128D 1200 6502 6581 ACA1230 ADF Amiga breakfast CF compo D.I.Y. demo diner Dremel EasyFlash Ethernet Floppy Guitar Hero HDD home HxC2001 Jeroen Tel Kickstart knop KS3.1 microIEC Mod mssiah official paddle party Ragtop results ROM RTC scene SDCard SID SX-64 SX64 uIEC unofficial VIC20 x2010 µIEC
Patient: Commodore SX-64 (serial numbers on the casing and on the internal do not match 🙁 )
Symptoms: “white” screen and takes no input or squeaks at: load “$”,8
Diagnosis: Patient is brain dead
Documentation: Original SX-64 Portable Computer Schematics by Commodore, part no. 314001-05
Diagnostics: CPU board transplant and the patient is alive again, so somewhere in the CPU board we got some headache!
1. First thing i did is swapping CPU board and the SX-64 boots again. So we have to narrow it down.
2. Exchanged all the chips from the working board to the non-working board, still no go.
3. Replaced capacitors C17 and C21 , both 10 µF 25v 85°C, as they seem a little buffed, still no go.
Wait! First we need to measure to make a more educated guess! This is where the Club Mate comes in handy.
Now Ray Calrsen’s schematics, the original SX-64 Portable Computer Schematics by Commodore, part no. 314001-05 and not the least the Ray Carlsen’s diagnostics instructions (local mirror) comes in handy.
We used a oscilloscope to determine the basic functions like voltage and clock settings. Eventually after suspecting the 74LS139 we decided to desolder this Decoder/Demultiplexer and place a socket on the board. After exchanging the IC the patient was still brain death.
So back to the drawing board: exchanging all chips again (as the rest of the board seems to be in a working shape). We found the following ICs a defective;
- UD3 – 251104 – Kernal
- UD4 – 901226-01 – BASIC ROM
- UD7 – 6510 – CPU
- UE5 – 6581 – SID (replaced by 6581R3)
- UE4 – 906114-01 – PLA
After finding working replacement ICs I felt like the 15 year old boy again when I got the C64 for my birthday. 😉
Never mind the errors on the diagnostics as there is no additional diagnosis hardware attached, the machine is working OK. 😉