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Normal Apple II Plus Boot Behavior

oldpcguy

Experienced Member
Joined
Sep 23, 2021
Messages
146
Recently I acquired a non-functional Apple II Plus computer (which I've posted about in other threads). The initial problem was that it would not power on. After inspecting the power supple (but not doing anything more than blowing the dust out with compressed air) the system suddenly powered on. The screen was garbled and I identified the issues as a bad memory chip in the first bank of memory (where the zero page and stack are located). Replacing this chip and I was able to bring the computer up to a BASIC prompt and run some simple programs.

When attempting to run commercial software there were a number of issues with doing so. Suspecting more bad memory I was able to write a short assembly language program which I had typed into the computer using the monitor. This program identified two bad memory chips in the second bank and one in the third. Installing new chips and now I can run commercial software (such as Castle Wolfenstein).

I do have a software hardware test program which runs and hasn't reported any problems. Great I say. However, I have observed that the keyboard begins to act wonky after a period of time. I have not yet isolated a pattern (i.e. time, particular software, etc) but I have to power off the computer and leave it off for a period of time (i.e. a quick power cycle, even after waiting 30 seconds, does not fix it). When I eventually power it on (10 - 15 minutes later) all is well. Has anyone experienced this issue before?

Also, and the question from the title: What is the normal Apple II Plus boot behavior when a Disk II drive is connected. Without the Disk II the system immediately goes into BASIC. With the Disk II it starts the drive (with the normal clunking) and then continues to spin until I press the reset key or insert a bootable disk. It's been so long since I've worked with an actual Apple II Plus I can't recall if this was the normal behavior. I believe my Apple //c attempts to boot off the floppy and, not finding one, times out with a message.

So oh wise forum...what is the normal boot behavior of an Apple II Plus with a Disk II drive attached and no disk in the drive?
 

DistantStar001

Experienced Member
Joined
May 8, 2019
Messages
53
First: I hate that! Something dead just decides to work when I haven't done anything to conceivably fix it.

I have a PSU that would cut out randomly for months. I took it apart, removed, tested, and reinstalled the capacitors, reflowed the solder joints, and nothing! Then one day, out of the blue, it just decided to work, and hasn't given me a problem since. I'm always afraid that it's going to brake again.

Second: YES! I have encountered a similar problem to what you have described! For the most part, it works fine for the first few hours. But after a while, random characters appear on the screen every time I would hit a key. The Space bar was particularly bad. I'm guessing due to the concussive force.

Typing "HOME" in BASIC would clear the screen, but entering programs (either commercial or in BASIC) would malfunction or give errors. At one point, the issue was so bad that it repeatedly print inverted @'s to the screen, beep, and repeat.
Turning it off and letting cool, tends to return it to normal operation. My best three guesses at this point are: 1) a dodgy IC (possibly RAM) somewhere with an intermittent failure, 2) a loose connection, or questionable socket, or 3) a dry solder joint that is exasperated by the heat from extended use.

I thought it was a bad 9334, but the problem persisted after replacement. So as of yet, I haven't figured out the issue. But then, When I got it, it was apparently dead with no video or beep. So progress... In any case, I ended up getting another motherboard while I continue to troubleshoot the issue. If I figure it out I'll try to remember to post it

Third: Yes what you describe is normal boot behavior for an Apple ][ Plus (also a //e and Franklin ACE 1000 as well). Both my boards behave in a similar manner on proper boot up.
 

oldpcguy

Experienced Member
Joined
Sep 23, 2021
Messages
146
First: I hate that! Something dead just decides to work when I haven't done anything to conceivably fix it.

I have a PSU that would cut out randomly for months. I took it apart, removed, tested, and reinstalled the capacitors, reflowed the solder joints, and nothing! Then one day, out of the blue, it just decided to work, and hasn't given me a problem since. I'm always afraid that it's going to brake again.

Second: YES! I have encountered a similar problem to what you have described! For the most part, it works fine for the first few hours. But after a while, random characters appear on the screen every time I would hit a key. The Space bar was particularly bad. I'm guessing due to the concussive force.

Typing "HOME" in BASIC would clear the screen, but entering programs (either commercial or in BASIC) would malfunction or give errors. At one point, the issue was so bad that it repeatedly print inverted @'s to the screen, beep, and repeat.
Turning it off and letting cool, tends to return it to normal operation. My best three guesses at this point are: 1) a dodgy IC (possibly RAM) somewhere with an intermittent failure, 2) a loose connection, or questionable socket, or 3) a dry solder joint that is exasperated by the heat from extended use.

