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Vectrex - Sound, Game Plays, but small white dot?


MonkeyMagic

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Hey guys,

 

I'm new to the forums, saw few people talking about Vectrex stuff and I need a little help :-/

 

I bought a vectrex recently, came boxed, got 6 games with it as well all boxed with overlays. I was over the moon, until I turned it on.

 

When I turn it on, sound comes out and I can hear the game playing in the background. However the screen has a tiny white dot on the bottom left part of the screen. If I unplug the X,Y,Z cable on the logic board the DOT will move to the centre of the screen. Makes me think its an issue with the logic board and the X,Y not getting enough power?

 

Anyway I have cleaned all the inside, cleaned the front two IC's cannot really get to the others with removing the whole logic board, which will be my next step.

 

Anyone got any thoughts on what the issue might be?

 

I have had a look at the solder joints to all the power leads and they look in top notch order, is it worth re-soldering these regardless?

 

Really appreciate any comments or thoughts you guys have.

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My new project is to repair this white dot Vectrex I just bought, although I think I am running out of things to try!

System starts with sound and the built-in game. White dot at bottom center of screen.

> cap kit. Done. All replaced (extremely hard to do as it is so easy to tear up the board traces). No change.

> swapped the two small socketed IC's near the back of the logic board with ones from working unit. No change. Both work in working Vectrex.

> reflowed solder in power connection from logic board to power board. No change.

> replaced Q502 BU407 NPN. No change.

> desoldered IC6622, installed 40-pin socket, swapped with working Vectrex 6622. No change. Both CPUs work in working Vectrex.

> checked continuity. All seems ok.

> voltage checked at power board per Service Manual. OK.

As I said I'm running out of things to try.

I've read most of the information on the Internet on repairs...

Any suggestions on what to do next? (I don't have an oscilloscope unfortunately.)

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@Ataritard - Did you just remove them, clean the ports + chip then reseat? Also did you remove the bottom board to do this or just leave it in place? I did manage to get the two near the back of the unit out and cleaned, but there are two larger ones a little deeper I cannot currently get to. Did you do those ones also?

 

@iesposta - I'm going to get a oscilloscope, from what I've read most people seem to track down the problem much faster by using one.

 

Cheers for advice so far guys.

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Update#1

My new project is to repair this white dot Vectrex I just bought, although I think I am running out of things to try!

System starts with sound and the built-in game. White dot at bottom center of screen.

> cap kit. Done. All replaced (extremely hard to do as it is so easy to tear up the board traces). No change.

> swapped the two small socketed IC's near the back of the logic board with ones from working unit. No change. Both work in working Vectrex.

> reflowed solder in power connection from logic board to power board. No change.

> replaced Q502 BU407 NPN. No change.

> desoldered IC6622, installed 40-pin socket, swapped with working Vectrex 6622. No change. Both CPUs work in working Vectrex.

> checked continuity. All seems ok.

> voltage checked at power board per Service Manual. OK.

As I said I'm running out of things to try.

I've read most of the information on the Internet on repairs...

Any suggestions on what to do next? (I don't have an oscilloscope unfortunately.)

Swapped the power board from the "white dot" Vectrex into my working Vectrex.

This results in my working Vectrex showing the same white dot in the same location (bottom center).

So there's a fault in the Power Board, or the Yolk Board.

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@iesposta - Good working tracking down the problem. When you did the cap kit, did you notice any orange glue like substance on any of the power board caps? I have just noticed that one Cap on the power board seems to have some orange substance on it, dripping down onto the power board, its solid now, but I'm wondering if the CAP has leaked or if that is meant to be there?

 

I reseated all the chips today, that didn't improve anything. I'm not sure if its worth re-flowing the solder because it all looks to be in very good condition, is it worth doing it anyway?

 

Cheers guys.

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I have just noticed that one Cap on the power board seems to have some orange substance on it, dripping down onto the power board, its solid now, but I'm wondering if the CAP has leaked or if that is meant to be there?

Not sure about the Vec, but I got some ARII boards for my PP II cab, and saw that, and thought the caps were bad, so decided to change them..

Well, after hours of cleaning, I realized it wasn't leaky caps but it was glue of some type...

Not sure if this is the same as you're seeing, but figured I'd mention it..

 

desiv

(Good news is that I have probably the cleanest ARII boards around now..) ;-)

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It's glue. I checked 2 Power Boards and they both have the glue on the biggest caps.

@iesposta - Good working tracking down the problem. When you did the cap kit, did you notice any orange glue like substance on any of the power board caps? I have just noticed that one Cap on the power board seems to have some orange substance on it, dripping down onto the power board, its solid now, but I'm wondering if the CAP has leaked or if that is meant to be there?

