Weller WR3M display has no contrast - Page 1
Forum section: electronics / repair

author: fatbeard
author_rank: Contributor
timestamp: August 04, 2025, 08:25:44 pm
content: While re-installing my WR3M station after a pause of 6 months, I noticed the display stayed blank while the unit works as expected, just the display did not show anything. Controlling temperatures beyond the preset ones is, well, challenging...Expecting a broken wore or loose connector I started digging into it; only to find that the displayisactually working, just with no contrast at all...Checking the display controller (PCF8576CHL) I found the VLCD pin on 0V and thought that was the poblem, only to discover later that that pin is connected to GND on the main board... Nothing seems overheated, burnt or broken; I'm at a loss on how to fix this.Schematics don't seem to exist, and spare parts are, hgrmmm, cost-prohibitively priced (if one can even find them).On top of all that, the display controller chip is obsolete...Does anyone have any suggestions on how to fix this?

author: Potential Resistor
author_rank: Contributor
timestamp: August 04, 2025, 08:41:00 pm
content: Hi, not so much a suggestion on how to fix electronically, but was wondering about your situation........You say: "the display is actually working, just with no contrast at all".Does that mean if you wear some polarised sunglasses (or a polarising camera filter) is the display then visible?If the answer is yes, then perhaps you could use a piece of polarising plastic in front of the display like the old calculators.

author: fatbeard
author_rank: Contributor
timestamp: August 05, 2025, 08:52:04 am
content: Nice idea, worth at least a try...But it will have to wait until I comleted the gnireenigne (reverse engineering) of that PCB and re-assembled the unit...Will keep y'all posted.UPDATEWell... the thing is back together, far enough anyway to test the display.Both the polarising filter and backlight didn't work...Scoped the signals going to the display: looking good, 5Vpp for the most part. Some pins are 1/3 of that, some pins have a staircase-type of waveform touching all three levels. Kinda what you'd expect directly on an LCD...Next step is finding out if the display itself is gone, or the driver.For that, I ordered one display driver from Aliexpress. May be a fake, dunno; for €3.28 including shipping I'll take the risk...I also have an older LCD panel where I can access the panel itself, bypassing that driver. It wil show gibberish if the Weller dislay is shot, or lack contrast if the PCF8576 is shot...to be continued...

author: Potential Resistor
author_rank: Contributor
timestamp: August 05, 2025, 03:27:11 pm
content: Sounds like you are getting to the bottom of it now. Good luck with those parts ;-)

author: fatbeard
author_rank: Contributor
timestamp: August 05, 2025, 10:11:28 pm
content: Thanks, I'll need it.Turns out that the LCD itself is shot: the backplane pins are no longer connected; the connection between the two glass planes is broken somehow.Only with capacitive coupling (by my hand) to the backplanes I can get some response while exciting it with a 1kHz 5Vp-p square wave...I have one lead for a replacement, so I'll try that first.Alternatively I will have to pull out all the stops and design a new PCB with a graphic display and a processor that interprets the I2C data coming from the main PCB. Problem with that is that apart from the backplane pins I don't know which pin on the LCD is what...But for the moment that is a few bridges too far for me.When the time is right Idohave the dereenigne (reverse engineered) schematic.

author: Potential Resistor
author_rank: Contributor
timestamp: August 06, 2025, 01:03:51 pm
content: Hope you have some luck with the replacement lead you have in mind.I see the unit you have is very expensive.......Here is another idea......I was looking around and managed to find some pictures of the relevant items that we are discussing here (see attached pictures).There's a picture of the front of the PCB module in question, and the rear of it. Also, pictures of what the LCD panel could and should typically display. Finally, I looked at some of the other significantly less expensive Weller stations (WE1010 & WD1) and what their LCD panel appears capable of displaying.Maybe the size and capability of the LCD is different on the other models. Maybe it isn't?? It looks the same to me (I can definitely just see the "%" and the "S" on the WE1010 display) I imagine they would use the same LCD display for a range of products???Anyone out there know for sure?So perhaps you could get a replacement from one of those other inexpensive models. A spares or repairs unit that doesn't heat up but has a good display to swap out with yours.

author: fatbeard
author_rank: Contributor
timestamp: August 06, 2025, 03:27:04 pm
content: As luck would have it, Weller used the exact same display in multiple models.As Murphy would have it, the exact same defect troubles most of those models...On ebay is a complete front with display and all for sale, but the total cost is close to half of a complete 2nd hand unit; so not really an option.I also found a German firm that claims to be able to supply a spare PCB with display for just over €120 so I ordered that; we'll see if that amounts to something, I have no high hopes since the website is kinda dated...Someone else directed me to a hackaday project that covers this exact same problem:https://hackaday.io/project/188741-replacing-broken-lcd-of-weller-wd1.Looksverypromising, I plan to use most of that project. Biggest problem now is finding the right display module: I want to use a graphic LCD, definitely NOT an OLED, OLEDs don't live that long (the unit will be powered on most of the time)...

author: Potential Resistor
author_rank: Contributor
timestamp: August 06, 2025, 04:33:53 pm
content: I've just read the hackaday article.....Gosh! what a lot of work they put in to that. I don't think I'd go that far, I'd rather just replace with the same from another unit, perhaps with some thought toward a modification to help prevent future problems. Unless it is just some form of material degredation that is immpossible to prevent, that is.Hope you find a suitable solution ;-)