Topic: Vectrex problem! Can anyone (Phu?) help?  (Read 2971 times)

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Offline Spirantho

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Vectrex problem! Can anyone (Phu?) help?
« on: May 23, 2014, 08:03:43 PM »
Hi everybody,

I finally got a Vectrex - I've not seen one since I was about 10! Of course, it doesn't work.
It was sold to me as being occasionally working, but for me it's never worked after about 20 tries.

The symptoms:
1) The machine is thankfully working perfectly behind the screen, as far as I can see. I can hear everything running as normal.
2) The entire display is shrunk down to a horizontal line about an inch long only visible with brightness on full. The line starts faint at the left, running to the right where it terminates in a bright point.
3) The line is positioned towards the upper right of the screen.
4) The line is moving according to what the game does, but it's not at all recognisable as what it should be - I can just see that the shape is changing.
5) Pressing the reset button makes the line change to a dot slightly away from where the line was, before it returns to being a line again when the display starts up.

I've seen various repair logs of no dot, or of a dot, or of a collapsed axis, but not of a short line which is doing something.

I've already re-flowed the solder on any power connections I could find (the wires between the CRT and side PCB, and the side PCB and back PCB. I've also removed and replaced the relevant plugs on those wires between the boards. I have also lifted up one end of the socketed chips and pushed them back in again.

One other thing: how long should I leave it before I can safely open the machine again after trying it?

I believe this is fixable as the problem seems to be related to the display driver rather than the CRT; I'm hoping no-one's going to prove me wrong :) I can fix a C64 easily, and I can do a Spectrum with my eyes closed (almost) but when it comes to CRTs, I'm as nervous as anyone of that voltage...

Any help would be great as I don't want to go into a live Vectrex with all that voltage in there....

Edit:
I've been thinking (dangerous, I know...)...

I don't think the tube Yoke has a fault because both axes are wrong.
The line I can see I think is the actual picture.
The dot is the dot that should be visible in the centre of the screen, which is why it's only visible when the brightness is turned up.
Not sure why the line leading to the dot is so faint though.

My primary thought is that the LF347 or LF353 Op-Amps aren't getting their +/- voltages. I'd expect if they were getting just +ve, then there'd be no movement to the left, and  the same with -ve and the right, but I guess if the voltages are wrong there could be all sorts of biases, which could cause this.
I wonder what I would see on a working vectrex without a -5V line (probably a dead 7905 I'd guess), would it just affect the signal and not the logic? I'd guess so.

« Last Edit: May 23, 2014, 10:06:38 PM by Spirantho »
Ian Gledhill
ian@mutantcaterpillar.co.uk but with a hyphen between "mutant" and "caterpillar"
Mutant Caterpillar Games - vintage computers and games in our shop!
http://www.mutant-caterpillar.co.uk/shop/

Offline Womble

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Re: Vectrex problem! Can anyone (Phu?) help?
« Reply #1 on: May 27, 2014, 04:17:13 AM »
I cant help you with the fix but I would advise you keep the brightness down, you will get ferocious burn in from that bright spot.
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Offline Spirantho

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Re: Vectrex problem! Can anyone (Phu?) help?
« Reply #2 on: May 27, 2014, 11:22:28 AM »
Don't worry, it's only on for short bursts of time for that very reason.

I just went inside it again this morning to clean the ICs which are socketed, and to reflow some solder joints. It started up with haywire lines which were a bit different, but after a minute or so went back to the previous small horizontal line.

