Breadbin developed a fault.

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yaztromo
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Breadbin developed a fault.

Post by yaztromo »

Got a breadbin that has begun to have issues. I'm guessing the PLA might be on it's way.

Main symptoms are random characters appearing on the screen, and characters changing to other characters.

Programs sometimes won't load. When they do they might play fine or have issues:
- Background shimmering white pixels in Leaderboard and Bruce Lee 2
- Park Patrol title screen has vertical brown lines on it, but plays fine afterwards
- Scrolling around in the Ultimate cart usually produces artifacts.

Any ideas what chip it could be?

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eslapion
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Re: Breadbin developed a fault.

Post by eslapion »

VIC-II seems to be overheating or has developed heat sensitivity after overexposure to heat.
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yaztromo
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Re: Breadbin developed a fault.

Post by yaztromo »

Like I said though I did swap the VIC with another one. It's possible I could have two faulty VICs I guess. Will check that possibility out. Thanks.
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Re: Breadbin developed a fault.

Post by eslapion »

yaztromo wrote:Like I said though I did swap the VIC with another one.
Reread your OP... don't think you mentioned.

What remains is possibly a faulty PLA (would you like to try our new PLAnkton? ;) ) or a bad DRAM chip.

Check voltages too. What PSU do you have?
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yaztromo
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Re: Breadbin developed a fault.

Post by yaztromo »

eslapion wrote:Reread your OP... don't think you mentioned.
Sorry eslapion, right you are :) I must be loosing it.
What remains is possibly a faulty PLA (would you like to try our new PLAnkton? ;) ) or a bad DRAM chip.
Already ordered the PLAnkton :D I'm hoping this is the fix, but for some reason I suspect DRAM. Are there any good RAM testing programs out there?
Check voltages too. What PSU do you have?
Running dual wall wart. Checked voltages, they look good.
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eslapion
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Re: Breadbin developed a fault.

Post by eslapion »

yaztromo wrote:Are there any good RAM testing programs out there?
Diag cart... put the ROM image in a 1541 Ultimate I or II.
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Re: Breadbin developed a fault.

Post by yaztromo »

Small update.

Turns out I do have a bad VIC-II. Which is responsible for the shimmering pixels. I put the chip in another board and the same thing happened when it warmed up.

To add confusion to the problem, I tried replacing the VIC-II with a working ceramic one from another board (the board had come with a non-ceramic). I think it just doesn't like the ceramic VIC-II, and that is what is causing those random characters to appear. If I put the ceramic VIC-II back in it's original board it works fine.

Got the diag cart image installed in the Ultimate and tested it on my C64C to see what a good result looks like without a test harness. Will try it in the "faulty" breadbin when I can get my hands on another VIC-II.
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Re: Breadbin developed a fault.

Post by dudz »

this symptom can also be a sign of the main clock being slightly off - not uncommon with the old board that doesnt have 8701 in its clock generator circuit.
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