Hi Chuck, It is very interesting and unexpected. These displays were replaced for no other reason than they were difficult to read, and now this particular sample is just fine.
I have a couple more, I will try to cycle them through my prototype. I know that I have had a number of clocks with VFDs that became unusable for the same reason over the years. This is the first time that I get one to restore itself. Not sure how much of that would be useful with the 3548 display. Didier KO4BB On April 28, 2015 11:05:19 AM CDT, Chuck Harris <[email protected]> wrote: >Hi Didier, > >That is most interesting! > >The architecture of the displays is such that there are multiple >cathode wires, one over the top of each "row" of segments, usually. >The cathodes are run dark, so they are barely emitting, and cannot >really ever burn out. > >I have found the ugly looking displays are the result of the cathodic >emission right under the wire being better than between the wires, >rendering a mottled appearance. > >In some of the early clocks and alarm clocks, that used VFD's (since >the US clocks are always in 12 hour display mode) if they were changed >to 24 hour mode, after a long life, the "E" digits that make up the >most significant digit were always much brighter than the rest of the >digits on the display, rendering a "2" where the newly lit horizontal >segments were brighter than the rest. > >In any case, I have some VFD's that have been in continuous use since >I graduated from college, and that was a long, long, time ago. And >they are still going strong. > >I have to wonder about the failures in the 3458 display. My instinct >tells me that it isn't the VFD but rather the driver/power supply that >has failed. Probably a bad electrolytic capacitor if things go the >way they usually do. > >-Chuck Harris > >Didier Juges wrote: >> After the thread about the 3458 display, I went back to one of those >VFD >> that I mentioned in my earlier post. These had been used with only a >few >> digits turned on on the first line, the rest of the display being >normally >> turned off and only used occasionally. After several years of >continuous >> operation, the digits that were used had lost brightness and more >> interestingly, the other digits had also lost brightness but also >looked >> botched (the brightness was very uneven). >> >> It turns out I have been using one of these old displays on a new >project >> (it's a development job, so the unevenness does not bother me at the >moment >> since this display will not ship). After about 2 weeks of continuous >use >> where most of the digits are used, the display is now just about back >to >> normal. somewhat dimmer than a new one, but the unevenness has >completely >> disappeared. >> >> It looks like either the digits themselves, or the cathode wire, had >become >> contaminated as a result of not being used, and a few days of >operation >> restored their activity. >> >> Even more interesting, at the moment, I cannot detect a difference in >> brightness between the old digits that were on for several years and >those >> that were not. The display is generally dimmer than a new one, but >the new >> ones are a different part number, the original device having been >> discontinued, so it may also be that the new display is brighter >because of >> process improvements by the manufacturer (something the manufacturer >> advertised when they introduced the new device). >> >> On this development job, most of the digits are used, and the display >is >> constantly changing (scrolling messages). >> >> Anyhow, I thought it would be interesting to mention. >> >> Didier KO4BB >_______________________________________________ >volt-nuts mailing list -- [email protected] >To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >and follow the instructions there. -- Sent from my Motorola Droid Razr HD 4G LTE wireless tracker while I do other things. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
