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Help with unknown circuit type

Imctkh

New Member
Hi there,
I'm trying to repair the remote control for my trolling motor (it's a motorguide Lazer 370RF). The remote is a foot pad with buttons. Inside is a sheet of plastic film with these little white leads running all over it (see picture). The one that supplies power seems to be burnt out. If you try to scrape off the white stuff, there is no metal inside to solder to.

I'm sure if I knew what this setup was called, I could find a video showing me how to repair or bypass the broken lead. However, no combination of words in Google has given me any luck. Anyone know what it's called, or better yet, how to fix it?

Thanks,
MitchIMG_20190612_184425144.jpg
 

Beau Schwabe

Active Member
Do a search for "Silver conductive pen" ... that's how to fix it. You will not be able to solder to it. The next big question is, why would that have burnt out?
 

DrG

Member
I may not be seeing this clearly, but it looks like it has already been repaired once.

I can't tell if there was a trace in the area between my blue lines that came off, or if there is a trace there, but on the other side.

The area in my red outline looks very much like someone repaired it using some copper tape (something like this https://www.amazon.com/Conductive-Shielding-Repellent-Electrical-Grounding/dp/B076H4NPRR/ref=asc_df_B076H4NPRR/?tag=hyprod-20&linkCode=df0&hvadid=216767879473&hvpos=1o1&hvnetw=g&hvrand=14171606063556337347&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9007812&hvtargid=pla-386214563660&psc=1 but not as wide). Note how you can see that it (the repair piece has been placed on top of the original trace with the repair piece being cut diagonally near the connector).Not sure what to make of the rectangular object within my red area - maybe more of such tape.

Do you have continuity from just before the repair to just after the repair? It may not be working for other reasons. If there is poor continuity, you could replace/redo that trace. Silver pen was already mentioned maybe some kind of conductive adhesive as well. Or, maybe I am just not seeing it correctly.

118838
 
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Imctkh

New Member
Do a search for "Silver conductive pen" ... that's how to fix it. You will not be able to solder to it. The next big question is, why would that have burnt out?
Thanks, I will try out the pen.

The reason it's burnt out is because it sunk in the lake (along with my boat) :)

To DRG's question - I made the mark inside the red circle. I was scraping at the wire hoping to expose some metal that I could solder to. As far as what's between the blue lines, it's not part of the circuit. It's a feature of the plastic pad that the circuit is stuck to.
 

unclejed613

Well-Known Member
Most Helpful Member
these are known as "membrane keypads". first time i ever saw one was some kind of video game console in the 1980s. i think it was the "Intellivision" controllers were made like this, and there was a part of the keypad that flexed while in use, and eventually the traces would begin breaking. the only "repair" option was ordering a new controller. the breaks always happened on a right angle fold of the membrane, and using silver paint wasn't a very reliable way of fixing it since that corner was always flexing a bit while the controller was in use.

one possible "fix" for this one would be to build a switchbox with real switches. there's not a big complex set of switches, and only 9 wires.
 

alec_t

Well-Known Member
Most Helpful Member
The sixth wire from the left going into the connector at the bottom looks pretty corroded too.
+1 for the new switchbox idea.
 

Imctkh

New Member
these are known as "membrane keypads". first time i ever saw one was some kind of video game console in the 1980s. i think it was the "Intellivision" controllers were made like this, and there was a part of the keypad that flexed while in use, and eventually the traces would begin breaking. the only "repair" option was ordering a new controller. the breaks always happened on a right angle fold of the membrane, and using silver paint wasn't a very reliable way of fixing it since that corner was always flexing a bit while the controller was in use.

one possible "fix" for this one would be to build a switchbox with real switches. there's not a big complex set of switches, and only 9 wires.
Thanks for the name of this setup. I'll build a switchbox if the conductive pen fails. The only replacement I can get for this thing costs $400 :rolleyes:
 

Imctkh

New Member
Hi All,

So I succeeded in fixing the corroded circuit with the silver conductive pen. However, it seems there are quite a few more issues with the "membrane keypad." Some of the buttons don't work, and some of them initiate multiple functions (sometimes not even the one they're supposed to). Anyway, I believe that there is water trapped between the sticky plastic layers of the membrane causing the circuits to short, and I think that the amount of time it would take to figure out the issue and fix it is not worth it.

So, moving on to the switchbox idea (thanks unclejed), I tested the circuit board and all of the functions are working properly using a jumper wire. Now I just need to figure out how to permanently attach the wires to the board for the switchbox. Images of the circuit board will be attached. It had some sort of waterproof coating on it, which I was able to remove from the bottom. So far, I have failed in removing it from the top, but I could remove it from small areas if necessary.

Hopefully, someone will have a better way to do this than I have come up with. The three options I see are:
1. Attempt to cut open the existing male connector and solder wires where the "ribbons" used to be. This is currently my preferred option, but I'm not sure I will succeed at getting it open without destroying it.
2. Desolder the wire connector from the top of the circuit board and solder the wires through the circuit board. This seems rather difficult, but better than option 3.
3. Solder the wires to the bottom of the board - this would be in the middle right of the picture where there are 10 solder joints in a line. This seems pretty difficult as they are quite close together and I'm not that great at soldering circuit boards. I'm sure I will have issues keeping them separated.

Any ideas are greatly appreciated!

IMG_20190620_222752842.jpgIMG_20190620_221333358.jpgIMG_20190620_221423421.jpg
 

Beau Schwabe

Active Member
Initially I thought I would offer to design a small circuit board with tactile push buttons, but looking at your photos I would consider reworking both boards. The main board doesn't appear to be too complex and looks to measure about 2.5 inches x 2.5 inches. It's hard to see what all is under that silicone which BTW is not the greatest thing for copper traces on a PCB. Normally I charge $60/hr for contract work, but I would cut that in half for this project. PM me if you want and we can discuss the details further.
 

Imctkh

New Member
Initially I thought I would offer to design a small circuit board with tactile push buttons, but looking at your photos I would consider reworking both boards. The main board doesn't appear to be too complex and looks to measure about 2.5 inches x 2.5 inches. It's hard to see what all is under that silicone which BTW is not the greatest thing for copper traces on a PCB. Normally I charge $60/hr for contract work, but I would cut that in half for this project. PM me if you want and we can discuss the details further.
Thanks Beau. I am somewhat determined to fix it myself at the moment, but I'll let you know if I fail.
 

unclejed613

Well-Known Member
Most Helpful Member
if you can find some ribbon cable (like what used to be used for IDE hard drive cables) you can use that... from the looks of the connector in the picture that shows the 9V battery clip, it looks like 0.1 inch spacing. ribbon cable with 0.1 inch (2.5mm) spacing is inexpensive and easy to find.

the best bet will be to carefully remove the connector, and replace it with one end of the ribbon cable. this requires desoldering the connector. if you need to, find a board you don't care about and practice desoldering/soldering on it first. once you get confident that you can desolder without lifting pads or removing a feed-through, then tackle the controller. if you get a desoldering tool, i think the big blue ones are pretty good since they have a large cylinder volume and strong spring, which makes for a stronger vacuum.


under that silicone which BTW is not the greatest thing for copper traces on a PCB
there's silicone RTV compound available that is non-corrosive, and specifically made for use on circuit boards. it doesn't ooze acetic acid (vinegar) like the household RTV compound.
 

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