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Introduction

This document details how to diagnose and replace a faulty power supply on the Amiga range of computers.
Options for replacement using either an ATX PSU or smaller, compatible switchmode supplies are presented for the reader.

Contents

Original Amiga power supply ratings
Measured power consumption figures
ATX power supplies
'Brick' power supply alternates
Amiga ATX PSU adaptors
ATX colour code
Connectors
Re-wiring the original power lead
CD32 power supply mod
CDTV power adaptor
Wiring diagram for A1500/A2000
Wiring diagram for A3000/A3000D
Wiring diagram for A4000/A4000T
FAQ
References

Original Amiga power supply ratings
This information has been collated from original power supply labels, schematics
or emails from fellow users. The information is presented here to help you
evaluate alternative supplies.

Amiga A500, A600 & A1200

A1500/A2000

+5V @ 20.50A
+12V @ 8.00A
-5V @ 0.30A
-12V @ 0.30A
Note: This system requires a 'tick' circuit which provides a 50/60Hz +/-10% reference signal to the video chipset or motherboard jumper J300.
Will require a simple linear regulator circuit using a 7905 or equivalent, to generate -5V

A3000
+5V @ 17.25A
+12V @ 3.00A
-5V @ 0.2A
-12V @ 0.3A
Note: This system requires a 'tick' circuit which provides a 50/60Hz +/-10% reference signal to the video chipset. Changing motherboard jum
per connect jumper J350 across pins 2-3 to ensure that the machine generates the TICK signal from the VSYNC signal.

Will require a simple linear regulator circuit using a 7905, to generate -5V

A4000
Information taken from A4000 PSU schematics
+5V 10.00A
+12V 4.00A
-12V 0.40A

A4000T
Information taken from A4000T specifications
+5V  25.00A
+12V 10.00A
-5V 0.30A
-12V 0.30A

Measured Amiga power consumption
The following measurements have been made on Amiga systems

ATX power supplies

The most commonly available, high power supply is the ATX power supply. There are two distinct variants, the original rectangular box type and the picoPSU type:

Original ATX power supply, widely available

This type of supply is best suited to towered or big box Amigas. The +5V line can supply 15A or more and the +12V line will be of similar capacity.

picoPSU originally from Mini-box.com, available from multiple suppliers

The picoPSU uses an external mains to 12V power adaptor. The +12V is switched through and the +5V, +3V3 and -12V, as provided by the original, l
arger ATX power supplies.

Both supplies require the PS-ON signal (green wire) to be grounded to switch on the power supply. This ca be achieved by wiring between the two signal
s or using an adaptor board, sold on this website.

This is a popular power supply for the 'wedge' Amigas as it is small enough to fit inside the Amiga and is silent.
picoPSU power ratings
The picoPSU is available in six power ratings, the specifications are below:

'Brick' power supply alternates

Perhaps you would like a smaller alternative to an ATX power supply, well there are a number of alternatives.

Meanwell P50A
Fellow Amiga user, Chris Edwards emailed me to say that he has succesfully used a Meanwell P50A13D-R1B
power supply. It has the following specifications:
+5V @ 4A
+12V @ 2A
-12V @ 0.2A

The original Amiga power lead is required and the DIN plug of the new, Meanwell, supply needs to be cut off.
It is available direct from Meanwell and from Mouser.

www.meanwell-web.com/product-info/ac-dc-power-supply/adaptor/26-100-w/p50a/product/P50A13D-R1B 

www.meanwelldirect.co.uk/product/50W-AC-DC-Triple-Output-Desktop-Adaptor/P50A13D-R1B/default.htm 
www.mouser.com/ProductDetail/Mean-Well/P50A13D-R1B/?qs=%2fha2pyFadugmanyf43etyFr%2f4SUcIFWZ%252bhGrT6UYltDHb0VfotuPtQ%3d%3d 

Amiga ATX PSU adaptors

A number of ATX power adaptors for all Amiga models are available from this website. The technical details
 are on this page and they available to purchase from the sales page
ATX colour code

Provided as a reference

 With the exception of the A500/A600/A1200 with their specific square DIN plugs you can still purchase
power connectors for the other Amigas. In this section the relevant part numbers and more importantly suppliers,
are listed.

Suppliers:
RS Components http://rswww.com
Rapid Electronics http://www.rapidelectronics.co.uk

ATX connectors
The ATX connectors are from the Molex Mini-Fit Jr. range.

If you are making a wired lead (with no PCB) to adapt an ATX PSU to an Amiga, you will require this connector.
20 way dual row panel mount plug  RS 418-0150
Molex part number 3901-2201
You will also require the crimp contact, RS 324-8003 or Rapid 22-3850
These are expensive (£11 for 100)!

If you are connecting into a PCB or wish to (carefully) solder onto the tabs, the part is:
20 way dual row vertical header RS 172-8923

I have personally bought and used all these connector types successfully.

