Amiga power supply guide


Amiga power supply guide V1.12
February 2016

Recent updates
Added information on the power ratings of stock power supplies
Added more information on ATX power supplies, relating to minimum loads and +12V balance
What to look for when purchasing a picoPSU and spotting fakes.

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
picoPSU ratings
Spotting fake picoPSUs
Minimum loads
'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

Type

Part number

+5V current

+12V current

-12V current

Combined power rating

A500 type 1*

312503-02

2.5A

1.0A

0.1A

25.7W

A500 type 2**

312503-03

4.5A

1.0A

0.1A

35.7W

A6000/A1200

391029-02

3.0A

0.5A

0.1A

22.2W

A600/A1200

391029-03

3.0A

0.5A

0.1A

22.2W

* Heavyweight PSU manufactured in Germany might also be a 4.5A PSU, email received from another Amiga User:
Hello Ian, I was just looking at your Stock Power Supply Ratings table and checked it against my own A500 PSU.

I have the 312503-02 that is made in Germany. Which should be heavy  weight and only have 2.5A at 5V.
But it is definitely the lightweight one and shows a rating of 4.5A at 5v.

Maybe there is no hard rule about the model number and the weight/rating?

Thanks, John Beaumont.


** Lightweight PSU manufactured in Malaysia

CD32
+5V @ 2.00A
+12V @ 0.50A

A1000
Information taken from emails and A1000 PSU schematics
+5V @ 8.00A
+12V @ 1.00A
-5V @ 0.25A
Note: This system requires a 'tick' circuit which provides a 50/60Hz +/-10% reference signal to the video chipset. Without it, the A1000 will not work.
Will require a simple linear regulator circuit using a 7905, to generate -5V

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.
Would 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 jumper connect across pins 2-3 to ensure that the machine generates the TICK signal from the VSYNC signal.

Would 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

System

Configuration

+5V current

+12V current

System power

A500

With A501, floppy only

1.55A idle, 2A peak

0.022A

10.25W

A600

Stock with 2 MB RAM, no hard drive

1.71A

0.03A

8.9W

A600

Stock with 2MB RAM and hard drive

1.94A

0.03A

10.06W

A2000

Bare,system, floppy only

2.5A

0.05A

13.1W

A1200

Bare system, floppy only

1.4A

0.07A

7.84W

A1200

Bare system + hard drive

1.84A

0.07A

10.04W

A1200

+Viper T1230/28 RTC + 8MB RAM

2.01A

0.07A

10.85W

A1200

+Apollo 1240/25

2.5A

0.07A

13.34W

A1200

+68060 card, 2xHDD & SCSI card

3.0A

0.07A

15.84W

CD32

Stock system

1.1A

0.07A

6.34W

CD32

+SX32 Pro 030/50, Floppy  & HDD

2.19A

0.07A

11.79W



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
atx_psu

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
picoPSU-90-b

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, larger ATX power supplies.

Both supplies require the PS-ON signal (green wire) to be grounded to switch on the power supply. This can be achieved by wiring between the two signals 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:

Model

+5V current

+3V3 current

+12V current

picoPSU-80

6A

5A

4A

picoPSU-90

6A

5A

5A

picoPSU-120

6A

6A

7A

picoPSU-150-XT

6A

6A

8A

picoPSU-160-XT

8A

8A

8A

 

 

 

 


Note on picoPSU purchasing. Most ebay auctions will list for example, the 90W picoPSU but only supply a 60W mains
adaptor, the one I purchased was like this (though it was clear in the description) If you need the 90W/120W/150W power
supply, ensure you purchase a mains adaptor rated correctly.

Spotting fake picoPSU adaptors
In response to comments from fellow Amiga users, I have provided some information on spotting fake picoPSU supplies. First lets take a look at a couple of genuine parts.

