Jumping power from J4 on IO to Mainboard issue

[biggiesmalls23]

This is my second x0x build, first went down really well, ran it to some issues here and there but got through them.

Having the strangest issue atm with bulding the VCO, my problem is jumping the 5.33v and 12v onto the mainboard from the IO board, it just wont give me any reading at the D31and IC9 as show in the picture, im getting 0.3v not the 11.84 im sending from J4 on the IO. I thought it was the ribbon cable i used first, desoldered that and put on 3 sepearate cables, that didnt work either, getting nothing at all!! I should be getting 5.33v from what looks to be pin one from IC9 (shown in the picture) but i get 0.0v.. Im starting to think that my mainboard is defective, its from the same batch of TT and my previous one worked without a hitch at this point, really frustrating me as i wanna build the VCO but if i cant even get the 5.33v and 12v onto the mainboard then the testing of the VCO isnt gonna work.

I tested the 5.33v and 12v from IO cables directly with the multimeter and they show me my correct outputs. Where could this be going bad? It simply isnt giving power to the mainboard..?

[biggiesmalls23]

looking at this thread, feels like a similar issue ? : viewtopic.php?f=12&t=24810

I tried taking ground from the metal hole on IC20 but didnt get any result.. ?

[decoder23]

maybe this topic might help you a bit. i had troubles with one of my x0xb0xes too some time ago.

viewtopic.php?f=12&t=22281&hilit=weird+voltages

[MMM]

Let's do this step by step.

You say that you get the correct readings directly on the IOboard cable. The middle cable is ground.

So connect this cable to J4 and measure on the J4 solder pads of the mainboard. Again, the middle solder pad is ground.

Then measure pin 1 of IC9 against that middle pad.

Alternatively you could also measure IC11; pin 4 should be ground, pin 3 should be 5.33v and pin 8 should be 12v.

[biggiesmalls23]

So this is where i am, i have nothing soldered onto the mainboard except the socket for J4 ribbon cable. Ive tested again this morning, on the J4 on IO board (socket as well) i get : left pin 11.84V/Ground/5.33V as it should be.. i connect the ribbon cable to J4 on the mainboard, test the solder pads on the back and i get 0/0/3mvDC.. i test IC11 pin 3 i get 3mvDC, i test IC9 pin 1 i get 3mvDC. This is testing from ground on J4, ground on IC9, ground on IC20...

what the?!? Like i said in the previous post, ive tried 2 different ribbon cables now, wires that i made and tested were working, it still wont give me the voltages im sending from J4 on the IO?

[MMM]

Without the power cable connected to the mainboard, measure the resistance between the ground pad and the two other pads.

[biggiesmalls23]

Hey MMM,

Thanks for the reply, it was a short between ground and the 5.33v rail where the socket of J4 goes, it was so tiny i couldnt see it but under the magnify i could, fixed and all is well. Now facing another issue, im gonna start a new thread for it tho, VCO is built but only getting half the voltages required for the square wave.