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C16 - Black Screen

A

AndyWelly

New Member
Joined
Sep 25, 2022
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Hi, I've got a C16 which I has sat in my attic for years. I've recently pulled it down to check if it works and all I get is a black screen.

Power seems fine (9V, drawing ~650mA) with 5v internally. Master clock, CPU clock and a composite video signal (though black) are all being generated. PLA and Kernal chips are warm to touch, with 8501 and TED warmer still. I don't have another C16 to swap the custom chips with but I do have a scope etc to probe further.

Are there any checks I can do to try an isolate which what might be wrong ? The service manual seems to indicate testing and fault determination by device swapping which is a litte tricky given the rarity of the main chips.

Thanks!
 
Hi, I see you posted this months ago, and nobody ever replied! Did you ever make any progress on this? I usually come on these forums when I WANT help, and rarely stick around to GIVE help. Shame on me....
 
It's either going to be the CPU (most likely) or the TED (almost as likely) or it can be ROM. RAM would give you a garbled screen, usually. It is difficult to determine which without working chips. Also, there is very little interest in these machines, so there aren't a lot of people restoring them regularly. Sorry.
 
rittwage said:
It's either going to be the CPU (most likely) or the TED (almost as likely) or it can be ROM. RAM would give you a garbled screen, usually. It is difficult to determine which without working chips. Also, there is very little interest in these machines, so there aren't a lot of people restoring them regularly. Sorry.
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Why you gotta be like that about the Plus/4, Pete? :ROFLMAO:

I'm just razzing you. I have a fetish. Dunno why, I just love them. But I agree. It's most likely the CPU. If the OP comes back here (just realized he's in the wrong forum), we can talk about it further. I have replacements for the CPU if he needs one.
 
KevinO said:
Why you gotta be like that about the Plus/4, Pete? :ROFLMAO:

I'm just razzing you. I have a fetish. Dunno why, I just love them. But I agree. It's most likely the CPU. If the OP comes back here (just realized he's in the wrong forum), we can talk about it further. I have replacements for the CPU if he needs one.
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I have a couple of Plus/4's with bad CPU, are you hoarding them? (Just kidding)
I was going to order a couple of those 6502->8501 adapters from Australia.
 
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