MC2100els-50w treadmill blown PSU help
Good day folks. Today I've got something kinda special: it's a power supply/motor control unit for a treadmill. When I got it, it was in pretty bad shape: a lot of blown components on it, but thankfully someone before had replaced most of them...not sure if the values are correct, but better than nothing. Problem is that it's still missing two components, both SOT-23, making the job very difficult. Have a look at the pictures: the STR G6653 SMPS IC was blown and the missing parts are linked to its VCC pin. A quick look at the traces pretty much tells me this is a linear regulator using a zener and a transistor. The transistor's collector comes from the "VCC AUX" rectifier diode directly above the heatsink, the emitter is the "output" to the IC and other stuff like optocouplers and stuff and the base is that zener diode with ripped pads. You can also see R35 is in series with the diode - classic zener regulator AFAIK. Trouble is...what are these parts ? The transistor has some visible markings to help up and I made it to be 2Xx - a MMBT4401 NPN, which makes sense. Trouble is the diode: part of it has a hole punched through so I can't make out the first letter there...I think it's a J, but J3 corresponds to yet another transistor, funnily enough, not a zener. Would it be safe to try a 15v zener and cross my fingers (with the series lightbulb of course) ? It's a standard SMPS circuit - it's the motor control side that's complicated. Hopefully that part still works...come to think of it, I could probably abandon the SMPS entirely and power the secondary with a 12v adapter to see if the micro is still OK...don't think the SMPS portion interacts with the motor control side in any way as far as I can see...what do you guys think ? Pretty difficult one here :|
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