• Please review our updated Terms and Rules here

Apple II plus issue

retrogear

Veteran Member
Joined
Jan 29, 2014
Messages
1,063
Location
Minnesota
Yes, see if you have a pulse on pin 15 now. If so, then it was bad IC or socket connection, etc. Don't worry how noisy a signal is. I have a 200Mhz scope and very surprised how much noise is present on signal paths. TTL is just transition logic so the window is around 1V to 4V and noise outside of that doesn't seem to matter. That's just my observation. So now you get just one beep at power on? You might want to connect your keyboard, do a reset to get one beep, type some random keys and press return to see if you get a beep for syntax error. That would be a major step forward. It is very likely you have multiple problems.
 

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
After swapping the chips there is no response from the keyboard or reset button. I did check pin 15 again, and it appeared to be constantly at +5. No single beep at start up either. (I didn't mention that earlier because I plugged the speaker in after powering up. I have the circuit board completely out of the case so I don't accidentally short something) The trace flickered a bit sometimes, but I couldn't really see any negative going pulses.
 
Last edited:

retrogear

Veteran Member
Joined
Jan 29, 2014
Messages
1,063
Location
Minnesota
Well, if swapping F12 and F13 changed your symptom, I would think F13 was bad. Putting it in F12 socket means a bad chip is running the ROM select lines, killing any ROM routines like the beep. Maybe swap them back to see if you're back where you started. If so, you need to replace F13 to proceed further.
 

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
When I swap those chips back I get the symptoms back again. So the first thing I will do is get the new chip. While I am waiting get those chips is there any other part of the system I could be looking into?

I don't think this matters, but does the suffix and prefix on the chip matter? Or as long as it has 74LS138 as the main part of the number will it be okay?
 

retrogear

Veteran Member
Joined
Jan 29, 2014
Messages
1,063
Location
Minnesota
For the most part, the prefix and suffix shouldn't matter, but maybe others know more on that. Seems like I read that it does on some. I have some DM prefixed chips that don't seem to work.
I agree with what rittwage said that you should be getting other characters output like the ] prompt. You might have some kind of video or character generator type problem yet. Hopefully a new
F13 will reveal more clues. It's hard to test further w/o a functioning keyboard. You did a B10 swap that changed symptoms too so might want to get one of those and B1 that you said got too warm.
Or even the chip that had the suspicious substitute #. Depends on price, of course.
 

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
Awesome. I think I found some deals for the chips. Before I order them does anybody know if these numbers will be not be compatible? I can't remember off the top of my head, but the Apple II chips do have some different suffixes, and I think prefixes too.

SN74LS74AN
74S175N or SN74S175N or 74S175P
SN74LS138N
 

retrogear

Veteran Member
Joined
Jan 29, 2014
Messages
1,063
Location
Minnesota
Sams indicates SN74S175N or 74S175 for B1. Both my A2+ boards have 74LS175PC, go figure ...
Some of my chips are SN. I'm sure SN prefix is ok.
One of my good boards has DM74LS138N so forget what I said about DM ... I think as long as you match the basic number you're fine
 

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
I was finally able to order the chips. After they arrive and I swap them out I will let you all know what the results are.
 

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
The chips arrived in the mail. The first chip I replaced was F13, the SN74LS138N. I figured I would go ahead and swap out one chip at a time to find out if a particular one was bad. So I went to turn on the machine and the apple gave me the prompt.

Should I go ahead and replace the other chips we were thinking about replacing to be on the safe side or am I good to go?

Next when I tried to type a simple hello world program Applesoft basic freezes and I have to press reset. Sometimes when I was messing around it fell out of basic and into the monitor. Pressing reset didn't clear the screen either. The old prompt just moved up a row and a "cursor" was next to it too. Would this problem be indicative of an issue with ROM, RAM, or something else?
 
Last edited:

retrogear

Veteran Member
Joined
Jan 29, 2014
Messages
1,063
Location
Minnesota
Earlier you said you swapped B10 with another IC and your video had no output then you put them back. Did you get a new B10 chip? If so, try it. Also you said you had shorted pins on B2, try that too.
 

KC9UDX

Space Commander
Joined
Jan 27, 2014
Messages
7,468
Location
Lutenblag
The reset functionality you mention is perfectly normal. There is a switch that controls whether you need to press just RESET or CTRL RESET to do an actual reset. You have it in the CTRL RESET position. It will do exactly what you described in that case, which is issue an NMI.
 
