AFK-BM2 Baking Machine Repair
This repair is about the AFK-BM2 Baking machine that no longer baked and was brought in by my nephew. And was from his wife’s parents who hoped we would be able to fix the problem.
The difficulty with these repairs is the problem not being able to find any decent service manual. And finding matching replacement parts often won’t be easy either.
Strangely only the rubber motor drive belt could be found when was searched for matching parts.
But the belt and the motor were fine. Just the not working heater element was the problem here. My brother took it upon him to do the most time consuming part of this repair and disassembled the baking machine, and then I took some of my test gear with me to examine this machine further.
Previous 2 photos showed the front and the backside of this baking machine after the top cover, dough hooks, and the metal baking insert shell were removed. The motor belt under de bottom plate drives the center rotor mount. And above it the square heater element mounted on a vertical placed metal plate is visible plus the also on it mounted temperature sensor with the 2 blue wires including the 2 temp fuses with the 2 x 2 white high temperature resistant wire tubes (2 for TF1, and 2 for TF2).
Above photo shows most of the connectors and parts and their function. Including Temp fuse TF1, TF2, Relay Rel1, and the Heater element connector. The disconnected heater element measured a resistance of about 88 Ohm which represents a power dissipation of (230VAC^2)/88 Ohm = about 601 Watt. And this matches also with the given power consumption on the label of this machine.
To make sure the heater element also worked we connected the heater coil first with a safety light bulb in serie to the 230VAC power line, and after that without one directly onto the 230VAC mains. And it worked splendidly so was not the cause of the not working heater.
I then tested all diodes, transistors, 7805 5V regulator, BT137 and other parts with my Peak Atlas DCA75 Pro, my DMM and other digital meter and all checked out just fine! Also the transformer with marking label AC-XB0001B 220-240VAC 55mA worked splendidly giving a secondary VAC of 12.3V (both white wires to the diodes). And this also fed the 7805 regulator that was fine too measuring an output voltage of 5V DC.
The pcb was marked with text XBM838/938-P02 2004-01-05 KB-3151 130 degrees Celsius.
The blue 2 wire temp sensor measured a resistance of 117.4 kOhm. Temp fuses TF1 and TF2 were placed in series. And first it seemed that TF1 was an open connection (defect), and only TF2 was okay. But after the TF temp fuses were repositioned under the clamp on the vertical metal plate on which also the temp sensor resistor was mounted, both were fine but still the heater element failed to function.
The heater element was switched with a relay marked on the pcb as Rel1 with text: Zanty ZTUC-D12HS 28VDC 15A 125VAC 10A/250VAC 15A/28VDC. Measuring the relay coil resistance gave an open connection so the coil was broken and the relay needed a new replacement. Below the solder side with removed bad Rel1 relay.
Next photo shows the component side with the removed Rel1 relay. D9 is the Rel1 coil diode that protects driver transistor Q8 against high induction voltages.
Also the black big 460V motor capacitor next to the transformer checked out fine! And of course we already knew that the motor was fine too.
Conclusion: after we replaced relay Rel1 with a new 12V coil with 250VAC/ 10A switch (see photo below) the baking machine worked again like a new one. Although we at first were uncertain what relay voltage we needed, because the original relay marking text revealed no coil voltage, we measured about 14.5V DC over the coil diode D9 without any relay attached. Which confirmed we just needed a 12V DC replacement relay.
Above photo on the right shows the baking machine looking in from the top with the cover open.
Previous photo showed another clear view on the solder side of the pcb and the black vertical plastic frame it was connected to with 3 screws. On this pcb the 9 pin top row connector connects to the removed cover with the switches that was fine and housed the processor/controller board.
Afterwards we only needed a new matching relay , solder, the right equipment and a lot of time to examine and check all parts and their function.
In washing machines and dryers the used relays often only have 4 pins. Where pin 5 is left unconnected or just missing like with the original now replaced bad Rel1 relay was the case. But these relays are in function the same because pin 5 often is not needed being the switch pin which only connects when the relay coil is unactivated (off state).
And normally most of the cases only the make contact switch pin is needed when the relay coil is activated anyhow. Which only requires 4 pins being 2 pins for the relay coil and 2 pins for the make switch contact.
This article now will certainly be a great help for those in need for the right information to also fix their AFK-BM2 baking machine. Information that couldn’t be found on ElektroTanya or any other site where normally many different service manuals and schematics are kept.
Albert van Bemmelen, Weert, The Netherlands.
Please give a support by clicking on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.
P.S- If you enjoyed reading this, click here to subscribe to my blog (free subscription). That way, you’ll never miss a post. You can also forward this website link to your friends and colleagues-thanks!
Note: You can read his previous article on Examining And Testing Of FDC To USB Adapter