Thermal Arc TIG 180 button membrane repair/replace.

[Pete.]

I have this thermal arc welder which features a membrane keypad on the front panel. The keypad has some embedded LED's and all but one of them has stopped functioning, and that one is very flaky.

I have tried but had no joy in finding a replacement keypad so I'm looking for some guidance with a view to replacing or substituting the LED's. In the manual you press certain buttons and some of the LED's illuminate in a particular sequence. The keypad itself works, but not having the LED's makes it difficult to tell which settings are invoked.

Here is the membrane keypad with its embedded LED's. I'm not averse to drilling through the membrane, de-laminating it to get access to the solder pads or anything else so long as I can get those lights working again. Looking for some ideas.

Cheers
Pete.

 

[Agroshield]

Is it literally just LEDs and switches?

Make a few photocopies of the back of the board and go over each of the nine traces with a highlighter pen.

Perhaps you could highlight the LEDs for us on the rear view.

The blue lines look like under- or over-passes in the 'roads'.

Then you might be able to breadboard a replacement.

The manual would help verify the logic of what you draw.

When BigClive shows double-sided boards, he mirrors one side in the photo so it is easier to associate front and rear views (see front bottom right 2 LEDs and rear bottom left same items).

 

[Seadog]

The LEDs are obvious to me. They're the pairs of pads which are close together.

 

[Pete.]

@Seadog is correct. It's just blister buttons and LED's on this membrane.

Ok so new evidence. I've just heated up and peeled the cover off one corner to expose an LED without disturbing any buttons.

Now, I can trace each solder pad back to its respective terminal in the connector Which is 2nd and 8th from the top in this case. With my multimeter in diode mod eI can make the diode light up by putting the probes across it. Then if I go from the solder pad to the ribbon connector each side of the LED in turn I get continuity BUT if I try to do it through the LED i get nothing. So this diode is working and the pads are connected to the ribbon connector. It seems to me that the only thing left is that the diode has become electrically disconnected from the pads.

 

[Seadog]

That sounds likely. I'd be tempted to buy some very expensive silver paint to repair, rather than risk soldering.
I used to repair DEC keyboard membranes this way, so I can say that it makes an effective repair.