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.
I found no trouble with any of this.
Then I went to:
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?