The problem was as you can't TSOP flash a 1.6b Xbox, and you want to make a Slimbox (without DVD Drive) thats softmodded, you have to use the PCB of your DVD Drive in the case as the xbox checks for the presence of a DVD Drive on bootup.
Just using the PCB of the DVD Drive makes the xbox think that the DVD Drive is always open, and as the softmod (well the one I used anyhow - nDure) is activated by turning the console on via the eject button, you have to press the eject button several times to get the softmod to run. In order for you not having to do this, and start the softmod up with a single eject button press, you have to kid the Xbox into thinking the DVD tray is closed with no disc present. This involves a little bit of soldering, but not too much.
First off this is for the 1.6 / 1.6b versions
of the Xbox - you can use this on earlier versions, but you might as well flash the TSOP (see the tutorial sections on X-S homepage) with a bios that doesn't need a DVD Drive present - if you do want to do this to an earlier one the 3.3v point on the LPC is in a different location to the 1.6's - again have a look at X-S's homepage under tutorials - original xbox. This is all taken from XBOXCUSTOMS69 post HERE
who explains the lot really.
1. Take the yellow DVD power lead from the xbox, and with the 12 pin end (the end that plugs into the DVD Drive - not the Xbox end) facing you (have a look at XBOXCUSTOMS69 post above - the diagram on the left under DVD Power end of cable is the one you want) clip about halfway down on the yellow wires going to pins 5,6 and 7. Make sure you havn't got the cable the wrong way: pins 1,3,5,7,9, and 11 are on the top if the two guide rails for the plug are at the top.
2. You will be working on the wire coming from the xbox plug side of the cable - not the DVD side (as you're kidding the Xbox not the DVD Drive!). Expose the interior wire on the end of the clipped cables (about 5mm should be good), and on cable 11 or 12 (Ground/GND) scrape away about 5mm of yellow shielding carefully (don't sever the cable!). Twist the wire from cables 5 & 6 together.
3. Grab a length of spare thin wire (one that will fit the LPC holes on the Xbox motherboard - LPC holes being where a modchip would normally go) of a decent length to reach from the LPC area of the Xbox to the DVD power lead I used about 15cm, just incase I need to reposition the DVD PCB at any point.
3. Flux and tin (coat with a little solder) all exposed wire, this makes it easier for the solder to adhere to the soldee
4. Grab your Xbox motherboard, and looking at the top side of it, solder one end of the spare thin wire to the 3.3v hole on the LPC: see here
(page 3 at the bottom, the green (vcc 3.3v) dot on the left not the one on the right, it's not connected).
5. Now take your prepped DVD power cable (and again you're soldering to the Xbox side of the wires, not the DVD Drive side) and solder the twisted together cables 5 & 6 to the exposed wire on cable 11 or 12 (depending on whichever you chose). This grounds 5 & 6.
6. Then solder the spare thin wire you attached to the LPC 3.3v hole to cable 7 on the Xbox side of the DVD power lead.
7. Use electric tape/shrink tubing to cover all exposed wires where you've just soldered them, as you don't want to short anything!
8. Plug in the DVD PCB to the DVD power cable and IDE cable, re-assemble your Xbox and boot by simply pressing the eject button once - you're done!