EEVblog #1192 - Power Meter LCD Repair

Repairing the faulty LCD in the Voltech PM300 power meter.

#Repair #LCD

Bitcoin Donations: 38y7DE8HEHNj8fGDtUr4PkCn9nWxiorvvy
Litecoin: ML7oQokTwB38bgzzjLDbRV97HKAHuwRfHA
Ethereum: 0x11AceA38DCA9DbFfB4F35f3F746af65F9dED28ce

Support the EEVblog through Patreon!

Buy anything through that link and Dave gets a commission at no cost to you.

Stuff I recommend:

Donate With Bitcoin & Other Crypto Currencies!

[ChipGuy]

This is a MGLS-24064 from Varitronix. It will fail again. Better replace it with Winstar WG-24064. They don't use hot bar shit anymore and put the 64 lines on the edges of the zebra strips. 16 on each corner. Lasts forever.

[maulerrw]

For these crappy carbon non-solderable strips I've repaired them by using the microscope and having a light behind the flex, and look for gaps where light comes through the traces indicating a crack in the conductor.
I'd then take a fresh Stanley blade and slice the top layer off and repair with silver conductive trace repair, then a bit of conformal coating for bonus points.

[SwapPartLLC]

That flex connector is most likely adhered with anisotropic conductive film (ACF) via a process known as tape automated bonding (TAB) . Same method is used in television manufacturing for attaching flex connectors to the LCD and driver boards. This type of issue, commonly referred to as tab bond failure, was very common in the early days of the LCD television. In my experience, trying to reheat them never works. Sometimes we were able to wedge something between the metal bezel and the connection at the LCD, which is usually where the failure occurred, and the pressure would help to maintain contact. One of those silicone heat transfer blocks or some folded up electrical tape were what I used. It was a temporary repair which could last anywhere from minutes to years, but could never be considered reliable. The alternative was scrapping the TV, so there was really nothing to lose. So my suggestion, if the problem comes back, would be to position something under that metal bezel to apply pressure to the offending area.

[seancsnm]

I remember soldering individual wires to a Ti-83 calculator to replace the LCD flex cable. Was such a messy fix, but it worked!

[johnnyjoseph]

BMW instrument clusters have the same problem with the same kind of hot bar attachment flex ribbon. In the automotive industry we remove the ribbon and replace it with a new one. Fortunately it's such a common problem that the ribbons are readily available.

[Oldgamingfart]

Quite a common problem with the original Nintendo Gameboy systems. The 'fix' seems to be to to heat quickly and evenly across the entirety of the ribbon connector with a flat/ chisel tip soldering iron. Tried it myself before and it does work! :)

[mfx]

Use elastic bands to put pressure on the screen while testing.

[petski]

Most of these PCB to glass flex connectors use a thermal set conductive epoxy. In production the hot bar cures and sets the epoxy which is why the flex does not detach when the bar is removed. The bad news is that once cured, it cannot be softened or re-flowed by heating again. I have personally had to clean and solder the Capton type flex cables on many LCD displays but this can only be done on the PCB side connection. Note that you can get new epoxy but it is expensive and has a very short shelf life even if refrigerated. The flex in this video looks to be conductive paint so all bets are off.

[ElmerFuddGun]

That's a weird "1" in the "CH1". Missing the right half serif at the bottom of the one. It looked like it was missing a vertical line but it goes through the zero bellow.

[vBunny]

#1630 this will be back for review. Good to see you number them beforehand now :D

[russell]

There's a saying I've heard when it comes to electronics: there's no component so cheap and shitty that it can't be made even cheaper and shittier.

[Hackinside]

There is a soldering Iron T shape which has a silicon pad in the tip of it for LCD ribbon repair

[djmikolajczak]

When I repaired lcd screens on Motorola pages back in the 90's, I simply laid a piece of wax paper across the hot bar and then ran the soldering iron, on a low setting, across the wax paper. This method worked great because you could apply pressure and controlled heat at the same time.

[waveinversion]

I fix LCDs on radios and pagers all the time, I use a Hot bar attachment on a pen soldering iron and a silicone pad between the iron and the flex to keep the flex connection from melting. I've found that depending on how cheap the LCD flex connection is you can normally get one or two reheats out of it before the glue gives up the ghost.
It seems that humidity is what causes the glue on the flex to give up most the time. Or being around industrial cleaning products. One of the hospitals I take care of use Motorola LS350 pagers and their cleaning staff will kill the LCDs all the time. I've taken to putting Clear nail polish over where the LCD flex bonds to the PCB to get some more life out it. I've been doing this for about a year now and I've seen a sharp drop off on them failing. From about once every other month too better than a year.(I still haven't seen the first one I did this on come back for a new LCD yet.)
On the flip side some of the Motorola Jedi series hand held radios used these type of LCD Bonding(Like on the MT2000 and JT1000). I have one of these radios that I use for our tower crew which has yet to have the LCD fail. The unit was built in 2003 and I picked it up used in 2010. I know we have put it through a lot of snow and rain while the tower crew is using it without the LCD flex bond giving out.
I'm not really sure what they use for the glue but it seems that there is a lot of variation in it in how well it stands up to the environment you put it in.

Also, most the time I only fix the bond to the PCB, I've only had a few fail on the bond to the glass of the LCD. When the bond to the glass fails I just order a new one, I've had very poor luck fixing that side of it, mostly I think it's because my hot bar is just the wrong shape and causes too much damage when I use it on the glass. But it's not been much of an issue because that side hardly ever fails.

[adaminsanoff]

I bought one of these LCD displays on Ebay back in 2017 for $9 brand new including shipping. Amazing how much price can vary.

[GadgetUK]

The technique you used there will likely fix it for a long while. The same technique is used on the Nintendo Gameboy (although using an iron rather than hot air). You nearly always notice that the display gets much worse whilst doing the heating. Only when it cools down does it start to then behave normally and the lines pop back in one at a time. It's almost like the resistance of the connection increases with the temperature I think.

[TheRealSasquatch]

I've previously repurposed the heating element from a domestic vacuum sealer - works reasonably well.

[NivagSwerdna]

I did wonder if it would end badly... but surprisingly.... it came good! Bonza.

[PeteJohnsMusic]

“Bloody trying to bloody film things is just ridiculous”. Quote of the day and something I’ve probably said too. 😅

[oldestnerd]

How about wedging in some non-conductive foam to keep pressure on the strips you were heating up?