EBAY: LED Display Module FLUKE 8840A/42A (DIY Kit) replace broken, damaged VFD

[AHOL]

I'm glad you liked it!

It was originally planned that the size of the letters will be the same as the original, but it had to be reduced, otherwise the adjacent characters will glow.
Magnification is possible, but it will be necessary to increase the displayed area, this is due to the technological process.
This will offset the display slightly from the original.

If colleagues support this idea, then you can try, by the way, you can make the ERROR symbol red.
How is this idea?

[batpuncher]

Recieved a couple, both working great.  Now I can try to find out why the 42 doesn't seem to power up.

[AHOL]

Dear colleagues, a new batch of modules.

Welcome: https://www.ebay.com/itm/154612343972

Best regards.

[Paceguy]

I'm glad you liked it!

It was originally planned that the size of the letters will be the same as the original, but it had to be reduced, otherwise the adjacent characters will glow.
Magnification is possible, but it will be necessary to increase the displayed area, this is due to the technological process.
This will offset the display slightly from the original.

If colleagues support this idea, then you can try, by the way, you can make the ERROR symbol red.
How is this idea?

Could there be a way to mask off the sides of the LED's to eliminate the glow effect on adjacent LED's inorder to accommodate larger letters?

[AHOL]

For clarity, I will show the difference in the displayed area, when changing the height of the letters





I have not made accurate measurements yet, this is an example.

But the creation of a module with enlarged letters is possible only after the completion of this project, since it requires financial costs.

[xwarp]

DO WANT!!!!!!!!!!

[Zucca]

This module uses a custom-made, industrially produced 7-segment display

Can you give me more information about how to produce/get such a custom LED display? Who is your supplier?

[AHOL]

Dave described how to design a custom multiplexed LCD display. https://www.eevblog.com/forum/blog/eevblog-1055-how-to-design-a-custom-lcd/

The LED display design is no different, even a little simpler.

According to your prepared drawings, any display manufacturer with more than 5 years of experience can handle the production of a display.

[AHOL]

Hello all,

Thanks to everyone who purchased the modules.
A new batch of modules will be ready for the New Year.
Unfortunately, COVID-19 is making its own adjustments.

I'll let you know.

P.S. If you wish, share a photo of the repairs made.

[bikeNomad]

I just installed one of the v4 displays in an 8840A which turned out to be broken. So I may decide to de-solder it.
But the display looks great.
Here's a comparison: the meter on the top has the LED display replacement, the meter on the bottom has a nice bright VFD display, and the meter in the middle has a somewhat dimmer display.

[BU508A]

Very cool! Thank you! 
I'm a bit late to the party so I'll wait for the new batch. 

[Cubdriver]

Very impressive!  Nicely done.

-Pat

[Kjo]

I can attest that the 2nd gen versions work just fine, albeit with annunciations that are a bit too small. I hope 3rd gen displays are better in this regard.

While one should be concerned about loading the +30V supply, it is quite tolerant of modest level conversion loading without impacting A/D performance. See the following thread I created on a universal OLED replacement display.
https://www.eevblog.com/forum/testgear/fluke-884042-series-universal-replacement-display/msg3862550/#msg3862550

I have used both active and passive 30:5V level converters to drive the OLED controller. The loading on the +30V supply varies from 500ua to 1.5ma per signal (8 grids, 11 segments), depending on the translator choice, and the main PCA passes all self tests. Of course this design cannot compete on cost with the blue LED replacement. There is just too much circuitry and assembly to do that.

On another note, one should be cautious in assuming that a blue LED replacement offers an inherently higher reliability or longevity than the original VFD. While I have LED based equipment from the 80’s that works flawlessly, this photo shows my 5year old Frigidaire LED display. It is rather obvious that modern LED devices are not flawless.


AHOL has not yet provided us with much manufacturing information, let alone reliability and longevity data. I don’t expect his volume is adequate for that anyhow. Still, it has brought back from the dead 4 of my Fluke 884X meters! For that I am thankful.

