Hp 3457A LCD backlight mod (also for 3478A) - Page 1
Forum section: electronics / projects

author: onlooker
author_rank: Frequent Contributor
timestamp: May 05, 2013, 11:07:41 pm
content: This is in answering bingo600's question in my other post about Fluke 343a calibrator fix.QuoteI thought others may be interested too.This HP 3457A backlight mod. is based on others method with my takes. But, in any case, be very careful and I can't guarantee all info are 100% accurate or correct in your case (do it on your own risk, so to speak).The three pictures and comments there-in should give some general info. The steps are,1). The key materials: white LED stripe(e.g. ebay), reflector (e.g. broken laptop LCD), and light guide (e.g. broken laptop LCD). You can replace them with the similars.2). Remove the LCD assembly from the 3457a and measure the gap (HxLxW) between the PCB and the LCD glass (I don't have the numbers at hand). These will be used to prepare the reflector and light guide. Be careful the connector pins are VERY fragile and strangely some are aged worse than others.3). Cut the reflector and light guide into size to fit into the gap. Make sure no scratch and no chipping when cutting. The light receiving side is better on the original edge.4). Remove the LCD glass part from the assembly. They are held together by two holders with mechanical force.5). (!!!Be very careful!!!) Peel off the old reflector on the back of the LCD glass. The two are glued together by tape like glue. The safer peel force should go along the glass surface direction instead of normal to it.6). Clean off the sticky residue on the back of the LCD glass without scratching it. Scratching can damage the light polarizer on the glass (I was told). A lot Alcohol can do the job, but paint thinner will be more effective.7). Assemble back the LCD assembly. But don't connect the connectors yet.8 ). Insert into the gap in the assembly with the new reflector and the light guide. They should be in loose fit.9). Construct, connect and temporary glue you LED light source as shown in the picture.10). Connect the connectors without force the pins in. The original connector clip should not be used any more. Then, screw the back cover on as shown in the picture. It will press on the pins with minor force to make good contact.11). Slightly adjust the position of the light source to reach best light uniformity. Black permanent mark can be used to damp the light intensity. You may want to change resister value to adjust the light intensity too.The result:Backlight installed (Edited: J702 connection should be to 1 and 2):Before backlight installed:Materials needed:

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: May 06, 2013, 01:12:53 am
content: The customization looks nice but I am happy with the passive display so I don't have any urge to do this. Otherwise nice workThe thing I want to do is get a non-destructive, non-invasive way to readout/restore the CAL ram. Free electron suggests you can do this via HPIB but I looked over both manuals and can't figure it out. Has anyone done this?

author: nadona
author_rank: Regular Contributor
timestamp: May 06, 2013, 01:27:00 am
content: Thank you very much for sharing the secretsI sold one just because of the dim readability.Now I have to buy one again to try this

author: BravoV
author_rank: Super Contributor
timestamp: May 06, 2013, 01:35:54 am
content: Thanks for sharing !Really tempting to mod my 3468A too.

author: AlfBaz
author_rank: Super Contributor
timestamp: May 06, 2013, 03:43:21 am
content: Quote from: chickenHeadKnob on May 06, 2013, 01:12:53 amI remember free writing that, will have to look for it. I should be receiving an agilent gpib/usb dongle any day now and you have now made me curiousEDIT: I'd be interested in seeing what the cal info is. It would be interesting to see if you could glean how much it drifts between cal's

author: grenert
author_rank: Frequent Contributor
timestamp: May 06, 2013, 04:24:44 am
content: Thank you very much for sharing!Without the reflector, how does it look bright room light?

author: bingo600
author_rank: Super Contributor
timestamp: May 06, 2013, 05:08:08 am
content: @onlookerThank you for sharing thisIt will make my 3457A much more readable if you just have a glimpse on it ...I just have to "kill" an old lappy for LCD reflector parts/Bingo

author: onlooker
author_rank: Frequent Contributor
timestamp: May 06, 2013, 01:35:34 pm
content: A picture is updated for correcting the LED power connection in the schematics.For the reflector alternatives, one can try a piece of white paper or something more reflective (silver gift wrap). The white LED is very bright and it can wash away the digits display. That is why one may want to adjust the brightness. Other materials can be used for the light guide too. But one from a laptop LCD is a better choice since it is designed for light uniformity. This is achieved with having variable thickness, and small light diffusing bumps on the surface. The light guide can be inserted in with either side in front, but the background texture effect is very different: one is smooth and the other is a fabric look. I like the fabric look. With the smooth look, small scratches on the guide surface will be very noticeable.

author: cellularmitosis
author_rank: Unknown
timestamp: February 04, 2014, 03:37:57 am
content: I took a different approach with my HP 3478A. Now that electroluminescent tape and inverters are so cheap on ebay, I decided to give that a shot.I'll call this a mild success, with two caveats:1) The LCD glass is polarized, which means the EL tape won't be as bright as you'll expect. As it was, it is just bright enough to make this worth-while in a well-lit shop.2) This solution will not outlive the 3478A by any stretch. EL wire and EL tape have a finite lifespan.

