Hello all. I am a newcomer to the board. I recently purchased an Apple II Plus from eBay. Aside from a 16K expansion card, it is a bare system. No monitor, no disk drive or controller, no other expansion cards. Just the computer itself (I've separately purchased a disk drive and controller, still waiting for them to arrive). However, I know that the computer will still boot into the BASIC prompt even if no disk drive is attached, so I decided to play around with it anyway.
However, while doing so, I noticed some odd glitches that I'm fairly sure shouldn't be happening. Keep in mind that 95% of what I know about the Apple II Plus is based off 20 year old childhood memories, so my troubleshooting expertise when it comes to this old system is fairly nonexistent. However, I did try a few different things that I was readily able to recall from memory, and came up with the following symptoms:
1. Attempting to use the LIST command almost always kicks it into the program monitor at address E851, but sometimes instead it returns a divide by zero error, then freezes. The only exception to this problem is if no program code exists in memory, in which case LIST just displays a blank line and returns to the BASIC prompt, as it is supposed to do.
2. Attempting to assign a variable (For example, setting X to equal 10) kicks it into the program monitor at address E916.
3. Attempting to run the following invalid one-line program:
10 GOTO 20
Returns "UNDEF'D STATEMENT ERROR IN" with no line number given for the error, then immediately after kicks it into the program monitor at address E851
4. Attempting any math function (1+1, 9*64, 3/0, etc.) kicks it into the program monitor at address E916.
On a whim, I did a CALL-151 to enter the program monitor, dropped it down to address 0000, then did a sort of "poor man's" memory read test by holding Rept+Return, letting it read and scroll all the way through to FFFF. Whenever it would glitch, I manually went back through and stepped it one address at a time until locating the exact address that caused the glitch. These are the results I got, the addresses that caused problems and what they did:
C050 Random patterns/text/colors on screen
C080 Hard freeze
C083 Hard freeze
C084 Hard freeze
C087 Hard freeze
C088 Hard freeze
The glitch caused at C050 could be cleared by doing Ctrl+Reset. The rest were hard freezes that required the power to be turned off and back on.
Admittedly, these may be normal, and my lack of in-depth knowledge of the Apple II may make me think it's a problem. However, there is undeniably something wrong with this computer, and this is all I was able to come up with using my limited knowledge. Until I receive the disk drive and controller card, the diagnostics and tests I am able to run are quite limited.
As previously mentioned, the computer did come with a 16K expansion card. However, the problems persist even with the card removed.
So, I felt it necessary to turn to the experts here for assistance. Childhood memories that consist almost entirely of just using the system to play games really isn't enough for me to solve this problem on my own. I appreciate any assistance.