| Electronics > Repair |
| Prisma elevator door controller, damaged psu, need identify components |
| << < (4/8) > >> |
| Harry_22:
The oscillator frequency according to ST datasheet is around 90kHz. Two chips are currently under consideration: UC3842B max 100% Duty Cycle/ 90kHz drive operation frequency UC3844B max 50% Duty Cycle/ 45kHz drive operation frequency |
| timeandfrequency:
--- Quote from: PiotrMisiuna on December 04, 2024, 07:18:29 pm ---Z13 and Z14 open circuit, tested out of circuit. --- End quote --- Might be high voltage zeners (tens of volts), even if one junction drop should be found in one way : any marking on them ? Package is known as 'melf' https://services.taiwansemi.com/storage/resources/datasheet/ZM4728A%20SERIES_E2301.pdf and wattage seems to be 1W https://www.mouser.fr/c/semiconductors/discrete-semiconductors/diodes-rectifiers/zener-diodes/?mounting%20style=SMD%2FSMT&package%20%2F%20case=MELF Check if your parts size correspond to a 1 W zener in melf package. The circuit around Q32, Z13 and Z14 needs more attention/refinement, because it goes beyond the application note. On this page : - Figure 5 gives interesting information about the required voltage to power the UC3842, but this will be useful later. - Figure 6 explains how most SMPS controllers like the UC3842 are powered : startup power comes from the mains DC rail (about 324 VDC in Europe) via 'Rin'. Once running, an auxiliary winding 'Waux' provides power through D1. Let's go back to your latest schematic. The 'aux winding' is present and the main power for U10 comes from D12, and this seems OK. R114 is probably 'Rin' and even if the paint is peeled off, the value you measured (100 k) is probably correct, because the UC3842 asks for at least 1 mA to wake up. Additionnal information : at 100k, the current is around 3.1 to 3.2 mA, which is more than enough to wake up the PWM controller. R114 seems to be a 2W resistor. However, it is wise to replace the part with a new one. --- Quote from: Harry_22 on December 05, 2024, 03:14:09 pm ---Two chips are currently under consideration : UC3842B max 100% Duty Cycle/ 90kHz drive operation frequency UC3844B max 50% Duty Cycle/ 45kHz drive operation frequency --- End quote --- You are right, and to solve the riddle, the transformer ratio and primary inductance is probably required :palm: |
| Harry_22:
Please check the both zener connection. PS Seems they are the same 18-20V to get 17.3-19.3 start at Vcc. |
| PiotrMisiuna:
:palm: yes, you are correct. I need to stop making this edits at 1:00am. as to the transformer, it has a sticker, no meaningful results in the search engines thou. markings at the top just refer to the type of the core. |
| timeandfrequency:
--- Quote from: PiotrMisiuna on December 05, 2024, 10:25:56 pm ---as to the transformer, it has a sticker, no meaningful results in the search engines thou. --- End quote --- Yes it is for sure a custom made part and we won't find any datasheet. If we really need to know the transformers' ratio and primary inductance to validate the PWM controller reference, those intrinsic parameters have to be measured... :scared: |
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