Broken massage bed remote control

[Mrelektrik]

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.

[AKM]

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.

[tom66]

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.

[Mrelektrik]

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.

I 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.

[tom66]

What is device U1 on the lower PCB?

[Mrelektrik]

What is device U1 on the lower PCB?

It's a shift register M74HC59581

Google finds this datasheet - http://www.nxp.com/documents/data_sheet/74HC_HCT595.pdf

[tom66]

You have checked the buttons are OK and not stuck down?

[Mrelektrik]

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.

[tom66]

R13 tests OK? Check soldering around that area and on connections it hooks up to.

[Mrelektrik]

R13 is ok. I think I will try to unsolder the display from the upper part and see what happens.

[Mrelektrik]

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.

[David_AVD]

Buttons are fine, third row is not working.

Did 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?

[miguelvp]

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?)

[Mrelektrik]

Buttons are fine, third row is not working.

Did 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?

They are fine, I checked them with multimeter.

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?)

It'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?

[Zero999]

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.

[Mrelektrik]

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.

But I have unsoldered the display from top PCB and everything is working except thrid row of buttons.

[David_AVD]

Is it possible, that the shift register is faulty?

Entirely possible.   

[Mrelektrik]

I will try to replace it with 74HC595 TEXAS INSTRUMENTS.