I ran some wires out the back so that I can check voltages without the casing off, and I'm getting some pretty strange values. I'm suspecting the capacitors, but I'm not sure how to get the logic board out. It's the removal of the PCB on the back of the CRT that worries me, they're so brittle...
Ian Gledhill
ian@mutantcaterpillar.co.uk but with a hyphen between "mutant" and "caterpillar"
Mutant Caterpillar Games - vintage computers and games in our shop!
http://www.mutant-caterpillar.co.uk/shop/

Offline AndyRCM

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Re: Vectrex problem! Can anyone (Phu?) help?
« Reply #3 on: May 27, 2014, 06:48:12 PM »
I do have a copy of the schematics - would that help? and I do know PHU knows quite a bit about these beasties. :)
"I could see the faces of those who led pissing themselves laughing" - Funeral Pyre by The Jam

Offline AndyRCM

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Re: Vectrex problem! Can anyone (Phu?) help?
« Reply #4 on: May 27, 2014, 06:51:25 PM »
I have sent the PDF to your email address on your account. It is actually the service manual. :)
"I could see the faces of those who led pissing themselves laughing" - Funeral Pyre by The Jam

Offline Spirantho

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Re: Vectrex problem! Can anyone (Phu?) help?
« Reply #5 on: May 27, 2014, 06:56:10 PM »
Thanks for that :).

I found that the ground wire wasn't giving any connection at all to my other wires coming off the power cable inside. I assumed the wire must have broken but it seems not... but if it didn't have ground nothing would work, surely.
Very odd... maybe more than one ground connection?
Going to investigate further tomorrow....
Ian Gledhill
ian@mutantcaterpillar.co.uk but with a hyphen between "mutant" and "caterpillar"
Mutant Caterpillar Games - vintage computers and games in our shop!
http://www.mutant-caterpillar.co.uk/shop/

Offline Spirantho

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Re: Vectrex problem! Can anyone (Phu?) help?
« Reply #6 on: May 28, 2014, 10:06:23 AM »
I've just taken the power board out of the Vectex.
That's an experience I hope never to repeat again! So many awkward wires soldered between the power board and the fragile CRT.... not nice! Interestingly I noticed the ground connector on the logic->power board was discoloured, no idea if that's a co-incidence as the connection seemed to be ok.

Time for a recap!

Edit: Most of the caps done.. just ordered the unusual ones now.
« Last Edit: May 28, 2014, 11:30:54 AM by Spirantho »
Ian Gledhill
ian@mutantcaterpillar.co.uk but with a hyphen between "mutant" and "caterpillar"
Mutant Caterpillar Games - vintage computers and games in our shop!
http://www.mutant-caterpillar.co.uk/shop/

Offline Spirantho

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[MOSTLY solved] Re: Vectrex problem! Can anyone (Phu?) help?
« Reply #7 on: May 30, 2014, 01:39:00 PM »
Well.. the good news is that I completed the recap of the power board. I've not done the logic board, yet, but there's only a few caps on there and they probably aren't the fault.
The bad news is that it still doesn't work.
The other good news is that it does exactly the same as before. This means it hasn't blown up and nuked the entire town (as I always fear when I mess with large capacitors, let alone CRT tubes).
The other other good news is that I ran the wires out the back - and this time I had the ground wire conected properly. +5V is fine. -5V is fine. -13V, however, is +0.69V. I think we have found the culprit.

Now I just need to find the solution.

Oh, I am so looking forward to taking it all apart again.... going to wait till Monday to give the CRT chance to discharge....
Any advice on that -13V would be very gratefully received. I've already checked the diodes D101-D104, by the way, they seem fine.

Edit: I just got life from it! It is the other pole of the power switch at fault - I didn't think it could be that because the -5V line was good, but there we are - it's power switch! Now I just need to find a way to clean it without taking the whole bloomin' thing apart again...
Edit2: This thing is insanely noisy with the buzz when the display works! And that's after a recap of the power board. I'll have to see if I can implement one of the solutions....
« Last Edit: May 30, 2014, 02:54:58 PM by Spirantho »
Ian Gledhill
ian@mutantcaterpillar.co.uk but with a hyphen between "mutant" and "caterpillar"
Mutant Caterpillar Games - vintage computers and games in our shop!
http://www.mutant-caterpillar.co.uk/shop/