Products > Test Equipment
Fluke 8840A/AF 8842A VFD Display Replacement
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SilverSolder:

--- Quote from: Kjo on June 26, 2023, 01:42:45 am ---VFD offer design flexibility not easily achievable with discrete LED modules. (Even today). I think they were also brighter and offered fixed mixed color with different phosphors historically.
Graphic LCD &  OLED can now offer similar design flexibility.
I also think they this particular Itron display had some manufacturing issues that made its reliability and lifetime bell curves much broader for some reason, leading to  fading not seen in other VFD displays. I have seen microwave ovens just as old as Fluke 8840A meters with VFD displays that are still working brightly. But I have many more 8840A than microwave ovens, so the data is poor.

--- End quote ---

OLED has its own durability issues?  -  LED seems pretty reliable, I have some ancient HP units from back when the LED segments were individual dots...   they all still work, after ~50 years.
Kjo:

--- Quote ---OLED has its own durability issues?  -  LED seems pretty reliable, I have some ancient HP units from back when the LED segments were individual dots...   they all still work, after ~50 years.

--- End quote ---

I understand your point of view, but anecdotal experience is not useful without a boat load of data. I can counter your observation with real, modern 21st century product design using 0805 SMD discrete LEDs in user interface displays that burn out withing about 5 years. Electrolux refrigerator displays from 2012-2019 used discrete LEDs to form both 7 segment functions and text annunciation. All segments and text that is in static ON condition will eventually burn out. Segments and text that are not always ON will display full brightness. There is no repair for this failure other than replacement of the display module with a NOS unit. The design flaw is not that they used discrete LEDs, but that the bias selected caused premature failure that was likely understood at the time, but ignored.

Apple makes millions of iWatches with OLED displays. I doubt the failure rate of these displays is a more than a micro-percentage of the failure rate of Electrolux displays. My point is that in the field of amateur equipment repair, the choice and result of device replacement selection is far more variable than big time manufacturers efforts. And if they can screw up by design or by ignorance, amateur work cant expect to land with statistically better results.

kjo - KO3Y
AVGresponding:
Premature failure in modern LEDs is as you pointed out, a deliberate design choice; they are overdriven. OLEDs on the other hand degrade even when off, though since it takes several years, smartwatches are likely to have been replaced by newer models before there's a significant quantity in the RMA chain.

In any case, VFDs and GDTs are where it's at. You can keep all your silly diodey stuff   :P
SilverSolder:

--- Quote from: Kjo on July 09, 2023, 02:57:42 am ---
--- Quote ---OLED has its own durability issues?  -  LED seems pretty reliable, I have some ancient HP units from back when the LED segments were individual dots...   they all still work, after ~50 years.

--- End quote ---

I understand your point of view, but anecdotal experience is not useful without a boat load of data. I can counter your observation with real, modern 21st century product design using 0805 SMD discrete LEDs in user interface displays that burn out withing about 5 years. Electrolux refrigerator displays from 2012-2019 used discrete LEDs to form both 7 segment functions and text annunciation. All segments and text that is in static ON condition will eventually burn out. Segments and text that are not always ON will display full brightness. There is no repair for this failure other than replacement of the display module with a NOS unit. The design flaw is not that they used discrete LEDs, but that the bias selected caused premature failure that was likely understood at the time, but ignored.

Apple makes millions of iWatches with OLED displays. I doubt the failure rate of these displays is a more than a micro-percentage of the failure rate of Electrolux displays. My point is that in the field of amateur equipment repair, the choice and result of device replacement selection is far more variable than big time manufacturers efforts. And if they can screw up by design or by ignorance, amateur work cant expect to land with statistically better results.

kjo - KO3Y

--- End quote ---

That absolutely makes sense.   

We are rarely see "over-engineered" products like that light bulb that has been working for >100 years at some fire station in the US.  We are getting (too) good at targeting a specific design life, after which we are supposed to scrap/recycle the product and buy a new one... easy monthly payments!  Given this philosophy, is it any wonder that not much weight is given to longevity considerations?

But still...  VFDs are generally doomed to go dim over time, in my experience.  Which reminds me, I've got to fix the VFD in the microwave, it is now so dim I can hardly see it...
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