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TI 99 MBX Expansion not working properly?


INTVCruise

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Hi guys, I managed to acquire a few MBX expansion units last month. The only game I have to test them with is Baseball. One unit seems to work fine. I can advance the runners by tilting the joystick up like the manual says, but the second unit will not advance the runners no matter what I do; thus, I think the inputs are not being read correctly. I know that the cable harness coming out of the back of the units are good because I swapped the working units with the bad one and both sets work. I think I read the MBX has it's own controller signal input chip, and I believe that that is the problem atm as there is no damage to controller port 1, and just to be sure I reflowed the connector in case there was any cracked solder joint but no change at all. If a chip is indeed the problem is that an off the shelf part that can be swapped, or would I need to find another MBX unit? I have never owned one of these units prior to this so any help would be appreciated.   

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7 hours ago, INTVCruise said:

Hi guys, I managed to acquire a few MBX expansion units last month. The only game I have to test them with is Baseball. One unit seems to work fine. I can advance the runners by tilting the joystick up like the manual says, but the second unit will not advance the runners no matter what I do; thus, I think the inputs are not being read correctly. I know that the cable harness coming out of the back of the units are good because I swapped the working units with the bad one and both sets work. I think I read the MBX has it's own controller signal input chip, and I believe that that is the problem atm as there is no damage to controller port 1, and just to be sure I reflowed the connector in case there was any cracked solder joint but no change at all. If a chip is indeed the problem is that an off the shelf part that can be swapped, or would I need to find another MBX unit? I have never owned one of these units prior to this so any help would be appreciated.   

 

From this thread:

  • There's an 8K ROM in the thing that has some data (speech rom, or code for the 6809 CPU)

The chips in the MBX include:

  • GI GP1000 - Speech Recognition and Synthesis
  • MM52664MBX/N - 8K 24 pin ROM (which we've read out and have a copy of - has 6809 code in it)
  • ADC0809CCN - Analog to Digital Converter
  • HM6116 - Two RAM chips
  • HD68A09 - 6809 CPU (also runs the Coco!)
  • HD68A21 - Peripheral interface adapter
  • 8 pin ADC0831CCN - 8 bit analog to digital converter
  • Assorted 74LS chips and a LM324 and some other LM chips (CD4066, LS74, LS02, LS125, etc)

 

So, it depends on which IC is one doing the joystick interface, it might be the ADC, in this case.  We don't have the schematics, so doing a pinout and guessing is probably the best bet.

 

More investigation here from earlier about trying to emulate/reconstruct one:  

 

 

From Mainbyte:

 

image.thumb.png.bc04f1b2f4aad084dc3c38ad2706768b.png

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  • 1 month later...
9 hours ago, Appeelicious said:

Did you ever get the second one working? There's so few MBX out in the world one can only help we can nurse a few back into functionality. My ideas are terrible, if i were in your boat, best I could do is socket every chip on both MBX, swap chips until the second works and the first doesn't, then pray it's a replaceable part 

Hi, haven't gotten the time to try to fix it. I was also thinking that but don't want to mess up the working one. If anyone out there works on these I wouldn't mind paying for it to get fixed. 

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On 12/21/2023 at 7:38 PM, Appeelicious said:

It's tough because they aren't common enough that I've heard anyone working on them.

It's a lot of testing, trial, and error.  Most of these ICs are regular and can be replaced.  The joystick, not so much.  We'd have to trace where the inputs from the joystick are going (likely to the two ADCs through some passives), and also look at where the PIA is hooked up, to the 6809.  (I'm guessing one ADC for each joystick, and they probably offer some input to the PIA, along with the keyboard matrix.  The 6809 processes this input, and probably sends it out through the joystick port.  No idea what the MBX joystick port is besides a ground, there's two other pins in use there.   Maybe audio in?

 

Always remember, the MBX source code is available... https://forums.atariage.com/applications/core/interface/file/attachment.php?id=190583

 

:)

 

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2 hours ago, acadiel said:

It's a lot of testing, trial, and error.  Most of these ICs are regular and can be replaced.  The joystick, not so much.  We'd have to trace where the inputs from the joystick are going (likely to the two ADCs through some passives), and also look at where the PIA is hooked up, to the 6809.  (I'm guessing one ADC for each joystick, and they probably offer some input to the PIA, along with the keyboard matrix.  The 6809 processes this input, and probably sends it out through the joystick port.  No idea what the MBX joystick port is besides a ground, there's two other pins in use there.   Maybe audio in?

 

Always remember, the MBX source code is available... https://forums.atariage.com/applications/core/interface/file/attachment.php?id=190583

 

:)

 

The MBX source code README file gives the probable answer to the use of the two pins in the joystick port, @acadiel. You have a send and receive queue for communications between the TI and the MBX. A nice, hacked serial communications port, just like Joytalk did somewhat later.

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