uKenbak-1 Assembly Troubleshooting

[Justin Kusmierczyk]

I just finished assembling my uKenbak-1 and when turning on the first time I got white lights 6-1 illuminated, but otherwise it appeared unresponsive. Unfortunately each time I turn it on, I get a different combination of white lights, nothing consistent. Occasionally the yellow input light will illuminate but only faintly. I have checked and rechecked my work, I’m confident I have the correct orientations and no solder bridges, I also do not feel like I have overheated any component.

Would someone have any suggestions about how to troubleshoot?

[famousd...@gmail.com]

I have never seen that behavior before.  I guess the first thing I would do is try reprogramming the ATMEGE328p.  Do you have an Arduino Uno that you could use for this?  If not, I could send you another preprogrammed chip.

[Ricky Bryce]

I've had similar issues on other projects, and things like that start getting frustrating.  For me, it's usually one of two things:  1)  Be sure the flux is cleaned off the board...  especially around the crystal.  2) Lack of bypass capacitors on the power input to the processor.  I'm not sure if the uKenbak-1 has bypass capacitors, so the first thing I would try is to re-clean the board.  Flux can be conductive.  Also re-check each pin under a magnifying glass for good solder connections, and to be sure you don't have any splatter between the pins.     Sometimes it helps to take a break and come back to it!  Maybe try a "cleaner" power source too if possible.  Recently I put together a Southern Cross that was extremely erratic.  After I re-cleaned the board, it ran fine, and has not stopped since!  The oscillator circuits are very sensitive, and even touching that area of the board will usually cause very strange things to happen.

[Justin Kusmierczyk]

Thank you for the advice. I spent some more time  examing, cleaning, and reflowing without success. I will email Chris and to see if will take a look.

[famousd...@gmail.com]

Are you able to reprogram the ATMEGA328p?  That is the first thing I would try.

[Ricky Bryce]

Can you post some high-resolution images (both sides), just to see if anything stands out on the board?  Sometimes I can look at something a hundred times, and not see what's wrong, but someone looking over my shoulder can spot a problem in seconds.  What voltage are you getting on pins 7&8 of the Atmega328 with the unit powered up?  

On Wednesday, September 6, 2023 at 11:51:32 AM UTC-5 yor...@gmail.com wrote:

[Justin Kusmierczyk]

I am getting .75 volts on pins 7&8 of the Atmega128. I am now consistantly getting the lights pictured below, but I still don't appear to be able to interact with the unit.

[Ricky Bryce]

That's interesting.  I'm surprised you are getting any lights at all if it's just .75v.  According to my understanding, at 16MHz, you would need at least 4.5v to run at 16MHz.   How many volts are you getting between 5v and ground on the USB to TTL adapter?   Can you also check the voltage between ground, and the output of the power switch when it's on?

[Ricky Bryce]

Another test you can do is to check the output of the USB to TTL Adapter with the power switch both on and off.  If the voltage drops significantly when you turn on the switch, there could be a short somewhere on the board that we would have to track down.

[famousd...@gmail.com]

You still haven't answered my question: are you able to reprogram the ATMEGA328p?  That is the FIRST thing you need to try.

On Friday, September 8, 2023 at 4:31:32 PM UTC-5 yor...@gmail.com wrote:

[Justin Kusmierczyk]

I don't have the hardware to program the ATMEGA chip. I am getting 5v on the USB TTL and at the switch.

[famousd...@gmail.com]

You can send it in and I can diagnose it.

[Justin Kusmierczyk]

Thanks Chris working great now. Too bad the final cause remains a mystery.