 

I reseated all the chips today, that didn't improve anything. I'm not sure if its worth re-flowing the solder because it all looks to be in very good condition, is it worth doing it anyway?

 

Cheers guys.

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It sounds like you all tried this by working on the power board, but here's what the Vectrex FAQ says:

 

 

7.4) My Vectrex just shows a white dot when I turn it on. I can hear

the

game playing but there is no picture. Can I fix it?

 

 

There is 1 common problem that will cause this symptom. Inside the

unit

there is a 4-wire power connector connecting the side board to the

bottom board. Often units with no picture have bad solder joints on

this connector. Try resoldering the pins and see if that helps.

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@iesposta - Yeah well I'm not 100% sure, I noticed it on the big caps, but this is on one of the smaller ones and it seems to have dripped and covered another component next to it. Also on a side not, if you unplug the 3 pin connector for the X,Y,Z and turn it on, what happens to your dot? Does it move to the dead center of the screen? Or does it stay where it is?

 

@boxpressed - Yeah I tried that already unfortunately, I believe that is only a fix if the DOT is in the center of the screen.

 

I tested the boards power connections. It seems that the board is getting enough power and power is making it around the logic board. So this makes me think that it is a signal problem and that it is not making it to the screen for some reason.

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@iesposta - ..., if you unplug the 3 pin connector for the X,Y,Z and turn it on, what happens to your dot? Does it move to the dead center of the screen? Or does it stay where it is?

No change in dot position. Remember this Power Board makes the working Vectrex display the same thing.

Sad Taiwan Vectrex:

post-29575-0-26732700-1338668423_thumb.jpg

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Update #2

Swapped CRT Board Assembly. No change.

The last few high level parts on the Power Board are

3 transistors: Q503 2SC1921 NPN, Q504 2N3905 PNP, Q505 2N3904 NPN

2 transistors 2N384 N-channel JFET

IC103 LM386-3 1.5W AMP

IC501 LM555 Timer (Do timers go bad?)

And IC401 which is: LM379 Dual 6W AMP under the big heat sink and under its own heat sink. I thought this had to do with sound (being an AMP) but is this driving the vectors?

Maybe one of these 7 parts?

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I read in the trouble shooting guide that a faulty IC401 can cause no vector / white dot. This could be the problem.

 

However what you have said has pretty much confirmed for me that it is my logic board that is the issue, as my dot jumps around when I unplug the X.Y.Z cable.

 

Don't suppose anyone knows where I can get replacement chips? I'm going to try re-cap and re-chip the logic board.

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UPDATE#

 

Does anyone know what voltage should be coming out from the X,Y,Z - I tested them earlier and X = 9v - Z = 9v - however Z = 0.5V. Is the Z supposed to output a lower voltage??

 

Tried reading the service manual but it does not say what the desired output should be from these connectors.

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UPDATE#

 

Does anyone know what voltage should be coming out from the X,Y,Z - I tested them earlier and X = 9v - Z = 9v - however Z = 0.5V. Is the Z supposed to output a lower voltage??

 

Tried reading the service manual but it does not say what the desired output should be from these connectors.

 

My working Vectrex shows less than half a volt on Z.

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Cheers for the voltage response, mine is also just under half a volt now I have double checked. Defiantly seems like I'm getting correct power at every place I need, just need to track down the little bugger that's messing with my logic board signal.

 

Let me know how it goes once you have installed the LM379S. Where did you order the part from?

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Don't suppose anyone knows where I can get replacement chips? I'm going to try re-cap and re-chip the logic board.

eBay has chips. I read VIC-20 computer has 6522 chip, or eBay.

It seems if it's not reseating chips, connector wires, cap kit, or 6522 fix, all the threads die without, "I replaced ________ and that fixed it."

Here is one fix that worked: http://www.guddler.co.uk/logs.html

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I think I need to replace the DAC as well. When reading through what you posted he said he used the correct: MC1408CP 8 bit DAC

 

However all I can find on Ebay is this - MC1408-8N 8 BIT DAC

 

eBay Auction -- Item Number: 2807096937271?ff3=2&pub=5574883395&toolid=10001&campid=5336500554&customid=&item=280709693727&mpt=[CACHEBUSTER]

 

Do you think that will be ok or does it need to be exactly the same?

MC1408P8

search for MC1408P8

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Update #3

White dot Vectrex FIXED!

It was IC401 which is: LM379S Dual 6W AMP under the big heat sink and under its own heat sink used in the deflection circuit.

Wouldn't you know it is the trickiest part to change. Also since there is a heat sink connected to this chip, there is no notch, but a slight hole offset at one end underneath. I could easily have put it in the wrong way.

post-29575-0-44373200-1339198663_thumb.jpg

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