What's this Mega Drive mod do?

I personally don't know the exact details behind this, but I've worked on several Genesis Model 2's before that've had this jazz installed by someone. They've always been wired exactly like this too, and all of them with a brand new AC Adapter plug.

Obviously there is a reason for bypassing the traces of the system. I imagine the answer is likely either corrosion, or incompatibility with the non-Sega replacement jacks.

I do know, however, that this system had it's AC Adapter plug replaced and that's why it's wired that way.

Except, without those wires, the system would get no power. So clearly they're doing something.

 

But the wire goes from one part of the same trace to another on the same trace. It's like having a wire connecting 2 points, then just putting another wire in doing the same.

Wish I had an md2 to open up, the 3 I have are all md1's.

Need to get the wires off and get a good up close picture or scan.

Edit:
Bought one off ebay

 

Sometimes, if the trace is too small or the copper clad too thin, the trace can become too resistive and make the voltage drop. The wire would fix that.

Seems unlikely, though, as this trace looks kinda big.

 

I've seen those 2 black wires before - even in some units that didn't appear to have ever been worked on. I suspect the purpose is to attempt to equalize the current flowing through those vias - without those links, the via closest to the jack would be carrying more current than the one furthest away, because it would be on the lowest resistance path.

 

people are saying it doesn't work without the wires in place though, which wouldn't be the case if it's just for current (surely it would just blow the vias one at a time until it stops working, adding wire back wouldn't help then as vias dead)

Also, other devices manage this just fine without wires? (and again, surely they would fix that in the next board revisions)

 

Jesus. Keyboard Error: Press F1 to Continue..
Let me quote that once more for the sake of it:

"as if" equals to "maybe". Ie = "it looks like maybe they misdesigned the pcb" and "maybe there is a design flaw" = same thing, different wording.
What a beautiful person you are. Amazing.

 

Already answered that post, could go on for a long time if you are just going to copy and paste your posts.

You are focusing on the tiny part of the post, when the rest of it explains what I'm saying and why.

 

No you didn't. You answered what you thought I said. Not what I actually said.

 

Which part of while someone has it open its worth checking are you not understanding?

I'm not saying I think it's that at all, but just to be sure he may as well check.

 

Neither did I, my kind sir.
What part of "as if" don't you understand?

 

Well, "as if" is the same as "as though" not maybe as you claim.

"it looks as though they misdesigned the pcb"

Maybe it's a lost in translation issue, but your statement as written comes across quite matter of fact. That's why there were post afterwards trying to explain why that seems unlikely.

You are completely over looking the fact this issue persisted across revisions, which if it's a design issue doesn't make any sense. They would have wanted to fix that and avoid the extra work adding a fix.

You went on a triraid about how I'm not giving any answers, when all I was doing was saying why the answers people suggest didn't seem to make sense of being the issue. By working out what is NOT the reason can help to figure out what WAS the reason.

Maybe it is a design issue and sega were just useless and couldn't fix something quite simple. But it seems highly unlikely to me, both because I don't think they were that useless and because the evidence of the fix and what people are saying happens when the wires are removed don't suggest that.

 

You are completely overlooking that I never claimed a design flaw as fact. Not once.

 

This is a waste of time.

Yes ok, you are correct.

 

I'm curious - have you ever done, any sort of extensive CAD designing? It's not for everyone, as it takes a lot of patients and time which many people can't or don't have the ability or time to do.

With that being said... Sometimes when you need a PCB to fit a certain size, not everything can get connected. Lot's of times, the ground layers get cut off by extant traces. Yeah - you could add another layer of highly expensive copper silkscreen to your PCB, or just fix the problem by using some external wires.

If the above was the cause for the wires on Genesis 2's, Sega would have, without a doubt, chosen to wire the AC Adapter input to the EM Filter (with a wire), because adding an extra layer of copper to a PCB (especially for something so trivial) would be stupid expensive.

 

Only as a hobby/side business. So yes, I have experience, but certainly wouldn't claim to be a professional. However, the copper layer isn't the silkscreen.

But its not a space/routing issue then using a jumper wire - the traces and vias are already there after all and those wires on the ops pictured quite clearly lead from one end of a trace to the other, there is nothing being connected that wasn't already connected before.

The current thing sounds plausible, until you realise it's multiple board revisions and that yourself and others have said you get no power without the wires, but when you put them back it works.

I repair stuff for a living (often to component level) , talking things through, thinking what it isn't and reasoning your way to the answer is how you figure things out. We have some great minds and experience here, I'm sure we can figure it out between us.

That particular board revision (which isn't the one the op has) , but the others don't do that. That's why we are having this discussion - no theory fits all the shown boards or reasoning yet.

I'm not here to argue, I'm just interested to find out the cause/reasoning, when it doesn't seem to make a lot of sense. But obviously sega thought there was good reason to do it.

 

For disjoint/distant ground planes that's typical, but for connecting a trace to itself it's uncommon. Although we often think of traces (metal in general) as an equipotential, it's not always true when the conductor has a very small section, as is the case with pcb traces. That'd go along TriMesh's explanation, as the trace could be somewhat resistive and more current flow through one via than the other causing issues; the wire would fix that as its section is big and thus its resistivity is small. Although what issue it's causing really is intriguing, as even if it heats, it should at least boot with or without the wire.

Any idea to explain why it wouldn't boot without the wire @TriMesh?

 

No, no idea at all, unless the voltage drop across the vias is really excessive and the input to the regulator ends up below it's dropout voltage. Having said that, I'm pretty sure that the board I was looking at *did* boot up with the wires removed - but it's voltage drop then it might be dependent on how much headroom the PSU has, the local line voltage, the current phase of the moon, etc., etc.

I think it's also pretty safe to assume that the wire has a much lower resistance than the trace does, especially since consumer stuff is normally manufactured with the lighest weight copper they think they can get away with. If you were in a low labor cost environment, it could easily be cheaper to add a couple of patch wires rather than bumping the whole board up to a heavier copper weight.

 

He's right!

It screamingly obvious what the issue is with that board. The wires a useless at best!

 

x

 

You mean the one where SEGA would just slap those wires on it and hope for the best? I did make it a point that I was simply guessing.