author: alexwhittemore
author_rank: Frequent Contributor
timestamp: May 23, 2014, 12:13:43 am
content: Quote from: cellularmitosis on February 04, 2014, 03:37:57 amHow'd you get your LCD out in the first place? I can't figure out how to get the bezel surrounding the front panel off in order to get at any of the screws holding the panel on.

author: baoshi
author_rank: Regular Contributor
timestamp: May 23, 2014, 04:35:54 am
content: Do you have any viewing angle issue after the mod? I modify one using a EL panel, but find now I'm very difficult to see the reading from below the meter. Seeing from above is ok.

author: cellularmitosis
author_rank: Unknown
timestamp: May 28, 2014, 03:30:25 am
content: Quote from: alexwhittemore on May 23, 2014, 12:13:43 amHey Alex,I actually had the same problem: I couldn't figure out how to get the front bezel off, and there was one screw which I couldn't reach because of that. I ended up taking a pair of flush cutters and severing one end of the blue plastic LCD holder. When I reassembled, I just hot-glued the severed part back together. Kind of hacky, but its not like I'm looking to preserve the resale value of this meterHere's an album of the electroluminescent driver construction. It's just a transformer, fuse, bridge rectifier, 12v regulator, capacitors, and the EL inverter, all from the junk bin, hot-glued to the inside of the meter.http://imgur.com/a/sm5YePlease note that the fuse holder exposed 120VAC, which is dangerous if operating with the case open.

author: alexwhittemore
author_rank: Frequent Contributor
timestamp: May 28, 2014, 04:55:37 am
content: I actually just found it scouring the service manual. Basically, take off all the screws and components attached to the chassis (connectors on the back, transformer mounting screws, two ground lugs, back panel input connections, and the power switch slots out when you loosen the screws), then the entire pcb+front panel assembly slides out the front, THROUGH the bezel. Bit of a PITA to just get to the LCD.

author: alexwhittemore
author_rank: Frequent Contributor
timestamp: June 03, 2014, 10:07:58 pm
content: Holy everloving god guys, getting the reflective backing off my LCD was the WORST! How'd you guys do it?I peeled the layer off, but of course some of the silver backing got left behind, not everything came with. I managed to scrape that off with a fingernail no problem (though a pain), but the WORST was the glue underneath it! Holy crap! This stuff is awful! It doesn't dissolve in isopropyl basically at all. I guess a little bit. It doesn't dissolve in ethanol whatsoever. I ended up having to use acetone on it, but acetone is so volitile I'd put it on a paper towel, it'd spread the glue around a bit, then dry off leaving it all behind, but in a new spot. I ended up coating both sides of the LCD in a thin layer of sticky opaque goo!I ended up having to make a bathtub out of tinfoil to soak the LCD for a couple minutes, then manually scrape off the glue with a fingernail STILL IN THE BATH. And even after all that, I had to throw the bath away and bathe the LCD in fresh acetone two more times, because when I pulled it out the acetone-glue mixture would just instantly evaporate leaving behind a bunch more glue!And even after all that, I still haven't found a donor LCD, so I still don't have a backlight

author: cellularmitosis
author_rank: Unknown
timestamp: June 04, 2014, 06:13:27 am
content: Wow, that's a bummer. I got lucky and mine just peeled off all in one go.

author: SgtRock
author_rank: Unknown
timestamp: June 04, 2014, 06:52:20 am
content: Dear Onlooker:--Wow! Hell of a job. I just love it when people keep old classic equipment in play by customizing to be better than it was before. I will warrant that this operation in being duplicated by numerous folks right now."A three legged dog goes into a bar and says "I'm looking for the man that shot my paw"Jim Varney 1949 - 2000Best RegardsClear Ether

author: alexwhittemore
author_rank: Frequent Contributor
timestamp: June 25, 2014, 10:25:52 pm
content: So I sadly had to admit defeat on this one. I ended up getting some cuttable EL panel (really, they just give you a bunch of electrode attachment points and as long as you include both sides in a given shape, it works) and cut a piece to size. It worked well, except it was a bit mechanically unstable and the piece I cut started being intermittent. It required constant pressure on the electrode to maintain contact. Even that wouldn't have been a HUGE issue, but it also FILLS the inside of the case with electrical noise, even with the inverter and supply outside. I noticed a 20x increase in the zero measurement for AC Volts, and I don't really want to find out what that does to other ranges or function. When the panel was mechanically stable, I didn't notice any other issues, but during intermittent connection I did see that, as the panel flicked on and off, all kinds of other things went haywire with the LCD showing ROM error codes and ADC connection problems and all kinds of stuff. The high frequency noise from the circuit cutting in and out must have caused those, but jeez, I definitely don't want to see what else might go wrong.I slipped a bit of white note card in as a backing and tossed all the EL stuff in the junk drawer for the next project.

author: Chipguy
author_rank: Unknown
timestamp: July 26, 2014, 05:52:49 pm
content: Thats a good modNow I kinda regret to have sold mine

author: michaeliv
author_rank: Frequent Contributor
timestamp: April 12, 2016, 10:48:07 pm
content: Thread resurrection time !!!!Does anyone know if heat will damage the LCD display ? I want to heat up the display before removing the aluminium foil in order to make it easier.

author: deepspace
author_rank: Contributor
timestamp: February 13, 2018, 12:29:16 pm
content: Thanks for mod and inspiration ..