| Electronics > Repair |
| BERNINA power supply board (Switch Mode) issue diagnosis and beyond (fixed) |
| << < (11/15) > >> |
| max.wwwang:
--- Quote from: tautech on December 22, 2024, 07:50:37 am ---Stick this in your datasheet records: https://www.ti.com/lit/ds/symlink/uc3844.pdf --- End quote --- Readling closely this very moment. :popcorn: |
| max.wwwang:
--- Quote from: tautech on December 22, 2024, 07:45:15 am ---Variable PSU and a current limiting resistor normally finds reverse breakdown voltage with little fuss. --- End quote --- Gotcha. This requires it to be taken off the board if I understand correctly. --- Quote from: tautech on December 22, 2024, 07:45:15 am ---Connectivity issue somewhere or something intermittent with the diode or its snubber. There's really not much to check in a standalone winding on the secondary side. --- End quote --- If the secondary side is all good, i.e. problem is on the primary side, is it possible to have all other voltage rails working like a dream with only one rail scrap? I just don't understand how this is possible. |O --- Quote from: tautech on December 22, 2024, 07:45:15 am ---If nothing is obvious get out the magnifying glass. A little story about a MIG welder I repaired years ago after it had taken a fall..... Seemed simple enuf in that a small PCB mount transformer that provided control supply was only mounted by its through hole pins and in the fall the transformer had yanked on one and broken the fine copper to the primary. Poor construction not having a zip tie around it so to not rely on just the pins. |O Anyways, seemed an easy fix as RS had the exact transformer so it was briefly tested and sent back to the customer. A week later it was back and on further inspection a few cracked solder joints were found and repaired on the SMD part of the PCB. All was well one would think but another week later it was back ! :palm: After spending ages looking for cracks none were found then a EE buddy suggested I flex the PCB and listen for clicking. Sure enuf clickity clack all day long. I ended up hand reflowing every component on that PCB and never saw it again. :phew: --- End quote --- Key word is magnifying glass, and potentially physio therapy (which I found useful in one project). Gotcha. :popcorn: |
| inse:
--- Quote from: tautech on December 22, 2024, 07:45:15 am ---Sure enuf clickity clack all day long. I ended up hand reflowing every component on that PCB and never saw it again. :phew: --- End quote --- Or the owner became tired of sending in the unit all the time… 😉 |
| tautech:
--- Quote from: inse on December 22, 2024, 08:38:28 am --- --- Quote from: tautech on December 22, 2024, 07:45:15 am ---Sure enuf clickity clack all day long. I ended up hand reflowing every component on that PCB and never saw it again. :phew: --- End quote --- Or the owner became tired of sending in the unit all the time… 😉 --- End quote --- :-DD Nah I inquired a few times over the next few months and confirmed I'd won ! :phew: |
| inse:
--- Quote from: max.wwwang on December 22, 2024, 08:12:13 am --- If the secondary side is all good, i.e. problem is on the primary side, is it possible to have all other voltage rails working like a dream with only one rail scrap? I just don't understand how this is possible. |O --- End quote --- Don’t waste any thought on the primary side, the flyback transformer is just like a normal iron core transformer: no secondary voltage at all: primary (circuit) broken One secondary voltage missing: secondary (circuit) broken. Don’t make it more complicated than it is… |
| Navigation |
| Message Index |
| Next page |
| Previous page |