Galaga repair

Zinfer

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Well, I thought I was doing ok on this scratch build cabinet project. However I am thinking I may have a RAM problem regardless of what the game says in diagnostics.
I think this looks a little off and a little fuzzy.
First of all, are there any Galaga Pro's out there that repair these on a normal basis?
Secondly, any guesses? Should I just up and remove all 8 2147's and place the 2 2148's without knowing for sure what the problem is? I don't know a good way to test 2147's in circuit.
Any help is greatly appreciated.

Here's what I am seeing:
IMG_0235_zps2mszqtgn.jpg

IMG_0227_zpshu7ftf3y.jpg
 
That's strange!

I haven't seen this one before. I'd start by looking at the 74LS161/163 ICs and the ICs at 3A/5A that all feed into controlling the 2147/2148 RAMs.

Raymond
 
Ok, I adjusted convergence best I could by eyeballing it. It may be off still by a small amount. It's really hard to see and adjust from the back even using a mirror. Your face pretty much has to be planted on the screen.
After adjusting, the wing sprites still appear off to the left a bit and off center from the body sprites. Maybe this is ALL a convergence problem? Not sure of any other way other than eyeballing it.

IMG_0254_zpsicc9thup.jpg


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IMG_0265_zpsfbrlqvxe.jpg


Not sure I'm imagining things or making a mountain out of a mole hill. I do notice a audio tone after the explosion sound of startup, however it resets again and clears. So I am thinking there is a problem somewhere.

NOTE: Blue wings are off to the left on the first picture set. Now off to the right after adjusting convergence. Red was off to the right - now after adjustement - off to the left.
 
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Is there any better way to adjust convergence? This is looking like it's all a convergence problem.
 
Is there any better way to adjust convergence? This is looking like it's all a convergence problem.

The most effective way is with the monitor out of the game allowing full access to adjust and see the effects real time. Adam from One Circuit did a great video on it on youtube. That video has given me the confidence to tackle this on a couple monitors soon.
 
That got it. I had to bust out the Galaga docs. Come to find out, if you flip the diagnostic switch, that grid pattern stays up for a mere 2 seconds. If you flip the service switch back off, the grid pattern stays permanently.
With that I was able to get it adjusted through the use of a mirror. I could look up from behind the monitor as neither bezel was in place yet.

That's about as close as I'm going to get it. It was all a convergence issue. Wondering if I should glue gun it or just leave it - they're not going to move on their own.

IMG_0266_zpssux4sdke.jpg


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