Tip: fixing a remote with blocks of bad buttons
Posted: Tue Jan 27, 2009 10:19 am
If you have several buttons that don't work, and I'm not talking about worn out buttons were you have to press it hard to get it to work, I'm talking about where a whole set of buttons don't work.
This is caused by a broken trace somewhere on the PCB. If you look at the octal codes for the buttons, you should notice that they all start (or end) with the same code. For example, the buttons might be S40, S41, S42, etc or S01, S21, S31, etc.
Normally, you would assume that you have to find where the trace is broken and repair it, but unless you have an obvious spot where the batteries leaked or something like that, finding the break could be close to impossible.
Well, I have a tip for you. You don't need to find the break in order to fix the remote, all you need to do is find two spots on the remote that should have connectivity but don't. The easiest way to do this is to have a working remote handy that you can compare with, but you could also do it using a schematic.
All of the traces that link the buttons need to find their way back to the MCU chip eventually, so what I did with a remote that I just fixed was, using the good remote, I put one end of a multi-meter on one of the affected buttons and then I tried touching the other end on the various punch-thru holes around the MCU chip until I found one that matched. As this wasn't a convenient place to solder, I followed it away from the MCU until I found a better hole that was out in the open. I then confirmed that this hole and the affected button had connectivity on the good remote, and that they didn't on the bad remote. Then I followed the trace from the button to a punch-thru hole. Again, I confirmed that this new hole and the MCU based hole had connectivity on the good remote and didn't on the bad remote, then I soldered a fine wire between them on the bad remote, and voila, my non-working buttons came back to life!
This is caused by a broken trace somewhere on the PCB. If you look at the octal codes for the buttons, you should notice that they all start (or end) with the same code. For example, the buttons might be S40, S41, S42, etc or S01, S21, S31, etc.
Normally, you would assume that you have to find where the trace is broken and repair it, but unless you have an obvious spot where the batteries leaked or something like that, finding the break could be close to impossible.
Well, I have a tip for you. You don't need to find the break in order to fix the remote, all you need to do is find two spots on the remote that should have connectivity but don't. The easiest way to do this is to have a working remote handy that you can compare with, but you could also do it using a schematic.
All of the traces that link the buttons need to find their way back to the MCU chip eventually, so what I did with a remote that I just fixed was, using the good remote, I put one end of a multi-meter on one of the affected buttons and then I tried touching the other end on the various punch-thru holes around the MCU chip until I found one that matched. As this wasn't a convenient place to solder, I followed it away from the MCU until I found a better hole that was out in the open. I then confirmed that this hole and the affected button had connectivity on the good remote, and that they didn't on the bad remote. Then I followed the trace from the button to a punch-thru hole. Again, I confirmed that this new hole and the MCU based hole had connectivity on the good remote and didn't on the bad remote, then I soldered a fine wire between them on the bad remote, and voila, my non-working buttons came back to life!