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Sega Mega-Tech Restoration

mourix

mourix

Student
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Netherlands
You know, for me these restoration journeys are almost more fun than the gameplay itself. So let's start a new one with this original Sega Mega-Tech! 8)

Up front, things are just your basic 30 years of wear and tear. Gotta replace locks, CPO, buttons and clean a whole bunch:

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Up back and around, things are not as nice..The rear door is missing, and the backpanel is severely kicked in. Additionally, the bottom plate also has a crack so the entire cab is wobbly. I'm on the fence whether to stabilize the backpanel or make a new one entirely:

vqlANvLl.jpg
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When I picked up this machine I immediately noticed the main monitor was not original. There should be two Hantarex MTC9000's in there, but the main screen is a Kortek KTM-F. After sliding down the cab from the second floor we found this green connector on the floor. Later at my home the main screen did not light at all. You know why? I figured out the green connector is the AC in for the original MTC9000, and the red and white wires are the AC in on the Kortek. I definitely want to improve this. For now, it literally just had to be shoved in there:

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So that leaves me with this:

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Electrical inspection time:
The main board works with all 8 original games.
The sound is really tinny. Maybe a main board recap needed.
The power supply -12V line measures -16V. This voltage does not go to the PCB so it's fine..
The menu screen is very sharp but way too bright.
The main screen is quite blurry. Not sure if that's dirt or focus. Also the adjustment board of it had a broken pot.
Finally, all lamps are missing....

I've got big plans for this machine. At the end of the run, it will be almost like new.
As a hardware engineer, I also want to design some custom game carts for it. This time open source for everyone :)

To be continued...
 
Nice cab, I don't think we had them in the states, or at least I never saw one. Super Hang On and After Burner one the same machine? That's awesome.
 
This weekend I stabilized the foundation. Basically the entire side was cracked and wobbly:

lSazvJdh.jpeg


I hid 6 long screws below the metal protection bars along the bottom. For good measure I put some extra metal braces, long screws for the feet and lots of wood glue. This is now most definitely the strongest section of the entire cab:

98jbzEJh.jpeg
 
Documentation sharing time

The cab included a written manual for the Hantarex MTC9000, but the changed main screen was a Kortek KTM-F with no manual available online.
I ended up tracking down the missing manual on UK ebay. Damn, post brexit import duties and shipping cost were higher than the item...

Anyways, here we are:

M8UVbQHh.jpeg


After a night of scanning and Photoshop now free for everyone:
Kortek Sejoo KTM-F Technical Manual Eurocoin Vision Series
Hantarex MTC 9000 Service Manual 14"-20"
Hantarex MTC9000/A Circuit Diagram 14"-20"
 
Weren't the gerbers shared at some point? Or was it for Mega-Play?
 
Blio Seri said:
Weren't the gerbers shared at some point? Or was it for Mega-Play?
Click to expand...
I have not been able to find them. Seems lots of free info used to be on the now dead Jammaplus forum..

I got big open source plans though:
  • Repro 16 bit cart
  • Repro 8 bit cart
  • Megadrive converter
  • Master system converter
 
Front kickplate cleaned up well after some magic eraser and black permanent marker action. Also added new locks, screws and obligatory Sonic keychain.

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The Dutch regulatory sticker plexiglass was cracked up pretty bad. To keep it stock, I just 3D printed some washers to hide most of the damage.

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Currently I have reverse engineered both the Megadrive and Master System based carts. These are on the way from China as we speak:

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I'll do a full write up once I got them in and tested.
 
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In today's update: a warning for people wanting to recap the Mega-Tech PCB.

I wanted to try a recap because my cab sounded like a smartphone. So I made the cap list here and got to work.

I own a decent soldering/desoldering station so usually it's a breeze, but not this time. This board got all the difficulties.. Multilayer ground planes, small through holes, bent leads and thin traces right next to cap pads.

After hours of soldering it does look nice though:

aX22GzD.jpg


However this is what I was greeted with when I plugged it in. Crapp.. Back to debugging I guess.

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NES4Life has a nice write up on this so I knew which area to look at. Finally found the issue:

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I added one blue botch wire to the green factory botch wire seas:

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But hey, we are back!

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But... now the left speaker was dead. After a bunch of digging that was a 3mm track without a connection so a solder blob got it back.