Amiga A500/A600/A1200 connectors

You can purchase new, square 5 pin DIN plugs from a4000t.com/store/index.php?main_page=product
_info&products_id=204
Alternatively you can chop the lead of your old PSU and wire it up to your new
 PSU using the guide detailed here

Amiga A2000 connectors

Information required

Amiga A3000 connectors

AMP part. 172171-1 (Plug), and 170366-1 (Terminals)


Amiga A4000 Mate-N-Lok connectors
The A4000 power supply  connectors are from the Amp Mate-N-Lok range.
To make up a new power supply lead you will require:

6-way Mate-N-Lok housingRS 848-874/ Rapid 22-4608
AMP part number is 1-480704
Mate-N-Lok pin 14-20 AWG RS 849-085/Rapid 22-4672
AMP part number is 926894-1
Note: you have to buy the Mate-N-Lok connectors in packs of 100 pieces.
You will require the above items to make a new power connector for your A4000 desktop motherboard.

If you want to fit a new motherboard connector you will require this part:
Mate-N-Lok 6 pin PCB RS 129-5221/ Rapid 22-4644
AMP part number is 350711-1

ATX to AT power adaptor

I found this whilst hunting through the RS catalogue, an ATX to AT adaptor, perfect for the A4000T and
some bridgeboards, RS part number 214-739 and at £4.13 cheap too. It converts the ATX power lead to
the P8/P9 leads required by your system.
Re-wiring the original power lead for the A500, A600 and A1200

 Required tools & parts
A pair of wire cutters,
A pair of pliers,
A small flat blade screwdriver,
A terminal block connector,
A multimeter/tester.
Optional, a Soldering Iron + solder

You will have to cut the lead off your Amiga PSU. This is easily done with a pair of cutters. Strip the ends of the wires

As Commodore never used a standard wiring scheme for their PSU's you need to ascertain which PSU pin connects to
which voltage.
This picture of the power plug should help.

• To ascertain which pin connects to which wire, either use the continuity function of your meter or use a couple
  of batteries, 3 pieces of wire and bulb to work out the connections.To make the connections to the PC PSU you have two options.
  i) Cut off the PC motherboard connector and connect the power wires from there. If you choose this method, be sure to insulate the
  unused wire.
  ii) Use one of the peripheral power connectors (4 way type) that would be used to power your CD-ROM, HDD etc, I prefer this method.
  I like to take a spare plug or socket and wire it up to the Amiga's PSU cable.With reference to either the AT PSU or ATX PSU colour code
  cross reference it to that of your power lead.
  On the power lead of my original Amiga PSU it had the following colour code:
  

  Amiga colour	ATX colour	Supply
  Red	Red	+5V
  Black	Black	0V/GND
  Brown	Yellow	+12V
  White	Blue	-12V

  
  
  Always check the wiring of your existing power lead, Commodore were not consistent with their wiring.
  Testing the new power lead

1. Cut the wires from the PC PSU as appropriate and connect them, via the terminal connector block to your Amiga PSU lead.
2. Do not worry about the Shield of the Amiga PSU cable, it will do nothing if you connect it to ground.
3. Power up the PSU but without your Amiga connected, check the voltages that come out of each pin to ensure they match those shown above.
4. If the voltages are correct, you can connect the lead to your Amiga and power the system up.

For reference, this is how I wired up my Amiga PSU. I used a blue wire to connect the -12V from the Motherboard connector
to the Amiga PSU cable
.

For reference this is the pinout of the square DIN connector on the Amiga.

If you own a CD32, you can easily make a power lead up. All you need is a 4 pin DIN plug and to wire it up as shown here
 and for ease of use use a PC 'Y' cable to connect it.

For reference, here is the pinout of the CD32 when looking at the connector:

CDTV power adaptor

The easiest solution for the CDTV is to purchase a CDTV power adaptor and use a picoPSU power supply, as shown here
To utilise the existing CDTV remote on/off switch requires an adaptor circuit to invert the polarity of the PSU-ON signal, which
the CDTV adaptor provides.

Wiring details for A1500/A2000

The main issue issue you will encounter with the A2000 is connecting to the Motherboard. You can either cut off your original power lead
and re-use the existing lead or buy a new one. A new connector is an Molex 2139 (KK) 3.96 MM 14 way connector.
 In addition you need to change jumper J300 to cover pins 2-3, so that the TICK signal is
provided internally by the VSYNC signal.

NOTE: Originally the information I had suggested J200 should be connected across pins 2-3, this was incorrect, as J200 control the light pen input.
The information above has been corrected to U300, which does in fact select the clock source for the TICK input.

An alternative method to generate the Tick signal is by using this circuit on Aminet: Tickit.lha, be warned this circuit connects directly to
the 220V AC mains, do not build unless you are competent in working with the AC mains, if in doubt do not build it.

