Fixing the internal fuse of a Sega SMS 2, MD 2, Mega CD 2 and others
This Requires Soldering skills and a basic knowledge of electronic components.
This is a more "unique" fix, I have not seen this anywhere on net before. It took a few hours to find this on my Mega CD 2... But should relate to all "newer" Sega hardware. They are not in the MD 1 or SMS 1 as far as I have seen.
This info applies to the PAL (AU - EUROPE) and NTSC (USA). (And possibly most other versions as well)
The internal fuse is a resistor like component that sits at the back of the Mega CD 2 near were the switch is to sense if the CD lid is open.
On this board the fuse is located on the soldering side, labelled "F301", and is rated at 2.5A. It is beige in colour( US Mega CD 2) OR Bright Green (My PAL Mega CD 2).
All you have to do is use a fuse holder with wire fly leads. Solder one of the leads to either end of the PCB were the legs of the internal fuse are.
Pop in a 850mA fuse (AU PAL Mega CD 2) Will be higher around 1-1.5 A for the MD 2 or SMS 2. (don't exceed 2A).
1. Open Mega CD II, Remove the screws (5) that hold down the metal shield (Red Arrows). Also there are 2 metal "tags" that hook under the slot were the MD connects to the Mega CD (Blue Arrows). These need to be bent back so the shield can be lifted up.
2. The shield has been removed. The fuse is located in the red circle area.
3. View from the left hand side.
4. Close up of the fuse marked "F301"
There are a few versions of Mega CDs and Megadrives that don't use the fusible resistor like the one in the picture above. Instead underneath the PCB in about the same location is a white rectangle surface mounted fuse. Should have like X.X A on it. To fix this... you do the same thing.. But solder each end of the fuse holder to each side of the surface mount fuse. I think it is still labelled "F301" though. Below is a picture of it...
Extra info for the Sega Master System 2 PAL "IC BD M4Jr. PAL" AU SMS 2
The unit I have here does have the 7805 Reg, but no resistor like fuse. There for the power goes through a different route. All these parts need to be checked. The power comes through from the power connector to an inductor marked "JV" , ( there should be connection through this with a little bit of resistance ) Then through the switch (again when on the "ON" position there should be a connection through this) up to a diode marked "D2" (use diode checker on multimeter) Current flows through it in the direction of the arrow marked on the PCB. If the controller jacks are at the bottom of the board (closest to you). The current through the diode will be right leg to left leg. Then the power goes to the 7805 "I" Input leg.
If any of these parts do not show a connection from leg to leg, then the part is most likely faulty (Open Circuit) and will not allow the power to get to the regulator.
You could also use the volt meter on the multi meter to check for the AC power pack voltage along the path of the power from the connector to the 7805. This will also show which component is not working.
If anyone wants to know what values of components to replace... I can find then out in time.
