Recovery of an old Fluke 8020a with a bad LCD

[Excavatoree]

I knew I kept those faded old 70 type displays for a reason!  Now I've got plenty to practice on.

[sonicj]

its easy. you gotta really try hard to mess up the front of the glass. the polarizer was surprising tough on this fluke. even if you mess it up, you can use the polarizer from another lcd or just order up some fresh film for a couple $. optical adhesives can be expensive, but aren't required. in fact, some of the polarizing films come with adhesive already applied.

you could also remove the back polarizer & reflector, replace with a transflective surface and then add EL film for backlighting. the fiber optic backlight stuff is balla'! 

easy/cheap way to add some bling/character to otherwise boring and dated gear!
-sj

[Excavatoree]

Thanks for the info.  I didn't realize how easy it was to remove the polarizer.  More importantly, I discovered that the "faded LCDs" that I had are fine - it's the polarizing film that deteriorates.   Reports of the demise of several of my LCDS were greatly exaggerated.   

[ModemHead]

Thanks for the info.  I didn't realize how easy it was to remove the polarizer.  More importantly, I discovered that the "faded LCDs" that I had are fine - it's the polarizing film that deteriorates.   Reports of the demise of several of my LCDS were greatly exaggerated.   

Add me to the this club.  I have an old beat-up 29-II with a badly faded display that I thought was a lost cause, but after removing the old polarizer and adding some new polarizing film, the contrast is restored!  BTW, I found that strong citrus solvent (specifically, "Goo-Gone" brand) helped in removing adhesive without damaging anything.

Many thanks to the contributors in this thread.  I've learned a useful new repair technique.

[Excavatoree]

The 29/76/79 LCD is almost impossible to find, so the motivation for being able to fix these is greater.  I found a gentleman selling the 21,23,70,73,75,77...type LCDs on e-bay and bought a lifetime supply (before his price went up, I guess as his stock depletes the cost rises) but I hadn't even considered that I can restore my 29s.

If you don't mind telling me, where is a good place to order polarizing film?  Does the stuff with adhesive work as well as using a separate adhesive?


FOUR YEARS LATER EDIT:  The situation about the 79 and 29 LCDs has changed.  Someone was selling  29/79 (maybe 76?)  LCDS on E-bay in massive quantities at low prices.   This was a "game changer" and these are now readily available and at lower cost.

[ModemHead]

The 29/76/79 LCD is almost impossible to find, so the motivation for being able to fix these is greater.

You can say that again. I picked up a broken 79-II cheap just for the LCD, but it turned out to be very easy to repair, so I just demoted the 29 to back-of-the-truck-seat-in-case-of-emergency duty.  It was usable if you held it at just the right angle.

If you don't mind telling me, where is a good place to order polarizing film?  Does the stuff with adhesive work as well as using a separate adhesive?

I got some of this from American Science & Surplus. It doesn't have any adhesive. I just cut a piece slightly oversized and let the bezel hold it down. Seems to work OK.  The only thing is that I had to turn it 45 degrees, so the cutting was somewhat wasteful.

[jwhitmor]

Beautiful, professional, job!   

I have been trying to find a way to salvage my favorite old Fluke 8020A for years. I bought it at a time when they cost "real dollars", and I used it to troubleshoot my first computer project, (which had 14,000 hand soldered joints). I have the through pin LCD replacement. Do you have any sort of circuit interconnect table or diagram you would like to share? If not, I will wait until I am snowed in for a couple of days, and use that time to figure it out (in between chucking logs into the fireplace).

Thanks!
J. R.

[lowimpedance]

Beautiful, professional, job!   

I have been trying to find a way to salvage my favorite old Fluke 8020A for years. I bought it at a time when they cost "real dollars", and I used it to troubleshoot my first computer project, (which had 14,000 hand soldered joints). I have the through pin LCD replacement. Do you have any sort of circuit interconnect table or diagram you would like to share? If not, I will wait until I am snowed in for a couple of days, and use that time to figure it out (in between chucking logs into the fireplace).

Thanks!
J. R.

 I must admit that I cannot locate the scribble that passes for a connection diagram, however you should be able to work it out easily from the 8020a schemattic  (fluke website if you dont already have), and your lcd datasheet. Note the main IC is similar to the ICL7106 which has plenty of data on the web, (curiously enough Intersil also made a reversed pin connected version which is luckily not common. I repaired an old Keithley with the more common 7106 doing a dead bug style wiring to get the connections right!). The only other point to make is the mechanical fitting, I was able to remove the right amount of plastic from the moulded plastic support so that the LCD sits on and could get the protective plastic cover to fit by milling it out in my workshop at work. So if you dont have access to something like that then you could use a dremmel etc very carefully to do the job, (and take your time). Solder all your wires needed to the pcb first, (wire wrap wire works a treat), then attach the LCD mount and connect each to the required pin. As long as you get the back plane right any other mistakes can easily be identified and corrected.
 When done the display will look better than the origional fluke in good condition, well mine does, ( I have other flukes to compare).
Good luck
cheers
LowZ

