Reply 40 of 73, by snufkin
Ok, try looking at this resistor on the top side:
Measure the resistance from both sides to pin 28 on the register. I'm hoping that the side furthest from the edge connector reads close to 0. If that's true then the other side should connect to Vcc (pin 35 on the register). If those are both true (one side is !LE and the other Vcc) then that's the pull up resistor. If you can remove that, then recheck the resistance from !LE to Vcc and it should read much higher than before.
If it's not that resistor, check the ones nearby.
Without that pull up then it might (and this is very might) be possible to add a pull down by using a pencil to draw between the Y and GND pins in the previous photo. Use a soft pencil and make a wide trace, then measure the resistance between them. But it'd be better to try and fit the 10k resistor that you will have just removed. It's really not too hard to solder things this size, just give yourself time and patience, and have a pair of small tweezers and a magnifying glass to hand.
[edit: Just realised I'm being dense. The pull up has to be connected to the input of where the inverter would be, so it's only connected to !LE through that 0 ohm link next to the inverter pads. So removing that 0 ohm link will disconnect the pull up from !LE. At which point a weak pull down (like a pencil link) on !LE should work. So:
1) Remove the 0 ohm link. This should disconnect output Y (which goes to !LE) from both pin 147 REGE and from the 10k pull up.
2) measure the resistance from output Y to Gnd and to Vcc. Y to Vcc was about 10k, should now be much higher.
3) draw a nice heavy, wide pencil link from Y to Gnd and recheck the resistance. Make sure the line doesn't touch input A.
If this works, can worry about making a more reliable mod later]
[edit2: scratch the pencil idea. I just gave it a go and I can't get the resistance low enough when drawing on the smooth surface of the PCB (ends up around 200k, think it would want to be <50k). So it probably won't reliably pull the !LE low. So you'll need to either solder a wire or draw a line. I've never used a conductive pen so don't know what to recommend. I suspect that for this purpose any will do. But soldering a wire really wouldn't be that hard. Use a single strand of some multistrand cable, slightly over length, hold one end with tweezers and solder the other end to the furthest pad, then solder the nearest pad, then use a sharp knife to trim the wire to length. Or just use that 0 ohm link.]