IMSAI 8080 Stopped Working Suddenly

[dcmiller8]

Good morning!  My IMSAI 8080 replica suddenly stopped working properly this morning. It worked properly since it was assembled, but suddenly this morning it is not responding to the keyboard in the interface. I am able to load disks and check the library, and I confirmed the boot settings were correct. Sometimes all the lights will just go out and the console will say the system is offline and try to reload unsuccessfully, and sometimes it shows the lights as though it's running, but I get no response from the terminal and no keyboard inputs are accepted. I have reset using the button on the back of the device and even changed the boot configuration, but still no success.

Is this a known problem with an easy fix or has the hardware suffered a failure of some sort?

Any help will be appreciated.

[Dale Chatham]

You say it has worked "since it was assembled".  How long is this?

Here is a google search with images of cold solder joints:

https://www.google.com/search?q=cold+solder+joint&client=firefox-b-1-d&sxsrf=ALiCzsZOnQwEcdvV3ysiwiP0w5oJebQlUQ:1666356588465&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiG35iErvH6AhWRrmoFHRAbCFgQ_AUoAXoECAEQAw&biw=2176&bih=1150&dpr=1

If all else fails, reheat all solder joints and see if that fixes it.

Suspect cold solder joints. 

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[dcmiller8]

It was assembled around September 5, 2022. I used it daily until this morning. I did take it apart and look for cold solder joints (we are a full electronics repair facility and have all of the soldering equipment for SMD and through-hole and desoldering stations) under an electronic microscope and I checked the connections for continuity with our meter but no trouble was found there. I don't know enough about the design to be able to troubleshoot much further. I did test the socketed ICs with our test equipment (which, surprisingly, isn't always accurate as we've checked several TRS-80 Model 3 and 4 units and chips that tested bad were actually good the next time we tested) and they all tested as good. I haven't done a full component-level diagnostic, as I was hoping someone may have had a similar experience and could point out the problem. If it's something internal to the ESP32, then I wouldn't know what to look for there. The confusing part is that the ESP32 unit is at least functioning partially, since wifi is functioning, I get the GUI interface on the computer, can load disks, view the library, the manual and control front panel switches. I also noticed that sometimes just putting it into "RUN" when not connected to the external computer via wifi will cause the unit to shut down completely, requiring a full reset using the reset button on the ESP32. Sometimes it will run again after that (but still no terminal or keyboard response), and sometimes it will just shut down again. The same happens when run from the external computer via wifi. I'm not sure it can be a software issue, since nothing was done to the software that came on the unit. (No updates installed.) With that said, I am a hardware person, NOT a software person. I wouldn't even know how to begin to install an update to the software.

Thank you for the suggestion, it was a very good place to start looking for trouble. I can't tell you how many televisions, radios, computers, etc. that we repaired by reflowing the solder.

[steve...@gmail.com]

Just a suggestion ...

Check to make absolutely, 100% certain that the IMSAI 8080 is getting adequate DC power. Flakey behavior (which seems like what you describe) is a common symptom of inadequate DC power in the IMSAI. Many previous builders wrestled with problems caused by poor DC power, including me. I couldn't and wouldn't guarantee that it is your cause, but it is a distinct possibility. Eliminating it as a cause can be an important early step in getting you back on the air.

Good luck, I hope this helps,

-- steve

[dcmiller8]

Good morning!  Thank you for the suggestion to check the DC power. I've confirmed that the power is good and swapped with another supply which also tested good. Unfortunately, my IMSAI 8080 is still malfunctioning.

There doesn't seem to be much support for this type of issue and I seem to be the only one experiencing it, which leads me to believe that it's a hardware malfunction specific to my device.

Not much I can do at this point, should I send it to the curb for recycling or are there any other suggestions that perhaps I haven't tried?

[csh...@gmail.com]

Have you tried resetting the NVS?  Changing the logging level from "full" to "none" and back again?  

Any chance anybody changed your wifi password?  You mentioned "we" are a shop, maybe there's more than one person around?  

If anything is bad, the most likely place would be the ESP PICO board... fortunately they're not very expensive to replace, but you'll have to reprogram the bootstrap and whatnot and you've mentioned that's not your area.  Though if you're using the CP/M command line on your IMSAI, and if you assembled you kit... you're more than qualified.  

Good luck.

[Le Fauve]

Disclaimer, I'm not an expert, but when my IMSAI stopped working, it was caused by an error on the SD card, so it may worth trying to re-image it, or replace it.

Since you can access the web interface, this can be done easily by drag'n dropping the correct image file (update.bin) on the SYS: icon.

At the next reboot the image should be regenerated (you may want to save any disk image on which you have created/modified file before this, though, as I'm not sure how this is handled by the update process)

If it still doesn't work, you may try to reflash the ESP32 too (that worth a try before trying another ESP32 board).

Everything I know about reflashing can be found on this page: https://thehighnibble.com/imsai8080/update/#updating-the-%C2%B5sd-card-image

Good luck!

Eric