[jwhitmor]

Thanks for the great tips. I do have the LCD data sheet, but I figured the 8020A schematic was unobtainable. I will scrounge a copy, or use the generic ICL7106 pin-out to work out the details. The LCD fits everywhere except the bottom pins, so I will either drill holes for them, or mill off the bottom edge of the holder. If it is too thick to allow the factory cover to slide in, I will probably try using some thinner plastic sheet to make a new cover. The Fluke piece with the painted mask is 0.130 thick, so I have some room to fudge, and I will no longer need the exact pressure on the LCD that Fluke needed to make the elastomeric contacts work, so if I can fit it in it is sure to work.
I kind of wish everybody made a mirror image version of their IC's, because it would save me when I print and etch a PC board backwards!

Thanks again,
J. R.

[jwhitmor]

URL for FLUKE 8020a SCHEMATIC:
http://assets.fluke.com/manuals/8020A___imeng0000.pdf

complete manual scan in .pdf with the schematic in section 7 (near the end).

[jwhitmor]

I followed the lead of "lowimpedance" and once again have a working Fluke 8020A. The part I used (in the U.S.) was a "Lumex LCD-S3X1C50TR/A"  (0.5 high, 3.5 digit, LCD, glass). It fit precisely between the side edge guides, and under the factory cover, after some milling away of interfering plastic on the display holder. The project took (me) about 5 hours to complete.

Here is a photo of the new LCD powered up, with the old "blackened" LCD lying just below it.


A photo of the completed assembly, along with some of the essentials to do the job, and the old parts no longer needed.
(the IC in the background is from another project)


I can post a listing of the wire connections (in .pdf form) if anybody else wants to try this.

I never would have attempted this without the inspiration "lowimpedance" provided.
J.W.

[Kiriakos-GR]

congrats ... jwhitmor

You did a fine job with it..
Did you connect and test, the low-batt indicator ? ( on the LCD)

[jwhitmor]

Yes, the "LO BAT" indicator in the upper right corner of the Lumex LCD comes on when the battery supply falls to ~7.5 VDC. The LCD also has an "OVER" (over range) indicator, but there is no discrete output from the 8020A logic to drive it. Instead Fluke used a unique "stacked electrode" arrangement in their LCD, where the over range indicator shared an output with the half digit ("1") indication. It looks like they did a logical "AND" (in their LCD) with the drive for the three full digits, and if the three full digits AND the OR/1 output were both driven (high), it displayed a "1" but if the full digits were blanked (low), AND the OR/1 output was driven (high), it displayed the over range indication. Not sure exactly how it worked, or why they did it, but my meter still indicates an over range by blanking out the three full digits, which is enough for me. I try not to over range my meters anyway 

[lowimpedance]

Excellent job JW
 Your meter looks pristine in the photo, (not 'yellowed' like mine).
Job well worth it, now another 8020 ready for another 20 years! .

Cheers
LowZ

[jwhitmor]

Actually, mine was turning yellow too, but while I had the PCB out of the case, I scrubbed the case with a soft rag and some automotive cleaner wax. I went really easy on the front panel markings. The LCD came from an on-line division of Farnell named "Element14." It was less than 4 $US (plus $5 for shipping). The really funny part is, that none of my new "genuine Fluke" test leads will fit the 8020A. The rubber skirt that surrounds the banana plug is a little too big. I have the originals "somewhere" and if not, I will put some long straight banana plugs on a new set.

[david77]

Good job!
Another Fluke meter saved from the skip   .

They may not be compliant to current safety regulations, but I'd still trust them more than any cheapy
China meter. I bet the 8020 survives 230VAC on the ohms range... no don't try it  .

[Kiriakos-GR]

The really funny part is, that none of my new "genuine Fluke" test leads will fit the 8020A. The rubber skirt that surrounds the banana plug is a little too big. I have the originals "somewhere" and if not, I will put some long straight banana plugs on a new set.

haha no-shit ..  

Same story also with the the desktops 8010A & 8012A ,
and only the latest 8050A will accept the latest Fluke leads, the ones that work with the 87V and 28II.

I did a long investigation, and found nothing (as an old product code for them).

straight banana

Yes the only solution , but avoid the very cheap ones with rubber cover.  

[jwhitmor]

I do not remember the 8020A having the HV fuse which seems to be standard in the new fluke meters, but I do agree with David77. A guy I knew used a cut-rate meter to troubleshoot a light fixture on a small airport runway. Guess he did not know they run at high voltage, because the meter flashed over internally, and blew the cover to pieces. He was OK because it was cold outside, and he had gloves on. The meter, and his composure were both destroyed. Next time he works on HV, he will probably try using his "Wiggins" tester.
J.W.

