Paperboy won't start

Encom

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I'm working on a Paperboy, when you power it on, it displays a screen full of random characters. I've checked all the voltages, rebuilt the connectors that supply power and reseated all the chips. Does anyone have any suggestions on what I could try next?

Thanks
Rich
 
Could be a lot of things but without test gear you are working blind. However RAM is often the weakest part on any system so it's a good place to start shotgunning!
 
I have pretty much the same issue. Try reflowing the solder joints at the main power plugs of each board. What kind of voltages do you get at your test points on the boards and ARIII?
 
I measured the voltages on the board and they are all what the schematics say they should be. Based on the screen, I think it may be a problem on the video board so I started pulling Rom chips to see what would happen. It changes what garbage shows on the screen but not a whole lot else.
 
Read my post on my issue. Its almost identical to yours. I will be checking the crystal with a probe to see if the CPU is even working or not.
 
I took a look at the boardset with the scope last night and there is no activity on the data bus, memory or IRQ lines. The only activity that I found was that the clock circuits. Which appeared to be working properly. Disabling the watchdog didn't change the situation at all.
 
Is the clock signal getting to the correct pin on the CPU? Is the CPU in HALT? when the watchdog was disabled was the CPU in RESET?

A crashed CPU can sit there doing nothing, if it is socketed then it is simple to rule the CPU itself out. It is not a likely candidate for the fault but if its easy to rule out then you might as well.
 
I've made some progress. Now I have activity on the data lines and can see that the CPU is actually doing something. I put another CPU in and the problem didn't change.
 
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