C64: no picture

[leofoe]

Hey guys, I picked up a C64 breadbox. I hooked it up to my A1084 and I got the basic screen, but it was flashing. Switched the beast off an on again: no picture at all. Reseated all removable chips but alas!
There must be some C64 experts among us Amigans. Any help appreciated.

[motorollin]

Hmm, have you got another C64 you can swap any chips? I think sometimes a dodgy SID can cause video problems.

--
moto

[Ilwrath]

Ick.... Black-screen C64 is the hardest to test/repair.

Personally, I'd tend to suspect VIC before SID chip problem.   Is it just the video that's out, or is the whole computer not completing self-test to get to the READY prompt?

(In other words, is the computer hanging before READY, or just not DISPLAYING anything?)  Can you hook up a 1541 drive to it and type LOAD"*",8,1 and see if the drive grinds?  :lol:  As stupid as that sounds, if the drive DOES respond to the blindly typed command, you know the computer is at a READY prompt you just can't see.  Then you test the VIC and probably the capacitors in the display circuit.  If the drive does not respond, you know the computer isn't completing self-test, and you start testing everything that can cause self-test to fail (lots, unfortunately).

[leofoe]

@motorollin: Unfortunately I do not have (yet) a spare one.
@Ilwrath: I hooked up a 1541 of which I don't know if it works. As soon as I switch on the C64, the red led comes up for a few seconds. When I type the command you said, nothing happens :getmad: .

[motorollin]

@Ilwrath
Correct me if I'm wrong, but I think SID is used for timing in the video output. A dodgy SID can cause corrupt displays, and if it dies completely then the video won't work. Of course, there are lots of other things it could be :-(

@leofoe
If it doesn't respond to any commands, then it looks like it's dead :-(

--
moto

[amiga92570]

Sid is the audio chip. In Fact the c64 will work fine if you take the sid chip out, just no pad, mouse, or sound operation. Try going through these steps.

UA4 THRU UA7 & UB4 THRU UB7 8 RAM CHIPS (4164) on CPU board.
     Blank screen, no border. Shorted chips will get warmer than the
other RAM chips. Partial failure can produce screen or program "freeze"
or "garbage" screen. An abnormal (less than 38,911) number of bytes free
or "out of memory" error on startup screen is a RAM problem.

UB2 906108-02 (6526) CIA on I/O board.
     Startup screen normal, but no serial or user port access. "File not
found" error when drive accessed. Cartridge works. Partial failure:
characters may show as blocks on startup screen or screen will fill
with lines inside border.

UB3 906108-02 (6526) CIA on I/O board.
     Startup screen normal, but no cursor. No keyboard or joyport
access. Partial failure: some keys or joystick positions don't work.
Cartridge works.

UC1 CD4066 QUAD "SWITCH" IC on I/O board.
     Proportional mouse or graphics tablet doesn't work. Check also
SID chip UE3 on CPU board.

UD1 901225-01 CHARACTER ROM on CPU board.
     Blank screen w/ border. "Garbage" characters where startup page
info should be.  Cartridge works.

UD2 7406 LOGIC on I/O board.
     No (or intermittant) serial (drive or printer) access.

UD3 251104-01 KERNAL ROM on CPU board.
     Blank screen, no border. Cartridge works.

UD4 901226-01 BASIC ROM on CPU board.
     Blank screen with border. Cartridge works.

UD7 906107-01 (6510) MPU on CPU board.
     Blank screen, no border. Cartridge doesn't work.

 :huh:

[leofoe]

Thanks for this guide.
As I have no spares I will first obtain another C64.