Strange Vectrex Fault, any ideas?

[vtk]

hi guys,

 

i have a vectrex here, with a strange fault

i made a quick video showing the fault, here is the link to watch the video:

 

http://drive.google.com/file/d/0B7wL60tHjgC0YTU4d3diOGEzeHM

 

please note: this is not a problem with the controller as i tested using some different '100% working good' controllers

(problem also occurs if there is no controller plugged in)

i also tested using a cartridge (instead of just testing with the built in game 'minestorm') .. the problem occurs with cartridges also

 

to summarise the fault in the video:

the vectrex graphics are messed up, but using the controller, if i push the controller joystick LEFT or DOWN, the loud buzzing goes away, and the graphics change/improve (less garbled looking.. so for example, you can read text/words on the screen)

if i push the controller joystick RIGHT or UP, the graphics change a very little amount, and the buzzing 'pitch' changes, and is louder in volume

 

i did another test and plugged in two controllers into joystick ports 1 and 2

when i push LEFT or DOWN on BOTH controllers at the same time, then the gfx come even closer to being normal (still a little messed up, but not too far away from being 'ok' !)

 

other notes: there is no sound/music. but, the speaker is working; the buzz comes out of the speaker and gets louder if i turn up the volume knob

when using the controller, the spaceship in minestorm spins around, however i cannot move the spaceship (thrust), or fire lasers

 

does anyone have any ideas as to what the problem might be please?

note: i do have an identical (hong kong model) spare vectrex here, working 100%

 

regarding testing: the only thing i have done is, cleaned the vectrex inside, cleaned the chip sockets, and also cleaned the pins of the removable chips

i also gave the pcb plugs/sockets/pins a clean

... also, i had a look at the soldering joints for dry or bad solder (note: i didnt look for hours with a magnifying glass, but instead just a quick look over, and didnt see any obvious bad solder)

 

if anyone has any suggestions please let me know.. i do have a multimeter and can test things like voltages and continuity, etc

 

thanks!

 

 

 

 

[fiddlepaddle]

Not an expert, but it sounds like maybe a capacitor issue...

[Rolo]

Maybe the DACs not zeroing properly? Vectrex software must frequently recalibrate the integrators by calling an inbuilt BIOS routine to shift point (0,0) back to the CRT-center. Looks like yours is working, but looses center of screen.

Maybe IC305 (4066 quad analog switch) or adjacent components (IC303, LF347 quad opamp)?

Did you run the DAC-offset-test of the test cartridge?

And maybe the joystick-test, too.

 

Could give some hint to the problem, maybe.

Just a guess.

[vtk]

hey guys thank you very much for your help

i was just having a little look at the problem now, and had a look around the internet for help, in case someone else had the same problem in the past

i noticed an interesting post by Richard H, on these forums

he said that the vectrex AY sound chip, does not just control sound, but also controls something to do with the joystick Input/Output

regarding my faulty vectrex, i have the issue of no sound at all, and also the strange behaviour with the joystick controller, so im wondering if there might be a problem with my AY chip (or the socket soldering/contacts)

i do hope that's the issue! that would be a nice easy fix

as i already mentioned, i have an identical (hong kong model) vectrex here, so i can test the working AY sound chip from that vectrex unit with my faulty vectrex unit

i will try that test tomorrow, and certainly post back the results

 

if i dont have any luck with the AY sound chip, next i will try your suggestions Rolo. im not sure i can run the test cartridge, as dont forget that my screen is badly messed up, so i wouldnt be able to read or see any of the test results

 

regarding capacitors, that would be the very last thing i look into. why? because:

1. my vectrex warms up very fast when i turn it on (the screen comes on in just a few seconds). i think if capacitors are old and worn, the vectrex would take some time for the screen to come on/warm up.

of course that said though, there may still be a capacitor which went bad (regardless of age/hours of use).. so i wont rule out a problem with a capacitor/capacitors

2. it seems to be a common thing that people with faulty vectrex's do, they change all of the capacitors* (takes money, time, not a small easy fast job)... and then, after all that trouble, the fault they had with their vectrex is not fixed and still occurs. so, personally, i really want to rule out as much other stuff as i can, before starting to look at capacitors

 

thanks again guys!

