Piggy back an IC
The piggy back method gives you an educated guess identifying the faulty IC. Just push a known good memory chip over the chip to be tested. If the fault changes/improves, you have a good chance of pin pointing the faulty chip without soldering. This method has been done many times in the Arcade scene / repairs.
note: do this at your own risk btw 🙂
Black screen?
- Do you see a flash? No, replace the clock generator 8701 (small chip next to the VIC chip).
- If you see a flash on power-on, first try to remove the SID; still doesn’t work?
- Replace the VIC chip; still doesn’t work?
- Replace the PLA (906114-01); still doesn’t work?
- check this video:
another problem can be your power supply, here’s how you can test your power supply:
Another video with a black screen repair:
More blackscreen repairs
2 cases of black screen repairs:
Cassette problems (datarecorder)
Cassette motor will not turn when FF/REW or PLAY is pressed.
Cause:
- check fuse inside computer or
- 2SD313 TRANSISTOR, CASSETTE MOTOR DRIVER
Power supply (PSU) issues
POWER PACK: +5VDC at 1.5Amps and 9VAC at 1 Amp
Can produce many problems like blank screen (red power LED on, dim or off), program lock-up, “garbage” screen, hum bars moving on screen, hum in audio, damaged RAM chips, intermittant operation after warmup, etc. As common a failure as it is, the supply should be checked (by substitution) first.
No cursor?
You can still type and it seems to work, but no cursor is shown!
The problem can be Ram(1) and Character ROM. See the whole thread here.
Looking at faulty chips
Future proofing your Commodore 64
Hi.
I have a commodore 128. And when I try to load a game by typing “Load”*”,8,1″ it always says “device not present”. I tried it on both 128 and 64 modes. But it shows the same message. I tried to readjust the serial port connector but I still get the same response that the drive is not present. I have a commodore 64c also and the disk drive works fine on that.
Could u please let me know what the problem is?
Regards
Erix..
If the drive works on one machine but not the other, it sounds like there might be a problem with the 128’s CIA chip (Complex Interface Adapter – MOS 6526). That controls things like floppy and cassette drive access, keyboard, joysticks, etc. I’d start troubleshooting there by replacing that chip.
– PT
Now the error that caused these to be recalled seems to be what was known as the sparkle bug . Apparently, the video chip, the VIC, caused light blue sparkles on a dark blue background when it heated up. Furthermore, customers were complaining that the color scheme of the C64 seemed rather garish. This was caused by assembly line workers adjusting the color saturation all the way up, resulting in overpowering colors. Add the fact that Commodore needed to ship the C out in time for the Christmas season and you ll find that many early models had defective VIC chips, simply because when production lines encountered a shortage of these chips, they d go to the bin with the defective chips, remove the label and put them in anyway. Nonetheless, Commodore overcame these problems and the rest is, as they say, history.