My girlfriend introduced me to her TI-99/4A from when she was a kid, it has been stored in her family's garage since the mid 1980's.
We took it back to our house, plugged it in, and I've fallen in love with this computer. I purchased a FlashROM99, a TiPi, and a sidecar 32K expansion.
The only thing I have found that is not functioning correctly with the computer is that instead of only Function + 9 resetting the computer,
the keys 6,7,8,9,0 reset the computer, regardless of any other key being pressed / alpha lock on or off, joystick connected or disconnected.
I have run memory test and all banks show OK.
I tested the voltage from the external and internal power supply with a multimeter and all seems to be normal there.
To rule out the keyboard, I disconnected the keyboard and when shorting the appropriate pins for numbers 6,7,8,9,0 the same reset behavior persists.
Interestingly enough, when first powering on the computer if it's been sitting, and I open up TI BASIC, I can get those numbers to show up briefly when pressed,
though a lot of other garbage (letters and numbers not pressed) appears and then the reset behavior reemerges and stays.
I would be tempted to ignore this problem, however it is necessary to use parentheses in order to call on certain devices and functions when using the TIPI,
and any press of the 8 key will reset the computer.
I have read other posts regarding the TMS9901 being a problem for some, but when searching I can't seem to find any similar behaviors described that prompted their replacement.
Has anyone else seen anything quite like this? I don't see any obvious signs of corrosion or leaking / bulging capacitors. I have replacement capacitors and TMS9901s (eBay seller recommended in these forums!) just in case but I wanted to see if anyone has any suggestions before I start replacing parts just in case it's a common problem and I can focus on the right spot first.