Anticept Posted September 20, 2016 Report Share Posted September 20, 2016 My flap controller went bad. I was still getting a readout, but the 0 position was malfunctioning. Programming did nothing to resolve it. It was reading out dashes (---) like when you move it to manual up and manual down, so I pulled the controller out and started reverse engineering it. I know enough about electronics to get myself in trouble, but I am by no means an expert. But, I do know that almost every electronic component has an ID on it, so I start IDing things. The small tiny stuff is just generic components like resistors, transistors, etc, but I overlayed text to show what the big important devices are. Turns out, this version of the flap controller only sends 5 positions (-6, 0, 15, 30, 35) to the microcontroller. The other two, manual up and manual down, bypass the board entirely and just send a signal to the relays to roll the motor one way or the other. That's a good clue! That means that when the controller doesn't have a signal, it still provides an indication of some kind! So now, with the voltmeter, I start tracing out some of the pin positions. First, I verify that the rotary switch is actually getting good contact. Uh oh. Nope, not getting good contact on two pin positions, moving the switch causes jitter. It's a pretty generic switch so I just opened it up, clean the contacts, and replaced the wiper. Retest. Still no 0 position, but the flicker is gone now. Back to the bench! After a while of studying this board, I get to one of the chips. There's not much between the switch terminals and the microcontroller, and I've already verified the controller is making good contact. I pull the number etchings off the chip and go look up the datasheet. This chip is a darlington transistor array. I don't know enough about electronics to say what this chip is used for in this circuit design, but the data sheet has a block diagram, and basically it's just amplifying to the corresponding pin on the opposite side. When I start testing the terminals... oh. The 0 position is all wonky on this chip. I take my physical measurements of the chip, comb the datasheets to figure out which version this is (and holy crap, there are a LOT of versions!), and put an order on mouser for 2 at a whole whopping $0.58 each. Now, these are SMD devices. Surface Mount Devices, if you will. Lots of pins. It's about time I get a real electronics workstation, so I pick up this nice piece for ~180. Hot air gun, soldering iron with vacuum, desoldering vacuum, digital control... and lots of tips, including one that will work well for drag soldering. Technically this should be attributed in the cost of repair too, but I've been looking for a reason to buy this anyways! So, I swap out the chip, cross my fingers and plug it in. VOILA! It works! $1300 saved with only a few bucks in parts plus a soldering station that will be used many times more! Now to clean up those diode mounts. My fault because I got things a little too warm near them and they moved a bit, and I moved them back but not very well. I'll be redoing them. Quote Link to comment Share on other sites More sharing options...
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