53131A/53132A/53181A Question

[5065AGuru]

Hi,

Does anyone know if the display and the power supply assemblies are the same in all 3 of these counters?
My display is starting to dim and I thought I'd keep an eye our for some junkers.

Thanks,

[kj7e]

Yes, they are the same.  I would recommend a new VFD from eBay, replaced mine last year and its like new again;
https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg2696306/#msg2696306

https://www.ebay.com/itm/1PC-NEW-HP-Keysight-Agilent-53131A-53132A-VFD-Display-Counter/173868447306?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

[NoisyBoy]

If the VFD is all you want, why not just buy a replacement?  eBay has it for under $100.

[tkamiya]

WOW!  Nice!  Mine are starting be quite a bit dim....  It's kind of pricey for copies (not genuine, right?) of the original though. 

[james_s]

I'd be kind of surprised if they're copies, I don't think HP manufactured the displays themselves anyway. Even if they were copies, <$100 for a custom VFD sounds quite cheap to me.

[tkamiya]

I am certainly not accusing this seller.  I've bought from him before.

But custom may be but when done in thousands, the cost basis might be surprisingly low.  These counters are popular and numerous, and many of them are starting to dim.  Yet, in typical HP fashion, rest of the equipment will last and last.  A good business opportunity for sure with someone with some initial capital.   

[syau]

Same seller also sell “compatible” VFD display for HP/Agilent gears include 3458A. Too bad they they don’t make VFD for Keithley Gears.

[TomT]

These displays are like CRT's, and over time the filament/cathode grows weaker, and the phosphor is burned, so replacement is the only way to resolve this.

They are also very specifically designed for the HP counters, having special text along the bottom, and right sides, and comma's/semicolons, none of which are available on any other display.

At this point, the eBay option is about the best.  Just look closely at the pictures to see if there are any indications of phosphor burn, as it is likely that these are used.  Often you can see lines across character segments, which are right behind the filament/cathode wires.  If they say they are new, be careful.

I have been considering an LED based replacement, but it's not an easy project to undertake.  The electronics is easy, but to make the display look anything like the original is a royal pain.  Especially the text at the bottom and right, and the comma's.

[james_s]

This is a somewhat old thread and the ebay displays appear to be sold out so that may not be an option now.

It may be possible to have a run of replacement displays made, I was surprised a few years back when someone got a small run of custom LCD displays at a price that was much cheaper than I expected. I suppose a custom LCD could be a viable option for instruments like this although I think the VFD looks a lot nicer. If somebody made a graphical TFT or OLED panel with the right aspect ratio that would probably result in a nice looking display but getting the size and aspect ratio right is the challenge. A custom LED display might be viable, COB LED module with a molded plastic light guide, I have no idea if anyone makes those in small quantities but China has impressed me before.

[TheSteve]

Since this thread was bumped and for the sake of completeness I'd like to add that the 58503A and 58503B series of GPSDO's also use the same VFD.

[TomT]

Hi Steve,

Your idea of using a 58503A/B display on 53131A/53132A/53181A counters may or may not be viable, as I have not found a manual that shows the actual display.  The problem is with the status text segments at the bottom and right of the display.  VFD's are very nice to look at, but since they are vacuum tubes, their life expectancy is far less than LED's.

The idea of an LCD display does sound like a good idea, but there would also have to be drivers for the LCD segments and digits.  There are some nice 14 segment SMD LED displays available, but they only have decimal points.  Punctuation segments would have to be added between each digit of the the LED displays.  Status text would have to be done with side lit engraved plastic.  It may be possible to have special SMD displays with the decimal/colon/comma/semicolon segments incorporated.

My primary reason for the 14 segment SMD LED's is that the processer spits out the 14 segments, punctuation, and status segments already decoded as a serial string, and goes into a 32 bit shift register with high voltage outputs to drive the segments and digits of the VFD.  My current design uses 4x 74HCT595's, and some current limiting resistors.  I am about to order displays from Digikey, and will breadboard it to operate in parallel with the current display in my counter.

Since the display data is already decoded, converting it to work with an OLED or any dot matrix display would take too much to add.

[james_s]

It's possible to have fully custom LCD displays made, with whatever segment and custom character layout you want. Someone on this forum did it a while back with the display for a vintage handheld computer. I think LCD is the worst looking of potential options though.

I haven't checked but I suspect the encoding to the display is something trivial like SPI. It is actually very easy to decode this and convert it to whatever arbitrary format you want using a microcontroller. I have a computer interface in my early 90s Pro-2004 and 2006 scanner radios that does just that, it captures the SPI to the display and uses that to read the status of the scanner. That interface was designed over 20 years ago around commodity parts.

[TomT]

I am currently looking into both custom LED and LCD options, but LCD's react slower than LED's, so LCD's may not make the grade.  They can both be made to look much like the VFD displays.  A new post has been started for the project, titled: "HP/Agilent 53131A/53132A/53181A Conversion to LED Displays".

As for the encoding, it's actually considered decoding, and it is done in the processor on the main board.  The data, in this case ASCII character data, is encoded binary data, not meant to be directly read by humans.  It is decoded to be displayed.  The data is sent serially with a clock, not unlike SPI, but much simpler, as there is only clocked data sent.  No addressing, or programming of registers.  The only returned data is that which was clocked in with the previous 32 bits, as the next 32 bits are clocked in.  For more information on this method, look up a simple version of the IC used for the VFD, called a 74HC595.