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1980s_john
January 15th, 2011, 04:17 PM
Hi,

One of my Apple IIs has a fault and I am looking for some advice please. When powered on, it doesn't beep, and the video shows a series of blockly vertical bars - looks like graphics characters. Pressing Reset has no affect.

I have another identical machine (Apple II Europlus) which I have just got working, this had a faulty PSU and a faulty F0 Applesoft ROM. I could start swapping chips, but there must be a better way.

Regards,
John

Druid6900
January 17th, 2011, 03:00 PM
There are a number of things that can cause a problem like this, but, as always, I find, more often than not, it's the RAM, usually the first bank.

Take your first row of RAM (closest to the back of the machine) and swap it for the last row. If it boots, one of the chips in the last row is bad.

tezza
January 17th, 2011, 05:17 PM
Druid!

You are still alive after all. I thought you might have gone the same way as some of our vintage computers (i.e. become erratic and grumpy then crashed beyond repair!) (-:

Yes, that's what I usually do with my Apple II Plus when it shows this symptom. The sockets can be dodgy in these machines too.

Tez

1980s_john
January 18th, 2011, 02:35 PM
Hi,
Thanks for your replies. I've tested all 48K of RAM in my 'good' machine, and swapped row E (8000-BFFF) from the good machine into row C (0000-3FFF) of the bad machine. This produced a slightly different pattern of vertical bars, and the RAM tested OK in the good machine.

I then plugged in a logic probe and looked at the 6502 pins. This showed the clock was OK, and pressing reset took the RES pin low. The address pins are stuck at FFFF. Of the 7 data pins, D2 is stuck low, all the rest show activity. I assume this is either the display circuit or the DRAM memory refresh doing its stuff. D2 line is therefore suspect, I assume I should look at all the bus driver chips next?

Regards,
John

Druid6900
January 18th, 2011, 05:18 PM
Druid!

You are still alive after all. I thought you might have gone the same way as some of our vintage computers (i.e. become erratic and grumpy then crashed beyond repair!) (-:

Yes, that's what I usually do with my Apple II Plus when it shows this symptom. The sockets can be dodgy in these machines too.

Tez

Yeah, still alive. How do you think that NZ is getting an infusion of Kaypro FDC chips and data separators? :)

Druid6900
January 18th, 2011, 05:20 PM
Those and the data buffer chips would be my next choice if you have those measurements.

tezza
January 19th, 2011, 01:06 AM
Yeah, still alive. How do you think that NZ is getting an infusion of Kaypro FDC chips and data separators? :)

Ah ha! Now I know!

Anyway, good to see you on here again.

Tez

1980s_john
January 19th, 2011, 03:35 PM
Those and the data buffer chips would be my next choice if you have those measurements.

Thanks. After swapping a few chips without any change I followed the 'Apple II troubleshooting' guide under the section 'No reset or no response'. After about 4 chips I swapped B6 74LS257, which is a latch between the keyboard and the databus. This fixed the problem - hurray! Unfortunately I found I had killed one of my A2 keyboards (two PCB, but all-in-one key switches). This was either when I shorted the keyboard on the metal base plate (tut tut!) or when I disaseembled it to repair a broken plastic plunger (or it may have been dead all the time - this machine never worked before!).

I am looking for a replacement Applesoft F0 ROM 341-0015, I have two more Apple IIeuroplus to work on so will raid those in the short term.

Thanks for a very helpful forum,
Regards,
John

Druid6900
January 19th, 2011, 07:35 PM
I think I have some of the Apple II+ keyboard decoders (if they are the same as the North American ones) and I may have a F0 ROM from an incomplete set (not sure if it's Applesoft but the number will tell)