Philips 46PFL5507 - Q552.4E - DPS130 - dead stand-by - shorted ceramic C910 - open resistor R915 - dead chips DDA010, ST9M101

This Philips did not do anything once plugged in. Not even the stand-by light was on. That's a pretty clear indication of a broken standby supply. I could not measure any voltages coming out of the power supply and quickly concentrated on debugging the stand by circuit.

That was pretty tough. I found out that the PWM chip did not have its required VCC activation voltage. The reason for that was the open 2.2 Ohm fuse resistor R915, which is connected directly to the main capacitor's V+. The diodes all measured ok. The PWM chip had no short, neither had the line, which the resistor was connected to, so I soldered in a 2.2 Ohm resistor to check.

Booom! It took a fraction of a second to kill the new resistor. How is that possible? There was no measurable short and neither did I find any burn marks anywhere.

After some intensive research, I found a schematic in a Russian forum thread, which fit my power supply model DPS-130 well enough. The only component left, which could cause a short, was the capacitor C910. A 1kV 22pF thingy, which did not look suspicious at all. I unsoldered it and voilà! No reading. It was dead, but not with a measurable short. My DY294 transistor tester confirmed the high voltage instability. Amazing how it did survive without any burn marks.

For a quick and dirty test I replaced the cap with a 4kV 33pF and the open resistor again. Supply not working. At least the short was fixed. Thus, the PWM chip must be broken, too. It still did not charge the starter capacitor (which tested ok, by the way) with Vcc. It is responsible for starting itself up once V+ is present at its drain pin. After the startup phase, it would feed itself through a secondary winding in the transformer.

I ordered 22pF 4kV caps via eBay and DDA010 chips via AliExpress. Three weeks later, the DDA010 arrived. I swapped it and the 22pF cap. Supply still not working. The PWM chip did not build up its Vcc startup voltage. I measured again. There was a constant 100 Ohms against ground on the Vcc rail. Under those circumstances, the starter capacitor cannot charge!

The only suspicious part left was IC902, an ST9M101. The original is impossible to find. The alternative part number is Infinno IM1M101-T6G. The documentation of this chip is ridiculous. It is used to sense the presence of the high input voltage. It can disable the PWM chip.

A jumper wire was conveniently located between the PWM VCC line and IC902. I opened it up and finally, the PWM chip was starting. However, it rebooted in a loop. IC902 was definitely defect, too (or maybe the PWM chip had not been dead in the first place). IC902 is also connected to the FB (feedback) line of the PWM chip and I assumed it was causing some trouble there, too.

Ok, another order from Aliexpress. On eBay there are repair kits available with DDA010 + IM1M101 pairs.

Enough with the blondes already, hallo Frau Green!