Luxor ABC 1600 Power Supply Unit -------------------------------- This is reverse-engineered documentation based on the small information in the service manual and practical inspection of the PSU. In the service manual the PSU is called "Rovsing" and is produced by LK power systems. If I open up the shield box of the PSU a hand-written label on the PSU says: Type: 3150A -1A 8509 s/n 6664 (The serial number is obviously going to differ on other PSUs.) The PSU has one 240V AC input and different outputs like this, the 240V AC input is separated slightly from the outputs a bit like this, left to right from the side: Y = Yellow W = White B = Black R = Red LB = Light Blue G = Gray AC input DC output 240 V in GND Y W Y B R LB G B | | | | +------------------------+ From checking the standard Molex connectors that are connected to a standard floppy and MFM harddrive, we can immedieately identify the voltages: B = GND R = +5V G = +12V Remains the light blue and yellow leads. The service manual says the PSU can give -12V as well so that must be one of the connectors. The two power connectors to the CPU and graphics board are called "Mate-n-lok", male connectors with 5 leads. On the schematic page 31 we can see the big CPU board power connector with pins numbered 1-5, and by cross-referencing what we know to be +5V, +12V and GND we get this list, the last column shows the looks of the pins, and this also matches what is printed explicitly on the circuit board: 1 Y POWFAIL D 2 R +5V O 3 B GND O 4 G +12V O 5 LB -12V D There is a second connector to the graphics card: this one has only GND and +5V connected to pins 2 & 3 of the Mate-n-lok connector. So we can conclude the assignments: Y = Yellow W = White B = Black R = Red LB = Light Blue G = Gray AC input DC output 240 V POW in FAIL GND +5V -12V +12V GND GND Y W Y B R LB G B | | | | | | | | 240 V +------------------------+ AC The fan is mounted White = GND Yellow = +12V Replacement PSU --------------- A normal ATX power supply works fine for this machine with the proper adaptions, but you need one with a low profile and 150W out. Sparkle Power SPI150-FA is a viable candidate for this, and that is what I used. As the new PSU has a standard IEC power input I soldered an IEC (cobra) connector cut from an ordinary power cord onto the 240 V input (after the front switch) to the old PSU making sure to isolate the leads with heat-shrink tubing. The GND lead was soldered to a ring style wire-end connector and screwed in with the other ground leads to the chassis. The molex connectors coming out of the ATX PSU can be connected directly to the floppy, hard drive and SASI adapter board as these are following the now established molex standard for GND, +5V and +12 V supply. The fan leads were soldered to a molex tap cable so the fan can be connected to the molex as well. Again made sure to isolate the leads using heat-shrink tubing. The big challenge is the ATX power connector. This PSU has a 20 pin micro-fit molex (the other standard is 24 pins). I solved this by acquireing a ATX micro-fit molex 20 to 24 pins adapter which has a 20 pin female connector. This one was named "CABLE-249 ATX POWER CABLE 0.14 M 20 pin Female - 24 pin Male" and produced by Nedis B.V. in the Netherlands. I cut off the 24 pin connector and use the wires from that end for creating an adapter to the ABC 1600 PSU connectors. The POWER_FAIL signal on the ABC 1600 is active high, meaning it is driven HIGH to indicate that the power supply is failing and the operating system will expect this to be low and fires an interrupt parking the harddisk and shutting down the operating system if it goes HIGH. This is not compatible with the ATX standard pin POWER_GOOD which is normally HIGH and the ATX supply drives the line LOW to indicate power failure. Hence the adapter inserts an inverter on POWER_GOOD to connect it to POWER_FAIL. The inverter is supplied by +5V SB (standby power) to make sure it is always correct. I solved this by soldering an inverter on the line using just a standard TTL 74LS04 IC and a piece of breadboard, powered from the +5V. A cheap solution is of course to just ground the POWER_FAIL signal. But since the operating system takes special care to deal with power failure this is generally speaking not a good idea. The circuitry is there to deal with sporadic power failures such as fuses going out on the mains supply. Another wire is the POWER_ON signal which is active low. This we just wire to GND because the ABC 1600 has no soft switch or software control to turn the machine on or off.