Texas TI-58C: (in)famous constant memory issues

[jebem]

(11-07-2014 03:45 PM)Den Belillo (Martinez Ca.) Wrote:  RE: "- CAUTION: The calculator can be damaged if the charger/adapter is connected without the battery pack installed."
About 10 years ago Joerg Woerner confirmed to me that this is true.

And I have just confirmed that my TI-58C RAM memory chip was also another victim of such irregular procedure performed by the previous owner. Details below.


Toshiba TC5047AP-1 Memory chip replacement arrived today.

After waiting for almost one month for the replacement memory chip, it finally arrived today. I am surprised to be able to find these old chips for sale in the market, so I have ordered a few, instead of keep buying additional TI-58C machines hoping to be able to find/build a working one. I like this electronics hobby after all.




Time to extract the old defective memory chip.
I still remember the technique we used to apply to remove the TTL and MOS DIP style chips in the good old days - just use a proper cutter to remove the offending component with zero damage to the PCB.



The underside of the memory chip reveals some nasty effects, probably caused by the high current passing thru the pins, thanks to a combination of high voltage from the power adapter used without the battery pack and the battery electrolyte leaking.




Removing the old chip pins and prepare the PCB for the new chip.
I like this audio grade Wonder Solder by TRT (rosin flux core leaded solder). It is very easy to work with, making very good joints, and shows excellent conductivity as well.



Time to insert the new memory chip and assemble the machine.
As I do not like the keys to jingle in the slots, I have applied a new thicker foam as well.




Testing time....

I was rewarded with a working machine. It can store data and programs once again!