Apple IIs (load of old) progress report

[tezza]

These old Apples IIs are not proving easy to ressurect, even with the welcome assistance of several folk on here. The good news is the IIe Platinum has been diagnosed and only needs a replacement ROM, which I've ordered. It's also cleaned up quite well so that's one down.

However, the 5 II+s are another story. None of them fired on power up. Checking the boards, I found two of them had missing components (transistors, capacitors). Some of these looked as if they had just rusted and snapped off. Many of the ICs had rusted legs which just fell off on extraction.

Anyway, cleaning and mixing and matching I've ended up with three workable (clean) boards with all components present and three working PSU (and three clean undamaged cases and keyboards). The Apple II Europlus and two clones. Unfortunately none of them work. They all come up with garbage screens and don't get to the beep. As none of them work, I can't simply do a chip substitution. I suspect several RAM chips might be at fault, and not just one in each unit.

One approach to checking RAM would be to use another working (good) type that uses the same type of RAM as the test machines so I can sort the good RAM from the bad RAM. I've got three computers of this type but using them is not straightforward. The Osborne is a little flaky and I want to avoid using it as a test machine, the TRS-80 model 1 is pristine and I don't want to touch that if I can avoid it and the System 80s all have piggy backed chips with changes in the circuitry so it's not just a case of substitution.

If only I could get one Apple II+ working, I would be able to diagnose all three.

I think I need to delve into the literature and get to know the electronics better. I've got plenty of books which deal with the hardware. It's just a learning curve I was hoping to avoid.

Tez

 

[mwillegal]

Hi Tez,

If the video display is stable, your DRAM should be ok, though there is the still the possibility of bad bits. Once the machine is up, you can run a DRAM test, such as the one included in the programmers aid ROM. Connect a speaker and see if you are getting a beep when powered on. The power on beep routine is called almost immediately after boot. If not beeping, the processor is having issues reading and writing memory.

Most likely source of problems is the address decoding logic, but this can be tricky to figure out, without the right tools. I've had lots of issues with flakey sockets on these old boards due to the poor quality sockets that Apple used. This is more likely than a having a bad chip, though either or both is possible.

Check my web page at http://www.willegal.net/appleii/appleii-repair.htm

If you are going to spend much time on this, I high recommend finding an oscilloscope of some sort to debug with. Otherwise you are kind of shooting in the dark. I took a chance on an old 100 MHZ tektronix 465 that was listed on eBay. It had a broken switch and some broken knobs, but otherwise worked fine. I found replacement knobs and fixed the switch. In total it cost me about $120. These devices can also be found at local Hamfests/swapmeets.

I have enjoyed working on the old Apple gear with the same tools that WOZ and company would have used. However there are also very good USB based digital oscilloscopes/logic analyzers on the market that can be obtained for fairly small money.

Regards,
Mike Willegal

www.willegal.net

 

[tezza]

Hi Mike,

Thanks for the advice. I think an oscilloscope (and learning how to use it) is going to be necessary at some stage, and not just for the apple. I'm getting quite a few of these old machines now.

At least practically all the chips in the Apple II+ ARE socketed, a far cry from what we see now. This also makes repair very possible, assuming a correct diagnosis can be made.

Tez