Black Screen Issue : VIC20CR

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mrr19121970
Vic 20 Nerd
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Black Screen Issue : VIC20CR

Post by mrr19121970 »

Yes the worst kind of fault. I read and followed Ray's guide

I have tested the following IC's, with these results:

UAB1 6522 VIA INTERFACE, KEYBOARD-SERIAL - GOOD

UAB3 6522 VIA INTERFACE, JOY-USER-SERIAL-CASS - BAD
UB7 6560-101 VIC VIDEO/AUDIO - GOOD
UC4 74LS138 LOGIC MEMORY CONTROL - GOOD
UC5 74LS138 LOGIC BLOCK CONTROL - GOOD
U14-U15 MB8416A RAM MEMORY - GOOD
UE10 6502 MICROPROCESSOR - GOOD

UE12 901486-07 ROM KERNAL - BAD

The screen stays black even with the BAD ICs replaced with known good ones. UAB1, UAB3 and UB4 also currently removed. Faint vertical black lines are visible. Userport reset responds.

Anything obvious that I've overlooked?

Update


Maybe I answered this myself? I removed the 7406 from a known working machine and the screen stays black. I inserted the 7406 into the working VIC and still stays black. I don't have any more 14 pins sockets to test. Grrr.
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mrr19121970
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Joined: Tue Jan 19, 2016 9:22 am
Location: Germany
Occupation: IT service manager

Re: Black Screen Issue : VIC20CR

Post by mrr19121970 »

Ok, postie brought me 1 new 14 pin socket. Soldered it in and bam, another VIC20 comes back from the landfill. Why do I always get other symptoms as Ray describes? Says nothing about can cause a black screen

COMMODORE VIC20 COMPUTER - DIAGNOSTICS AND REPAIR
UB4 7406 LOGIC SERIAL PORT BUFFERS
Normal startup screen. Serial port (disk drive) access problems.
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joshuadenmark
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Re: Black Screen Issue : VIC20CR

Post by joshuadenmark »

You rock! Great new 8)
Kind regards, Peter.
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mrr19121970
Vic 20 Nerd
Posts: 873
Joined: Tue Jan 19, 2016 9:22 am
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Re: Black Screen Issue : VIC20CR

Post by mrr19121970 »

I was so chuffed, that I decided to treat the old lady to a steam bath and face mask too...
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