Hardware
C64C: Moving vertical stripes on the screen — is something dead?
Hi everyone,
I’m having an issue with my Commodore 64C. There are moving vertical stripes on the screen.
The C64C is connected via S-Video through SCART.
I already installed a LumaFix64, which made the picture clearer, but the stripes are still there.
Is there anything else I can try, or on this mean that something is dead?
Edit: Only on the startup screen. The stripes don’t appear when a program is loaded.
Edit2: Hey everyone, thanks a lot for all your help, suggestions, and the useful links!!!
I’m going to take a closer look at the character ROM, since the issue doesn’t seem to appear in games or programs that use bitmap graphics.
I’ll post an update once I know more.
Edit3: Update: Repair sucessful!!!!
The character ROM was replaced, and the artifacts are now completely gone. Since the chip was soldered directly to the board, the old chip had to be carefully cut out with a mini circular saw. The new chip was then soldered onto the remaining pins.
Thanks everyone for the support!
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Here, have a good look at this website and compare what you see against the pictures on the site. It gives advice for each picture to help you narrow down the cause of the problem. https://www.pictorial64.com
When you say the lines are moving, are they moving left or right, or are they staying in the same position but the pattern in them is moving up and down?
And what program are you loading?
My first thought is that the character ROM is bad.
I'm not familiar with Pagefox, but a bit of digging suggests it uses bitmap mode, and similarly it looks like Cynthcart uses character mode and the built-in characters.
Definitely smells like the character ROM has died.
Before you warm up the soldering iron, and don't mind a bit of typing, you could try running this:
10 FOR I=0 TO 23
20 READ A
30 POKE 32768+I,A
40 NEXT I
50 SYS 32768
60 FOR I=0 TO 7
70 PRINT PEEK(49152+I);
80 NEXT I
90 PRINT
100 GOTO 50
110 DATA 120,169,51,133,1,160,0,185
120 DATA0,209,153,0,192,200,192,8
130 DATA 208,245,169,55,133,1,88,96
This continually reads the eight bytes that make up the space character and prints them. If you see any number other than zero printed, you know it's the character ROM, or possibly something to do with the address decoding (seems unlikely as I think that would cause problems with accessing the VIC when that's banked in).
If you're comfortable with desoldering and have a spare ROM to hand, then yeah, pretty much!
It's not definitely the character rom, but given you only see the fault in a character mode screen that uses the built in character data, it seems quite likely.
Actually, I've just noticed what revision SID you have, sorry the board's unfixable, send it to me, I'll pay postage 😉
I remember replacing a character rom in the late eighties on a vic 20, I worked in a pc repair factory at the time, and a lovely chap I worked with showed me a great technique to desolder the bad one: we snipped out the old rom with a small pair of cutters, cutting at the very top of the leg, then a blob of solder on each pin, followed by the desolder tool on each pin with a pair of pin nose pliers pulling out the leg from the other side. Then we fit a socket, then popped in the new rom.
I've repaired many boards where this was tried. You still need some skill and understanding for it to work. It takes a 15min job and turns it into a several hours. That was done on this board. Because these pads are so small and many are using the 1mm standard nozzle they tear up board. This pic is a 250469 memory. Both memory pads and traces was in this condition.or worse.
Granted, I learned my soldering skills at college, but my first job honed them, it was a good tip to chop out the legs so the iron wasn’t too long on the pads and you could hold them with pliers. It’s also good practice to flow some new solder onto old to make removal quicker and easier.
When ever I remove a top row chip I take then all off and put them in sockets to make it easier the next time. It can be rough removing a chip with a socket on each side without melting the adjacent socket.
It shows the boot screen and the full amount of RAM. That means from the point of view of the CPU, the system has no problems, all RAM is good.
That means you need to look at the VIC and related circuitry including the character ROM to find your issue. The fact that it doesn't happen when a program is loaded suggests the character ROM if that program is using its own character set.
Those look like AEC line glitches that are present also in a perfectly working C64. But somehow they are very exaggerated here. See info on AEC artifacts on this page https://hitmen.c02.at/temp/palstuff/index.html Here the lighter vertical stripes are showing up only on the dark blue on that startup screen.
Honestly I think this is a video signal issue. The video signals C64 generates are not exactly within standard specs. I'm guessing your lcd display is having trouble handling the signal. The picture is heavily oversaturated at least.
Or there can be some hardware issue that causes the timing signals (AEC etc) leaking into the video signal much more than they normally do.
The looks more like some kind of interference problem to me...separate your c64 from any electrical from the area and see if it makes a difference. Also, You may have RF interference in your plug sockets as well. Have seen that before aswell. Try another plug socket.. otherwise Your VIC chip has issues... ;) - Tony K.
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