EEVblog 1702 : A Most Interesting REPAIR - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: August 18, 2025, 10:58:25 pm
content: A repair of this Tennismatic T1000 remote control was way more interesting than I expected.https://tennismatic.com/main/page_products_ball_machines_t100_series.html00:00 - Tennismatic 1000 Tennis ball machine remote control00:53 - Battery snap ohms measurement01:17 - Battery current measurement02:29 - It's a row/column thing02:57 - Teardown05:20 - Membrane inspection06:44 - Membrane keypad continuity test07:25 - Pro Tip: Using multimeter as a shorting lead. Testing the microcontroller.09:27 - Is it the membrane connector?10:17 - What would take out the entire keypad?12:10 - Closer inspection of the contacts12:44 - Ah Ha! What's this?13:48 - Inspecting and testing the row membrane connections15:01 - Conductive silver ink time16:41 - The culprit identified18:48 - Let's try some fresh conductive silver paint21:36 - DAMN IT! Dave goofs.22:56 - How conductive silver ink/paint works24:01 - Measurements after curing26:01 - Winner Winner Chicken Dinner

author: ahakman
author_rank: Regular Contributor
timestamp: August 19, 2025, 01:29:12 am
content: Commenting here because YouTube is up to their old tricks again, and almost none of my comments show up if I check in an incongnito tab (but they show up for me logged in in a regular tab). Maybe only one in 50 or one in 100 comments I leave actually shows up for anyone other than me. That used to happen occasionally, but in the last week, it's just gotten insane. I did just change my profile picture to Clippy - maybe that angered the YouTube godsI've had a similar, yet different issue with almost the exact same kind of membrane keypad right at the connector. Maytag dishwashers use the exact same kind of membrane for the "touch" switches at the top of the door to set all the settings and start the cycle. It's a very wide spread issue that they ALL fail eventually, and because the keys are glued to the top plastic part of the door, they sell the replacement part with the plastic door top for like $500, even though the membrane is worth $3. Basically just the typical anti-consumer crap to get you to buy a whole new dishwasher.After a while the buttons get flakey and actually start "pressing themselves", and or you can't press them at all, because the micro controller thinks some of the other buttons are already pressed. I took the connector shell off, and noticed if you look in the light just right, you could see rainbow patterns between the pins of the connector where they're crimped to the flex / silver traces. I guess with the moisture there (it being a dishwasher), some kind of electro-migration was happening, and it was forming conductive bridges between the pins. Scraping between the pins with some tweezers under the microscope and verifying with a meter no high resistance connection between the pins anymore solved the issue completely. It was NOT easy to track that fault down though, and I ended up peeling the layers of the keypad apart and troubleshooting that side first (again, I figured moisture got in there). I was able to put the whole keypad back together with some fresh double sided tape that I had from doing some LCD repairs in the past.Of course in the factory, they could've solved that problem by putting a 5 cent blob of epoxy over those pins where they crimp to the traces to keep it watertight before shoving it into the connector shell, but that wouldn't sell more dishwashers.Anyway, long story short, those membrane keypads with the silver conductive traces are HORRIBLE for long term reliability, and in reality are a very sure "planned obsolescence" failure point. Always check what's going on right at the crimped pins at the connector - that seems to be where the issues are.

author: BradC
author_rank: Super Contributor
timestamp: August 19, 2025, 01:42:42 am
content: When I was doing my apprenticeship as an tech with Wormald Security back in the early 90's, we used to see this all the time on Australian made "EDL 223" alarm panels. So much so we had a local WA company make up new membranes for us which we use to keep in stock to replace any that came in. They also suffered terribly from bad 40 pin wafer DIP sockets on the CPU's. So we'd change the membrane on the keypads, change the sockets on the main board and send them back out.Must have been a process problem at the factory with the membranes.Edit : Checking my long forgotten notes, the bubbles over the buttons on the membranes also used to crack. The membranes we had made were completely flat.

author: richnormand
author_rank: Unknown
timestamp: August 19, 2025, 03:11:01 pm
content: Silver paint use to be my primary choice but I have had great success over the years using Ted Pella Inc. PELCO Colloidal Graphite in an isopropanol base. About $10US.https://www.tedpella.com/technote_html/16053%20TN.pdfhttps://www.tedpella.com/SEMmisc_html/SEMpaint.aspx#_16053Initially got it for coating samples for SEM work.In situations of high temperatures or vibrations I found it to be better than the silver based stuff. The only caveat is will have a higher resistance than the silver.A prime example was on a Genn-Air oven control panel. It is located over the oven door and it does get hot there. The flex cable conductor was decomposing exactly as you demonstrated but in addition the traces were removed or scraped by the connector contacts pressure when the flex was inserted in it . So initially the contacts were good but after a few months of temperature cycling, thermal expansion/contraction and vibration it would go bad again. The PELCO graphite has solved the issue now for several years (Also worked for my microwave touchpad).

author: firewalker
author_rank: Super Contributor
timestamp: August 19, 2025, 07:43:21 pm
content: You should always try and read the firmware of those devices. I was even socketed.Alexander.

author: EEVblog
author_rank: Unknown
timestamp: August 19, 2025, 11:57:14 pm
content: Quote from: BradC on August 19, 2025, 01:42:42 amDid you know Bill Gjura?

author: BradC
author_rank: Super Contributor
timestamp: August 20, 2025, 04:33:40 am
content: Quote from: EEVblog on August 19, 2025, 11:57:14 pmDoesn't ring a bell. Being in WA we were a long way from the manufacturing and support base.