Friday, 26 July 2013

Double Dragon - Repair Log - Day 3

Double Dragon - Repair Log - Day 3

Fixed the 1 & 2 player buttons I/O.. and all looks good for this one!

Though on my bartop i do get the occasional sync roll!?! :( .. I found the schematic to see where the sync pin leads to, but if goes off one page & must become Japanese on another. :/

I scoped the signals around the video connector and supply, and I get a god solid 5v power rail, RGB going from 0-1v and the sync line going from 0-2v .. Large 0 pulse (v blank) with finer 0-2v pulses in between (h blank).

I compared the signal with some other boards and it looks legit :D which suggests another theory..

Are the sync issues due to the CGA-VGA converters I'm using on my flat-panel?

Short answer.. Yes. The pcb was verified working by the owner on his CRT.

WARNING! (To anyone working on one of these boards!)

I had to re-fit the four board spacers back between the two boards before it was taken away..

Oh boy!!! :S

On double dragon there are two plastic spacers ... and two metal ones ...  

I placed them in a rather arbitrary arrangement, tightened the bolts & powered up.. 
Wait for it... F***in shite loads of smoke poured out of my Jamma loom!!!

Turns out that.. Well you know the big fat traces that run around the outside of the PCB'S? They're usually earth / ground / 0 volts, right?

Not this time! One surface of each board is 0v and the other is 5v. Two of the corner bolt holes are seperated buy a split in the PCB track (running round the edge) - two are not.

If you get the metal corners wrong then it's smoky time - so please be careful and make a note of where they came from when you take the boards apart!

I assume the metal rods actually carry the power and ground from the top to the bottom board (when in the right corners) & the 0 & 5v on each side of the board is acting as RFI suppression.

Luckily there was no real damage done.. The direct short through the metal board spacer rods protected the board.. I'm just gunna need some heavier cable for my 5v line. ;)

"A dragon with two metal teeth!"