Commodore 128

A Commodore 128 home personal computer

PCB rev. 7

A 1530 Datasette model C2N tape recorder

C128 psu - P/NO: 310416-03

input 220V AC, 50 Hz, 0.3A - fuse T315mA T40/E

output 5 V DC 2.5A

output 9 V AC 1 A - fuse T1.4A

C64 ports

ROM cartridge expansion slot (44-pin edge connector)

RF modulator output (RCA connector)

8-pin DIN (262 degree "horseshoe"): composite video output, separate Y/C outputs, sound input / output

serial bus (proprietary serial version of IEEE-488, 6-pin DIN plug) for CBM printers and disk drives

PET-type Commodore Datassette 300 baud tape interface (edge connector, digital cassette motor/read/write/key-sense signmals, GND, + 5V DC)

User port (edge connector, TTL-level signals)

2 x screwless DE9M game controller ports (compatible with Atari 2600 controllers): digital joysticks, analog paddles, light pen, Commodore 1351 mouse, graphics tablets (like KoalaPad)

Power supply: 7-pin female DIN connector: 5V DC and 9 V AC

C128 only ports

RGBI video output (DE9 connector)




Carlsen Electronics - Commodore repair, Commodore 128 & PET Alive!, Zoomtape - ZoomFloppy support for 1530 / 1531 datasette,,, Vanessa's Projects, Retro Commodore DIY Open Source Stuff, BIT-C-128, /pub/schematics/computers/c128/,

more links

[M]ouse - PS/2 to C64 mouse adapter, mouse1351, World of Jani - repair, Ruud Baltissen's hardware projects, - C128, Github C64-Switchless-Multi-Kernal-27C256-adapter, ctools, C64-PSU, c128cpm, 40-80-column-mode-cable-with-switchable-for-C128, c64-sd2iec, sd2iec-revisited, Pi1541, console5 wiki Commodore 128, Unijoysticle2,

other links

Turbo Rascal Syntax Error - IDE for development, cc64 - small C compiler written in Forth,

local links

Commodore 1571,


2021-04-16: broken trace between C96 / L5 and AC input of CR13. Fixed by soldering in a patch wire on the solder side of the PCB. The trace between '+' out of CR13 and C102 / C106 seems to be broken also. I'll need to double check and fix.

2021-04-13: tested a few components in circuit with my cheap Chinese component tester.

CR11 - shows up as two diodes (probably ok)

C102 / C106 - measures 966.1 uF esr= 0.15 ohm, they are in parallel so that is ok

CR10 - diode, ok

unsoldered one leg of the CR11 and tested again, shows up as diode, so it is ok.

C102 - unsoldered, tested, measures 84.5 nF = ok

2021-04-13: voltage measurements:


C95 - 10.43 V AC

C96 - 10.52 V AC

C106 - 184 mV DC (11.5 V)

C102 - 184 mV DC


C107 - 4.91 V (5.2 V)

C98 - 5.007 V (5.2 V)

2021-04-13: the warranty label fell off. It reads:


" (b) "


2020-01-09: replaced the following components

  • C61 10uF 25V - old 10.97 u 5.0 ohm
  • C62 10uF 25V - old 11.31 u 3.4 ohm
  • C63 10uF 25V - old 9.8 u 1.0 ohm
  • C80 2.2 uF 25V - old 2359 nF 6.4 ohm
  • C85 10 uF 25V - old 11.16 u 5.4 ohm
  • C88 10 uF 25V - old 11.12 u 4.7 ohm
  • C91 1 uF 50V - old 57 nF 8.8 ohm
  • C92 10 uF 25V - old 10.86 u 4.1 ohm
  • C101 10 uF 35V - old 10.04 u 1.9 ohm
  • C104 220uF 50V - the old one measured 212.6 uF, esr 0.11 ohm
  • C105 330uF 50V - old measured 301.3 uF, esr 0.13 ohm
  • C106 1000uF 50V - old 1003u 0.22 ohm
  • C107 100uF 25V - old 95.03u 0.77 ohm
  • C111 10uF 16V - old 11.41u 3.8 ohm

not tested yet.

