Sega Genesis (Sonic's) Repair Adventure!

Hey guys!!

I bought a box of Sega Genesis a while back, and have a total of 8 now I believe.

I plan on repairing a few off them, and mod one with an O/C switch.

So far I have started to refurbish a GEN1 (IC BD M5 USA V3)

* replaced all capacitors
* desoldered and installed a NEW edge connector 345-064-520-202
* desoldered and installed a NEW MC68000P12F 16mhz 2c913 QEMF9040 (for O/C)
* replaced both 7805's

This Genesis had issues with picture quality, and one game I had wouldn't boot past the SEGA trademark screen. (Little Mermaid)
The Little Mermaid cartridge, actually acted strange on two of the consoles. On the IC BD M5 USA V3 it wouldn't boot past SEGA logo. On the IC BD M5 USA it will boot, and play but the audio is garbled. This game runs fine on another model I have yet to identify.

After I recapped the IC BD M5 USA V3 The picture quality improved, but the Little Mermaid still wouldn't boot. Next, I socket-ed the CPU so that I could try different MC6800 in it. (trying to get a stable O/C) After I installed the socket I was getting weird issues with Sonic Spinball, and Sonic 2. The GFX would randomly get garbled, and the games would lock up. Only Sonic 1 is running fine on this console. I removed the socket and soldered the CPU directly to the board. I was getting random lockups and GFX still. After double checking all the connections on the CPU, I then figured that the issue might reside with the edge connector, so I replaced that too.

I still have GFX issues, and was wondering if anyone could direct me to the next logical steps/thing to replace..


your thoughts are greatly appreciated!

Is it possible that I have bad VRAM chip? IC10?

Sonic 1 plays without error, and I am thinking that Sonic 2, and Spinball may use more VRAM then Sonic 1.

I was hoping to get some input before I start desoldering more parts.

Could the SRAM chips cause GFX issues?

Where would you start?

Update: 4/22/15

I left Sonic 1 running over night. Guess what? No issues, it didn't freeze. I need to find some more games to continue to test on this machine. I'm convinced that the issue is with the SRAM or VRAM, and how games were probably written differently in later titles. Do we have Genesis repair experts in the forums?

Update: 4/23/15

The O/C is the same for all models.. Pin 15. the trick is to find a CPU that can handle the 13mhz signal from the cartridge slot.. That's why I bought a 16mhz CPU..


I cleaned the PCB, and took a heat gun to the back of the PCB to re-flowed some of the solder joints. While I was heating the PCB Spinball seemed stable. Eventually the whole system overheated, and turned off. When I let it cool down a few things got better.

*Sonic 2 seems to be working
*Sonic Spinball has less GFX issues, and eventually hangs.
*The Little Mermaid, now locks up at the Sega Logo instead of playing the Sega animation.

Still waiting for my Hakko 300 before completely socket this board.

What exactly does the Z80 control on the Sega Genesis? I thought I read it was for the Sega Master System somewhere.

Update: 4/24/15

I left Sonic 2 running over night. No crashes! YAY!

Now I'm beginning to wonder why The Little Mermaid will not boot, and if its related to why Spinball has its issues.

Has anyone here had a cart that wouldn't work in one Genesis but yet it worked in another? What was the cause?

I know my connections are good on the cart, and I traced the connections from the cart to the CPU and the SRAM.

 

Did you clean the games?

 

Sonic 1 is one of the few, and I mean few, Mega Drive/Genesis games that actually halt and display on error message if something goes wrong. I'd say replace the VRAM from a working unit and see if the issues go away. IF not, replace the SRAM from a working unit. If you still have issues, I don't know what you should do then. Hopefully someone can shed a light on this.

I'm sure there are experts here. I'm not one of them but I have taken apart my Genesis Model 1 VA6 before. I did the Japanese/English switch mod and the 50/60Hz switch mod to mine. I want to overclock it but can't find instructions for my Hitachi CPU. Seems everything is for the Motorola brand CPUs.

Not sure if you can on that board but if the jumpers are there, once you get it working, definitely do the region mods (cutting cart slot, 50/60Hz mod, JP/EN language mod). If you don't do the 50Hz color fix mod after installing the 50/60Hz switch, you will need an RGB SCART/RGB JP-21 cable to play PAL games in color. Otherwise, using composite cables will give you a black and white, unstable, and off-center image. The 50Hz color fix corrects the composite video issues. It's not worth it if you use RGB, since that is currently the best way to hook up a Genny.

 

The Z80 is used for mostly audio in Genesis mode. It is used as the CPU in Master System mode, leaving the 68000 idle. That's partly how Master System games work on the Genesis.

However, actually playing Master System games on the Genesis is a different story...

 

Has anyone here had a cart that wouldn't work in one Genesis but yet it worked in another? What was the cause?

 

Glad to hear you're making progress - although you'll find that a bit of research into how the console functions (and computers in general) will pay dividends in fault-finding - rather than just replacing components willy-nilly. VRAM is highly likely.

Without special gear, you're pretty much just going to have to stick to the swap and pray method, though

Personally, I'd say reverse the overclocking modifications until the machine works - you're just introducing potential problems to the mix by running it non-stock.

BTW, merged your posts - try to use the edit button more often! As a general rule, if nobody has replied within a week of your last post, edit rather than posting again. Thanks!

 

Thanks for the feedback, and the suggestions. You were mentioning the correct equipment. What did you have in mind?

As for the O/C I don't currently have any O/C going on. however I am using a 16mhz CPU mentioned in the OP.

I have another board that is socket-ed, and this 16mhz CPU is working fine with this game not O/C. I decided to solder this CPU in because I felt that socket I installed had horrible solder connections when I tried to socket this PCB.

I plan on sourcing some VRAM, and seeing if it will resolve my issues any further. I just wish that these were socket-ed on this model.

 

I've got a hunch that's your problem. Have you tried it using the original CPU or did you just go and swap CPUs without even testing the original first?

 

Before I touched this unit I didn't have Spinball, so I was unable to test with that game. However, I tested a few other games, and The Little Mermaid was one that just wouldn't boot past the Sega TM. I have tested this SAME CPU on another Genesis PCB with Spinball though, there were no issues I left it running over night. I am wondering if the issue that is causing The Little Mermaid not to boot is the reason why Spinball is having issues too.

When the PCB had a socket-ed CPU I did try the original CPU with Sonic 2 and the GFX issue I explained earlier still existed, this is why i decided to solder the CPU directly to the board.

I ordered some VRAM from Alibaba so we will see where that leads. I'm sure that others here have had issues where a cart would work on one system but not another.

Would be interested if anyone ever fixed their issue, and how.

 

some days ago I modded a gen 1 va3 exactly like yours, with 10 mhz it crashed randomly and worked perfectly with 12 mhz. Can't explain why, though

I didn't change cpu, used motorola found in it.

16 mhz is not too much to pretend it doesn't crash?