[Kiriakos-GR]

The desktops 8010A & 8012A & 8050A , they do have High voltage Fuses in them.
But it is on the PCB , they also have glass fuses at their face plates ... as primary.
Plus an third fuse after their transformer ..  

I bet that high level of humidity helped in such HV accident.

This is another good reason , of why I feel very nice, by having next to me the waterproof 28II .

And I will continue to thanks our Dave for that, as long I live..  
  

[alm]

The fuse is only used for current measurements, which are typically not used when troubleshooting light fixtures, except by mistake. Sounds like just bad design or bad reading of the specs by the user, if it was not designed for this over voltage.

[donbrenrik]

jwhitmor; that was great replacement.  Ordered 2 LUMEX lcd units from Mouser to repair my 8020A used in
80s when I worked for data general here in MA area.  Would appreciate it very much if you cound email me PDF for wiring connections.  I have LUMEX Data sheet and Fluke pdf manual.  Thanks again for the fine article and pictures of the 8020A; as well as the LCD part number.  Bye for now.

don71bren@verizon.net

[lowimpedance]

jwhitmor; that was great replacement.  Ordered 2 LUMEX lcd units from Mouser to repair my 8020A used in
80s when I worked for data general here in MA area.  Would appreciate it very much if you cound email me PDF for wiring connections.  I have LUMEX Data sheet and Fluke pdf manual.  Thanks again for the fine article and pictures of the 8020A; as well as the LCD part number.  Bye for now.

don71bren@verizon.net

Hi Don
 See below my origional response to JW at the time when he repaired his fluke. Note the IC used by fluke is similar to the INTERSIL ICL7106 LCD driver, so use that data sheet in combination with the Fluke manual to get the PCB connections. Have a look at my pictures in post 1. The mechanical mod to the LCD housing to accomodate the new LCD is most likely the hardest part. Take it easy dont rush and before you know it the 8020 will be ready for many more years of service. Have fun, and if JW is reading this and can forward a wiring diagram well all the better.
Just recently I have aquired another 8020a with a dud display(at the right price of course  ), a job for a rainy day ----

LowZ
 

Beautiful, professional, job!   

I have been trying to find a way to salvage my favorite old Fluke 8020A for years. I bought it at a time when they cost "real dollars", and I used it to troubleshoot my first computer project, (which had 14,000 hand soldered joints). I have the through pin LCD replacement. Do you have any sort of circuit interconnect table or diagram you would like to share? If not, I will wait until I am snowed in for a couple of days, and use that time to figure it out (in between chucking logs into the fireplace).

Thanks!
J. R.

 I must admit that I cannot locate the scribble that passes for a connection diagram, however you should be able to work it out easily from the 8020a schemattic  (fluke website if you dont already have), and your lcd datasheet. Note the main IC is an ICL7106 with plenty of data on the web, (curiously enough Intersil also made a reversed pin connected version which is luckily not common. I repaired an old Keithley with the more common 7106 doing a dead bug style wiring to get the connections right!). The only other point to make is the mechanical fitting, I was able to remove the right amount of plastic from the moulded plastic support so that the LCD sits on and could get the protective plastic cover to fit by milling it out in my workshop at work. So if you dont have access to something like that then you could use a dremmel etc very carefully to do the job, (and take your time). Solder all your wires needed to the pcb first, (wire wrap wire works a treat), then attach the LCD mount and connect each to the required pin. As long as you get the back plane right any other mistakes can easily be identified and corrected.
 When done the display will look better than the origional fluke in good condition, well mine does, ( I have other flukes to compare).
Good luck
cheers
John

[jwhitmor]

donbrenrik,
I have been away from the eevblog, and apologize for the delay. I Emailed the information to the address you provided, and will try to attach it here as a zipped .pdf file. The plastic support under the original LCD is too deep and a little too tall to fit the new LCD under the cover glass. I removed the plastic that got in the way with small files and a Dremel tool. There was not much holding a couple of the legs to the support when I was done, but it has worked very well so far. It may be possible to save a bit more plastic on top, by shortening the legs a bit, but that may present some problems too. There is room under the plastic support to route some of the individual wires that replace the ribbon cable. Just be a patient and neat as possible. I do not believe the "Over-Range" indication can be made to work without additional logic circuits, but the digits "blank" on an over-range, so you know if (when) it happens.
Cheers!
jwhitmor

[Kiriakos-GR]

Great work jwhitmor 

I saved one copy of your PDF too.

[SgtRock]

To All:

--Great work. This post contains a wealth of info on old fluke displays. I saved an old 77 by replacing the DA chip and the elastomeric conductors. I got the new grey rubber (instead of pink) conductors and a NOS DA chip from Fluke for $25 shipping included.

--Now, seeing what you fellows have done with old LCD displays, I cannot wait to get my hands on an old Fluke meter (cheaply) that needs this kind of work. Special thanks to Kiriakos, who like Odysseus, is never at a loss.

"The difficulty is not so great to die for a friend, as to find a friend worth dying for." Homer
Best Regards
Clear Ether