2nd Adapter made up however, there was a problem. After drawing up a diagram of how the orientation of the connectors should be in order to reproduce a 1 to 1 cable, I seem to have taken my eye off the ball and wired the connector back to front - You can only imagine the level of cursing that I created upon dicovering this. This was especially frustrating as I made exactly the same mistake when I made the cable last year, which is why I was trying to be careful that I didn't do it again, ah well the best laid plans and all that.
1.) The mistake. Both connectors should be the same way up; with the connectors in this orientation pin 1 = pin 30, and pin 30 = pin 1, doh!
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2.) I decided the easiest way to rectify the problem was to pull all the pins out of the IDC connector, flip them 180deg, and reinsert them. The pins pulled:
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3.) Turned out pulling the pins and reinserting them was super easy. Here's the correctly oriented pair of adapters:
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4.) Continuity testing of the adapters attached by the IDE cable thew up an issue on one of the pins, pin 28 was not showing any continuity. I forgot about this. Pin 28 is the cable select 'Slave' pin on the grey IDC connector of the IDE cable, and as a result is not present. The image below shows the IDE cable with the pins of the grey connector exposed. Pin 28 is seen to be missing:
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I switched the grey connector for the black one (which has all pins present) and thought that was the end of it. It turns out that pin 34 of the blue connector is used by the cable select (CS) too and is absent from this connector. Since pin 34 was not used for the TFT control signals I went ahead and tested the newly made wire.
Test failed. There was apparently a short in the wire somewhere causing the controller board to go into hybernation to protect itself. This left me somewhat confused until I remembered that the IDE80 cable I was using is setup to have every other wire (of the 80 available wires) pulled to ground. It occured to me that those wires must be attached to one of the pins of the IDC connectors and this must be causing a short circuit.
It turns out that the above is true, however it's not just one pin; the IDC connector has the ground wires attached to pins 1, 19, 22, 24, 26, 30, and 40 - no wonder something was shorting in the DP2MBPR controller. See all of the above IDC issues in the below image (taken from http://www.allpinouts.org/index.php/Ultra_ATA_66/100_IDE
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I have now abandoned using an IDE cable and have instead purchased a 15cm IDC to IDC 40 wire ribbon, this should iron out all of the above issues. As always I'll update when I've tested the new wire.