Sega CD Model 1 burnout

[jokker]

Just bought one of these and it didn't work upon receiving it so I opened it up to have a look and what do I see?

http://reasonablyinteresting.com/~jokker/burntside.jpg
http://reasonablyinteresting.com/~jokker/unburntside.jpg

It appears to be one of the capacitors across the poles of the murata inductor that just exploded or shorted. Does anyone happen to know the rating for those capacitors? I have no issue grabbing a new one and soldering that on since it just appears to be some surface damage but I'll bet the capacitors should be replaced.

Also it has one of those fusable links on the top and I figure it should have prevented this however it appears to be shorted as well so would this be a case of the fuse didn't quite go in time?

Thanks
_Troy

[hellfire]

try cleaning it off

[jokker]

yeah I did that just after I took the pictures as well as removing what was left of the very dead capacitor. There are no values on any of the surface mount capacitors so I have no way that I know of to determine it.

[TriState]

Apologies for my first post here being a "bump" but I've got a Sega CD Model 1 apart on the floor with this same problem. If I just knew the values of these caps...I could probably get this thing working.

Anyone brave enough to open one of these up and check?

[raylydiard]

ok that board is not as bad as the one i had the other week to repair as it was rust on the metel sheliding and as i had a spare pcb just replaced it.
it look like a sort or a shurge charge whent to the board.
hope you fix it i do have other spare one at home.
most of the vales on the board are 10uf 16v and 100uf 16v lots of them.
and prob a fuse as well.

[Topy44]

Hi,

I'm new here. :)

Sorry for bringing up this ancient thread, but i have the exact same problem.

I replaced the fuse, replaced the burned cap and bridged TR4. But still no reaction from the Sega CD... :(

Did anyone _successfully_ repair a device with this problem?

It was caused by connecting an NES power supply (don't ask...), which as you probably know delivers 9V AC instead of DC. It was only connected for a few seconds.

Pic of what my power board looked like before repair:
http://www.t44.org/mcdpowerboard1.jpg

The Model 1 is ridiculously rare here (Germany), so i really, really want to fix this... And because its one of my favourite consoles. Even though its an US import model, the PAL ones are impossible to find. I use it with my MegaDrive 1 and the also silly rare Datel CDX Pro which i fortunately got with original Box when I bought the Sega CD. :)

[APE992]

I'd have to imagine that its a SMD resistor that has been completely toasted. Without a board in front of me it looks like the part above could have been fried as well, whatever it is. I can't make out the writing in OP's picture.

Since it is just the power board it should be easy to replace/rebuild.

[Topy44]

No, its a capacitor, notice the C marking on the board. As said above, I already replaced it. The one beside is also a capacitor, and is tested and ok. Also, as far as i understand the circuit those are just secondary filter caps, it should work fine even without those.

I can upload some closeups of both sides of the board if you want, maybe you can make out the PCB traces. I really hope that it didnt blow through and damage the mainboard...

[Squeept]

Damage that severe can actually blow the traces off the board. Make sure there is continuity from the component that you replaced to the next spot on the board where it should go. You may need to run some jumper wires.

[Topy44]

Nope, power arrives both at the component and further down the board.

[APE992]

No, its a capacitor, notice the C marking on the board. As said above, I already replaced it. The one beside is also a capacitor, and is tested and ok. Also, as far as i understand the circuit those are just secondary filter caps, it should work fine even without those.

I can upload some closeups of both sides of the board if you want, maybe you can make out the PCB traces. I really hope that it didnt blow through and damage the mainboard...

What I see is a big fat black spot on the board with an SMD device in the middle of it all. Now next to that black spot I can see C22 but two components have clearly been destroyed and probably more up top. Since you say it was destroyed by a NES power adapter (I've seen that happen as well) you probably toasted TR4. You CAN'T bridge TR4 and expect it to just *work*. It was there for a reason and without diving into details it has all to do with power distribution.

And you do know that testing a SMD capacitor for continuity isn't testing it for capacitance right? Its probably worthless now and needs to be replaced.

[Topy44]

Heh, sorry, i thought you had an intact board to compare. Here is a post-repair closeup:
http://www.t44.org/mcdpowerboard2.jpg

[Topy44]

As far as I understand the circuit, TR4 is simply there to turn on the Sega CD as soon as the Mega Drive tells it to, by switching the main power input dependant on a signal from the Mega Drive. Bridging it should therefore turn it permanently on. Besides, I tested TR4, it seems to be working, though one can never be sure with in circuit tests. I could try to desolder it to test it properly, but since its back is soldered to the board with a big blob of solder it might be hard to get it off without breaking it for good. Dont have any darlingtons around to replace it right now...

C22 and C23 seem to connect VCC to Ground across the pins of the suppressor coils (I hope thats the right English word, I only know the German word), simply acting simply as filtering/stabilizing caps. Removing them should not do anything except slightly decrease the devices tolerance to bad power supplies.

Please correct me if i am wrong on any of this.

And yes, I know how a cap works, thankyouverymuch. :) But just to be sure, I also replaced C23, doesnt make a difference.

Do you know the pinout of the flex cable that connects the power board to the main system board? I would like to check if power actually reaches it.

[EDIT]
I just realized there are two vias between C22 and C23, one of which had its connecting trace blown by the burning cap. Will reconnect it now and try again.

[Topy44]

WOAH!
That was it! Fixed the two blown traces connecting C23 to the vias between C22 and C23, and it works!

[EDIT]
Not pretty, but it works: :)
http://www.t44.org/mcdpowerboard3.jpg

Proof:
http://www.t44.org/mcd1.jpg

[Squeept]

I knew a trace was burned up somewhere, unfortunately I'm not intimate with that board, so I couldn't be more specific.

I apologize... I didn't realize I actually still had one of those boards in stock and could have taken pictures or checked things out for you. If anyone else blew their board up and can't fix it, let me know, and I'll stuff it on eBay for you.

[APE992]

Not sure I'm seeing any vias there that I'm familiar with. Then again I'm a bit sleep deprived.

[Topy44]

There are two vias there. See the two coper wires I soldered on? Yeah. :)
They are connected to the pins of C23 with traces that got burnt away.

[APE992]

There are two vias there. See the two coper wires I soldered on? Yeah. :)
They are connected to the pins of C23 with traces that got burnt away.

Now I see what you're talking about. Never would have noticed given all the charring.

[raylydiard]

can i ask what value caps you used as i have one board like that and never known it was the caps even there.
i know i have fixed a few of these.

[Topy44]

I used 100nF ceramic caps just because i had those handy. Those are just filtering caps, so the value is non ciritcal. 10nf or 22nf would have done just as well.

[raylydiard]

Nice one will help me if i ever need to do that with other future repairs.