Sega Mega CD 2 - repaired it, then broke it again

I had a broken Sega Mega CD 2. It wouldn't turn on.

I put in a new fuse, got it working but it kept saying "please close cd door". I figured out it would work with the door slightly open. A little piece of metal inside was loose. It clipped into 2 holes in the circuit board but wasn't soldered in. I scraped away to expose some of the ground and soldered it in.

Turn it on - NOTHING WORKS, won't turn on. I check the fuse, it's fine but still won't turn on.

I undid the metal thing to ground soldering, STILL not turning on.
I think I know how I broke it. The original fuse was 2.5A.
I had a 2 and a 3. I figured 2 was safer so I tried it out and that didn't work - so then I tried 3 (which I am now regretting).

I think that it could be that I've just blown something else by having it on and it just happened to occur while playing with some other thing. Does anyone know what blows on a Sega Mega CD 2 if you don't have a fuse in place?

Any other ideas as to what it might be?

 

I believe there is more than 1 fuse, best to check them all.

 

There's a voltage reg there on mcd2 boards.

 

Thanks for the responses. Does it seem like the soldering in of the door-close metal shell to ground could be a bad idea? Should I remove it?

The fuse I repaced was labeled FL301, I've had a look around and it seems to be the only component marked as FL###. edit: removed false information

There's also some unknown blank rectangle next to the FL301, it doesn't seem to be marked and also lacks continuity.

I have no idea about this or what a voltage regulator looks like. Is it the little black box on the other side of the board behind the FL301? How would I test it?

 

Hmm I am sure I remember seeing more than one fuse on my sega cd2. I will have a look tonight, it has the samsung drive.

 

I'm going to go out on a limb and guess it was a stupid move to scrape away at the PCB and solder something in that wasn't soldered at the factory.

That said, can we get a picture of this part and where it is? You probably blew a nearby component.

 

I'm still not convinced that was the problem, but I'm still regretting it - if only for the fact that I could eliminate that as a potential reason for the break. I thought it couldn't do any harm because I was just connecting it to ground and EVERYTHING seems to be connected to ground anyway.
EDIT: I was stupid, only one of the legs was in ground, not both like I thought! I short-circuited my board!

Here's a photo, it's the little part that gets pushed into the clear plastic part when the door is on the closed position. It has two metal lips that poked through holes in the PCB and were bent over. My unit kept saying "please close door" so I tried re-bending it and it worked. Then after a while it became loose again so I soldered it in place on the other side of the board (not shown).

This is the top-right corner of the board, near some big big capacitors and (i think) the power regulator which is attached to the heat sink? You can see the CD connection cable plugged in just behind the heat sink.

 

If you are using an original AC adapter, you should be safe even if you change the fuse for a piece of wire. I don't think that's the problem. But in case you want to know, the next thing can really be the voltage regulator, it will burn in case you (for example) put the wrong polarity (plus/minus on adapter) on it:


Also soldering the metal "switch" is a good idea when it got loose. Maybe you broke something else when you had it opened (I just hope you didn't forgot to plug back those three connectors connecting the CD drive and the main board, in case you had them disconnected during the process ).
Close examine the whole board for scratches and also clean the connector between Genesis and SegaCD.

 

The pictured part is the lid detection sensor.

If you damage it, the console will be unable to detect that the lid is closed. :shrug:

 

Thanks for the helpful response. I used a power supply from a Megadrive 1 (same voltage, same current) so hopefully you're right. The fuse definitely didn't blow (so at least there wasn't more than 3A), but I just thought something in the 2.5 - 3.0 range may've blown something else. The voltage regulator looks fine, and isn't burnt or anything, could it be broken without looking burnt? How would I check it?

It definitely worked to hold it in place. I checked it for continuity with anything else and it did seem to be just a mechanical component and not something that had anything to do with the circuitry.

I checked the ribbon cable just then and it's fine. There were some fine scratches across some paths but I just checked them all (took a while) for continuity and it all seems okay. I resoldered all the surrounding connections near the metal clip to ensure that I didn't produce any dry joins when heating up that part of the board.

Also, I just updated my earlier posts about L402 and L403 not having connectivity - they do (though I still have no idea what they are, they kind of look like fuses). Turns out that my multimeter's terminals are just barely too fat to quite touch down that far. I wrapped some solder around the tips and used those to re-test it.

 

I just tested my SEGA power adapters with a Voltmeter.

On the Sega Mega CD's power adapter itself is written "10V 1.2A", but when I tested it - it shows 14.00 Volts.