The genuine 80W converter
Genuine-picoPSU-1 Genuine-picoPSU-2

The genuine 90W converter
Genuine-picoPSU-3Genuine-picoPSU-4

What to look for in a genuine picoPSU

  • The ATX power connector, is normally yellow, most cheap clones use white or clear connectors.
  • The main power inductors (two square objects) are yellow or light grey and have 'picoPSU Pat Pend' written on them.
  • Next to the two inductors (yellow or light grey) are two high quality black OSCCON capacitors. Cheap clones use yellow tantalums
  • the name is picoPSU, no space and not 'pico psu'/' Pico PSU'/PICOBOX
  • Compare any product you see for sale to those on the Mini-box website, http://www.mini-box.com/DC-DC
  • Purchase from one of the resellers listed here, http://www.mini-box.com/site/resellers.html I purchased mine from Fullspeed IT in the UK.
  • Compare prices, The prices start around 35 for the 80W supply,  up to 80 for 150W version. If it appears too cheap, it probably is
     

Take a look at the following fakes, found on ebay
Fake #1

haruyr_kb_pico
This fake pico PSU does not have the coloured connector or inductors and uses cheaper electrolytic silver can capacitors.

Fake #2
PICOBOX-$_12
This one also does not have the yellow connector or inductors. The design uses Tantalum capacitors(yellow colour)
 instead of the lower ESR black OSCCON, this variant will have more ripple on the output supplies.
Fake #3

PICO-BOX$_12Another 'PICO-BOX' supply
See the comments for Fake #1
Fake #4
picoBox-yellow-connector
This has a yellow power connector, like the original but does not have the coloured inductors. Again this has the cheap,
high ESR Tantalum capacitors, they increase the ripple and noise on the supply outputs.

ATX power supply minimum loads

It is worth noting that modern, high current ATX power supplies, have minimum load requirements. If you do not
provide the minimum load on each power rail, the voltage outputs may be outside of the specification. Trying to locate
actual minimum loading data was not easy, what the author did manage to locate is below.
 

Manufacturer

Model

+5V load

+12V1 load

+12V2

+3.3V load

-12V load

+5VSB load

Antec

Truepower series (330W to 550W) ATX12V 

0A

0.8A

0A

0A

0A

0A

Antec

Phantom 350

0.3A

0.3A

0.3A

0.3A

0A

0A

Antec

Neopower 380/480

0.3A

0.4A

0.4A

0.3A

0A

0A

Antec

Neopower 550W

0.3A

1A

1A

0.5A

0A

0A

Minibox

picoPSU-90

0A

0A

N/A

0A

0A

0A

Minibox

picoPSU-160XT

0A

0A

N/A

0A

0A

0A

Corsair, Evga and XFX did not provide minimum loads in their documentation.

A good ATX PSU test guidehttp://www.antec.com/pdf/article/info_DIYArticle1.html

+12V 'bias' of modern ATX power supplies and the Amiga

Reading various Amiga forums, the author has seen a number of comments that modern ATX power supplies, with the bulk of their power, coming from the +12V supply being less suited to the Amiga. This is not quite true. To meet the increasing power requirements of high end graphics cards in the PC and avoid changing the wire gauges, the modern PC PSU provides higher currents on the +12V lines but they can still supply more than enough for the Amiga on the +5V rail.
The following came from the Antec  NeoPower 550W supply

Output Voltage

+3.3V

+5V

+12V1

+12V2

+12V3

-12V

+5Vsb

Max. Load

24A

20A

18A

18A

18A

0.8A

2.5A

Min. Load

0.5A

0.3A

1A

1A

1A

0A

0A



This supply would work with the Amiga, it can supply 20A@5V, ideal for the A2000/A3000/A4000. Where it falls down is on the minimum load requirements for each of the +12V supplies One 12V supply would be used for the HDDs and CD-ROMs but the other two would need two 25W, 12 ohm resistors added to provide the required load and either a suitable heatsink or cooling fan to dissipate the heat.

