have had a good poke about with my oscilloscope and can't see anything obviously wrong. Am at a bit of a loss....

Pics are X and Y at the back of J403 and their returns from R413/R406 (taken on Minestorm). I don't have a diag cart.
(Ground taken from braid between logic and power board.)





The only other thing of note is when turning on, sometimes it plays the music instantly and sometimes there is a second or so pause before it starts. It never doesn't start though.
All the controller buttons works, albeit with lots of pressure.


I have been looking at the oscilloscope bits from https://github.com/Guimli/Vectrex-Repair-Manual/blob/main/Repair manual Vectrex 20230327.pdf and things look pretty similar, ignoring the few mistakes in it.
(Y output p69/70 I can't reproduce though, mine doesn't look at all like that.)

Heat doesn't seem to change anything, seems very reliably exactly the same problem at all times.
... anyone got any ideas ?

Cheers!
Rich

 

[daver2]

Hi. Welcome to VCFED.

I will take a look tomorrow morning.

Do you have a copy of the test/diagnostic cartridge?

If so, can you get the crosshatch display up and look at the X and Y signals on your oscilloscope.

Dave

 

[richud]

Hi Dave, Thank you!

Afraid I just have the bare unit, my friend 'kindly' lent it to me to fix! (have shorted dead thermal fuse on transformer and got power button working, then stumped with this...)

Clue/something that had been puzzling me was how the vectors on the text & ship [that goes into the distance on intro] look 'ok', but in the game the 'floating mines' (just looked up their name in the destruction manual!) have curved vectors that don't join?

 

[daver2]

Hi Rich,

Sorry, I missed where you originally stated you do not have a diagnostic cartridge.

A diagnostic cartridge would make this much easier - as it gives a nice, stable reference signal (on X, Y and Z) to look at with the oscilloscope. OK, we have to make the best use of what we have...

You need to identify first whether the problem is on the logic board or the power board.

You need to look at the voltage swings on the X and Y signals from the logic board to the power board (during the times when vectors are being generated) to see what the maximum (positive) and minimum (negative) voltages are. Compare and contrast the X and Y signals to each other. They should be of a comparative signal level (both the positive and negative levels) for an equivalent screen deflection.

Your oscilloscope is indicating the maximum, minimum and peak-to-peak of the signals - but including the 'spike' (which appears to be the largest thing on the oscilloscope trace - which the oscilloscope is using as its reference for the measurements). This could be misleading...

If I remember correctly, @miata has taken some oscilloscope traces from his repaired Vectrex that you may be able to use as a reference?

I assume you have checked the positive and negative 5V rails and the positive and negative 9V rails for the correct voltages with acceptable levels of ripple and noise? Always the best place to start. We have also known problems on the -13V rail that have caused issues.

Dave