2020-01-09: according the Commodore 128 page on the Console5 wiki, the parts are

  • C61 10uF 16v (E-8)
  • C62 10uF 16v (F-11)
  • C63 100uF 6.3v (F-13)
  • C80 2.2uF 25v (M-16)
  • C85 10uF 16v (E-15)
  • C88 10uF 16v (I-11)
  • C91 1uF 50v (H-19)
  • C92 10uF 16v (I-19)
  • C101 10uF 35v (G-25)
  • C104 220uF 50v (E-25)
  • C105 330uF 50v (35v OK) (E-24)
  • C106 1000uF 25v (D-23)
  • C107 100uF 16v (E-26)
  • C111 10uF 16v (G-25)

let me see if I can find them on the PCB.

2020-01-09: which revision? The PCB says Rev. 7

2019-11-03: useful information from VCFED forums: replacement for HOT diodes (fast switching): BY228, BY448.

2019-09-01: video solutions: CGA/RGBI to analog for the Commodore 128, Breadboard to circuit layout, Milling the PCB, which gives you analog RGB out, good for a GBS-8200 type scan doubler. The KiCad files are on Github FozzTexx/SeaGeelog, also mce2vga,

2019-08-23: the package from Console5 arrived in my mailbox.

2019-08-17: the package (from Console5) was shipped.

2019-08-16: I ordered a C128 cap kit from Console5. Price was USD 6.95, and shipping was USD 15.56 which in total is USD 22.51.

2019-08-16: unsoldered C102 and measured voltage over C105 - no, only millivolts there. Measured capacitance of C102 - it reads 84nF, should be 100nF so probably ok.

2019-08-16: unsoldered CR10 and measured voltage over C106 - still nothing (should be 11.5V). So C104, CR11, C102 or C106 is defective. Soldered CR10 back in.

2019-08-16: testing power inside the machine: 5V measured over C107 - 4.88V 11.5V measured over C106 - nothing. 9 V AC - measured of C95 - 10.3 V AC, over C96 - 10.1 V AC,

2019-08-15: if I ever get the C128 fixed, I could try to run P65Pas and generate code from Pascal for the machine.

2011-09-29: I got a Commodore 1571 drive for the machine.

2010-07-17: I used an ohm meter to measure CR13, it appears to be ok. Pins 3 and 5 of CN11 (the power socket) carries 10.6 VAC, the power switch (SW1) is ok, and the filter choke (L5) appears to be ok. C96 and C97 seems to be ok too. I wil try to change CR13, just in case.

2010-07-10: I located a pdf copy of SAMS Computerfacts CC18, which is the repair manual for the C128. Nice! Let's see... 5V is OK at CR15, but that U59, the LM340T12 (aka 7812) voltage regulator, doesn't have voltage in or out. Also, there is approx. 10 VAC over C96. No voltage over C106. Perhaps rectifier CR13 is broken?

2010-07-09: further checking verifies that +5 VDC is present on the cassette port (A-1 is GND, B-1 is +5V). +5V is also present on the user port (pin 1 is GND, pin 2 is +5V). Pins 10 and 11 on the user port is supposed to carry 9 VAC, but I couldn't measure that voltage there.

2010-07-09: I have a Commodore video cable (from my late 1084S monitor) 8-pin DIN to 3 x RCA phono, and a 2 x RCA phono to -SVideo adapter, so I tried that too. No picture there either, but my TV set briefly shows "SVideo" "PAL 50Hz" on the OSD.

2010-07-08: using the pinout here (note that the picture is of the socket in the computer), I verified that the PSU is working. + 5 VDC on pins 1 and 4, and 10.78 VAC on pins 3 and 5 (this should be about 9.6 VAC).

2010-07-08: I bought the machine from a fellow who advertised it on It came with psu, cables (RF and serial), manuals, three joysticks, a 1530 datasette, and about a dozen or so of tapes. No 1571 drive, only the manual for it. Visually the computer looks fine, a bit yellowed, but not worn or scratched. All keys operate as they should (no keys are stuck), and all sockets / connectors look fine. Connecting the RF cable to my TV set, tuning to UHF channel 36, and powering up the C128 verified that it was not working. The power led turns on (red) and my TV indicates a signal (the OSD briefly shows "mono"), but nothing else happens.