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Products => Test Equipment => Topic started by: dimmog on November 11, 2025, 03:01:11 am

Title: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on November 11, 2025, 03:01:11 am
The dual color LED display replacement for the HP / Agilent 34401A is finally ready, and we started shipping orders today!


Hubequip website: https://hubequip.net/products/hp-agilent-34401a-vfd-to-led-display-replacement-led-conversion (https://hubequip.net/products/hp-agilent-34401a-vfd-to-led-display-replacement-led-conversion)
eBay: https://www.ebay.com/itm/325714571683 (https://www.ebay.com/itm/325714571683)
eBay listing for UK buyers: https://www.ebay.com/itm/327219091572 (https://www.ebay.com/itm/327219091572)

__________________________________________________________


Prototype development in progress.

Looks good so far. The main problem was that the 34401A display board didn't have a +5V rail to power the LED display,
so we decided to use the filament supply with an extra LDO.

Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Zucca on November 11, 2025, 03:16:18 am
I hope you will sell at least 500 units... finally!
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: coromonadalix on November 11, 2025, 11:16:16 am
 :-+
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: the Chris on November 11, 2025, 08:50:21 pm
Awesome! Happy to see this product becoming real  :-+
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: The Doktor on November 12, 2025, 07:06:59 pm
Can the filament supply definitely handle that much current continuously? Would hate to see it kill the transformer in a short time.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on November 12, 2025, 08:11:58 pm
Can the filament supply definitely handle that much current continuously? Would hate to see it kill the transformer in a short time.

Good question. That was actually the first thing we checked before starting.
The VFD filament draws about 140 mA continuously.
The LED display consumes around 80–95 mA during normal operation and about 190 mA at power-on, when all segments light up during initialization.

I'm quite confident the transformer's filament winding can handle more than 140 mA continuously. HP engineers definitely designed it with some margin in mind.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on March 14, 2026, 12:35:38 am
We are currently experimenting with LED colors for the 34401A VFD replacement display. What do you guys think about a dual-color display?

Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: coromonadalix on March 14, 2026, 01:34:22 am
would be happy with theses photos  not too bright or dark,  not red  not dark blue  not orange, not green     loll
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on March 14, 2026, 01:44:20 am
would be happy with theses photos  not too bright or dark,  not red  not dark blue  not orange, not green     loll

After seeing it in person, I now think a single color display looks quite boring.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on March 14, 2026, 02:34:46 am
The dual color looks great!
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: the Chris on March 14, 2026, 02:36:59 am
Thanks for the update!

To me, the perceived brightness of the white elements seems higher than that of the cyan colored ones even though the cyan ones are the main elements. I like the idea of dual color use but I think that one has to make sure that the appearance of the large ciffers still dominates the display.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on March 14, 2026, 02:43:34 am
Thanks for the update!

To me, the perceived brightness of the white elements seems higher than that of the cyan colored ones even though the cyan ones are the main elements. I like the idea of dual color use but I think that one has to make sure that the appearance of the large ciffers still dominates the display.

In person, they look equally bright. It's very difficult to take a photo that accurately represents the true colors and brightness of both.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Zucca on March 18, 2026, 01:12:08 am
Maybe the "Error" annunciator in red color?
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on March 18, 2026, 02:00:18 am
Maybe the "Error" annunciator in red color?

And preferably a thicker font.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on March 18, 2026, 02:32:23 am
Maybe the "Error" annunciator in red color?

Red is not an option. It has a lower forward voltage, and we cannot add a separate current limiting resistor for a single segment.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on March 18, 2026, 02:34:38 am
Maybe the "Error" annunciator in red color?

And preferably a thicker font.

The font used for 'ERROR' is the same as for the other words. It just blinds the camera more, which makes it appear thinner.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Zucca on March 18, 2026, 02:42:09 am
Maybe the "Error" annunciator in red color?

Red is not an option. It has a lower forward voltage, and we cannot add a separate current limiting resistor for a single segment.

I will then use my red sharpie on the display glass  :-DD
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on March 18, 2026, 02:56:59 am
Maybe the "Error" annunciator in red color?

Red is not an option. It has a lower forward voltage, and we cannot add a separate current limiting resistor for a single segment.

I will then use my red sharpie on the display glass  :-DD

I hope this annunciator never appears on your unit 🙂
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on March 18, 2026, 03:00:21 am
Maybe the "Error" annunciator in red color?

And preferably a thicker font.

The font used for 'ERROR' is the same as for the other words. It just blinds the camera more, which makes it appear thinner.

That's the problem. The word error is the only one inverted with a white box, so it's now negative text. It will look better & be easier to read with a thicker font.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on March 18, 2026, 03:19:40 am
That's the problem. The word error is the only one inverted with a white box, so it's now negative text. It will look better & be easier to read with a thicker font.

Trust me, it looks much cooler in real life. The camera just refuses to cooperate on this one. 😄
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on March 18, 2026, 03:38:58 am
That's the problem. The word error is the only one inverted with a white box, so it's now negative text. It will look better & be easier to read with a thicker font.

Trust me, it looks much cooler in real life. The camera just refuses to cooperate on this one. 😄

lol, I believe you. However, I'm not wrong. It's harder to read with a thin font like that, and your customers will want to take photos of the screen. They'll also have trouble getting a clear photo with that thin font.

Design is my primary business. I'm not guessing how this works. ;)
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on March 18, 2026, 04:01:59 am
That's the problem. The word error is the only one inverted with a white box, so it's now negative text. It will look better & be easier to read with a thicker font.