You would be better suited using a 350W power supply or lower, they have more realistic minimum loads, which are met by the Amiga .For the 'wedge'  Amigas, use a 150W or lower supply

'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

Meanwell RPT-60B
Have not tried this but it does work
Specifications
+5V @ 4A
+12V @ 2A
-12V @ 0.5A
 
Sold by Mouser, www.mouser.co.uk/ProductDetail/Mean-Well/RPT-60B/?qs=V9a8iPeg90y32GHaWpmkvA%3d%3d
Check local suppliers.

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

Wire colour

Signal

Pin(s)

Red

+5V

4,6, 19 & 20

Black

Ground

3,5,7,13,15,16,17

Yellow

+12V

10

Blue

-12V

12

Green

PSU-ON

14

Orange

+3.3V

1,2,11

Grey

Power OK

8

Purple

+5V Standby

9



Connectors

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

the authorhave personally bought and used all these connector types successfully.

Amiga A500/A600/A1200 connectors

The user 'mech' at Eniglish Amiga Board (EAB) has connectors in stock, http://eab.abime.net/showpost.php?p=989238&postcount=10
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

the authorfound 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.
power-plug

  • 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, the authorprefer 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 the author wired up my Amiga PSU. I used a blue wire to  connect the -12V from the Motherboard connector
to the Amiga PSU cable
.
wired-atx-psu

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

Amiga motherboard power entry points

As viewed on the underside of the PCB.
A1200_mobot_power_pcb

CD32 power supply modification

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.

cd32power-closeup

cd32-power-adapter

 

 

 

 

For reference, here is the pinout of the CD32 when looking at the connector:
cd32-power-socket

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 the authorfound 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

Amiga pin #

Description

ATX colour

ATX pin #

1

+5V

Red

 

2

+5V

Red

6

3

+5V

Red

19

4

+5V

Red

20

5

GND

Black

3

6

GND

Black

5

7

GND

Black

7

8

GND

Black

13

9

+12V

Yellow

10

10

KEYWAY

No connect

 

11

-12V

Blue

12

12

+5V User

Red

4

13

-5V

N/A

 

14

Tick

N/A

 



Wiring details for A3000/A3000D

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

Amiga pin #

Description

ATX colour

ATX pin #

1

+VID

Red

4

2

+5V

Red

6

3

+5V

Red

19

4

+5V

Red

20

5

No connect

 

N/A

6

Gnd

Black

3

7

Gnd

Black

5

8

Gnd

Black

7

9

Gnd

Black

13

10

Gnd

Black

15

11

-5V

N/A

None

12

+5V_USER

Red

4

13

TICK

N/A

None

14

-12V

Blue

12

15

+12V

Yellow

10




Wiring list to connect an ATX PSU to an A3000T

Amiga pin #

Description

ATX colour

ATX pin #

1

Tick

N/A

N/A

2

-12V

Blue

12

3

-5V

None

N/A

4

Gnd

Black

3

5

Gnd

Black

5

6

Gnd

Black

7

7

Gnd

Black

13

8

Gnd

Black

15

9

+5V

Red

4

10

+5V

Red

6

11

+5V

Red

19

12

+5V

Red

20

13

Fail

Grey

8

14

+12V

Yellow

10

15

+12V

Yellow

10

16

+5V_USER

Red

4

17

Gnd

Black

16

18

Gnd

Black

17

19

Gnd

Black

3

20

Gnd

Black

5

21

+5V

Red

6

22

+5V

Red

19

23

+5V

Red

20

24

+5V

Red

4


Wiring details for A4000/A4000T

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:

Amiga pin #

Description

ATX colour

ATX pin #

1

PWR_GOOD

Grey

8

2

-12V

Blue

12

3

+12V

Yellow

19

4

Gnd

Black

3

5

Gnd

Black

5

6

+5V

Red

4



FAQ

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

Supply

Lower limit

Upper limit

+5V

4.75V

5.25V

+12V

11.4V

12.6V

-12V

-12.6V

-11.4V

From experience, the author has found that if the +5V line is less than 4.85V DC, you can get some weird
operations of your Amiga computer.

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 08 July 2017