Failed diode in treadmill power supply

Thread Starter


Joined Mar 6, 2021
Hi experts
Looking for some help with a treadmill power supply. A few weeks ago my treadmill stopped working after I noticed a flash coming from power board. It still is turning on and stopping after 7 seconds which to me meant magnetic optical sensor wasn't working. Removed cover and inspected sensor , the cable was chipped and shorted with treadmill body. Ordered a new sensor cable from eBay. Replaced the sensor and no change.. treadmill still stopping after 7 sec. Had to check further in the board and appears there's a diode connected to the sensor input pin. It's a glass diode with A blue stripe on it. It's reading 34 both ways on a digital multimeter set to diode test. My guess is it's a 5v zener diode but I am not sure. Want to order a replacement but just want to be sure before ordering.. I have two similar diodes in the circuit with variable readings in fwd and reverse mode without any labels. Is there a way I can be sure what exactly I need to order or ideally a way around to fix it. Attached is a pic.. the diode next to a white 2 pin input is the probable suspect.. thanks in advance



Joined Dec 29, 2008
Testing in-circuit can be problematic sometimes, due to connected components. If you take care, it may be possible to desolder one end of the suspect diode, and lift up the opposite end slightly, so that you can verify the diode test result.
A fine grade # of SolderWick mesh tape should assist in removing some of the solder at one end of the diode. The idea is to leave one end of the diode in place, if that is possible. ... So start off with a minimal heat level, in order not to melt both diode end connections.
... This is just a suggestion, and has not been tried before.
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