View Full Version : SEGA Multimega , input buffer ??? Long pressed keys act up!

14th October 2009, 19:15

I have a SEGA Multimega , that acts up me thinks... I will bring an example game with my actions so you can understand:

1. I load Gunstar Heroes, a nice contra-like game from the same team :)
2. By pressing B , the character shoots, keeping it pressed the shooting is continuous
3. After ~1-2mins, I decided to release B
4. Normally the shooting should stop, but NO! for 2-3secs more the character shoots like I am still pressing B ! then it stops
5. I was curious, that did not seemed right, so I connected my megadrive1 and tried the same: the shooting stops instantly no matter how long I press B.
6. This is not a B button issue or a pad one, tried different buttons and pad , the multimega behaves like it has some sort of freaky buffer for input and still receives data after I am not pressing the button...

WTF is wrong? If it was a normal megadrive I would not care that much, but it is a precious Multimega! Is it a "feature" or a malfunction? :shrug:
Anyone has any info? Or a Multimega or CDX to crosscheck?


14th October 2009, 20:49
yep, something fishy...
I was playing castlevania this time and I paused it for ~5mins or so... I unpaused and B was not responding, pressed it 4-5 times. Then pressed a couple of time A, it worked the second time and then B was working too. I did pause again on purpose and after 5mins I tried C. It worked first time OK , A+B where stuck again... B does not work EVER, unless it gets unstuck with pressing A twice. I wonder what are the controller caps on the mobo:


Z , answer me!!! :jester:

Kin Hell
14th October 2009, 21:12
No help keropi, but I just wanted to say I've never seen the mainboard for the Sega. Nice layout & a good looker m8y. :)

I hope Zeet's can help you. :thumbsup:


14th October 2009, 21:28
I am convinced that the caps need replacing...
Kin (package on the way btw) notice the 2 68000 cpus: one 8mhz for megadrive operation , and the 12mhz next to it for MegaCD operation! It still puzzles me why they did not use a 12mhz single cpu (underclocked to 8mhz in megadrive use) and they choose to have 2 68000s... They do not work together btw :jester:

14th October 2009, 22:03
I believe this to be a controll line issue,

Have you always had this problem? or is it recent, if the latter its possible something discrete has possibly malfunctioned,

theres not a lot on that board in discrete components, its very VERY revised! what ever happens I would need a very close Hires Pic of the board.

I must ask is this happening in one of the ports or Both?

If I am not mistaken the need for the 2 Moto 68k cpu's is the fact both are wired up differntly One goes to the Cart Port and the other to the CDROM loading sub-system if you had a cart in or got a read request from the CD subsystem it would crash, Also it was probably cheaper to use 2 CPU's as opposed to redesign it (with more logic) for a 1 CPU design, personally I LOVE IT!!

Its a beautiful revision of megadrive / megaCD such a shame they didn't add a screen and make it uber portable!!!

14th October 2009, 22:29
I have concluded it is a mobo issue... :sigh:
I have used 2 different 6button NOS controllers and 2 different older 3button ones, all original SEGA parts... all behave the same :sigh: ie B stucks after a while, and u can revive it with pressing A twice ... a fellow in segaxtreme commented:

I have rarely used this system, but IIRC I did face this problem in the past, but never actually minded it... I need to check the 2nd port, I see now that Probotector lets you play a single player game with 2 controllers connected, and u can use the 2nd controller :)

This is kind of weird; it sounds like you're somehow charging/discharging a capacitor. I can't say it's impossible that such capacitance exists somewhere inside the CDX, but the part where it gets weird is that B doesn't have its own controller port pin or register bit; it's shared with A and periodically switched by the game (unless the game doesn't read A or Start during gameplay, which seems unlikely), so it seems like any capacitance there should affect both A and B.

:shrug: I have no idea what to do, I would hate to abandon this little machine (not to mention a combo md+megacd looks messy, big and needs 2 psu's :banghead: )

Who is up to the task or replacing those rectangular caps near the ports? :ROTFLOL2: I think those are the caps in question...

edit2: I have tested with probotector: Pad1 has the problems described above, whereas pad2 works perfectly. No "memory" effect, no stuck , no nothing.... I also noticed that pad1 with the button B pressed, acted like I have pressed button A at the same time (change in fire mode, it has a screen visual to indicate that) and it appears that actually pressing it while B is pressed it does nothing, so all point that port1 has something wrong...

15th October 2009, 00:04

I can easly replace a cap for you my friend,

Are you sure its only PORT 1 that has this issue and not PORT 2.

a little confused my friend, your last post reads as though PAD1 in port 1 doesn't work properly and PAD2 in port 1 does work.

like i say.... i am easly confused.... please help =D

15th October 2009, 07:21
yes, I confuse my fellow men, it is a way of enforcing my views :jester: :jester: :jester: :jester:

It was a little late :ROTFLOL2: , so please assume that pad1 is the same as port1 and pad2=port2 ...
I started a 2 players session in Probotector and I had 2 players on screen: player/port/pad2 :jester: worked perfect, whereas
player/port/pad1 was erratic, with sticky B button, A button not always working and working on it's own and so on...
As a matter of fact I was loosing in the first minute of the game (it is intense!) with port1 , when I tried playing in port2 I went easily way deeper in the game... I am in the process of opening the multimega, it is a pain in the a$$

edit: OK , opening was not so bad, I have taken some pics they are here: http://rapidshare.com/files/293213770/k-multimega.rar
It appears there are components in the other side of the pcb too, :jester: Visually I can see nothing wrong, but I wonder WTH are those black squary thingies next to the ports... and how to see if one is bad

15th October 2009, 12:30
"Black square thinghies" (tm to Ker) usualy are SMD resistors. They are the type of component who works or not at all.