 

 

 

*of course it is still a good idea to change the electrolytic capacitors though because the capacitors in the vectrex are more than 30 years old now. you just have to be prepared to buy many capacitors and spend much time and work to change them all.

[SiLic0ne t0aD]

Seconded on replacing the AY-8912 PSG. Probably wouldn't hurt to replace all the caps while you're in there

[Rolo]

 

 

it seems to be a common thing that people with faulty vectrex's do, they change all of the capacitors

 

Well, I would follow that thesis. Of course, we know, electrolytic caps dry out and loose capacity. But on the other hand, the circuits often are designed with much tolerance. I never just change caps on my devices, because they are old. Usually the PSUs are affected first, which often produces some kind of noticeable 50Hz/60Hz artifacts and which can be measured with the scope easily. In this case I change caps.

[vtk]

hi guys

 

today i put the good vectrex AY sound chip from my working vectrex, into the faulty vectrex

 

the good news: i have sound/music working again, and also the controller seems to work ok now (in minestorm, i can rotate ship, thrust, fire, teleport)

 

the bad news: the graphics are still messed up, so it looks like this vectrex has multiple problems (aargh!)

 

ok, so next i will proceed in trying to find the problem causing the bad display gfx. i will report back here with the results

[Mayhem]

Where did you get the AY sound chip from, and how easy was it to replace? I suspect one of Vectrex units needs that replacing due to sound/controller issues.

[vtk]

Hello Mayhem,

 

I got the AY sound chip from my working vectrex to put into the faulty vectrex

 

so now i will purchase a second working AY-3-8912 sound chip from ebay. i notice on ebay there are many cheap AY-3-8912A chips, but i read on another forum that the AY-3-8912A is not compatible with the vectrex (also i read that the AY-3-8912P is not compatible). i dont know for sure if that is true though, but that is what i read on another forum

[SiLic0ne t0aD]

Glad to hear that AY PSG helped. :-)

 

I also forgot to mention, pull, clean legs/sockets and reseat all socketed IC's on the board. This may "jump start" a faulty chip that isn't functioning correctly due to being dirty/poor contact vs. failing all together

[vtk]

just to mention, i did remove all of the socketed chips when i had removed the pcb's for cleaning etc, i used serivsol super 10 switch cleaning lubricant on the IC sockets, and also the legs of the removeable IC's

 

i did some more 'swapping good chips from my good working vectrex into the faulty vectrex' today

 

a little unlucky perhaps, because, in my good vectrex the IC302 chip is socketed, but my faulty vectrex does not have the IC302 in a socket, but directly soldered to the PCB instead .. so i have not tested IC302 (well anyway, whatever that IC is/does.. i don't know )

 

IC301 and IC303 are socketed in both the working and the faulty vectrex so i tested those, but they did not fix the display issue

 

IC305 i notice is not socketed in either of my vectrex units, so it looks like i would need to de-solder IC305 from the pcb (unless someone knows a way to test IC305 with a multimeter?)

 

hmm, ok i guess i will keep trying .... but... pretty stuck here i guess. sigh

Edited December 18, 2015 by vtek

[SiLic0ne t0aD]

Did any of the X, Y, adjustment pots get bumped?

 

If you have a multi cart with the Test ROM, try running that and going through the test.. it may help try to narrow down the problem. Other than that, I'm kind of stumped..

[vtk]

i dont think the pots are in a bad position, - if i hold the controller joystick in the LEFT or DOWN position the screen does look quite good (size and position)

 

does anyone know what signal the vectrex controller sends to the vectrex unit, if you push the joystick LEFT or DOWN, as opposed to RIGHT or UP?

 

(eg. a change in volts ..? im just trying to figure out if this is a clue to the problem.. as it seems strange that the display is much less messed up if i push LEFT or DOWN on the joystick)

 

ps. i will try to run the test cart.. but as mentioned earlier, i may not be able to read or see much on the screen due to the messed up graphics (but perhaps i will get lucky and be able to push LEFT or DOWN on the joystick during the test cart operation, and then be able to see something )

Edited December 18, 2015 by vtek