Apple II (Rev. 7) only showing garbage at power-on, any tips?

[Huxley]

Hi all! A while back I picked up this gorgeous Apple II from a Craigslist seller. He'd received it from a family friend who worked for Apple back in the 80's, and I think it's an original Apple II case with a II+ Rev. 7 motherboard inside, but I'd love to be corrected if I'm wrong! The model tag on the underside reads "A2S1."

The seller mentioned that he was told that the last time it was used there had been some smoke from the power supply side of the machine - it was shut down, packed away, and not touched for ~30 years. With this in mind, I've decided to get it up and running again. As a precaution, my first steps were to give it a quick blow-out with my handheld air blower, and to install a brand new ReactiveMicro power supply.

The machine is remarkably clean overall, with no obvious signs of damage, abuse, liquid exposure, etc. It does look like the original owner was at least somewhat 'crafty,' as there's a tiny toggle switch installed in-line with the speaker, which I'm assuming is effectively a "mute switch."

Here's the dilemma: with the new PSU installed, when I power it on it will display a pattern of random text, blinking/flickering blocks, and/or shifting garbage.

• It has never beeped during any of my tests, although at this stage I can't vouch for the functional condition of the speaker and/or the DIY mute switch.
• Removing the Disk II card and/or shifting it to other slots seems to result in a new/different garbage pattern on screen.
• I've used some cotton swabs to carefully dab a bit of De-Oxit Gold onto the legs of every socketed chip I can reach (I haven't disassembled the machine fully, so I can't get to the ones deep under the keyboard yet).
• I've re-seated all the socketed chips - ROM's, RAM, CPU, etc.
• I've left it powered on for a few minutes and felt around the board - the CPU, ROM's and RAM get warm, but I'm not detecting anything I'd describe as "concerningly hot."

Here's a simple album with pics. Any idea what would be a good next step to troubleshoot and restore this machine?

 

[Arbee]

If you have an oscilloscope or logic analyzer that would be the best way to start zeroing in on what the problem is. From the screenshot we can at least tell that the master oscillator is running and the video circuitry is working, but the CPU appears to not be running.

Also, that machine definitely has an interesting history of some kind. From the date codes on the chips the board is from roughly mid 1981 but the ROMs are dated 1983.

 

[bibilit]

Can be a lot of things, but you can start with basics.

Only the bottom row of ram chips is required (the one next the keyboard) for a start. So remove all chips and only keep the better looking ones.

Can be a Rom issue also.

 

[Arbee]

Could be the bus transceivers next to the 6502 also. Adrian Black had a video about a year ago where that (among other things) was the problem. On a 40+ year old machine even the "reliable" standard TTL chips can fail.

 

[bibilit]

I agree with Arbi, but not easy when you only have one unit to play with and no spares to swap

 

[Huxley]

I return to you with a wonderful update: the Franken-][ lives!

I’ve been out of town for a week or two for work, but before I left, I put a little detox into every chip socket on the board and you just let it sit. I plugged it all back in tonight to resume tinkering, and I was getting the same issue as before, until I went through and carefully re-seated every chip on the board. Suddenly it’s booting up and running diagnostics with no faults detected!

View attachment IMG_0160.jpeg



It does still seem suspiciously, flaky at times, so there may be more work to be done, and also I cannot get any sound out of the speaker at all. Nevertheless, I am delighted that it seems mostly functional!

Thank you all for the helpful advice and suggestions