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| Agilent 34401A VFD replacement |
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| alm:
--- Quote from: coromonadalix on November 29, 2022, 03:44:00 pm ---the vfd will eventually deteriorate over the years ... gradually dim ... etc ... it's a sure fact Same problems for many vfd based instruments, since some of them are powered for very long periods .... --- End quote --- And OLED displays don't even need to be powered on to deteriorate ;) |
| coromonadalix:
--- Quote from: wasedadoc on November 29, 2022, 05:57:21 pm --- --- Quote from: coromonadalix on November 29, 2022, 03:44:00 pm ---the vfd will eventually deteriorate over the years ... gradually dim ... etc ... it's a sure fact --- End quote --- Don't count on that not applying to OLEDs too. --- End quote --- You need to check some oled meter displays substitutes threads, some of them are dying faster than the 34401A VFD itself ... |
| Veteran68:
The revision of mine is 10-05-02. So only 20 years old, not pushing 30+ like some of them out there. :) As I'm going through the menus tonight, I noticed a pattern in this "leaky" segment behavior. At least for the moment, it's happening whenever either of the bottom slanted segments are used -- either "\" or "/". So V, R, and N all show the extra segments (see photo). Whenever one is displayed, so is the other, and it doesn't matter the digit's position. So those two segment lines seemed to be tied together. I don't know if that's enough of a clue for anybody that's seen this behavior to narrow down the problem or not. When I get time here in the next few days I'll take it apart and look for bad caps or transistors, and if I don't see anything obvious I'll replace the driver IC when it gets here. |
| coromonadalix:
eh i could be wrong, the vfd controller could play tricks ??? but the problem will be, remove the vfd carefully, change the chip, put back the vfd But i would personally check before assuming its the vfd controller that all the supply lines and noise juuuuust to be sure they are clean Some people reported bad capacitors on the vfd pcb supply lines ??? you're dealing with old puppies from 20, 25 ... years old in some cases ?? my 2 cents, sure the vfd controller is not too pricey the 34401a sucessors aka 34410a and 34411a just had their end of life made in febuary 2022 ??? no original keysight vfd+pcb are available only clones ... or keysight repairs who cost like a new meter loll |
| robert.rozee:
hmmm... when one lower diagonal is on, so is the other. looks like it could be a short. do you see ANY characters displayed where one lower diagonal is ON, while the other lower diagonal is OFF? i'd be checking the display PCB for the dreaded tin dendrils. these are fine whiskers of tin that can grow between electrical contacts, developing over a period of many years. microscopically thin, but can grow up to half an inch or so long. these dendrils can be removed simply with a paint brush, although be cautious when brushed aside that they do not land somewhere else where they can cause mayhem! cheers, rob :-) |
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