[volt-nuts] dark display for 3458

[Didier Juges]

I have fielded two dozen pieces of equipment with 2x16 VFD from Noritake. These are on 24/7 and they were shipped over a 4 year period starting in 2000. In normal state, there are 4 digits always turned on on the first line. The other digits are rarely turned on.
The displays start being noticeably darker after 2 years and barely usable after 3-4 years. The digits that are not normally used seem to last much longer but they eventually get darker, just at a much slower rate. It may be due to contamination rather than the filament itself wearing out. By now, most have been replaced at least once, with a different part number because the old one has become obsolete.

Didier KO4BB


On April 11, 2015 11:37:49 AM CDT, Chuck Harris <cfharris at erols.com> wrote:
> From visual inspection, the filaments in these
>vacuu-fluroescent displays look like bare wire,
>which would make them some sort of doped tungsten
>alloy.. which doesn't really ever wear out.
>
>The only problems I have ever seen is due to
>phosphor fatigue.  The display stops glowing
>on whichever digit is on all the time... and
>you see this as unequal brightness between the
>digits.
>
>I have never seen a vacuum fluorescent display
>just fade away in any reasonable time.  They
>seem to go for years and years.  I have alarm
>clocks and ovens, and microwaves with these
>displays some of which have been glowing for
>around 40 years now, and still going strong.
>
>I have seen vacuu-fluorescent displays that
>have gone dark, and found that the reason is
>the filament supply has quit...usually due to
>a bad electrolytic capacitor.
>
>-Chuck Harris
>
>Don at True-Cal wrote:
>> The 3458A DISP? command, rather entered from the front panel or via a
>GPIB Command is not adequately discussed in the User's Manual IMO.
>There are four numeric values 0,1,2 & 3 plus the ability to enter a
>string value as mentioned below. All four values are supported via the
>GPIB, but only 0,1 &2 are valid modes for the front panel DISP? command
>- the front panel DISP? 3 seems to be accepted and interpreted the same
>as DISP? 1 (On). The value 0 (Off) seems somewhat pointless and simply
>places dashes across the display. The value 1 (On) is the default and
>normal mode. The value 2 (Msg) displays control messages only. These
>three modes would obviously offer no help to prolonging display life
>since the display filament would need to remain on. The interesting
>DISP? 3 (Clr) is the one in question rather is removes power to the
>display filament providing some help for display life. I'm not sure
>without actually getting inside and testing if filament voltage is
>present or not. Checking t
> h
>e
>>    schematics for a display filament voltage interrupter might also
>be a clue, but would still be firmware dependent. I use Agilent VEE for
>3458A control and plotting and have provided a dynamic display control
>using DISP? 0-3 modes and I often leave the display in mode 3 (Clr) for
>long plot cycles (sometimes weeks). In this mode, the display is
>completely blank, including no enunciator (sampling) indicators at all.
>My hope is that the display filaments are off. Anyone know for sure?
>>
>> Don
>>
>> -----Original Message-----
>> From: volt-nuts [mailto:volt-nuts-bounces at febo.com] On Behalf Of new
>> Sent: Saturday, April 11, 2015 12:09 AM
>> To: volt-nuts at febo.com
>> Subject: [volt-nuts] dark display for 3458
>>
>> Hi, again...
>>
>>    Now that I have the keysight connection expert running my two sick
>3458s, I don't need to look at data on the displays. To keep them from
>burning out, I wanted to turn them off.
>>
>>     I found a workaround of:
>>
>> DISP 0,'  (16 spaces) .'
>>
>> This put a period on the bottom of the blank screen and moves it 16
>spaces to the right.....
>> right off the screen!
>>
>> So now the display is dark and only shows things like the 'err'
>message.
>>
>> QUESTION - will this kill the 3458 or its display somehow?
>>
>> Willy
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