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

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bdunham7:

--- Quote from: Kjo on December 09, 2021, 03:53:20 am ---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.

--- End quote ---

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.

[attachimg=1]
[attachimg=2]

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:

--- Quote from: bdunham7 on December 09, 2021, 04:00:45 am ---
--- Quote from: Kjo on December 09, 2021, 03:53:20 am ---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.

--- End quote ---

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.

--- End quote ---

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.

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