Philips Air Fryer XXL (HD9654/90) Heating Issue - Seeking Advice - Page 1
Forum section: electronics / repair

author: w0nk1
author_rank: Contributor
timestamp: October 26, 2023, 01:27:10 pm
content: I'm facing an issue with my Philips Air Fryer XXL, model HD9654/90. Here's a breakdown of the problem:Startup:Upon powering on and setting a temperature (e.g., 180°C for 2 minutes), the display immediately shows 5 dashes.Fan Activity:The fan begins to spin, suggesting the unit is trying to start the cooking process. However, there's no heat being produced.Unresponsiveness:After a short period, the fan stops, and the unit becomes unresponsive. I have to unplug and replug to reset it, but the heating issue persists.Thermal Fuses:I've checked them, and they're intact, showing continuity.Temperature Sensor:When unplugged, it reads around 150 kOhm and decreases when exposed to a heat gun. But when connected to the PCB, I measure 220 Ohm at the connector, and this value doesn't change significantly with heat application.Given these observations, especially the unusual behavior of the temperature sensor when connected to the PCB, does anyone have insights or suggestions on potential causes or solutions?Any advice would be greatly appreciated. Thanks in advance!

author: Swake
author_rank: Frequent Contributor
timestamp: October 26, 2023, 02:44:32 pm
content: 150kOhm is a high value for a NTC sensor but it exists. As you say that resistance is reducing when heat is applied that sensor seems ok. Try searching for the specs of a spare part of that sensor and see if it matches what you measure.Not heating might be caused by a blown thermal fuse. Frequently found near the heater.

author: w0nk1
author_rank: Contributor
timestamp: October 26, 2023, 02:54:37 pm
content: Thanks for your answer! I checked both thermal fuses and they are fine. I accidentally touched the heating element during the "on" period and got a little electric shock, so I assume this is not the problem.According to the official FAQ page:https://www.philips.sa/en/c-f/XC000006976/the-display-on-my-philips-airfryer-shows-5-or-6-dashesIt is an overheating issue, which obviously makes no sense, but it could explain why it is not doing anything when it thinks it is already overheated during the startup.I don't understand why the Ohm value of the temperature sensor won't change when it is plugged to the PCB. It is always 220 Ohm, even without the sensor plugged into the connector. Could this be the right behavior?

author: Swake
author_rank: Frequent Contributor
timestamp: October 26, 2023, 03:26:57 pm
content: Quote from: w0nk1 on October 26, 2023, 01:27:10 pmQuote from: w0nk1 on October 26, 2023, 02:54:37 pmIt cannot be two things at the same time.If the sensor is 150 kOhm on its own and the PCB reads 220 Ohm without the sensor plugged in, then yes it is normal to measure just half an Ohm less than those 220 Ohm when the sensor is plugged in (assuming it is all resistive). This is a parallel connection of resistors. R = R1xR2 / R1+R2Should the sensor read 150k? It sounds somewhat high, but plausible, plenty of different models out there.Should the PCB connector measure 220 Ohm? This measurement is not very relevant. Depends on the circuit, can be totally different ones powered. But it is very low compared to the sensor indeed and that doesn't make the measurement any easier for your frier.Do you have a schematic, or can you trace it somewhat around that connector? Can you post pics of the thing?Do you have a variable resistor of about 150 kOhm to simulate the sensor; higher resistance is good too?

author: w0nk1
author_rank: Contributor
timestamp: October 26, 2023, 04:16:38 pm
content: QuoteIt is always 220 Ohm, with the Sensor plugged or unplugged.The Sensor alone reads at ~21 °C the mentioned 150 kOhm. I found some replacement parts for a similar model => 200 kOhm NTC temperature probe.QuoteUnfortunately, I have no schematics, but I attached a picture of where the temperature probe connector directly goes. All resistors in the image I checked are fine and in range. The caps had no shorts, but I don't know their values. It looks messy because I desoldered them out of the circuit for measurement - sorry for that.QuoteI tried a 200k potentiometer, but no difference at all.

author: fzabkar
author_rank: Super Contributor
timestamp: October 26, 2023, 05:18:49 pm
content: If the sensor is really reading 150Kohm, and if it is an NTC type, then a reading of 220 ohm would correspond to "very hot". This means that there is something wrong with the 220 ohm reading. Or am I missing something?

author: w0nk1
author_rank: Contributor
timestamp: October 26, 2023, 05:45:12 pm
content: Quote from: fzabkar on October 26, 2023, 05:18:49 pmI would definitely agree! But I have no clue where it comes from! :-/

author: fzabkar
author_rank: Super Contributor
timestamp: October 26, 2023, 10:22:41 pm
content: What is the resistance of C106? If it is 120 ohms, then there is your culprit.What is the resistance between R107 and the other end of R108?

author: w0nk1
author_rank: Contributor
timestamp: October 27, 2023, 06:47:02 am
content: QuoteIt is indeed in between the 115 - 120 Ohm range! (Measured in the circuit)Your conclusion seems to be correct. ^^QuoteFrom the right side ofR107to the upper pad ofR108, it is~220 Ohm.From the left side ofR107to the upper pad ofR108, it is~124 Ohm.BTW: The value for theR107is101. The red circle in my previous post's image hid the last digit.

