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

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

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 <cfharris@erols.com> 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 -- volt-nuts@febo.com >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.