Symptom: Parallel speeder (SpeedDOS, Dolphin DOS, etc.) doesn't work anymore or is as slow as original C64. Target : C-64 / 1541
Swap CIA #1 in C64 (U1) with CIA #2 (or replace CIA #2) | | V +-----------+ no | Okay now? |-------> Replace VIA #1 in 1541 (UC3 in old board) +-----------+ | | yes | V Replace CIA #2 (or #1, if you swapped CIA #1 with CIA #2)If the problem still occurs, or if either or both CIA and VIA are not socketed, check the parallel cable, the wire assignment of which depends on the speeder you use; for SpeedDOS and DolphinDOS V2, it is like this.
If it STILL doesn't work, check your speeder EPROM and / or EPROM switcher.
Note: If you don't wish to replace your CIA/VIA every now and then, you should keep in mind that you should never plug the parallel cable in/out when both C64 and 1541 are switched on! If you are too lazy to switch both machines off when you want to (un)plug the parallel cable, at least switch the C64 off while doing so.