author: fzabkar
author_rank: Super Contributor
timestamp: October 27, 2023, 09:24:54 pm
content: I think C106 is faulty.

author: w0nk1
author_rank: Contributor
timestamp: October 28, 2023, 01:21:25 pm
content: Quote from: fzabkar on October 27, 2023, 09:24:54 pmDo you think it is safe to remove it, or do you have an idea of a replacement value? Thank you so much for you support!

author: fzabkar
author_rank: Super Contributor
timestamp: October 28, 2023, 06:05:57 pm
content: I think the capacitor is probably filtering noise. You could at least remove it and confirm whether the low resistance goes away.

author: w0nk1
author_rank: Contributor
timestamp: October 29, 2023, 09:31:57 am
content: Quote from: fzabkar on October 28, 2023, 06:05:57 pmI desoldered it, but unfortunately, it is still 220 Ohm. This is driving me nuts!

author: Swake
author_rank: Frequent Contributor
timestamp: October 29, 2023, 09:46:59 am
content: 'More' information is needed. Please trace into a schematic the components from the connector up to the PIC.The picture that you have posted shows via's and traces going of screen and as component numbers are not sequential there is much more on that board.

author: w0nk1
author_rank: Contributor
timestamp: October 29, 2023, 02:52:00 pm
content: QuoteI tried to come up with a schematic (I am not an expert) and added Front and Back side images of the complete board.Can I do something else to clarify things?I am very happy that so many are willing to help me; thanks! ;-)

author: Swake
author_rank: Frequent Contributor
timestamp: October 29, 2023, 03:39:18 pm
content: Did just a quick check, have not much time right now but wanted to share this small finding:One side of the sensor is on the GND. The red circle you have drawn on the bottom side of R108. It is connected to pin 29 on the PIC, and also connected on the right side of R108 under the letter R there is a via, on the other side of the board it is clearly ground plane.The other side of the sensor is the red wire on the connector, right?

author: fzabkar
author_rank: Super Contributor
timestamp: October 29, 2023, 05:11:52 pm
content: I would think the top side of the voltage divider for the temp sensor would be connected to Vref+ (PIC pin #2) via another resistor. Perhaps Vref+ is shorted to ground???R108 is a 10 ohm resistor. I would measure the resistance between ground and each end of this resistor. This will tell you which side of the resistor the short is on.

author: w0nk1
author_rank: Contributor
timestamp: October 29, 2023, 05:20:27 pm
content: QuoteMeh, I have seen, that I got an error in the PIC pins labeling, it was the wrong side. I updated the schematic. The pins are:33 - 23.Thebottomside ofR108is connected to pin34of thePICand it is indeed connected toGND.QuoteYep, and the wire beside it, is the other pin of the temp sensor.// edit: BTW: I added an image of the PIC datasheet and hope it is the right one.

author: fzabkar
author_rank: Super Contributor
timestamp: October 29, 2023, 06:18:42 pm
content: I think pin #27 of the PIC is leaking to ground internally.

author: w0nk1
author_rank: Contributor
timestamp: October 29, 2023, 06:34:51 pm
content: Quote from: fzabkar on October 29, 2023, 06:18:42 pmThis would mean the MCU itself is dead, right?

author: fzabkar
author_rank: Super Contributor
timestamp: October 29, 2023, 06:43:48 pm
content: Quote from: w0nk1 on October 29, 2023, 06:34:51 pmYes, I can't see any other possibility.

author: w0nk1
author_rank: Contributor
timestamp: October 30, 2023, 08:44:00 am
content: Quote from: fzabkar on October 29, 2023, 06:43:48 pmThis is such a pitty!BTW: I desoldered thePICand now I measure something around9 kOhmand it is changing when applying heat to the temperature sensor.

author: Swake
author_rank: Frequent Contributor
timestamp: October 30, 2023, 08:49:17 am
content: I have no better conclusion unfortunately.A last chance is to replace the PIC but that would require that you can read it out. I would guess they set the protection bits on this one to make that impossible. Don't know much about PICs, there might be ways to circumvent that.

author: w0nk1
author_rank: Contributor
timestamp: October 30, 2023, 09:21:15 am
content: Quote from: Swake on October 30, 2023, 08:49:17 amOkay, thank you guys! Not sure it if makes sense to go into this rabbit hole - but we will see! ;-)

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 30, 2023, 01:04:07 pm
content: Controlling an air fryer isn't exactly rocket science, could probably just have the fan be constantly running and install a generic PID controller to regulate the temperature.

author: w0nk1
author_rank: Contributor
timestamp: November 26, 2023, 04:47:24 pm
content: Quote from: NiHaoMike on October 30, 2023, 01:04:07 pmSure, it is not, but I don't want to create "Frankenstein".I tried to dump the firmware with a PicKit 3, but of course, the read protection for the program code is active on the IC. I can dump the EEPROM part, but won't this help much? Any ideas to get around this, maybe glitching it with "easy" methods?