Broken massage bed remote control - Page 1
Forum section: electronics / projects

author: Mrelektrik
author_rank: Contributor
timestamp: May 01, 2014, 08:59:19 pm
content: Hi. I am trying to fix broken remote control that is used with massage bed. The display is broken as you can see on the picture. When I connect the device to the massage bed, it shows some signs on the display and first 2 rows of buttons (that's K1-K12) are working. Buttons in the third row (K14-K17) are not working and I am trying to find out why.I recognise all the components except the black blob on the back of the display. I checked all the resistors and they seem to be ok. It looks like a pretty simple circuit, so if some experts could explain how it works and give me some advice on fixing it, I would be really thankful.

author: AKM
author_rank: Contributor
timestamp: May 01, 2014, 10:16:27 pm
content: I am certainly no expert, but finding the PCB trace(s) common for the buttons in the non working row, and following them, should lead you to suspect components and connections. Check the solder joints and traces for brakes visually, and with the continuity tester; or put a little pressure on the joints with something non conductive and see if they start working for the moment.

author: tom66
author_rank: Super Contributor
timestamp: May 01, 2014, 10:22:40 pm
content: I'm unsure if it applies in this case, but I've encountered devices which multiplex the display lines with the buttons; it's possible shorted display lines could cause issues with the buttons.

author: Mrelektrik
author_rank: Contributor
timestamp: May 01, 2014, 10:43:04 pm
content: Quote from: tom66 on May 01, 2014, 10:22:40 pmI thought, that it should work without the display, so I tried to unsolder the top part. It was not working without it. I don't really need the display, I just need to be able to fully control the bed with all the buttons.

author: tom66
author_rank: Super Contributor
timestamp: May 01, 2014, 10:48:59 pm
content: What is device U1 on the lower PCB?

author: Mrelektrik
author_rank: Contributor
timestamp: May 01, 2014, 11:00:27 pm
content: Quote from: tom66 on May 01, 2014, 10:48:59 pmIt's a shift register M74HC59581Google finds this datasheet -http://www.nxp.com/documents/data_sheet/74HC_HCT595.pdf

author: tom66
author_rank: Super Contributor
timestamp: May 02, 2014, 08:23:49 am
content: You have checked the buttons are OK and not stuck down?

author: Mrelektrik
author_rank: Contributor
timestamp: May 02, 2014, 09:00:44 am
content: Buttons are fine, third row is not working. When I press buttons from the 1st and 2nd row, buzzer beeps and bed makes what is supposed to. When I press buttons from third row, nothing happens.

author: tom66
author_rank: Super Contributor
timestamp: May 02, 2014, 11:07:44 am
content: R13 tests OK? Check soldering around that area and on connections it hooks up to.

author: Mrelektrik
author_rank: Contributor
timestamp: May 02, 2014, 11:21:22 am
content: R13 is ok. I think I will try to unsolder the display from the upper part and see what happens.

author: Mrelektrik
author_rank: Contributor
timestamp: May 02, 2014, 01:12:43 pm
content: So I unsoldered the display from the upper part and nothing changed. 1st and 2nd row works, third does not. So I think that the problem is on the lower PCB.

author: David_AVD
author_rank: Super Contributor
timestamp: May 02, 2014, 09:43:17 pm
content: Quote from: Mrelektrik on May 02, 2014, 09:00:44 amDid you measure them with a meter? It's possible to have a faulty button where it feels fine mechanically. Make sure they are open normally and close when pressed.Also, were any of the buttons that are missing now ever fitted?

author: miguelvp
author_rank: Super Contributor
timestamp: May 03, 2014, 02:21:54 am
content: A camera pointing to the remote (assuming it's infrared) will show if the buttons work. It could be the receiving end that is not right (maybe?)

author: Mrelektrik
author_rank: Contributor
timestamp: May 04, 2014, 10:35:19 am
content: Quote from: David_AVD on May 02, 2014, 09:43:17 pmThey are fine, I checked them with multimeter.Quote from: miguelvp on May 03, 2014, 02:21:54 amIt's not IR remote control. It's wired. There is 7 pin connector on the bottom.Is it possible, that the shift register is faulty?

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2014, 05:44:37 pm
content: That black blob is just a, COB (Chip On Board), an IC who's die is directly attached to the board, rather than in a package.It could be the damaged display is shorting out some of the other connections which is stopping it from working properly.

author: Mrelektrik
author_rank: Contributor
timestamp: May 04, 2014, 08:23:41 pm
content: Quote from: Hero999 on May 04, 2014, 05:44:37 pmBut I have unsoldered the display from top PCB and everything is working except thrid row of buttons.

author: David_AVD
author_rank: Super Contributor
timestamp: May 04, 2014, 09:31:01 pm
content: Quote from: Mrelektrik on May 04, 2014, 10:35:19 amEntirely possible.

author: Mrelektrik
author_rank: Contributor
timestamp: May 05, 2014, 01:14:29 pm
content: I will try to replace it with 74HC595 TEXAS INSTRUMENTS.