Apple II+ @@xx still showing after much much testing

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Apple II+ @@xx still showing after much much testing

Hello,

 I have an AII+ that boots to a @@xx  repeating vertical bar screen. The computer is currently in a 16K, no card, config I think is best for testing. I pulled the other 2 top rows of ram, and the additional 16K card.

I have tested the PSU output and some continuity with a multimeter under load  doing:

-------

RESET on 6502 pin 40 should always be 5V while the machine's running. Clock on pin 37 (phi2) should be around 2V.

Voltage-wise check for:

5V pin 8 6502
5V pin 24 ROMs
5V pin 1 4116
12V pin 8 4116
-5V pin 9 4116

Next I'd remove all the RAM and processor to see if the display changes. With a multimeter set for continuity check that pin 2 (DI) on each *column* of RAM sockets is connected together (eg C10, D10, E10), also pin 14 (DO). Then check the address bus and CAS/RAS/WR line on each *row* (eg C3 - C10 pins 3-7 and 10-15). Google for '4116 pinout' to reference.  

check the Reset line - Pin 40 on the 6502 CPU.
Attach the common lead of your meter to ground
and the positive lead of your meter to pin 40.
Press the RESET or Ctrl with RESET key on
your keyboard and the voltage reading on you
meter should dip towards zero.

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I found no trouble with any of this.

Then I went to:

http://www.appleii-box.de/D06_resurection.htm4

I get screen output close to screenshot #5. Fom the caption, I checked 4) above the screen shots concering the databus.

All the LS chips tested good in my little tester. I was able to replace the 8T28 chips next to the CPU with a few I have onhand that are untested, but the look NOS.

I have checked a lot of other LS chips around the board and they all pass or were replaced with tested good chips. But not all ic's tested

Not sure where to go from here except to ram. But I do not know how to test ram except to do a way too many loading of chip swaps and power-on's. I hope there is better way.

Thoughts, suggstions, ideas?

Thanks 

 

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RAM, ROM, traces, capacitors

Hey that's SpeedyG's  web site.  Amazing resources on the web site, thanks SpeedyG!

https://www.applefritter.com/users/speedyg

The link was broken,

http://www.appleii-box.de/D06b_resurectionIIe.htm

Someone suggested http://www.vcfed.org/forum/forumdisplay.php?20-Early-Apple-%28I-etc-%29

There is hardware repair discussion on that forum.  And via this thread:

http://www.vcfed.org/forum/showthread.php?73358-Disk-Paying-the-idiot-tax&s=0a99e6c877e81f9780bfa24c76b07a55

I found some Apple II+ repair videos:

https://www.youtube.com/watch?v=sMNnbF6u0_Q

It looks pretty tedious testing RAM chips.  In the videos, Chuck Hutchins tests and replaces bad RAM.  He found bad (and hot!) ROM chips and, looked for bad traces, cleaned up traces and fixed shorts on the keyboard controller.  He also fixes some bad capacitors.

 

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Thanks for th reply.

Thanks for th reply.

  I had posted this same message already at VCF, and I had seen the vidoe sometime ago.

I think I need some specific help with this issue.

Suggestions on a post title that might attract additional help?

Again thanks!

mmphosis's picture
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Apple II freezing -- HaLT and (please don't) catch fire

I am not much of a hardware person, but from a software viewpoint, seeing that pattern indicates to me that the Apple II+ may be "freezing" on boot up.  Freezing means the software has locked up, one HaLT instruction (or infinite loop) on boot up and you could see that pattern -- this pattern usually appears briefly before the screen clears and prints APPLE ][ at the top of the screen.  So, any number of issues could be happening.  I did resolve some RAM issues in my Apple II+ some months ago by swapping in and out RAM.  It is easy to make the computer freeze if there is bad RAM or bad ROM or bad traces or bad capacitors or ...

In the video, he puts a thermometer on the chips to see how hot they might be getting.  When he removes the bad D8 ROM chip, the D0 ROM chip heats up.  It ended up that both of those ROM chips needed replacing.  He was lucky enough that on boot up the Apple II crashed into the monitor, and from the monitor it is possible to diagnose what might be bad.  The heating up of chips is a good reminder to be careful.  And, I wouldn't be opening up the power supply myself.

reference: https://www.imdb.com/title/tt2543312/

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That makes sence to me. I did

That makes sence to me. I did pull out D8, no change. I pulled out the CPU, and still got the same screen.

I could burn my own roms, but need the right files and the right eproms to use.

Since I have tested almost all of the 74LSxxx chips in my tester, the roms might be the problem.

 

mmphosis's picture
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having working spares

I didn't even think of the 6502 itself, as a bad CPU could also be the problem.  It really helps to have spare "working" parts.  I have a non-working clone Apple II with lots of working parts like RAM to swap in and out.  I suspect the ROM chips are bad on my clone because if I remember correctly it also only boots to the   @@??   pattern on the screen.

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I pulled out the CPU and

I pulled out the CPU and found the a leg had broken off in the socket. The break was too close to casing to resolder. I out in a new socket, and installed the only, I think, compatiable 6502, from a Atari 800 cpu card. It is not a 65c02.

I get the same screen on boot. Infact I get the samce screen with and without the cpu installed. SO it must be something before the cpu.

I wish I had a working AII along side, but I do not, so have to go the long way around to fix this one.

Any have some additonal ideas?

Again thanks everyone!

 

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Thanks everyone.I was able to

Thanks everyone.
I was able to get a working II+ to swap chips with.
There were many bad chips.
Rom 341-0020
Rom 341-0012
74ls367 with a broken leg at H5 that should be an 8T97
One of the two 8T28 H7, H8 were bad from my new old stock.
I can burn new ROMs by reading the good ones I have. But need to know what eproms to use.

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