I put in a backlight to my MGB and initially it was working fine (start up sound came on, LED lit, backlight lit, nintendo logo appeared, game started) but it had a single vertical line out. I taped down where the two ribbon cables meet in an attempt to fix it but straight after that it wouldn't turn on at all - only the backlight came on (and dimly). I removed the new tape but no change.

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I've since removed the two new connections but still it won't turn on at all - (no start up sound, LED not lit, nothing on the screen). I thought I'd possibly bridged the VCC (regulator 1 pin) and ground when attaching my backlight cable so I carefully desoldered that entire area and no change. I've tried removing the regulator 1 and 2 connections (carefully desoldering and lifting that side of the regulator up) and noted that the voltage being applied to VCC is around 1.2v. The batteries are rechargeables but the B connector registered 2.4v. Pin 5 and 6 on the regulator reported 0v.

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I used a fly wire to connect B directly to pin 1 on the regulator whilst it was still off the board and then pin 5 registered -15v and pin 6 registered 5v (which is what I'd expect) - but the VCC on the board, with no regulator attached, still registered 1.2v.

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Does anyone have any idea why the voltage getting to VCC is around half what I assume it should be? I don't have another MGB to check whether the voltages are normal, or to compare other test points, but it feels wrong - and obviously it isn't working!

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Edit: All of my testing has been on the main board only, the ribbon cable to the screen is disconnected. I'm pretty sure the mainboard at least lights the LED and makes the startup sound even if the screen is disconnected but if anyone can confirm that would be useful - I'd at least like to know which bit I broke!