28th October 2002 by Ian Stedman (ICStedman@techie.com) Diagnosing power supply problems -------------------------------- This document details effective methods of diagnosing power supply issues in Amiga computers. Some of the hints and tips are applicable to all systems. Contents -------- PC Power Supplies as replacements/upgrades AT PSU ATX PSU Dealing with power supply issues Example scenario Stock Amiga power supply ratings Power consumption figures for various Amiga models Removable Drives power consumption Hard Drives CD-ROM Drives Other PC Power Supplies as replacements/upgrades ------------------------------------------ It is quite common now to replace the under rated original Amiga PSU with a PC one, as PC PSUs start at 135W and go to over 500W it is easy to see why. There are minor differences in using an AT or ATX PSU to power an Amiga and leter on I will explain the witing. AT PSU ------ Not really used in PCs since 1998/99 due to the PC requirement that software can switch the PC off (or a Microsoft plan to stop their software crashing). Normally found in old/dead PCs (they have some uses). To hook it upto your Amiga you will need to note wiring of the square DIN plug (check the underside of the PSU) and then cut it off. Commodore never seemed to use the same colour code in all Amiga models so you will need to check your wiring with a multimeter. See the power connector section for more details. Once you have wired up the Amiga cable, connect a 21W car bulb across the +5V (RED) and 0V (BLACK) wires. This will provide a suitable load to turn on the PSU and you can then ensure you have the right voltages going to the right pins before pluging into your Amiga. If all seems well, connect to your Amiga and switch on! Important note. Modern PSUs have what is called crow bar protection, if you short it out or wire up backward, to cause a large power surge, it will switch off. Don't count on this, double check your wiring. Some AT PSUs had the mains switch inside the PSU housing, that is fine. Some had a mains lead that went to the power switch on the front of the PC case. If possible avoid this type unless your Amiga case has a suitable power switch. Final note, do not open a PSU case. Due to their operation, a typical computer power supply can have upto 400V DC stored within for a considerable time after power off. If you inadvertantly touched the wrong part you could be killed! ATX PSU ------- This is the type of PSU found on all modern PCs and within cases. There are 2 important differences to the AT PSU. The following conditions must be met. 1) You need to have about a 1.5 Amp load on the 5V supply for it to work. 2) You need to connect the PS-ON line to ground for the PSU to switch on. Condition 1 is easily satisfied, an Amiga uses enough current on the 5V supply. Condition 2 is a bit trickier. It is possible to create a simple circuit to use the push to make power button of an ATX case. A simpler solution is to bare back the insulation of the PS-ON wire (normally green) and of a ground wire (black). Then either twist them together or add a link wire, solder it an insulate it. Now when you use the mains switch on the back of the ATX PSU, it will switch on the PSU. the circuit to utilise the PC front panel switch is at http://mysite.freeserve.com/Stedy/Projects/ATX_PSU/ATX-Circuits/atx-circuits.html Dealing with power supply issues -------------------------------- Over the years there has been much talk of how to deal with power supply issues/intermittent crashes, mostly resolved by removing additional peripherals. Rather than use a 'suck it and see' approach, I decided to gather information on how to tell if your Amiga PSU is overloaded. To determine if your PSU is overloaded, just add up all of the power figures below, add to the power figure of your base model and compare with your PSU rating. Example, I own an A1200, with an Apollo 040/25, 32 MB RAM, 1.4 GB Hitachi Hard drive, External Floppy, Scan doubler & CD-ROM. Device Power @5V Power@12V ----------------------------------------- A1200+040 2.5A 0.077A 1.4 GB HDD 0.5A External FDD 0.7A Scan Doubler 0.5A CD-ROM, 52X 1.3A 1.5A Total 5A 2.077A The A1200 PSU supplies a lot less than this (3A @ 5V, 0.5A @ 12V) time to upgrade. You can use an ATX PSU, see my note elesewhere on that. Below is a list of every peripheral I could get my hands on and it's rated power consumption. If you have any info to add, feel free. Stock Amiga Power Supply ratings -------------------------------- A600/A1200 PSU -------------- +5V @ 3 Amp +12V @ 0.5 Amp -12V @ 0.1 Amp CD32 PSU -------- +5V @ 2 Amp +12V @ 0.5 Amp Power Consumption of various Amiga models ----------------------------------------- CD32 ---- +5V @ 1.1 Amp +12V @ 0.077 Amp with CD32+SX32PRO 68030/50 MHz + 16 MB RAM + 170 mb HDD +5V @ 2.19 Amp A600 ---- with no hard drive +5V @ 1.71 Amp +12V @ 0.03 Amp with hard drive +5V @ 1.94 Amp A1200 ----- Bare system +5V @ 1.4 Amp +12V @ 0.07 Amp A1200 + hard drive +5V @ 1.84 Amp A1200 + Viper T1230/28 RTC + 8 MB RAM +5V @ 2.01 Amp A1200 + Apollo 040/25 + 32 MB RAM +5V @ 2.5 Amp Removable Drives power consumption ---------------------------------- Chinon FZ534, +5V @ 0.7A ATAPI (IDE) Zip Drive, 5V @ 1.7 A Peak Hard Drives ----------- 2.5" IDE HDD, 340 MB, +5V @ 1.10 A (Hitachi DK221A-34) 2.5" IDE HDD, 1.4 GB, +5V @ 0.53 A (Hitachi DK225A-14) 3.5" IDE HDD, 10 GB, +5V @ 0.35 A, + 12V @ 1.6 A spinup, 0.6 A average (maxtor) 3.5" IDE HDD, 40 GB, +5V @ 0.55 A, +12V @ 2.5 A at spinup, 0.6 A average 3.5" SCSI, 20 GB, +5V @ 0.3A, +12V @ 0.79A CD-ROM Drives ------------- 4X CD-ROM, +5V @ 0.4A, +12V @ 1.2A (Mitsumi FX400) 52X CD-ROM, +5V @ 1.3A, +12V @ 1.5A (Samsung SC-152) 4X CDRW, +5V @ 1.5A, +12V @ 1.7A (Samsung SW204) Other ----- DCE External Scandoubler, +12V @ 0.5 A