Sega Genesis2 / MD2 clone

Recently, I acquired an old Sega Genesis 2 (Mega Drive 2) clone.

Top view:

Bottom view:

This particular unit has a few issues: 

- The power indicator doesn’t light up, even though the console powers on. 

- The Start button on the main gamepad doesn’t work. Moreover, the problem is definitely not with the gamepad itself – I’ve connected as many as four different ones, and none of them worked properly. It’s something with the ports or the electronics.

Time to disassemble the console – let’s see what’s inside and try to fix it. First, I’m removing the top cover:

The original Sega console had a single board with a large number of microchips, but this clone is significantly simpler in design: two boards with external interfaces and one with the processor and memory.

Interfaces Board

Equipped with a DC power connector, a 9-pin mini-DIN connector with audio-video outputs, and two switches. These switches allow changing the region (Japan/Other) and the video output type (PAL/NTSC).

Processor Board

7805 - linear regulator that provides 5V for powering the logic components.

LM324 - used as an audio amplifier.

M5M412128 - 1 Mbit FPM memory chip, Dual-Port DRAM.

CY7C199 - two 32 Kbit SRAM chips each.

The TCT6035 is located under the sticker.

Gamepad Port Board

Here we have the power switcher, reset button, connector for the power LED indicator, and two gamepad ports.

I immediately checked for voltage on the LED indicator contacts — a complete zero. Alright, then I’ll continue disassembling. I’m removing all the boards and examining their reverse side.

 

On the gamepad port board, I see: 

- The first gamepad port is covered in some kind of flux. Could this be the problem? I’ll try to clean it with isopropyl alcohol. 

- The LED pin has detached from the trace on the other side.

I re-soldered the pin, and that helped – the indicator now lights up. But the “Start” button still doesn’t work, so I’m looking further. I tested the continuity of the cable to the processor board – one of the contacts is not connected. And if you look closely, it’s noticeable:

Re-soldered. Checking – yes, the start button works. And finally, I can run something, because without the “Start” button, I only saw game title screens.

The next thing I didn’t like was how hot the 7805 linear regulator gets. It’s impossible to keep a finger on it:

More than 140°F (61°C). I’ll try replacing this regulator with a more modern switching one. First, I’ll check how much current the console consumes – measurements showed 180-190 mA. That’s not much at all; it could even be powered from a USB power bank.

I will use a DC-DC converter based on the MP2307. I’m removing the variable potentiometer from it; in my opinion, it’s an unreliable component. I’ve encountered a situation where such a converter powered a 3.3V microcontroller, and over time, whether due to vibration or some other reason, the potentiometer slightly changed its resistance. As a result, the microcontroller received an increased voltage of 3.6-3.8V and constantly rebooted and worked unreliably.

By the way, this board has traces for a 34063 DC-DC converter (U1), but many forums mention that it leads to a degradation of the picture on the screen. I hope my more modern converter won’t cause any issues.

I’m installing the new module in the same holes that were for the 7805:

And I’m checking what the console’s temperature will be now:

The hottest component now is the processor, with a temperature of 105°F (40.9°C).

And the new DC-DC converter only heated up to 100°F (38°C).

The replacement of the 7805 linear regulator with a modern MP2307-based switching DC-DC converter proved successful. This not only solved the problem of excessive overheating, significantly reducing the temperature of the entire device, but also potentially increased the overall reliability of the system due to a more stable power supply. Concerns about possible degradation of image quality associated with the use of DC-DC converters were not confirmed in this case. The console now runs more stably and with much less heating.