Commodore SX 64 I/O Board
- only two versions known (to me) 251106 Rev A and 251106 Rev 1, difference seems to be capacitor c9 that is missing in Rev 1.
- contains the logic and two CIA’s that the SX uses to communicate to external equipment like drives, printers and modems (and internal drive)
Integrated Circuits
| PCB Identifier | Chip Number | Remarks | Memory Location/bit |
|---|---|---|---|
| UC1 | 4066 | ||
| UB2 | 6526 | CIA 2 | $DD00-$DDFF |
| UB3 | 6526 | CIA 1 | $DC00-$DCFF |
| UD2 | 7406 | ||
| UE2 | 74LS74A | ||
| UE3 | 556 |
Schematics
Board Image
interesting about the C9 on the rev 1
I just ran into that issue installing a switchless jiffydos board
I think c= directly soldered it to the 556 on that version
if you look at the 2 picks of UE3 v1 has a resistor soldered on as a afterthought and the other its on the board properly marked as C9
um my bad UE3 has a capacitor …not resistor
shouldn’t try and type before my morning coffee
Schematic lists:
UC1 should be 4066
UE2 should be 74LS74
UB2 should be 6526A CIA
UB3 should be 6526A CIA
UD2 should be 7406
UE2 should be 74LS74
UE3 should be 556
Actually the circuit list is all wrong….
Dear Michael,
Thank you for telling me,
I listed the parts list of the floppy disk controller card instead of the I/O card.
I fixed the error.
Regards,
Jeroen.
HI,
a CIA in my SX 64 is giving me modem problems.
On the site of Ray Carlsen I found out I should replace CIA 2
So I looked for the right location of this CIA on this site.
Below “Integrated Circuits” it says:
UB2 = CIA 1
UB3 = CIA 2
But on the Commodore SX 64 I/O Board Schematics 251107 on this page it says:
UB2=CIA 2
UB3=CIA 1
One of them must be wrong?
Dear Sjoerd,
The table was incorrect, UB2 = CIA 2.
Be aware of the mistake in the SX64 userport, one of the 9 volt AC lines is connected to GND.
For some devices this connection needs to be “disconnect”.
See http://personalpages.tds.net/~rcarlsen/cbm/sx64/gnd-cut.jpg for a detailed image
Regards,
Jeroen.
Hi Jeroen,
Thanks for the remark about the userport problem.
The userport was already “fixed” in the last century.
Regards,
Sjoerd
I’ve been having trouble with my sx 64 not sending 5v to the user port at the back any ideas psu is fine no image display
Dear Ross,
the 5v of the user port comes direct from the connection of the I/O board to the CPU board.
so if the 5v line is ok, then check (refit) the connection between those boards.
it could also be a bad wire between the I/O board and connector Board, but that wouldn’t explain the black screen
also check SX repair notes from Ray Carlsen for more help
http://personalpages.tds.net/~rcarlsen/cbm/sx64/sx64.txt