Antarctic Star HZB-12B Portable Automatic Ice Maker Repair

The HZB-12/B is also sold as the AGLUCKY Z5880-RED. The HZB-12B is a very clever design. This is my first look at ice makers, so perhaps it is a common design. The manufacturer tells me there is no service manual available. Here's some of what I discovered as I worked on repairing a unit.

The system is driven by a microcontroller (the chip with the label on top in the second photo at the right). High current DC peripherals such as the water pump are driven by a ULN2003A Darlington array.

Though the block diagram in the manual indicastes there is a water level detecting switch, the "water level" detection is actually a flow detection. A collar through which water shoots into the freeze trough is grounded. Another wire hangs down into the stream of water. If the stream of water is present, current is detected between the wire and the collar. If the microcontroller turns on the pump and no water flow is detected, the system stops and the "add water" LED is lit.

The "ice shovel" motor is a self reversing synchronous motor. The microcontroller controls the ice shovel motor using an opto coupled triac driving a small triac to switch 120 VAC to the motor. The motor switches direction when the rotation of the shaft is blocked. This motor rotates the freeze trough which has a panel on the front of it. As the trough is rotated to horizontal, the panel (the "ice shovel") pushes ice out to the ice basket. The opposite end of the shaft from the motor has a lever that hits stops to reverse the motor direction and also hits microswitches to tell the microcontroller that the shaft has reached the end of its rotation. At one end of its rotation, the freeze trough is vertical (to dump out excess water and allow the ice to drop), and at the other it is horizontal to hold water that is to be frozen.

This motor is an exact replacement for the ice shovel motor. It comes with leads that are the correct length and connectors ready to plug onto the PCB. The lead colors are red and white, while the original ones were black and white, but this makes no difference.


Block diagram of system from User Manual


Front view of PCB


Back view of PCB


Reversing synchronous motor


Lever on end of freeze trough shaft hits stop and microswitch at each end of rotation

This video shows the system in operation. The video starts with the end of one ice production cycle. Note that ice has formed around the cooling probes that are poked into the water. The microcontroller runs the refrigeration system for one period of time for small ice cylinders, and a longer time for larger ones. When the freeze cycle is done, the trough is rotated to vertical, dumping the excess water. The freezing probes are then heated (possibly by sending hot compressed refrigerant to the probes) causing the ice to break free of the freezing probes. The synchronous motor then rotates the freezing trough back to horizontal as the ice shovel (panel with slots in it) pushes the ice into the ice storage basket. The freezing trough is then refilled with water. Note the wire hanging down into the stream of water. The microcontroller detects conductivity between this wire and a collar that the water is flowing through. If the pump runs for a period of time and conductivity through the water is not detected, the system stops and the "Add Water" LED lights. Note that the freezing trough is overfilled and water drains back into the water reservoir at the bottom of the unit. The overfilling ensures that the trough is filled even if the pump is not perfect. No water level detector is needed, and precision timing of the water flow is not required. Once the water pump stops, the freezing cycle repeats.


Video of ice making cycle

Though not the problem with this particular unit, this video shows how to disassemble the unit and unclog a water pump.

This video shows the original symptoms on this unit. At first, it appeared that there was something wrong with the "water level" sensor since the Add Water LED did not come on when no water was present. As discussed above, it was later discovered that it is a water flow sensor instead of a water level sensor, so the Add Water LED would not light until the pump tried to pump water to the freeze trough and found no flow. Since the Select button properly toggles between the L and S LEDs, the microcontroller is probably working.

About 15 minutes after power up, the Add Water and the Ice Full LEDs alternate. Though not clear at the time, this is apparently a signal from the microcontroller that something in the sequence has not gone correctly. As mentioned in the video, there was no DC current through the pump motor. Looking at the PCB with a scope, I found that the open collector output of the ULN2003A driving the pump had 12V on it. It should be near ground to run the pump. The corresponding input of the ULN2003A was low, so the microcontroller is not telling the pump to run. At this point, I still did not know what the proper sequence of operations was for the system. Repeatedly hitting one of the microswitches driven by the freeze trough shaft resulted in the water pump starting. At this point, a clamp on AC ammeter was put around one of the wires going to the synchronus motor driving the freeze trough. There was current, but the motor was not rotating.


Video of problem symptoms

Since the motor was getting current but not rotating, it was removed for inspection. The result is shown in the image at the right. The shaft could not be rotated in either direction. Some WD-40 was sprayed on the shaft and bushing bearing, and the shaft gently worked back and forth until free. Then a liberal amount of Valvoline synthetic SAE 0W-20 oil, the same I use on my Teletypes, was applied to the junction of the shaft and the bushing. The motor was then powered for several minutes to allow the oil to work into the bearing. Now and then, the shaft would be grabbed with pliers to simulate the shaft hitting a stop. After several tries, the motor properly reversed direction. The motor was then reinstalled and the video at the top of this page, showing proper operation, was shot. At this point, the unit has worked properly for about 24 hours producing at least 20 baskets of ice. However, the motor eventually froze again. A replacement was ordered. The new one was an exact replacement except for the color of the leads. The leads were the right length and included the connectors to plug onto the PCB.
Synchronous motor removed showing corrosion.

I look forward to comments and information on other problems people have found. In general, if the ice shovel does not move when power first applied, and the water pump does not run, have a look at the synchronous motor.

Good luck!

Harold
harold@hallikainen.org