Vectrex text display issues

[RetroTi]

I recently acquired a vectrex console after having been looking for one for a while. Unfortunately it seems to have a few graphical issues, such as lines not meeting up in some cases and being quite wobbly on some screens, but most notably that text on the screen is sometimes 'split' and occasionally is slightly off where it should be.

Here is a picture to illustrate the problem.
http://img14.imageshack.us/img14/4699/img0997so.jpg

Some games do not suffer from this issue but others do. It always happens on the same screens and is very consistent.

[Frankie_Says_Relax]

*shuffles thread to Tech & Restoration*

[RetroTi]

*shuffles thread to Tech & Restoration*

thanks for that

[FABombjoy]

Have you performed the adjustments in the service manual? There are a few thumbwheels that can easily change the vector alignment.

If you need to center the image on the screen, do not adjust the DAC offset control at the rear of the CPU PCB. This advice is given frequently but the correct method is to use the yoke magnets.

I have seen some issues with text rendering that are impossible to adjust out, usually involving the topmost line, as is happening in your pic. There is something about the BIOS's rasterized text routines that the Vectrex can have a difficult time with. I have a project Vectrex that has text problems but I haven't had time for a proper investigation yet. Other than not being visually perfect, it doesn't have much bearing on game play which is nice.

[RetroTi]

Have you performed the adjustments in the service manual? There are a few thumbwheels that can easily change the vector alignment.

If you need to center the image on the screen, do not adjust the DAC offset control at the rear of the CPU PCB. This advice is given frequently but the correct method is to use the yoke magnets.

I have adjusted the two thumbwheels on the side of the logic board, I believe there are no other adjustments possible other than the DAC offset. I will make further adjustments since I learned that the diamond shapes at the bottom of the adjustment screen are the most important and when I was adjusting them I was trying to make the large central one perfect.

I'm afraid I already followed the advice to center using the DAC offset, as the screen was significantly off center. I have no idea how to use the yoke methods and any advice on this would be very helpful if it would improve the graphics quality.

I have seen some issues with text rendering that are impossible to adjust out, usually involving the topmost line, as is happening in your pic. There is something about the BIOS's rasterized text routines that the Vectrex can have a difficult time with. I have a project Vectrex that has text problems but I haven't had time for a proper investigation yet. Other than not being visually perfect, it doesn't have much bearing on game play which is nice.

Yes, its always the topmost or two top lines, and it only happens on certain lines of text, always the same ones and always the same amount. Is it a problem with one of the chips or on the logic board, or is it more likely a display board issue?

[FABombjoy]

I have adjusted the two thumbwheels on the side of the logic board, I believe there are no other adjustments possible other than the DAC offset. I will make further adjustments since I learned that the diamond shapes at the bottom of the adjustment screen are the most important and when I was adjusting them I was trying to make the large central one perfect.

There are a few adjustments on the Power PCB: X and Y size, and HV, which should not be set without a scope and HV probe.

I'm afraid I already followed the advice to center using the DAC offset, as the screen was significantly off center. I have no idea how to use the yoke methods and any advice on this would be very helpful if it would improve the graphics quality.

The process in the manual requires an oscilloscope to set the DAC offset, although you might be able to put it back where it was and dial in the magnets. If you take the DAC offset too far one way or another, you'll see the vectors begin to fade out. You could possibly bring up one of the test screens and tweak the offset until it looks good, and then to center, you'll see two rings between the yoke and neck PCB. Mark them (just in case), loosen the yoke clamp, and adjust them until the image looks good and centered.

For reference, this process is at the top of page 15 in the manual.

Yes, its always the topmost or two top lines, and it only happens on certain lines of text, always the same ones and always the same amount. Is it a problem with one of the chips or on the logic board, or is it more likely a display board issue?

Last time I messed with it, things were pointing to the power board, but I had to shelve the unit to make time for other projects. I'm sitting on about 3 Vectrex units so it might be time to revisit