OK, so now I'm determined to give this a try. The plan is to take the 512K hybrid board which is arrayed with 16 256 RAM chips.
If what Pina says is accurate, I should be able to turn the 512K board into a 128K board by simply removing the decoder chip, 3 resistors and one cap required to recognize the additional 384K RAM. In addition there is a jumper mentioned above needing to be added in, which I should be able to fabricate out of a paperclip. Much less soldering than removing 16 RAM chips.
One question, after I remove the components, do I need to fill the pin holes with solder?
According to Pina, even though 512K worth of RAM is installed on the board, only 128K will be recognized without the decoder array installed. Now, he only mentions this for the original board onto which a makeshift decoder board must be inserted. However, it seems like this principle should apply to the hybrid board as well.
One thing that concerns me is this jumper for the 128K. Pina makes a specific point that when upgrading to 512K, that the jumper must be cut so that it cannot possibly reconnect. Now this could simply be so that the computer works properly, or could it be that the jumper could damage something with the decoder array installed? One would think Pina would have mentioned that as a trouble shooting step in the event one forgot that step should 512K not be present after power-up, though he does occasionally assume more than the novice reader and skip such details.
Ideally it would be fantastic to find a single pin in the 512K array that I could switch in and out with a dip switch to enable 512K or 128K. I think the only way to figure this out would be through experimentation, but is there any chance of damaging the RAM chips or other components by isolating pins one by one?
Could it be that merely adding or removing the jumper required for the 128K is enough to bypass the additional RAM decoding array?
The first thing I will do is remove all the expansion components. perhaps replacing them all with sockets, so at least a manual restore could be accomplished if no single dip switch option exists. This will also aid in testing.
Is there any risk to running 256 chips as a 128K?
Practical application to this? Easy, many 128K boards have been upgraded to 512K boards and there are any more 512K boards out there, not to mention cheaper, in general. This would be a simple way to restore a 128K board without the difficulty of replacing all the RAM chips (which are often hard to come by), and possibly damaging the boards. The original boards are a little more complicated since they require physically cutting traces on the boards, and removing the jury-rigged decoder boards can pull traces and create other problems depending on how they were installed.
If what Pina says is accurate, I should be able to turn the 512K board into a 128K board by simply removing the decoder chip, 3 resistors and one cap required to recognize the additional 384K RAM. In addition there is a jumper mentioned above needing to be added in, which I should be able to fabricate out of a paperclip. Much less soldering than removing 16 RAM chips.
One question, after I remove the components, do I need to fill the pin holes with solder?
According to Pina, even though 512K worth of RAM is installed on the board, only 128K will be recognized without the decoder array installed. Now, he only mentions this for the original board onto which a makeshift decoder board must be inserted. However, it seems like this principle should apply to the hybrid board as well.
One thing that concerns me is this jumper for the 128K. Pina makes a specific point that when upgrading to 512K, that the jumper must be cut so that it cannot possibly reconnect. Now this could simply be so that the computer works properly, or could it be that the jumper could damage something with the decoder array installed? One would think Pina would have mentioned that as a trouble shooting step in the event one forgot that step should 512K not be present after power-up, though he does occasionally assume more than the novice reader and skip such details.
Ideally it would be fantastic to find a single pin in the 512K array that I could switch in and out with a dip switch to enable 512K or 128K. I think the only way to figure this out would be through experimentation, but is there any chance of damaging the RAM chips or other components by isolating pins one by one?
Could it be that merely adding or removing the jumper required for the 128K is enough to bypass the additional RAM decoding array?
The first thing I will do is remove all the expansion components. perhaps replacing them all with sockets, so at least a manual restore could be accomplished if no single dip switch option exists. This will also aid in testing.
Is there any risk to running 256 chips as a 128K?
Practical application to this? Easy, many 128K boards have been upgraded to 512K boards and there are any more 512K boards out there, not to mention cheaper, in general. This would be a simple way to restore a 128K board without the difficulty of replacing all the RAM chips (which are often hard to come by), and possibly damaging the boards. The original boards are a little more complicated since they require physically cutting traces on the boards, and removing the jury-rigged decoder boards can pull traces and create other problems depending on how they were installed.