Capacitors are normally brown(ish) and they are major culprits for bad behaved circuits.

15th October 2009, 12:56
those black things (that have 3 legs, and all have printed on them 222 except the 2 on the edge of the pcb that are 271 btw) between the joystick ports are resistors? :?: wow, that I did not know :)

15th October 2009, 13:26
3 connection things are normally transistors. Can be other 3-leg devices like voltage regulators and even some few IC have that stunning number of contacts! :shock:

Oh, and a bad trasistor can cause those ill effects you are experiencing now.

15th October 2009, 13:39
:thanks: for the info rkauer !!! it is a starting point :thumbsup:

15th October 2009, 13:50
damn , I asked a fellow tech if he knows what those are, he said they could be transistors, but their 222 number makes no sense... :blink: 3 legs each, the middle is ground with no doubt...


15th October 2009, 15:11

(now dowloading your image pack)

these components MIGHT be at fault ONLY if they are in line with the ports and the controller.

Although they have 3 legs, I am more inclined to believe these some form of resistor net, again,
not sure if they are pulling up or down, over a late lunch I shall have a look at the pics and see if that gives me
an idea or two =D

15th October 2009, 15:18
Those things are EMI protection resistor+capacitor, very much like those used in A500/2000 ports for protection.

15th October 2009, 15:28
god damn rkauer! And I was wondering WHERE the hell have I seen those before!!!! :ROTFLOL2: :ROTFLOL2: :ROTFLOL2:
So a faulty one can buffle the line that controls A+B (they are on the same line) ....

15th October 2009, 15:49
The good nes for keropi is that I have enough spare for him to repopulate the whole lot for both ports =D

(old megadrive that the cart port broke on)

I will de-solder them and bag-em up with you new (modded) megadrive

I have pics.....

you know... all the work is essentialy done.... LOL I cannot help it my modding side wants more..
I want to strip the plastic, wash it.... and spray it....

completely inverse.... rather thanblack and white.... I was thinking.... white and black.. hang on!

a while back I designed a project based on a Singe Half ISA AMDK6-II 500 (256MBRam) SBC to run knoppix



I even designed the Joypad to USB device (based on the ATMega8) and programmed the chips LOL

the Cart area was to be a CDROM loading area with a flip top lid and a glassed (polymer) over vew port where the cart hole is... the central circile would be cut, rotated 180 and hinged for the DVDRW that would be installed below =D

I may have to revist this project, its been languising a good 2 years..

15th October 2009, 16:12

I have found the resistocap :ROTFLOL2: , buttons A+B are connected to... it is the first one in the right of the blue on/off switch .... how to measure if it is dead? got a brand new shiny digital multimeter :woot:

15th October 2009, 16:46

as its a combine unit I am not sure...

resistors when the are on the way out, normaly just go... and you can check this
with a multimeter set to 20, and take a reading before and after the resistor, of course

in most cases the resistor will not conduct and as such you will get a zero reading however
in a few cases you will get a reading and this is when you need to know the resistance of
the resistor.

I personally use two tests for a capcitor,

When turnned off, use a continuity test probe either side of the leg
(if its polarised get the probes the right way round) at low Farrads you should get a reading
this isolates if the cap is completely blown.

However a more acurate test (and one you will need to to is to test the capacitor) with
power running through the device, again you will need to know the rating of the capcitor.

A bit late in the day (as they say)

As we dont know what the rating is, marking 222 is at best a guess, I would say at this point its worth replacing...
I would perhaps even go as far as to say to use a component from Port 2 to replace it with.

If it solves the problem then you can hold on till I send you some spare components with your Modded megadrive =D

15th October 2009, 17:05
yes Z :thumbsup: I will try to replace with a part from port2, it will be the ultimate test !
Here's hoping I won't burn the pcb :ROTFLOL2:

15th October 2009, 19:25
damn , the more I look at it the more chicken I become to put my solder iron on it :ROTFLOL2: I am not good at soldering, my iron is crappy and only for bigger jobs and I think I will kill it somehow...

15th October 2009, 19:31

thats why you have my address and unlimmited credit for repairs my friend =D

15th October 2009, 19:37
Zetr0 repair service is just precious, that is why I pre-bought a lifetime subscription at a minimal fee :woot: :ROTFLOL2:


15th October 2009, 19:54
:woot: ITS MY BED OF MONIES!!!!!! :woot:

all one needs now is a cute chikita to roll around with on the bed methiks...

15th October 2009, 19:59
...and was enough to make a small ladder to climb on the top of it :woot: :ROTFLOL2:

Kin Hell
15th October 2009, 21:24
That's one seriously big stack of cash, whatever the currency! :wooha:


15th October 2009, 23:31
I have the same issue w/ my CDX, it delays the button response, especially when I'm playing 2 player. IDK, but maybe there is just a fault in some boards, or i need a cap replaced

16th October 2009, 08:09
could be a general failure in the systems... I 'll let you know if replacing those resistocaps fixed mine :thumbsup:

16th October 2009, 10:41
That's one seriously big stack of cash, whatever the currency! :wooha:

Unless it's Zimbabwean Dollars, in which case it's probably worth more as recycled paper! :jester: