Help with Fantasy pcb

TheEnglishTear

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Been troubleshooting this game for a couple of days now. First, the game wouldn't turn on...turned out to be a faulty power supply. Once the sceeen came on there was garbage like pictured below. I've reseated and replaced the 2114 ram, reseated and cleaned all socketed chips, swapped the ribbon cables and no change. The screen kept rolling with garbage but coined up and played fine with sounds. At first I thought it was a monitor issue but got the same garbage and rolling screen on another monitor. Tomorrow I will check and verify the rom info to see if there's a corrupt rom, but my question is, would the 46505 chip be faulty and causing the sync issues? How about the garbage screen?

Thanks
 

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Have you got a photo of the PCB

I would be starting around the crystal area and working my way through from there. if you got a schematic will make life a lot easier that way you should be able to track through until you find the SYNC output and see if its missing/not working correctly.
 
I'll post pics of the pcb in a sec. I've checked traces and cold solder joints, have looked at the schematics but can't make sense of it...just don't know how to read them just yet. My guess would be around the chip I mentioned, but I don't know what components to check around it
 

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Just start at the SYNC output of the edge connector and follow it back to that 74LS04 then to the 74LS86 then to custom using a ohm meter to make sure you got good connection there i would say you really need to check both 04 and 86 first before saying the customs no good see what outputs your getting on those first
 
Just start at the SYNC output of the edge connector and follow it back using a ohm meter till you find where it goes to if you find it hard looking at schematics

How do I know what chips are suspect? I have a logic probe but haven't used it just yet
 
you really need a scope to see the signal correctly a logic probe will show a signal but you can't say yes its the correct one or not
 
you really need a scope to see the signal correctly a logic probe will show a signal but you can't say yes its the correct one or not

Ahh. Well that stinks....I don't own a scope or know anybody with one. But I'll try to follow the traces and let you know what I find....let me know if there's anything else I could try. Thanks
 
Have you got a photo of the PCB

I would be starting around the crystal area and working my way through from there. if you got a schematic will make life a lot easier that way you should be able to track through until you find the SYNC output and see if its missing/not working correctly.

He's got video... the crystal and support circuitry are fine.
The video won't sync until the CPU configures the 6845.
The CPU won't configure the 6845 if the ROMs are bad.

This isn't rocket science.
 
Right o thanks for letting him know seeing that you know these video cpu pretty well you should be able to help him out
 
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