Commodore 64 Rev A 1982, Black screen, Scrambled graphics.

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zastin17
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Commodore 64 Rev A 1982, Black screen, Scrambled graphics.

Post by zastin17 »

So to start off I ordered a Commodore 64 from ebay. It came with the data set and some carriages, As well as the original books. It was in basically brand new condition. I plugged it in, hoping for the best and received a checkered board screen like this.
Image
I took it apart and decided to one by one insert all removable chips onto a newer 1984 board. Every single essential chip worked and the machine booted fine. I put all the chips back onto the older board and still got the checkerboard pattern. This told me that its not anything that can be removed from sockets. I also checked the 2200 uf capacitor and it was dead and not holding any charge. I replaced it with a identical counterpart. But it changed nothing. Recently is has started to just boot into a black screen without anything on the screen at all. Rarely but occasionally I do get the graphics corruption pattern but its usually just a black screen. However av is outputting since my TV responds to a signal when its powered on.The last time it "decided" to display something was earlier today. Since then it has outputted nothing but black. Since I tested all the chips in another board and it booted fine. It must be something else that's soldered. I am good with a iron and that's not problem, But I don't want to do anything unless I know whats wrong. I really want to fix this one since its a very early model and the case is in like brand new condition. I also noticed that there is a 3 pin package on a black heat-sync near the joystick ports. This gets extremely got when powered on. To hot to touch. I also noticed there is 2 ram chips that get hot. There the furthest left chips. I will mark the chips in the image that seem to get pretty hot. This is my board. Chips that seem to get really hot I marked in red.
Image

So what can I check?


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eslapion
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Re: Commodore 64 Rev A 1982, Black screen, Scrambled graphics.

Post by eslapion »

Rarely but occasionally I do get the graphics corruption pattern but its usually just a black screen.
You do know this means your tests have caused further damage, right ?

The 3 pin device with the heat sink near the joystick ports is a 7805 5V regulator. I suggest you check if it still outputs 5V.

I suppose a few of your DRAM chips are damaged and this was most likely caused by a problematic power supply. Using the same power supply to continue your tests is likely to cause more damage.

I suggest you get in touch with Ray Carlsen. Your board is assy 326298. Referring to it as "Rev. A" is usually meaningless as the European KU-14194 is also often referred to in this manner.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
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Gyro Gearloose
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Re: Commodore 64 Rev A 1982, Black screen, Scrambled graphics.

Post by Gyro Gearloose »

Where are you located?
The price one pays for pursuing any profession, or calling, is an intimate knowledge of its ugly side.
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