Thermomix is a popular kitchen "robot" in Europe. There're a few models (TM21, TM31, TM5). They're very expensive machines, and they cannot be bought at a normal home appliances shop. I'm trying to fix an issue with a TM21 unit.
Main problem was that temperature selection wheel was unstable. It's a 22KΩ linear potentiometer that lost contact easily, specially with appliance vibration while working. It's a Piher PC-16 bushless version.
I opened the pontentiometer and cleaned it. Now it's stable but the machine keeps doing something incorrectly (it did the same before). The temperature selection wheel has 10 positions (0, 40, 50, 60, 70, 80, 90, 100, Varoma). At 0 position it doesn't heat, and from 40 onwards it has to activate heater and the orange/red LEDs at temperature wheel side.
Well, the problem is that this one only activates heater and LEDs from position 70 onwards. On 40 and 50 it does nothing, like still at zero position.
I have another unit of TM21 to compare, and I'm tired of testing things (swapped potentiometers, tested voltage drop at potentiometer, etc.), always the same problem and no significant phisical differences between both boards. Finally I've noticed something curious: these units carry a 1Kbit EEPROM ST M93C46-BN6T. The controller is a NEC µPD78043FGF-060, it only has ROM, nothing programmable here. These appliances have no user data to store. Nothing can be programmed, recorded or customized. It wakes up the same way every time you turn it on. Why does it need an EEPROM?
I've tried to answer myself: I've put EEPROM IC from working unit to the other and the problem is gone!
Theories: since potentiometers used to select Temperature and Speed have some tolerance, perhaps there's some factory mode where the top and bottom voltage readings from the potentiometers are stored in the EEPROM.
I'm considering to get an EEPROM programmer and clone the data from the working unit into the trouble unit. If there's a factory calibration mode, I don't know how to enter it. I see no hidden buttons or open bridges. If it exists, it must be some funny combination of button presses.
Main problem was that temperature selection wheel was unstable. It's a 22KΩ linear potentiometer that lost contact easily, specially with appliance vibration while working. It's a Piher PC-16 bushless version.
I opened the pontentiometer and cleaned it. Now it's stable but the machine keeps doing something incorrectly (it did the same before). The temperature selection wheel has 10 positions (0, 40, 50, 60, 70, 80, 90, 100, Varoma). At 0 position it doesn't heat, and from 40 onwards it has to activate heater and the orange/red LEDs at temperature wheel side.
Well, the problem is that this one only activates heater and LEDs from position 70 onwards. On 40 and 50 it does nothing, like still at zero position.
I have another unit of TM21 to compare, and I'm tired of testing things (swapped potentiometers, tested voltage drop at potentiometer, etc.), always the same problem and no significant phisical differences between both boards. Finally I've noticed something curious: these units carry a 1Kbit EEPROM ST M93C46-BN6T. The controller is a NEC µPD78043FGF-060, it only has ROM, nothing programmable here. These appliances have no user data to store. Nothing can be programmed, recorded or customized. It wakes up the same way every time you turn it on. Why does it need an EEPROM?
I've tried to answer myself: I've put EEPROM IC from working unit to the other and the problem is gone!
Theories: since potentiometers used to select Temperature and Speed have some tolerance, perhaps there's some factory mode where the top and bottom voltage readings from the potentiometers are stored in the EEPROM.
I'm considering to get an EEPROM programmer and clone the data from the working unit into the trouble unit. If there's a factory calibration mode, I don't know how to enter it. I see no hidden buttons or open bridges. If it exists, it must be some funny combination of button presses.
CAPs POOF
Comment