Dual output flyback configuration with LNK304GN not starting - support needed
Posted by: jorgemef
on
Hello,
I am attempting to repair a Fridge CPU (KG36VVL30S.11). It had the resistor fuse blown and the LNK304GN shorted.
Replaced both with local store part but still not working. Checked all caps and resistors from the flyback and all checked good.
The polarized caps are with low ESR (~1ohm @10kHz and with right capacity).
Tried multiple thing but no go. The board is working with an external solution for the 9V and 5V rails with 250 mA for the 9V (powers a relay plus DC-DC converter for the 5V rail) and 350mA (powers CPU, circuitry and appliance led) for the 5V rail. So all seems normal as a load.
I am attaching the signal levels I could read on a multimeter and the reverse engineered schematic. Any hint on the culprit?
Cheers,
Jorge
Files
| Attachment | 大小 |
|---|---|
| DC signal at 5V rail. | 1.43 MB |
| DC signal at 9V rail. | 1.28 MB |
| Signal waveform at LNK304 FB pin. | 552.35 KB |
| Oscillation waveform taken at D pin. | 5.47 MB |
| Picture of the board flyback layout. | 1.4 MB |
| Reverse Engineered Schematic | 31.21 KB |
Local store part? It looks like the supply is trying to start up. Check the 4.7 uF input bulk capacitors to see if they are still good. .If those have dried up, the power supply might not be able to start.