A Commodore 128 is not simply a C64 with an extra mode. It is a three-way machine: a capable C128 with BASIC 7.0, a broadly compatible C64, and a Z80-equipped system intended to run CP/M. That makes this Commodore 128 buying guide less about finding any working beige computer and more about deciding which version, video setup and peripherals will let you use the machine as intended.
For many collectors, a tidy C128 with its original power supply and a working 1571 is the sensible starting point. For a more complete desk setup, the 80-column RGBI display output and compatible monitor matter just as much as the computer itself. A cheap base unit can become an expensive project if its keyboard, PSU, video lead and disk drive are missing.
Choose the right Commodore 128 variant
The standard flat C128 is the model most often encountered. It has an integrated keyboard, external power supply and separate disk drive requirement. It is practical, relatively easy to store and usually the least costly route into the platform. Look for a clean case, intact rear ports and a keyboard with no missing keycaps or badly yellowed keys.
The C128D is the portable-style desktop model with a detachable keyboard and built-in 1571 floppy drive. The original plastic-cased C128D includes a cooling fan and is a substantial machine, but it gives you a neat all-in-one system with the correct drive already present. Its keyboard cable is specific to the model, so an otherwise attractive unit without the keyboard or cable should be priced as incomplete.
The C128DCR is generally the collector preference. It has a metal case, a revised internal 1571CR drive, a detachable keyboard and no fan. It is quieter and often regarded as the tidier long-term machine, although its integrated design can make repairs more involved than on a flat C128 with separate peripherals. Do not pay a premium merely for the DCR badge if the drive is untested or the keyboard has faults.
All three versions have their place. A standard C128 suits someone who wants to build a modular system around a 1571, modern storage device and monitor. A C128D or DCR is better for a complete period-correct setup, provided it is genuinely complete.
Commodore 128 buying guide: check the video first
Video output is where many first-time buyers are caught out. The C128 has 40-column video for C64-compatible use and 80-column output for native C128 applications. These are not interchangeable.
The 40-column display is available through RF, composite and chroma/luma connections, depending on the cable and display. It is useful for games and C64 software, but it does not show the C128’s 80-column desktop properly. The 80-column signal is digital RGBI through a 9-pin D-sub connector, intended for a suitable Commodore monitor such as a 1901 or compatible 1084-series display that accepts TTL RGBI.
A modern television with composite input may be enough for casual C64 use, but it is not a complete C128 solution. If you want to use BASIC 7.0, word processors, terminals or CP/M software in 80 columns, budget for a compatible RGBI monitor or a tested converter. Ask the seller for photographs of both a 40-column and 80-column screen. A boot screen alone proves very little.
PAL is the normal choice for UK collectors. An NTSC C128 can still be interesting, particularly for North American software or a matching collection, but it may be awkward with PAL displays and timing-sensitive software. Confirm the machine’s region before buying, especially when importing.
Power supplies deserve more scrutiny than the case
The C128 uses an external PSU that supplies both 5V DC and 9V AC. Original units can still work perfectly, but age, storage conditions and previous repairs are unknown quantities. A seller stating that the machine powers on is useful, yet it does not prove that the 5V line remains stable under load.
Ideally, buy a machine tested with a known-good supply, or have the original PSU checked before extended use. A modern replacement PSU is sensible insurance for a machine you intend to use regularly. Keep the original unit if it is present and safe, as it is part of a complete collection, but do not treat originality as more valuable than a healthy motherboard.
Inspect the power socket and plug for heat damage, looseness, corrosion or improvised wiring. Avoid listings where the seller reports intermittent start-up, a black screen that clears after warming up, or a supply that has been opened with no clear explanation of the work carried out.
Test all three personalities, not just the boot screen
A C128 can appear healthy while one of its key functions is unavailable. At minimum, ask for a test in C128 40-column mode, C128 80-column mode and C64 mode. BASIC 7.0 should load cleanly in native mode, while the GO64 command should enter C64 mode. Returning from C64 mode requires a reset or power cycle, so that behaviour is normal.
Keyboard testing matters more than it does on a basic console. The C128 has extra function keys, a numeric keypad and dedicated editing controls that are useful in native software. Test every key, including RESTORE, RUN/STOP, cursor keys, the 40/80 DISPLAY key and the top-row function keys. Randomly dead keys can indicate dirt or a connector issue; whole rows or columns missing may point towards a more involved fault.
If possible, run a diagnostic cartridge or test program. At a minimum, look for stable colours, a clean image, working joystick ports, a responsive keyboard and no unexplained crashes after the machine has been powered for 20 to 30 minutes.
A working 1571 changes the value of the package
The Commodore 1571 is the natural companion drive for a C128. It reads standard 1541-format disks, supports double-sided disks and is relevant for software that makes proper use of the C128. It is also the drive most collectors want when assembling a system capable of running the machine’s wider software library.
A drive that spins is not necessarily working. A proper test includes loading a disk, listing its directory, reading several files and writing a file to a known-good disk. Listen for repeated head knocking or persistent read errors. These may be repairable, but should be reflected in the price.
A 1541 is still useful for C64 software and a 1581 can be an excellent addition, but neither is a straight substitute for a tested 1571 in a C128 collection. For CP/M use, confirm exactly which drive and boot media are included. A Z80 badge on the motherboard does not guarantee that a usable CP/M setup comes with the sale.
Decide what completeness means to you
For a working-user purchase, the priority is a tested computer, reliable power supply, usable video solution and a way to load software. A modern storage device can make the machine far more convenient than relying entirely on ageing floppy disks.
For a collector purchase, original components have more weight. The desirable package may include the matching PSU, 1571 drive, monitor lead, manuals, software, packaging and, for D-models, the correct detachable keyboard and cable. Boxes add display appeal, but they should not distract from the condition of the hardware inside.
Be cautious with terms such as untested, powers on and found in loft. Untested may be an honest description, but price it as a project. Likewise, a yellowed case is usually cosmetic, while a missing 80-column output, unstable power or failed disk drive affects usability and value much more directly.
Questions worth asking before payment
Before committing, request clear answers on the practical points that determine whether the machine is ready to use or ready for the bench:
- Has it been tested in C128 40-column, C128 80-column and C64 modes?
- Is the original PSU included, and has it been checked or replaced?
- Are all keys, joystick ports and rear connectors working?
- If a 1571 is included, has it read and written disks successfully?
- Which video cable is supplied, and what display was used for testing?
- For a C128D or DCR, are the keyboard and keyboard cable present?
Condition photographs should show the underside label, serial number area, ports, keyboard, power plug and any yellowing, cracks or case damage. If a listing claims a drive or monitor is working, a photograph of it in operation is more useful than a stock description.
A well-bought C128 is a machine to use, not just display. Pay for verified function where it matters, accept cosmetic wear when the price reflects it, and keep an eye out for the peripherals that turn a basic computer into a proper Commodore workstation. SellMyRetro’s Commodore listings are particularly useful when you need to source that missing 1571, RGBI lead, keyboard cable or original software separately.