USB Flight Simulator Yoke Button Demultiplexer Issue - Page 1
Forum section: electronics / projects

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: January 05, 2016, 11:36:23 pm
content: I got a flight yoke for free from my school because none of the buttons worked. Analog works fine, and if I remember correctly, I swapped this controller with one from another yoke to see if it was the yoke's wiring, and it was not. The issue (I THINK) lies in this controller:It has three chips:Decoder/Demultiplexer:74HCT138DMicrocontroller:CY7C63001C-PXC(couldn't find a quick datasheet, here is a mouser link)ADC (for analog inputs from yoke)TLC1543CThe issue is whenever I press a button, I get every fourth button pressed when I run a controller testing software.For example:I press button 1, buttons 5, 9, and 13 also appear pressed. Any button from this bank of four will activate the other three.I press button 2, buttons 6, 8, and 14 also appear pressed. Any button from this bank of four will activate the other three.I press button 3, buttons 7, 11, and 15 also appear pressed. Any button from this bank of four will activate the other three.I press button 4, buttons 8, 12, and 16 also appear pressed. Any button from this bank of four will activate the other three.Everything analog on this thing works flawlessly. What should I do to start troubleshooting? Where could the problem lie? For those wondering, I needed to put a scrap piece of metal in the socket for the micro as one pin was broken off, and I checked continuity on this pin, and it DOES check fine, so thats not the problem. I have already tried reflowing the demultiplexer with no change, and I have tried flexing the board, again, nothing.

author: SeanB
author_rank: Super Contributor
timestamp: January 06, 2016, 11:29:43 am
content: Have you checked for short circuits on the outputs of the ls138, or for a bad connection to pins 1-3 as these are the inputs. I guess the decoder is scanning the keyboard matrix and there are resistors dividing the scan down to button presses. Where are those resistors, there might be a shorted resistor or bad connection. Some photos of the complete board top and bottom would be good.

author: wraper
author_rank: Unknown
timestamp: January 06, 2016, 11:45:55 am
content: IMO 74HCT138D is faulty, not microcontroller.Quote

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: January 06, 2016, 02:05:57 pm
content: Quote from: wraper on January 06, 2016, 11:45:55 amI never doubted the micro, and I wanted to try out my new SMD rework station"If its already fucked, no harm fucking it up more"

author: sleemanj
author_rank: Super Contributor
timestamp: January 06, 2016, 03:22:20 pm
content: Put in a new 74HCT138D and see if it fixes it, not exactly hard to find or expensive :-)

author: ajb
author_rank: Super Contributor
timestamp: January 06, 2016, 04:29:00 pm
content: One of the pins on the Cypress part is folded up on itself. Maybe not the cause of the problem, but worth taking a look at.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: January 06, 2016, 06:22:31 pm
content: Quote from: ajb on January 06, 2016, 04:29:00 pmThis pin actually broke off, and so I fixed it by shoving a piece of flattened wire into the socket, and it makes contact with the broken pin stub on the micro. I already checked it with a multimeter, it is making a "reliable" connection.