I also tested the power adapter for my Megadrive 2; on that is written "10V 850mA", but when I tested it - it shows 13.77 Volts.

Is this normal?

 

Hypothetically the voltage regulator should bring that down properly, if it is fully functional.

That switch is mechanical but it completes an electrical circuit. I'm guessing it shorted something and killed it but not by drawing too much power which would cause the fuse to blow. It could also be a nearby transistor which feeds power to the whole board when the Genesis powers on. If it is damaged then it won't turn on. Thing is I'm not sure how to test it and I don't know of an equivalent part either.

 

I'll etch away around the solder of the metal so that I get the benefit of it being connected firmly without it being connected to ground. (Damn I wish I thought of that earlier!)

edit : I just realised what I did was actually far more stupid:
Only ONE of the connectors that I fixed the metal to was ground, the other is another, separate track. So I definitely shorted it out, now to find out what damage that caused.

Will look into the transistors as soon as I figure out how to.
Thanks!

 

Tough brake man , but this might be one of those situation were you repair one thing and another problem appears multiple times.

 

There are 4 transistors, Q201, Q202, Q302, and Q101. Q302 is the closest one to the site of my short circuit.

I know very little about this (NPN, PNP etc.) so.. I'm going to spit results out and hope someone more knowledgeable can interpret. I'm using the C,B,E markings on the board. I ran a diode test (using multimeter function that had the diode symbol and '2K' written on it). I tested these on-board without isolating them so I think some of these readings may be wrong but I don't want to start removing components if I don't have to.

Here are my results:

*no change
My multimeter reads "1." when not connected to anything. When I write "no change" this is exactly what I mean.

*grows
For a few tests, I found that the value grows rapidly then plateaus to just before 2.0. For example, I would see 0.8, 1.3, 1.7, 1.90, 1.91, 1.98.. then it stops progressing and sits on "1." <- the no-connection value. I think this is due to other parts of the circuit interfering with my reading.

Q201:
+ -
c b : grows
c e : 0.844
b c : 0.873
b e : 0.881
e c : no change
e b : no change

Q202:
+ -
c b : grows
c e : 0.843
b c : 0.876
b e : 0.882
e c : no change
e b : no change

Q302:
+ -
c b : no change
c e : no change
b c : 0.846
b e : 0.851
e c : 1.062
e b : 1.612

Q101:
+ -
c b : no change
c e : flashes a value very briefly, then no change. I think this is growing, but very quickly.
b c : 0.885
b e : 0.891
e c : no change
e b : no change

Thank you so much in advance for any help on this. Q302 seems like it may be broken, (b-to-e and e-to-b both give a reading), could I get a confirmation on this?

 

Just to be clear here, this thing consists of two separated metal plates that touch each other when the CD doors are closed (or - they are touched when the doors are open and then disconnect when you close the doors, I'm not sure now). So it's just a switch, nothing fancy. Can you do a photo of the PCB's bottom of the place where the switch is located?

To your transistor question - transistors can't be measured by a digital meter, you need an analogue one running on batteries, otherwise the transistor won't "open". Measure Ohmage (conductivity):
1. put positive on B(base). Negative on E(emitor) then on C(collector)
2. put negative on B(base). Positive on E(emitor) then on C(collector)
In one of these cases you must measure something, in the other NOTHING.

Next you need to measure between E and C. There should be NOTHING in both ways.

 

One side was ground, and the other section is a very thick section but it's not ground. Next time I open it up I'll post the underside. Thanks.

Thanks for this. I have a powered multimeter (but digital not analog), I've seen a lot of videos on youtube that use a similar multimeter but I'll read up a bit later to get a better understanding.

 

The top solder point is ground, the bottom is NOT a ground (I feel really stupid for not checking now). I just assumed they both were and, well, now here I am. I have since isolated the solder points by scratching the tracks away and checking for continuity to ensure isolation - unfortunately too late.

I suspect that the closest transistor (Q302, just to the right and below C304) is the problem. Assuming it is, how much variation is there between transistors (assuming both are NPN)?

 

If both sides of the switch were ground, it wouldn't be a switch as they would already be connected.

 

Neither were ground. This is a metal piece that isn't normally touching anything on the board. I soldered it for stability but in absent thought didn't thoroughly confirm that i was connecting to was actually ground. The piece itself isn't the switch. The switch is a flexible feather sort of switch and this piece of metal simply gets pushed into it by the door closing.