Embedded Files
Sega Genesis 2
August 15, 2023
I had a chance to pickup a well priced Sega Genesis 2 which was reported as not working / showing a black screen. I had recently worked on a first generation Genesis, but had never worked inside a Genesis 2 but I looked forward to seeing the differences.
I first wanted to confirm the black screen symptom console by plugging it in and using my Troy Aikman Football test cartridge. The system powered on and the screen was black just as reported by the seller. I performed the usual cartridge removal / reinsertion ritual to break through any light oxidation on the slot contacts, and then checked operation a few more times, throwing some resets and hard power offs in for good measure. What I noticed is that occasionally I would see the first licensing screen, but not every time and the power would also flicker off occasionally. So the good news was the system wasn't completely dead, there was just work to do.
It was time to get down to business and open the system to see what was inside.
Wow... bodge central. I believe that it's a factory job, but it may complicate the troubleshooting somewhat. I started to work from the power input to ensure that voltage was coming in cleanly. The first thing I noticed is that the barrel jack was a little loose. Looking at the solder points on the board I could see some cracks which explains the occasional power loss I was seeing. I reflowed the points, and confirmed that the port was solid.
Next, I confirmed that the voltage regulator was outputting the expected 5V, and I looked across all of the capacitors on the board but I didn't see any leakage or bulging.
The next usual suspect would be the cartridge port. If any pins were not making a good connection all sorts of weird things may start to happen. I used some IPA and a toothbrush to gently clean the pins inside the cartridge slot. I could see a lot of debris in the slot itself, but it wasn't going to be possible to extract it without risking bending some of the pins so it would remain for now.
After cleaning as well and I could I tested the system again but there was no change. Next I used a multimeter to run through all of the pins for the cartridge connector to ensure that they were all making contact with the PCB, and also that none of the pins were shorted together. Everything checked out, but it felt like it was worth the few minutes it would take to reflow all of the cartridge slot pins on the board just to make sure the connections were a in good shape.
Still no change so I began looking over the board for broken traces or other visual issues.
Bingo, found it! I created a jumper to rejoin the broken connection and powered up the console to play some football.
The same black screen greeted me, so this wasn't the issue, at least not entirely. Searching a little more around the board I found another spot where there was a broken trace, and I jumpered that one as well.
Still no change, and then it hit me. The broken traces that I found could be intentional, and may be tied to the bodge job that greeted me when I opened the console. I confirmed by tracing the break points back to some of the bodge work, so it seemed likely that these two breaks were in fact on purpose so I removed the jumper wires I had installed.
Moving on, since the right voltage was getting into the board, and the voltage regulator seemed to be doing it's job I needed to come up with another hypothesis to chase. I decided to check the resistors on the board to see if any were reading above their rated resistance but everything checked out. Next I decided to check the VCC pins on each of the ICs on the board and confirm that voltage was reaching all of them. Everything there looked good as well.
Time to try and clean things up a little better, maybe the debris in the cartridge port was interfering, even though I didn't think it was. Desoldering the port with the desoldering gun was pretty simple, but the port was also riveted in place. I drilled out the rivets, and then I was able to use to hot soldering tip to push them out of the connector to remove the port.
Oh look, a bodge wire on the port itself. Nice work Sega.
And another broken trace under the port too... again I believe all connected to the bodge work.
Without any other ideas coming to mind I decided to run the board through the ultrasonic cleaner. Sometimes just cleaning the board may sort out some issues, but I thought at the very least it would give me time to think of something else.
While most components should be fine to go into the cleaner some say that crystal oscillators may get damaged. Even though the frequency for the crystal on this board was nowhere near the frequency of the cleaner I didn't want to chance it. I confirmed that the crystal was outputting the proper frequency, and then removed the crystal from the board.
After six minutes of ultrasonic washing with some deionized water and a little Simple Green Crystal, the board was cleaned of flux residue and much of the debris was also removed from the cartridge port. I dried the board at 160F for about 45 minutes, and then used compressed air to push any remaining water off the board.
I inserted trusty Troy Aikman and powered on the console only to be greeted by the license screen and then the black abyss that had become all too familiar.
Without any other ideas I decided to return to the cartridge port. I had previously checked that the slot pins were well connected to the PCB and that there were no shorted pins so I decided to go a step further and trace each pin for the cartridge slot from the initial board connection, to the connections upstream to see if there was a problem I hadn't yet uncovered.
About 45 test points later I found something. A via for the A13 point on the cartridge wasn't connected between the top and bottom of the board. There was no obvious damage but the connection through the via was open. This meant the one of the SRAM lines was not connected to the cartridge port or the VDP. Time for my own bodge wire, take that Sega!
After putting the jumper wire in place I powered up the system. Victory!
What a journey! What did I learn? Don't give up on the cartridge port too soon. Check the normal power stuff which is quick to rule out, but then be diligent and check connections back a few steps if need be It's a tricky problem to catch because traces on the board were connected to the via just fine. It was the via itself that was the problem.
It felt great to chase that one down and learn a few things. Maybe it will give some of you a direction when you feel like you're stumped too.
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