Kjo - KO3Y

[bdunham7]

While one should be concerned about loading the +30V supply, it is quite tolerant of modest level conversion loading without impacting A/D performance.

It is regulated, so as long as it doesn't get loaded down below the regulated voltage all is well.  After all the VFD current loads it in the original design.  Have you measured the 30V supply with your design?

[Kjo]

I can’t measure a significant difference either DC or on a scope from the OLED, blue LED or VFD for that matter. I can sometimes lock on 20-40mv synchronous noise, but can’t match it to anything. Also, I have never found any information on the VFD grid and segment currents, so there is nothing to compare to.

[bdunham7]

I can’t measure a significant difference either DC or on a scope from the OLED, blue LED or VFD for that matter. I can sometimes lock on 20-40mv synchronous noise, but can’t match it to anything. Also, I have never found any information on the VFD grid and segment currents, so there is nothing to compare to.

If it isn't sagging noticeably it should be fine.  I measured the VFD currents when I was working on my now abandoned display project and IIRC it was low single digit mA for the segments.  Never thought to measure the grids.

[Kjo]

Just for a reference, here are 2 OLED pics. Digital power is from the 5VDC lug and digital ground lug. There is no modification to the Fluke main PCA. The OLED controller is on the back of the VFD PCB. The 2 16 pin flat cables plug into the controller as they did to the VFD PCB.




Because a microcontroller is used, there are 7 selectable display modes plus a display demo mode.

Kjo - KO3Y

[AHOL]

Great job.
Yes, OLED looks modern. In the beginning, I also went down the path of creating such a display,



I even bought a suitable display, but gave it up for several reasons:
1) Lack of a display that exactly matches the dimensions of the VFD being replaced.
2) The high price of a ready-made module.
3) Relative unreliability due to the large number of components.

But in general, such a replacement is possible subject to a number of conditions:
- Lack of additional termal and electrical instability.
- Do not obstruct the installation of the AC board.

What I mean. Placing the display controller board in close proximity to thin film resistors can cause additional termal instability.
Unsurprisingly, FLUKE shielded the Z101 resistor circuit, which is located next to the A/D ASIC.



It seems to me that this should be taken into account.
In general, the display has the right to live without distorting the operation of the multimeter.

[Peteg]

Thanks for sharing, looks great.

[Kjo]

I can’t measure a significant difference either DC or on a scope from the OLED, blue LED or VFD for that matter. I can sometimes lock on 20-40mv synchronous noise, but can’t match it to anything. Also, I have never found any information on the VFD grid and segment currents, so there is nothing to compare to.

If it isn't sagging noticeably it should be fine.  I measured the VFD currents when I was working on my now abandoned display project and IIRC it was low single digit mA for the segments.  Never thought to measure the grids.

Good reference point for the segments. The translation device I used also draws ~1.4ma from a high segment line (and the same for grids but that is always 1:8 ). The VFD grids are driven to 30v so I would expect similar or higher given the size.

[AHOL]

Glad to meet everyone in the New Year!
All the best for the New Year!

A new batch of LED displays are on sale.

Listing link updated (first post).
https://www.ebay.com/itm/154780459035

[BU508A]

Ordered one. Thank you! 

[jonpaul]

Hello very fine work: Does the kit include step by step instructions or one muse go thru this very long thread to extract the procedure?



I have never disassembled the 8842A. Approx Time  to do the entire process,  1 hr? 1 day?

I will buy IF  if the procedure is easy and obvious but no time in my life to use up a day.

Many thanks

Jon

[Kjo]

I have replaced 3 VFDs with these LED units. You need to follow the service manual to disassemble the meter and extract
the VFD PCB. It is easily done but not trivial. Care must be taken to not damage any of the hybrid modules on the
main board. Dont take short cuts. You must have the basic skills to de-solder the VFD also. The traces are easily
damaged with too much heat.

Installation of the replacement to the PCB is easy. Reassembly is the reverse of disassembly.
Not a 1hr job.

[ErwinsCat]

Hi, is this kit still available to buyers? the eBay link seems broken.