Power Supply for CPC and CPC plus

Background

The power supply for the CPC464,664 or 6128 is not in the keyboard unit, it is in the monitor or an external television modulator.

The CPC 464 and Plus computers require a single voltage of 5V. THE CPC 664 and CPC 6128 require 5V for the mainboard and 12V for their built-in floppy.

Power supply options

Monitor models

• The GT64 is the "Green Screen" monochrome monitor for the CPC464 and has the 5V power supply for the computer.
• The GT65 is the "Green Screen" monochrome monitor for the CPC664 or CPC6128 and has the 5V power supply for the computer and 12V power supply for the disc drive. It can also be used for the 464.
• The MM14 is the "Grey Scale" monochrome monitor for the CPC464+ and CPC6128+ and has the 5V power supply for the computer and disc drive.
• The CTM640 is the colour monitor for the CPC464 and has the 5V power supply for the computer.
• The CTM644 is the colour monitor for the CPC664 or CPC6128 and has the 5V power supply for the computer and 12V power supply for the disc drive. It can also be used for the 464.
• The CM14 is the color monitor for the CPC464+ and CPC6128+ and has the 5V power supply for the computer and disc drive.

TV Modulator models

• MP-1 is the television modulator for the CPC464 and has the 5V power supply for the computer
• MP-2 is the television modulator for the CPC664 and CPC6128 and has the 5V power supply for the computer and 12V power supply for the disc drive. It can also be used for the 464.

Power supplies for other vintage computers

Use a Spectrum +3 (or a +2A) power supply as not only can it happily supply your required 5 and 12 volts but the lead you discard can be used to make the Scart lead, as it contains six cores and has a six pin DIN plug at one end --- so all you need to buy is a Scart plug, jack plug and the screened cable. An added bonus is if you obtain the machine with the +3 power supply then you can use the disc drive as a spare for your CPC machine (yes they are the same).

Another excellent alternative as a Power Supply Unit, is as supplied by Commodore for their various models of computer. And with the advantage that they come with a mains on/off switch. 5 and 12 volts DC is available from all units so far encountered (but do check the base of the unit for specifications) with current ratings for the 5 volt supply at between 2.5 and 4.3 amps with 1 amp for the 12 volt supply. Modifications required are the same as for the Spectrum P.S.U.

Using a PC power supply

It is possible to use a PC power supply, however PC PSUs can be dangerous as they easily can pump out 25A or more on the 5V rail - one accidental short in the system and it fries the traces of the computers PCB.

There are ATX breakout boards available on e.g. Ebay or Amazon, which will add fuses to the 12V and 5V lanes of the power supply, so they can be safely used with the CPC and Plus. To avoid any harm to the computer, the 5V fuse should be 4A, the 12V fuse 1A.

Other options

As long as you meet the criteria in the next section, you should be good to go. Many 5V power supplies are good for the CPC 464 and Plus. For the 664 and CPC 6128, you sometimes can find power supplies e.g. for Cisco routers that provide 5V and 12V at a reasonable price. Some soldering will then be required to make an adapter.

You can even buy separate power supplies for 12V and 5V and use it with the 664 and CPC 6128.

Just don't buy cheap. If you can get a good deal, sure, go ahead, but don't fall for very cheap offers. E.g. don't be tempted to buy the cheap power supplies used for external hard drives just because they offer 5V and 12V.

Technical aspects

Power requirements

The power requirements are (information taken from the underneath of the keyboard unit from real machines):

• CPC464: computer and internal cassette player: 5V DC @ 2A
• CPC664:

computer: 5V DC @ 1.7A

internal disc drive: 12V DC @ 0.4A

• CPC6128:

computer: 5V DC @ 1.7A

internal disc drive: 12V DC @ 0.4A

• CPC464+: computer and internal cassette player: 5V DC @ 2.4A
• CPC6128+: computer and internal disc drive: 5V DC @ 2.4A

All voltages MUST be smooth, the CPC does not have an internal regulator!

Power connectors

To connect a power supply to CPC you need the following connectors:

• CPC classic:

  * 5.5mm/2.1mm power line plug (providing the 5V for the CPC)
  * 5.5mm/2.1mm power line socket (providing the 12V for the floppy)

• CPC+:

  * 5.5mm/2.5mm power line plug (providing the 5V for CPC and floppy)

• Outer diameter (A) is 5.5mm for all plugs and sockets, inner diameter (B) is 2.1mm for classic CPCs and 2.5mm for Plus
• short and long plugs exist, the ones used for the CPC and Plus are the short ones with approx. 9.5mm (C)

Pinouts for Power Sockets:

The +5V socket on the back of the CPC / Plus is wired as CENTRE POSITIVE, i.e. the central pin of the plug is +5V and the outer barrel is Negative (GND).

The +12V plug on the end of the wire dangling out of the back of the CPC 6128 is wired CENTRE NEGATIVE, i.e. the central pin of the plug is Negative (GND) while the outer barrel is +12V.