And now I own a nicely recapped Mega-Tech that almost killed it...and still sounds like a smartphone. I guess it was 80's speaker quality all along:cursing:
 
Progress update on the homebrew. I want more games in my collection, but even sports ones are getting expensive now. There are some guys selling repro gamecart PCBs, but I want open source everything ;)

For the whole library, we need both a Mega Drive and Master System based cart. The 171-5782 is the common 4M Mega Drive cart, and the 171-5783 is the common 1M/2M Master System cart.

To get both, these were the sport game victims of the day:

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After taking them apart and removing every component, I made scans of both sides of both boards and lined them up in Photoshop.

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Based on those master Photoshop files, I traced every track in Altium Designer software until I had an almost 1:1 reproduction of the layout and schematics to accompany.

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After lots of tidying up I ordered 10 pieces each from JLCPB. This showed up yesterday:

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The Sega Mega-Tech is pretty much a Mega Drive glued to an additional Master System that runs the menu screen. To make this duo work, the (same as home version) game rom is placed on a circuit board with an additional custom menu rom that contains the text to fill the menu pages.

The menu rom is a 27C256 that can be had from Aliexpress for cheap. So cheap even that my newly acquired T48 programmer freaked out because the Chip ID on them did not match the painted on manufacturer name.. But I got 3 out of 4 programmed in the end.

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For the 4M Mega Drive games, a 27C400 EPROM fits in without modifications. But with me owning like 5 copies of Sonic 1, I just desoldered an original game cart chip.

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I put it in the cab and was greeted with the following. YESSSSSSSS!!!!

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The Master System cart is a bit more complicated than the Mega Drive. The menu rom is the same 27C256, but the games themselves have special roms with built in mapper logic. This means the only easy way to make a repro is to remove a rom from an original Master System game as eproms won't work.

Hence, the game rom stealing continued:

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But the results continued too :)

PUIRbKK.jpg


There is still one mystery left. The original Mega-Tech cart has connections to ground a bunch of rom pins, but the traces are strategically drilled out on the 1M rom cart I had. Interestingly enough they also exist and are drilled out on the 2M Master System console games I own. I've experimented a bit with a cheap sports game rom and it has the same power consumption and behavior no matter if the ground connections existed or not... Does anyone have an idea about this, or is someone able to open up a 2M Mega-Tech cart to verify?

e4V9TjX.png


I definitely have some more game making and experimenting to do.

Once I am 100% confident on the design I will make a Github release and forum thread :)
 
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Ape Cosplay said:
Hi @mourix,
the SMS mapper is well documented over at smspower, it's actually quite simple (mostly latching data bits to drive higher address lines).
Depending what slots you need or want to support it can be easily implemented in a small PLD.
https://www.smspower.org/forums/18946-MinimalSlot2CartridgeDesign?highlight=mapper

A minimalistic slot 2 mapper is all you need for the following games:
https://www.smspower.org/Tags/Slot2Mapping
Click to expand...
Thank you for the tip! I was getting excited play with the Frugalmapper you linked, but unfortunately that one is known to not work on the Mega Drive. And the Mega-Tech is technically a Mega Drive... I will definitely google around for a slot 2 mapper that does fit.
 
The Mega-Tech carts are housed in Japanese Mega Drive shells. To make the repros complete I got this from Aliexpress:

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To make it fit, some small studs in these shells had to be cut and the DIP sockets removed. But after putting it in, something was off. It was like the edge connector is too short.

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To make sure, I opened the original soccer cart back up. Yup, too short.

IpLbRv2.jpeg


But now I put my repro in the original shell. See? My cart is correct:

Xl0wAV6.jpeg


So now I am in need of input. Do we adjust the PCB design release for these crappy shells? I am a tad unsure.
 
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mourix said:
Thank you for the tip! I was getting excited play with the Frugalmapper you linked, but unfortunately that one is known to not work on the Mega Drive. And the Mega-Tech is technically a Mega Drive... I will definitely google around for a slot 2 mapper that does fit.
Click to expand...
You're welcome. etim released a full mapper, supporting both the Sega and Codemasters ones in the same design (CPLD):
https://www.smspower.org/forums/9821-CPLDPagingICMapper
mourix said:
So now I am in need of input. Do we adjust the PCB design release for these crappy shells? I am a tad unsure.
Click to expand...
Find better shells? I bought Japanese MD shells before and they were perfect repros (but more expensive, maybe $4 each).
 
Ape Cosplay said:
Find better shells? I bought Japanese MD shells before and they were perfect repros (but more expensive, maybe $4 each).
Click to expand...
You're right. As a compromise though, I have decided make seperate "Redux" versions of the original PCBs that have longer connectors and tweaks to make reproductions easier.
 
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