What's this Mega Drive mod do?

Stop this seriously, constructive comments from now on. Deal?

 

no one gives a shit

 

and yet two of you can't stop giving lots of excrements.
i made it a point, that it was a guess, inb4 wellspoken and wellmannered gentlemen such as yourself would start tossing excrements. Still, it somehow went right above your enlightened minds.

 

Ok guys. Back on track.

Whatever you do. DO NOT REMOVE THOSE CABLES THEN POWER ON THE BOARD. I did so, and as soon as I plugged it in, I heard plastic burning, a whine, and started to smell a horrible smoke.

I tested this on the VA1.8, and those wires actually connect to two pads under the solder, like they were designed to be there. I'm just glad nothing bad happened and such. Sure worried me though. @americandad @Bad_Ad84

 

Excellent point. Sigged.

EDIT: Welp... nvm. The post is too long. Disappointing actually...

 

@SwampFox56 Hey, at least now I know what sigged means (thanks, google)

Lol at "nothing bad and such" . That sounds pretty bad imo.
It would be nice to see som photos of these "pads".

 

For all those wondering. This is the same VA1.8 board with the wires gone that starting frying itself with them gone. Those are indeed dedicated pads for that work. This had to be engineered for them. @americandad

 

What I asked earlier in the thread was if there were any vias under the solder (you will need to use braid to remove the solder). Already said that it looks like a pad that was designed to be there.

This was all to see if there was a manufacturing defect (like had been suggested earlier) and the vias didnt actually connect to the trace. So soldering to the top of the vias would fix that.

But so far, this seems like it was designed to be there - which was never disputed. Always said it seems sega must have had a reason for doing it, rather than it being a defect that was fixed after the fact. Just trying to figure out why its needed.

 

Same

 

The trace has higher resistance, which equals higher heat, which is above the tolerance of whatever the connector is built out of, hence it starts frying? Not that I've seen anything like that ever happening but it's possible isn't it? The soldered cables would then bypass this, since electricity always flows along the path of least resistance. Anyone tried measuring the resistance on that trace with and without the two cables?

Also note that some board types have a CM04RC04 filter on the other side of the board, connecting to the power supply plug, while some others use two bead inductors instead. And, the area that the cables trace over also have a lot of small pcb holes in them - perhaps those are in some way responsible for what is happening (their high concentration on a small size, that is).

I don't have enough samples to be conclusive but it looks like VA0-1 uses the beads, VA1.8, 2, 2.3 uses the CM04RC04 (and the two wires on the bottom), and VA3-4 uses the CM04RC04 and no wires.

Looks to me that it is a typical Sega board snafu, they made a new revision but found a last minute bug and it was faster to add the cables instead of creating a new board type. They do crap like that all the time.

 

I am planning to measure the resistances and voltages when my console arrives.

Will also be running it without the wires to test.

However, I have also been told that some boards of the same revision DONT have these wires and work fine. Maybe they subbed out where they were made and its limited to one factory's boards vs anothers?

Also, you arent bypassing that trace (on ops board anyway, not the one with wires to the folter) - its a wire to the same trace, the current still needs to go through the vias. Then you have the same problem on the other side of the board, but that seems fine...

Edit because of your edit:
Can you share the pics?

 

(had to edit my previous post multiple times, so instead moved the info here to a new post)

searched through my archives and I see two VA1.8 PAL boards, where one has the cables, one does not. The one without cables has less small holes in the area. So maybe that's what is causing the issue.

For reference:
171-6534A-21 PC BD MD2 VA1 PAL - much less holes on that specific trace, has no cables going around them.
171-6534B-20 PC BD MD2 VA1.8 PAL - lots of holes, has the two cables to go around the trace
171-6534B-21 PC BD MD2 VA1.8 PAL - much less holes on that specific trace, has no cables going around them.
171-6535F-10 PC BD MD2 VA2 USA - lots of holes, has the two cables to go around the trace
171-6615F-11 PC BD MD2 VA3 USA - lots of holes, but does not have extra cables...
171-7229B-11 PC BD MD2 VA4 USA - lots of holes, has the two cables to go around.

I'll check my own consoles.

 

The holes would make the trace effectively narrower and thus increase it's linear resistivity along with the heating. This is a very reassonable hypothesis, and what I'm saying since the beginning...

Hopefully Bad_Ad84 can verify for sure, it's a very interesting situation!

 

Maybe its what trimesh said - weight of the copper. But maybe it was limited to one factory and not another?

As it seems you have a VA1.8 with the issue but also ones without. Then you have VA2 with and ones without.

So there is an issue with some and not with others - seems like maybe an issue at one factory?

@Druid II - Do you have info based on serial/board revision like with the saturns on where they were made?

 

The linear reisitivity is basically the area of copper in a section cut perpendicular to the trace (for DC anyways), so it's completely logical a thicker copper clad would fix the issue.

 

Note that the boards are also different, like 171-6534B-20 vs 171-6534B-21, one with holes, the other without.

Unfortunately I don't have many Megadrives to compare, but the MD2 VA4 I opened up on the first try has the cables there. So I'll measure it now.

 

Your meter may not be able to measure it very accurately. I have an LCR meter with much finer resolution and accuracy.

However, there is no guarantee the MD2 ive ordered even has the wires! =/

So we are all on same page, the "holes" are vias - which are plated holes that link different layers of the circuit board together.

Regarding the board revision numbers - they are the same, except for the last part. Maybe thats the factory code that made them? rather than minor revisions?

 

Well, I could not measure any difference with and without the wires. They had a low amount around ~3 ohm either way.

However this unit worked fine with the wires removed, so it may not even be affected by the problem in the first place.

What versions are the boards that act up without the wires?

I've checked through McRetro's gallery, and all his PAL units are VA1 or VA1.8, have a -21 suffix, few vias, and have no wires.
I don't know exactly what the -20 and -21 is meant to be in this case. I don't have enough samples of Megadrive teardowns to get a conclusive answer. However I've seen -20, -21 and -30 suffixes used for PAL boards (as well as -10 and -11 for USA) on Megadrive 1s.

In fact I've only seen those board serial suffixes for Megadrives. Nothing else seems to use -10, -11, -20, -21 or -30.