Miele elp165-s motherboard after tny278GN replacement not starting - Page 1
Forum section: electronics / repair

author: PiotrMisiuna
author_rank: Contributor
timestamp: December 12, 2024, 09:06:47 pm
content: I'm braking my head over this one for weeks now. Maybe someone had similar case.Miele washing machine main board. They come in many different flavors and most of their PS are build around some version of TNY.I replaced the chip as well as the 120Ω resistor, measured every single component on the board and nothing seams to be out off.TNY in this configuration is driven without an optocouppler,I get mains passing filters to the main DC capTNY produces internal 5v so I assume is good.on the output of the transformer after rectification I get around 1V. only 0.3v gets to the pin 1 of TNYI checked with thermal camera, nothing gets hotI applied 12v to the KF50, draws 0.025A, regulator works fine giving 5V on the output.Any idea what can cause it to work this way?

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: December 14, 2024, 11:26:22 am
content: Hello PiotrMisiuna,I had a look to theTNY278 datasheetandapplication note.IMO, PI devised a really complicated chip :- EN/UV (pin nr 1) has dual function- BP/M pin (pin nr 2) has 3 simultaneous functionsAmong 75 pages of documentation, the sole clue about an implementation without an optocoupler isFigure 28.Miele probably designed his own schematic around the TNY278 without an opto on the BOM : 20 Cents saved per boardThis would be more than a day harship to fully understand how this chip works and what are every possible reasons that avoid the full start, or entering into protection or hiccup mode.Quote from: PiotrMisiuna on December 12, 2024, 09:06:47 pmNot sure : internal regulator (pin 2) should provide 5,85 VDC and below 4,9 VDC it triggers shutdown.If you mesure 5 V, it's weird.Q1) Check again the voltage at pin 2Q2) Try to mesure VBias (seeFigure 28)Q3) Can you probe the drain (pin 4) with an isolated scope or differential high voltage probe to check if the IC hiccups ? (normal mode : switching around 130 kHz)Q4) Did you check if the board behaves differently when inserted in the appliance ?Q5) Is the UL339 (LM339) somewhat involved in monitoring/controlling the TNY278 power supply ?(follow the tracks to see how it is interconnected)Q6) Are there parts on the other side of the PCB ?Q7) How many windings does the ferrite transformer have ?Q8) Did youringit ?I'm wondering if would not be easier to bypass the TNY278 power supply by using an external 12V SMPS.Q9) Can you try to check if the appliance works when feeding the board with external 12 VDC ?Using a lab power supply to perform the test would also allow to mesure the current drawn. Table 16 in the AN says 21,8 W max for the TNY278. A 2 A SMPS should be sufficient.Some external 12 VDC 2 A SMPS :https://www.reichelt.de/de/en/plug-in-switching-adaptor-24-w-12-v-2-0-a-hnp-24-120l6-p177030.htmlhttps://www.reichelt.de/de/en/switching-power-supply-25-2-w-2-1-a-12-v-snt-rs-25-12-p137085.html

author: PiotrMisiuna
author_rank: Contributor
timestamp: January 04, 2025, 09:17:16 am
content: I'm trying to reverse engineer the schematic but I'm a novice. The figure in the datasheet you pointed It is most probable application here, but I still don't see the resemblance in the pcb, ItI will post here anything meaningful.LM339 seams to only be related to the signals from other components.When inserted into device it remains in the same state. This model has a soft switch and I took it into account. It seams to me, thou the tny278 psu circuit wold be required to run for the micro controller to receive the signal through an optocouppler. (bottom left).The only scope I have is a joke - DSO shell, it is isolated, but I have zero confidence in it. I didn't made a ring tester yet. Before Digging into the transformer is a bit intimidating for me, I probably will do it eventually. First I want to learn as much from it as possible.Nothing on the other side. I made some better photos of both sides, I will post it with my schematicBypassing this psu is indeed what I consider as a final solution.I do not rush with this repair.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: January 04, 2025, 12:15:50 pm
content: Hello PiotrMisiuna,Quote from: PiotrMisiuna on January 04, 2025, 09:17:16 amIt is reasonable to think that this PS is always active, just waiting to wake up the microcontroller.Great, continue posting at your own pace, we're not in a hurry.Yes, there are two optocoplers at the bottom of the board : possibly PC813 or PC817.As you rather often dig into live circuits repairs, using a truly isolated oscilloscope would definitely keep you on the safe side, and this is far preferable than a vanilla scope + high voltage differential probe.Unforunately, such TE is really expensive and good second hand stuff is not easy to procure. So, it's truly an investment for safety and work efficiency.The less expensive without any serious flaws are probably those fromSiglent. They come with two isolated probes (*).(*) Probably something similar tothis one.