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May 12, 2017

Repair of an "Instant Pot" Pressure Cooker

Filed under: Uncategorized — admin @ 9:39 am

This post is about another case that reinforces my claim that “most repairs are easy” -especially when you know what to look for! One of my neighbours recently brought over a pressure cooker that had ceased to function. In quick initial tests, the unit powered up normally, and panel display and controls seemed functional, but the device heater did not come on. Other key observations were that the relay that supplies AC to the heater could be heard to “click” as expected. This relay is of a common type used in many appliances and electronic thermostats to supply relatively high currents to resistive heaters.

the patient, chest cavity opened

After opening up the base cover under the unit (just one screw needed to be removed, and the the cover rotated to removable position) I did a few quick electrical tests with a DVM (be careful of high voltages!). With the unit powered down and the heater quickly disconnected and out of circuit, I measured its resistance: about 15 ohms, appropriate for a heater of its power rating used at 120V. So, the heater seemed OK and not the cause of the unit not heating up. Next, I decided to look at the main power circuit board that contained the relay described above plus DC power supply for the display panel and some associated control circuitry. The board could be removed by taking out just 2 screws.

circuit board, in situ

Quick inspection of the underside of the circuit board revealed a highly suspect visible flaw in the solder at the common switch side of the relay. Essentially, there was a dark ring surrounding the relay pin between the pin and the solder on the board. Resistance measurements quickly confirmed no connection between the pin and the board. The suspect area is circled in red in the second photo below.

circuit board rolled over

circuit board, flaw circled

To perform the repair, I cleaned the pin of the relay with fine sandpaper, and then re-soldered it to the board. I left an especially thick cross-section of solder between pin and board, and along the full trace to the heater wire, since this is a high current path.
Quick reassembly and testing showed the pressure cooker to be heating and working fine again. One more appliance saved from disposal!

the repair

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