I completed assembly of 12 TTKS units over the weekend. My initial testing was that 8 units worked as expected. 2 units needed the filter capacitor on the power supply changed from a 1uf to 4.7uf 50v electrolytic capacitor. I’m unsure as to why these two units were seeing more noise, but it was a simple fix. The final design would not work with a 1uf ceramic capacitor and was exhibiting symptoms of IC noise.
One unit appeared to have a bad LiteOn LTS4301JG. I thought this was odd, but de-soldered the unit and replaced it. The replacemend 7 digit LED did the same thing. I resoldered the Max7219CNG and the 4 digit 7 segment LED and was unable to eliminate the issue. I’m going to assign that one to a damaged or defective trace somewhere on the board. The purple soldermask makes it almost impossible to make a detailed inspection, so I put in the bin of bad memories. I keep a bin with all my prototype and defective units in it.
The 4th unit shows no signs of what is wrong with it. It simply will not power up. No telling what the deal is and I’m opting to junk it instead of tearing it apart to find why it won’t power up. Everything on the board looks just fine, so I am thinking perhaps I damaged an IC. I was having some problems with heat transfer on the soldering iron the other day. I finally turned the heat up on it which helped, but I think the unit is just ready for replacement. It’s possible I stayed on a pin too long and burned the IC.
I did manage to salvage my last prototype unit. This unit was production ready but exhibited the power instability. I replaced it’s capacitor with a 4.7uf unit and it works just fine and passed programming and testing just fine. It does have a minor difference in the input, so I’ll send it to my Dad who had ordered one of the units on Kickstarter. I know he won’t be using the input on it so it won’t matter. Everything else is identical and functional.
While some would consider this dirty laundry and hide it, I consider it just part of developing electronic products. Anytime you manufacture something you are going to have failures. It’s nice to be able to pinpoint the cause, but it’s more important to have quality checks in place to make sure you ship good product. Sharing the ups and downs will ultimately help others who want to assemble kits and make products.