Last edited:

retrogear

Veteran Member
Joined
Jan 29, 2014
Messages
1,063
Location
Minnesota
KC9UDX is right. Maybe I am reading too much into your description. If you can make a disk from an image, get APPLE_CILLIN_hr.dsk from here:
ftp://ftp.apple.asimov.net/pub/apple_II/images/disk_utils/diagnostics/
It's a good diagnostic that requires little to actually run, then you can check the memory and ROM's.
Otherwise, a quick memory test is to get into the monitor ]CALL-151 and type this from the * prompt
800:FF N 801<800.BFFEM N 801<800.BFFEV
if memory is good nothing will display for maybe 10 seconds and back to * then repeat the string starting with 800:00
 

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
I did go ahead and replace B10 with a new chip and that did not appear to do anything. I also shorted out the two pins mentioned earlier, the text got messed up on the screen but nothing else happened the scrolling effect was not there.

As for the Applesoft issue I am completely unable to enter a program or issue a command. After I press enter the computer locks up and there is no cursor. All I can do is press reset to get the prompt back. Sometimes pressing reset repeatedly will get me into the monitor, and even then sometimes the monitor acts weird. It doesn't even fill the whole screen. It fills the upper quarter to half of the screen. Is this normal for the II+? When I get into the monitor I will try typing the memory test in.

Here are some pictures of what I am getting:

No prompt after pressing enter:
NoPrompt.jpg

The results of pressing reset several times:
AfterPressingReset.jpg
Note here that after each prompt a blinking cursor was present; the timing of my picture didn't catch those. The only active cursor was the one at the bottom of the screen.
 

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
I just ran the program and it produced the following output:

Code:
4E2F-FF (FF)
6850-FF (FF)
BFFF-FF (0D)
*

Now I did try to get into the monitor by call -151, but that wouldn't work. I managed to get into the monitor by pressing reset a lot and typing at the basic prompt. Another thing to note is that an extra v appeared at the end of the string I entered after I pressed enter. Would that affect anything?

I am re-running the code as I type this and the extra v did not appear. For the previous run the output happened right away. So far it appears that it hasn't completed its run.
 
Last edited:

retrogear

Veteran Member
Joined
Jan 29, 2014
Messages
1,063
Location
Minnesota
your ram chips are inside the white square outline. the row closest to the keyboard connector (row C) is the 1st 16k addresses 0 to $4000. a bad ram chip in that row will raise havoc with everything. try swapping that row with row D to see if it behaves
better, then run the ram test if you can't otherwise

EDIT - saw your previous post. row D is $4000-7FFF, row E is $8000-BFFF. not sure why it's returning equal values FF (FF)
 

retrogear

Veteran Member
Joined
Jan 29, 2014
Messages
1,063
Location
Minnesota
bear in mind the video display you see is mapped in ram at $400-7FF so in that 1st 16k of memory row C. random wrong characters on the screen can be bad memory in that row
 

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
I ran the program again. The second time it froze up, but I think that was because of a typo that I didn't catch (I had an extra <). It ran for like 30 minutes without doing anything so I had to reset.
Then I managed to get back into the monitor and I ran it again and got the message
Code:
4E70-FF (FF)

The third time I ran it I got no errors after a few seconds.

For testing purposes I have only left the first bank of RAM populated (row C). I will try swapping out another row of chips with that one. I am also trying to make the disk image, but my computer and IIe aren't wanting to talk over audio right now.
 

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
I just tried swapping some of my ram chips. Instead of basic freezing it goes into the monitor every time I press enter after entering a basic statement. It started out indicating address 0101, but now its indicating address 00DA. If it's any help here is what it displays:

Code:
00DA-      A=B9 X=FF Y=01 P=B5 S=89

I think that those are the registers and their values. I don't know too much about the II's monitor.

I am going to go ahead and try the last bit of RAM I have and see if that works.

EDIT: I swapped out the last set of RAM I have, and it produces results similar to the first set of RAM I had in row C.
 
Last edited:

retrogear

Veteran Member
Joined
Jan 29, 2014
Messages
1,063
Location
Minnesota
It looks like your ram test was passing so I'm wondering if you have a bad Basic ROM chip. If you can get into the * monitor, try E000L to list some of the ROM. Compare it to listings you can find online.
Maybe try reseating the rom chips
 

Old Computers

Veteran Member
Joined
Aug 30, 2012
Messages
510
Location
USA
I tried reseating the ROMs and that didn't change the symptoms. It seems like now any time I try entering a line in basic it just drops in to the monitor. I am not sure if that is because of the reseating the ROMs or just started happing that way.

As for the listing I got from the II, is that dumping the contents of the ROM at address E000? I am new at 6502 assembly and the II's monitor.

If I am reading the disassembly that I found correctly it appears that the first few bytes of my listing differs:
My listing:
Code:
0C
28
F1 4C
3C
D4

The listing's code at E000
Code:
4C 28 F1
4C 3C D4
00

I haven't gotten around to getting the disk made yet. My computer and IIe don't like to talk over audio with ADT Pro.
 
Top