How would you wire this?

Discussion in 'General Electronics Chat' started by jim55, Sep 2, 2015.

  1. jim55

    Thread Starter New Member

    Sep 2, 2015
    Hi guys,

    I'm trying to directly flash my BIOS from a second computer after a corrupt BIOS update. I'm a bit of a novice with electronics and was hoping to get some advice on how to best implement this schematic as a physical cable?


    I understand to connect the IC's 4 data pins(1,2,5,6) via a short length of wire(using a cut 40pin PATA cable) to 4 150 ohm resistors soldered directly onto the LPT connector pins(7,10,9,8).

    My question is about the power circuit and ground. I am using a spare PC Power Supply with the green PS_ON# wire of its 20pin ATX connector shorted to a black ground wire to turn it on. I understand the orange wire at pin 1 of the 20pin ATX connector carries 3.3v so I will use that as the supply.

    Following from the end of Power Supply's 3.3v wire, do I solder 3 breakout wires for the 3 3.3v pins(3,8,7)?

    Where on the cable do I solder in the 1mF capacitor? What must I make sure of about polarity? Do I connect the negative leg of the capacitor into the ground wire(going between LPT pin 18 and IC pin 4), and connect the positive leg of the capacitor to the same solder point where the 3 3.3v wires break out?

    Would an LPT port's ground pin be sufficient or should I take ground from one of the black wires on the 20pin ATX connector?

    Where does the 180 ohm resistor physically go in the cable? Is the 100nF a decoupling capacitor, where would it go?

    Any advice for laying out this schematic would be very appreciated. Thanks in advance.
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    most computers have a built in method to update the flash from empty. it should be on the motherboard info.
  3. jim55

    Thread Starter New Member

    Sep 2, 2015
    This motherboard doesn't have a dual BIOS or other method unfortunately. I tried every BIOS recovery method.

    This cable schematic should work but I'm just not sure where to physically lay out the components on the power circuit, the two capacitors and the 180 ohm resistor.

    Should the 1mF be an electrolytic capacitor and the 100nF be ceramic? Since there is no breadboard can I solder a small SMD ceramic capacitor directly across the legs of the through-hole electrolytic capacitor?
  4. Denesius


    Feb 5, 2014
    If you're doing a free form layout- put the caps as close to the IC leg as practical (soldering to the legs is ok, as long as you take care not to overheat, or apply heat excessively), the resistors in the signal lines can be next to the IC or near the other end. Try to use a heavier gauge wire for the power & ground supply. It would be good not to have the signal lines wrapped around each other, best if you could isolate them by twisting a ground wire around each one, but if the run is short (1-2cm) you needn't bother.
  5. Ramussons

    Active Member

    May 3, 2013
    Some BIOS flashing utility permit you to backup the existing BIOS. If you can do this, you only need to flash the Backup in the dead PC.