Being a two-grouper commercial machine, my Grimac of course has two lots of touch pads, one for each group. The left side work reliably.
But the right has always been hit and miss, mainly miss. Touch the pad and usually it doesn't respond.
They are about $250 each, a lot of money for what is a very, very simple circuit board and five micro-switches soldered to it.
After years of frustration, I decided to dismantle the right bank and see whether there was anything obvious which caused the problem. I've fixed electric window winder switches on my cars, and hoped these might have similar impediments: carbon traces around the contacts.
Four little screws secure the pads to the machine. Off they came. Easy.
Another 4 screws, from memory, secure the circuit board to the casing. Off they came easily enough.
As I said, the boards are very simple etched boards which connect the springy micro-switches to a multi-pin socket, which then connects via a ribbon cable to the computer controller.
Unfortunately, or fortunately, I could see nothing obviously wrong. No dry solder joints, no broken circuits.
Further dismantling would entail taking apart each switch, which are not designed to be taken apart.
I should have taken pictures, but I didn't, so I'll try and use a thousand words instead.
Each switch has a small thin metal cover, less than a centimetre by a centimetre. At each corner, the covers have a tiny hole, about the diameter of a sewing needle. Little plastic prongs come through those holes, and, during manufacture, they are clenched with heat to stop the covers falling off.
I was about to give up and put everything back together when I thought I'd give it a shot easing off a cover. Nothing to lose, after all.
Very gently with a knife blade I prised it off at each cover. Of course, the plastic prongs, the thickness of sewing needles, broke, so there was no way they could be re-deployed.
I found a small almost flat brass disc about six mm diameter inside the switch. When you touch the pad to run the pump, the disc flattens out, and the centre thus touches a contact and sends voltage to other contacts on the outside edge. Let go of the switch, and the springy disc bounces back from its flattened state and stops the contact with the centre electrode.
The disc looked grubby, enough to insulate the contact areas. I gave it a quick clean and turned my attention to how I would reassemble everything, having broken those little prongs.
Ah, what about my electric hot melt glue gun? Worth a try.
So I Put the cover back on the micro-switch, tacked little globs of glue all around the edge, cementing the cover to the switch body.
Put the circuit boards back in the base, and secured the base back into the machine.
Well, to my surprise, that one touch pad switch I fixed, works beautifully.
I am now encouraged to remove the touch pad once again and do a similar repair to the remaining 4 switches.
But the right has always been hit and miss, mainly miss. Touch the pad and usually it doesn't respond.
They are about $250 each, a lot of money for what is a very, very simple circuit board and five micro-switches soldered to it.
After years of frustration, I decided to dismantle the right bank and see whether there was anything obvious which caused the problem. I've fixed electric window winder switches on my cars, and hoped these might have similar impediments: carbon traces around the contacts.
Four little screws secure the pads to the machine. Off they came. Easy.
Another 4 screws, from memory, secure the circuit board to the casing. Off they came easily enough.
As I said, the boards are very simple etched boards which connect the springy micro-switches to a multi-pin socket, which then connects via a ribbon cable to the computer controller.
Unfortunately, or fortunately, I could see nothing obviously wrong. No dry solder joints, no broken circuits.
Further dismantling would entail taking apart each switch, which are not designed to be taken apart.
I should have taken pictures, but I didn't, so I'll try and use a thousand words instead.
Each switch has a small thin metal cover, less than a centimetre by a centimetre. At each corner, the covers have a tiny hole, about the diameter of a sewing needle. Little plastic prongs come through those holes, and, during manufacture, they are clenched with heat to stop the covers falling off.
I was about to give up and put everything back together when I thought I'd give it a shot easing off a cover. Nothing to lose, after all.
Very gently with a knife blade I prised it off at each cover. Of course, the plastic prongs, the thickness of sewing needles, broke, so there was no way they could be re-deployed.
I found a small almost flat brass disc about six mm diameter inside the switch. When you touch the pad to run the pump, the disc flattens out, and the centre thus touches a contact and sends voltage to other contacts on the outside edge. Let go of the switch, and the springy disc bounces back from its flattened state and stops the contact with the centre electrode.
The disc looked grubby, enough to insulate the contact areas. I gave it a quick clean and turned my attention to how I would reassemble everything, having broken those little prongs.
Ah, what about my electric hot melt glue gun? Worth a try.
So I Put the cover back on the micro-switch, tacked little globs of glue all around the edge, cementing the cover to the switch body.
Put the circuit boards back in the base, and secured the base back into the machine.
Well, to my surprise, that one touch pad switch I fixed, works beautifully.
I am now encouraged to remove the touch pad once again and do a similar repair to the remaining 4 switches.



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