After some research I found that the +5V_USER supply can be safely connected to the normal +5V supply as it is only used to provide
+5V to the mouse and joystick ports.

Control the PS-ON (ATX pin 14) either by using my circuit shown above or by connecting it to ground via a switch, which ever is easier for you.

Here is the wiring list from an ATX plug to your A2000

The first choice you will face when adding a new PSU is how to connect it to the Motherboard, you can either chop off the original lead or
buy a new connector. The A3000 desktop PSU uses a an AMP #172171-1 connector with size TBD inserts.

Similar to the A2000, the +5V_USER/+5V_VID supply can be connected to the system +5V wiring.

To ensure that the A3000 works, connect jumper J350 across pins 2-3 to ensure that the machine generates the TICK
signal from the VSYNC signal.

Control the PS-ON (ATX pin 14) either by using my circuit shown above or by connecting it to ground via a switch,
which ever is easier for you.

The A3000T takes a power FAIL signal from the original PSU which indicates when the power rails are operating out of tolerance,
when connecting to an ATX PSU you must connect this wire to the PWR_OK (pin 8) of the ATX PSU or your A3000T
will not power up.
Wiring list to connect an ATX PSU to an A3000D

The A4000 desktop machine is not too difficult to wire a new PSU upto, it only has 6 wires.
Importantly, the A4000 requires the ATX  PWR_OK signal to function, if you do not connect this, it will not work.

Note: PWR_GOOD=PWR_OK. A logic 1 level indicates that the PSU is operating normally.

This is the wiring list:

What voltages should the +5V, +12V, -12V rails be at?
±5% of the nominal line voltage, or in plain english:

What is the -12V supply on the Amiga used for?
It is used for the RS232 transceiver chips and to power the Op-Amps in the audio circuits.

What is the shield wire for?
In the original Amiga PSU, it is used to reduce the radiated emissions of the power lead. Inside the Amiga, the shield
 pin is connected to the Amiga system ground and back at the original PSU. When you re-wire the lead as shown in
 this guide, you will have maybe a 1 metre length of unshielded cable going from the PSU to you Amiga lead. This will
 radiate noise. Connecting the shield will make no difference to the radiated or picked up noise.

What is crowbar protection?
To reduce the risk of you totally screwing your system!
If you short a power rail to ground, circuitry inside the PSU will operate to reduce the outputs to a safe level
(typically less than 1 volt) until power is removed. The idea is to reduce the chance of blowing up a PCB when
you short circuit something (lower voltage, lower current). DO NOT RELY ON THIS SAVING YOUR SYSTEM
IT IS NOT 100%.

How much current can the peripheral connector (HDD/CDROM power cable) take?
I checked one of my adapter leads and it uses 18AWG wire. Referring to the Electronic Engineers handbook
 for this cable type and derating, I found that it was rated at up to 8Amperes per wire!
More than enough to power your Amiga mainboard.

 How much current can the Floppy drive connector of the Amiga FDD supply?

As best I can measure it, the tracking here is approximately 50 thou (1.27 mm). Assuming ½Oz copper, Mil Standard 275
rates this at 1.5 Amperes. It should only be used to power the floppy drive, not a PPC accelerator.

What is the best way to power my PPC accelerator?

Use another Peripheral connector (HDD/CDROM power cable) and adapt the plugs.
References

This article was created with reference to the following sources:

Commodore Amiga A500/A600/A1200/A3000 & CD32 schematics from my personal collection.
Big Book of Amiga hardware, http://www.amiga-hardware.com
The Hardware book, http://www.hardwarebook.net
The A3000 technical guide by Calum, Tsang, http://peach.mie.utoronto.ca/people/tsangc/amiga-index.html
Building an A3000 into an ATX case project, http://www.liukuma.net/amiga/A3000atx/buildingdescription.html
The A4000 hardware guide by Warren Block, http://wonkity.com/~wblock/a4000hard/main.html
The A2000 tower guide V1.1 by Bill toner, from Aminet, http://main.aminet.net/hard/hack/A2000T.lha
The ATX specification from Intel, http://www.intel.com/design/motherbd/atx.htm
Tickit, an alternative Tickit circuit, http://main.aminet.net/hard/hack/TickIt.lha
 

Glossary of terms

AC     Alternating Current
ATX   AT eXtended
DC     Direct Current
CD-RW CD Re-writable
FDD   Floppy disk drive
HDD   Hard Disk Drive
IDE    Integrated Drive Electronics
PC      Personal Computer or Piece of Crud ;)
PCI      Peripheral Component Interconnect
PPC     Power PC microprocessor
PSU     Power Supply Unit
RAM    Random Access Memory
ROM   Read Only Memory
SCSI    Small Computer System Interface

Updated 20 December 2014