Qix - almost running satisfactory

[ckong]

So I bought a Qix game about 4 years ago, but until recently it just has been standing in a corner a bit. Reason for this unthankful behaviour of me is the fact that the game had some serious technical issues and I lacked the knowledge to do something about it. And there was plenty other stuff that needed attention to, not all hobby related.

Anyway, lately I had some extra spare time and also the drive to go ahead and fix this game. So I did. The technical issues were gameboard and monitor related:
- faided colours and a blurry picture
- game freezes after a few seconds or minutes
- serious vertical foldover on both sides of the screen
- very shaky screen.

The previous owner had already done a lot of work on the gameboards, he renewed all 4116 rams, completely renewed the wiring, refurbished the dreadful power board (this game uses amongst others +5V, -5V, +12V and -12V), reflowed some solder joints here and there.

And what I did was not that much, actually.

My first attention went to the vertical folding issue. I swapped the original monitor for a NOS WG 19K7302 (this one is also able to process positive sync) and the folding was gone.    However,  I rather not use the NOS monitor, but instead I want to keep the original monitor in the cab. Therefore I grabbed the spare WG 19K4601, which was previously in the pac-man, and started swapping out boards with the monitor in Qix, a WG 19K4603. Soon enough I found that the folding issue was due to a broken horizontal/vertical daughter board. Therefore I decided to take the one from pac-man permanently for Qix (hence my wanted here: https://www.dragonslairfans.com/smfor/index.php?topic=5785.0  Issue one solved!!  

Next I gave the WG 19K4603 a complete new set of caps. That took care of the faided colours and blurry picture   Issue two solved!!  

I know that games often freeze because of voltage issues, so I checked the +5V and the +12V that went into all 3 game boards. And they were way too low: +4,7V and + 11,8V!  The -5V was OK (-5,1V), as was the -12V. I adjusted the positive voltages to +5,1V and +12,1V and this took care of the freezing issues. Issue three solved!!   The screen image also got less shaky, but still quite a bit.

Then I reflowed and/or renewed the solder on all pins of all connectors on all three boards (and that is a lot of pins) and I also did some other reflowing/resoldering here and there after thoroughly examining each board. And yes, the shaky image got again less shaky, but not so stirdy as I want it. To be sure that it is not a monitor issue, i again did a brief swap with the NOS WG monitor, and the shaky image is still there. Issue four partially solved.  

Next thing that I will do is renew most caps on the Data Sound board and the Rom I/O board (the caps on the video board were already replaced by the previous owner), I hope that this will take care of the remining shakiness. Or does someone has other tips?

Anyway, here are som screenshots of the game as it is now:







And here is my complete board set, including new battery replacement, and a picture of the power board:





Finally a nice shot from a part of the testscreen, very colorful!  



I love Qix and I really don't understand why I didn't take care of it much sooner. Shame on me!

[level42]

Do you have a video of the shaking ?

Are the caps on the PSU OK ? Set your DVM to AC. And measure across the caps.

Also....check the cap-kit job done by the previous owner....maybe there is a mistake in value or something else.


But hey.....you are beginning to look like a real technician my friend !!

[ckong]

Thanks.    And good hints. I will work on that next week, will also post a video. The shaky image is not that bad and the game is very playable, but still ...

[Q*ris]

 
Good job! Love that Game, and it's the only one that my girlfriend loves too 

[spectroman]

Great job !

that a realy nice game. If you got spare : https://www.dragonslairfans.com/smfor/index.php?topic=5771.0 ?

[vernimark]

     
it is one of my favourite games!!!
Great job!!

[gyruss]

 

[ckong]

Do you have a video of the shaking ?

Yep, http://youtu.be/VoklVy_lea0

I will receive more caps for the game boards tomorrow, let's see if this fixes the trembling. By the way, the output voltage to the chassis is 115V, which is OK.

With the caps on the PSU, you mean the big fat ones?

I hope to cure this, because the screen still is able to show one hell of a nice picture, crisp, focused and brightful. It's 33 years old!!

[level42]

I will receive more caps for the game boards tomorrow, let's see if this fixes the trembling. By the way, the output voltage to the chassis is 115V, which is OK.

No silly, I meant you had to measure the AC ripple which might be "riding on" the DC voltages

I'll repeat: Set your DVM to AC. And measure across the caps.



Yes the big fat one's.

[ckong]

Why didn't you say so!  

So,  to do this right,  guide me :

1.Do I have to power the cab? I guess so,  but just asking because normally you don't put current through a cap to test it.  But this is another kind of test.
2. Polarity is not an issue for this test? It doesn't matter if I attach the red lead or the black lead of the DVM to the + or -  of the capacitor?
3. What readings can I expect and what do they tell me? It will not say anything about cap capacity.
4. If there is an AC ripple,  then what?

[level42]

1. Yes. A filter cap (that is the function of those big caps on PSU's) is meant to get rid of any AC voltages still remaining after the AC voltage has been converted to DC. So, in theory, you should read 0V when you measure the AC voltage across the terminals of such a filter cap. In pratical sense there will be a slight AC voltage but it really should be very close to 0V.

Remember do NOT set/use the DVM in AC or DC CURRENT set-up or you will blow the fuse inside the DVM (if it has one ))

So, always set to Voltage measuring (i.e. don't move the measuring leads to another connection then you have normally).

A bit of theory:

After the AC has been converted to DC by the diode bridge the output of the diode bridge is DC but it's a very "bumpy" DC, see picture here:

The red bumps show how the DC looks without the smoothing capacitor.

Now, think of the smoothing capacitor in that picture as a reachargeable battery with very little capacity (compared to a real battery).

In the first "bump" (right-most voltage drawing) the capacitor gets charged up to the peak of the first bump. Than...since it still has it's electricity stored, it will start to "give off" it's electrity once the bump is going back down to zero, I indicated that with the blue lines.
Then the next bump comes up and charges the cap again, and so on and so on.
The result is that the voltage will stay around the top of the first bump, although it slightly discharges a bit of course.

Now, what we are trying to measure is the size of this ripple on top of the DC.
It should be as close to zero as possible. This is why those capacitors are so freaking big. A good working filter cap will give a value close to zero.

2. No, there is no polarity in AC voltages so you can switch them around like you want. Try it In fact, you can switch them in DC too, your meter will just put a - sign in front of the measurement.

3. see 1.

4. If you have more than about 0,2 V the cap needs to be replaced and this could be a cause for your jitter

[ckong]

Thanks for this info and the great drawing.  

In the meanwhile I did a bit of reading about AC ripple effects in (DC) caps here: http://www.learnabout-electronics.org/PSU/psu12.php  and together with your explanation I do understand the theory. Now, let's measure the practice tomorrow.  

Oh, yes, 'jitter' is the correct word.

[level42]

Just watched your video a couple of times (now have a stiff neck....thanks !)

I think it's the V-size pot.

I see no jitter in the horizontal (remember horizontal=when looking at the CRT in normal orientation) direction, only vertical.

It seems to jump in V-size a bit, not moving up and down.

Check what happens if you move the pot a bit...if it's jumpy/jittery replace the pot.

[ckong]

Will test that also, but remember, the jittering is also there with the NOS WG, although less than with the original monitor.

[level42]

AH....yeah....then it must be not the V-pot