I thought it was a bad 9334, but the problem persisted after replacement. So as of yet, I haven't figured out the issue. But then, When I got it, it was apparently dead with no video or beep. So progress... In any case, I ended up getting another motherboard while I continue to troubleshoot the issue. If I figure it out I'll try to remember to post it

Third: Yes what you describe is normal boot behavior for an Apple ][ Plus (also a //e and Franklin ACE 1000 as well). Both my boards behave in a similar manner on proper boot up.

Thank you for this information. I did some further testing and discovered the problem occurred after a period of time while the computer was sitting at the BASIC prompt. I powered on the computer, pressed the reset key, checked the keyboard and all worked well. I then left it at the BASIC prompt and when I returned a few hours later I experienced the problem.

That said I believe that I have identified the problem. My system does not have the standard character ROM but instead has a third-party character ROM with a switch that allows me to choose, I assume, one of two character sets at any one time. I decided to change the switch to the opposite setting and, in doing so, the problem appears to have disappeared. I performed the same BASIC prompt idle test as described above as well as performed some third-party diagnostics testing over night and all appears to be well. I have changed the switch back to the previous position and re-running the diagnostics tests.

One thing that may have been the problem is not the switch setting but the way it was mounted on the back panel. It was right up against the top case and it's possible the switch had pressure on it from the top case. I repositioned it so that the top case no longer interferes with the switch. Therefore the testing with the switch in the previous position may pass as well.

Here's a picture of the character ROM I am referring to:

Character ROM - Top.JPG
 

DistantStar001

Experienced Member
Joined
May 8, 2019
Messages
53
Good theory! Personally I don't have that mod, and I switched the ROMs between the motherboards, so I'm pretty sure that's not my problem.

Interesting that there are two sockets though. Is it possible that it's capable of accommodating two different ROMs? Maybe when the switch was triggered it was switching to the empty socket, confusing the computer? Also, what alternative character set does the ROM hold? Lowercase? Japanese? This computer looks a lot more intriguing now.
 

oldpcguy

Experienced Member
Joined
Sep 23, 2021
Messages
146
Good theory! Personally I don't have that mod, and I switched the ROMs between the motherboards, so I'm pretty sure that's not my problem.

Interesting that there are two sockets though. Is it possible that it's capable of accommodating two different ROMs? Maybe when the switch was triggered it was switching to the empty socket, confusing the computer? Also, what alternative character set does the ROM hold? Lowercase? Japanese? This computer looks a lot more intriguing now.

I have no idea as I am unable to find anything about this modification through my research. Perhaps if the label was still on the PROM I might have something to look up. When I toggle the switch I do not see any difference in character sets. Perhaps because the other chip is missing it "falls back" to the existing chip? I was thinking this was a lowercase character set modification. Or maybe it uses the later character set from the newer Apple II models? I can't really say.

I have been testing the computer all day with the switch in the previous position and everything appears to be working fine. It's currently running a looping memory test which I'll stop tomorrow morning. However, results so far have been positive. I suspect the problem may have been the top lid pressing against the switch which resulted in an in determinate state.
 

oldpcguy

Experienced Member
Joined
Sep 23, 2021
Messages
146
Your experience is almost exactly the same as mine when I got my Apple II Plus. When I first received it it would not power on. Like yours it mysteriously powered on after I opened the power supply. Memory failures appear to be one of the top things with these systems. I've had two Apple II Plus and about half a dozen Apple IIc's systems which required replacement of bad DRAMs.

Like you I wrote an machine language (thankfully I was able to use the Merlin Assembler to write it on a functional IIc system) to perform basic memory tests. I've discovered if the system has a garbled screen and won't boot to the BASIC prompt that one or more of the first row memory chips is likely the culprit. Once I have get it to boot I attempt to run APEX II diagnostics. If it fails to load then it's likely one or more of the DRAMs in the other two rows is bad. That's where my hand written machine code comes in handy.

Finally I did have one Apple II Plus which experienced keyboard problems. Not quite like yours but here is a thread where I posted about it. Hopefully you will find something useful there:

Troubleshooting Apple II Plus Keyboard
 
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