Trust me, it looks much cooler in real life. The camera just refuses to cooperate on this one. 😄

lol, I believe you. However, I'm not wrong. It's harder to read with a thin font like that, and your customers will want to take photos of the screen. They'll also have trouble getting a clear photo with that thin font.

Design is my primary business. I'm not guessing how this works. ;)

This photo was taken with an iPhone. It still doesn't look as good as it does in person. In reality, the display is sharper and has higher contrast.

Btw, how often do you actually see a unit showing 'ERROR'? 🙂
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on March 18, 2026, 04:10:02 am
That's the problem. The word error is the only one inverted with a white box, so it's now negative text. It will look better & be easier to read with a thicker font.

Trust me, it looks much cooler in real life. The camera just refuses to cooperate on this one. 😄

lol, I believe you. However, I'm not wrong. It's harder to read with a thin font like that, and your customers will want to take photos of the screen. They'll also have trouble getting a clear photo with that thin font.

Design is my primary business. I'm not guessing how this works. ;)

This photo was taken with an iPhone. It still doesn't look as good as it does in person. In reality, the display is sharper and has higher contrast.

Btw, how often do you actually see a unit showing 'ERROR'? 🙂

One more thing. We don't have enough space to make the 'ERROR' font any bigger. If we simply bold it, the kerning will be terrible.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on March 18, 2026, 02:57:55 pm
One more thing. We don't have enough space to make the 'ERROR' font any bigger. If we simply bold it, the kerning will be terrible.

You shouldn't just bold it-you also slightly reduce the font size and fix the kerning (if needed, but kerning shouldn't be effected unless your font sucks).

Which in the attached is easier to read?
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: GigaJoe on March 18, 2026, 10:50:12 pm
"ERR" , "-ERR-" no?
as well as ERROR to ERR0R , if it NOT monospace font
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on March 18, 2026, 11:41:05 pm
"ERR" , "-ERR-" no?
as well as ERROR to ERR0R , if it NOT monospace font

It's a printed screen; they can use whatever font they want. Hopefully, they won't choose Papyrus. ;)
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Zucca on March 19, 2026, 03:13:44 am
Matter of personal taste now.

Is it not possible to place a small red led that turns on when the Error signal is active?
I would love to see a little red light that warns me something is wrong, even when I am far away from the device.

Anyway you will sell a lot of those bicolor LED for the legendary 34401A... regardless this "error" discussion.... It is not so important.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on April 19, 2026, 04:29:51 pm
Matter of personal taste now.

Is it not possible to place a small red led that turns on when the Error signal is active?
I would love to see a little red light that warns me something is wrong, even when I am far away from the device.

The "Error" segment is part of the 10th digit on the display (common cathode). Red LEDs have a lower forward voltage compared to white or ice blue LEDs, and we can't add a separate current-limiting resistor for a single segment. So unfortunately, red is not an option.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: coromonadalix on April 19, 2026, 06:05:46 pm
for zucca   add an i/o port of the mcu to drive an big 10mm red led  loll   you'll see your error status


i would be satisfied with the last shown photo of the display, error status is visible    :-+
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on April 20, 2026, 03:48:10 am
One could put a little bit of red filter over the "ERROR" annunciator.  That would make it 'eye catching'.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Zoli on April 20, 2026, 04:29:31 am
Matter of personal taste now.

Is it not possible to place a small red led that turns on when the Error signal is active?
I would love to see a little red light that warns me something is wrong, even when I am far away from the device.

The "Error" segment is part of the 10th digit on the display (common cathode). Red LEDs have a lower forward voltage compared to white or ice blue LEDs, and we can't add a separate current-limiting resistor for a single segment. So unfortunately, red is not an option.
There's no room for two in series? >:D :-DD
Edit:typo
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on April 20, 2026, 04:13:47 pm
Matter of personal taste now.

Is it not possible to place a small red led that turns on when the Error signal is active?
I would love to see a little red light that warns me something is wrong, even when I am far away from the device.

The "Error" segment is part of the 10th digit on the display (common cathode). Red LEDs have a lower forward voltage compared to white or ice blue LEDs, and we can't add a separate current-limiting resistor for a single segment. So unfortunately, red is not an option.
There's no room for two in series? >:D :-DD
Edit:typo

= uneven brightness
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: edavid on April 20, 2026, 05:48:00 pm
There are "PC red" LEDs which have a blue die + phosphor.

(Not that I think you need to bother with that. I don't even think you should have the ERROR label reversed. As you pointed out, it's rarely used.)
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Zucca on April 20, 2026, 05:58:20 pm
for zucca   add an i/o port of the mcu to drive an big 10mm red led  loll

No, I will then trigger this:
(https://assets.gordonelectricsupply.com/tsimages/EDWRDSP00002_52_PE_006.jpg)

Quote
Description:
Edwards EWS-V9 Dc Motor Outdoor Warning Siren

Technical Description:
DC Motor Driven Type; 15 HP Power Rating; Cast Aluminum Housing Material; Non Corrosive; 122 dB at 100 ft Sound Intensity; 460/920 Hz Output Frequency; Edwards. Brand

UPC: 78264001049

Part Number: EWS-V9

Manufacturer: EDWARDS SIGNAL

Your Price:  $49,284.54 / ea
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Zoli on April 21, 2026, 06:06:49 am
There's no room for two in series? >:D :-DD
Edit:typo

= uneven brightness
It meant to be a joke, so let's carry on: just place the uneven one on the back of the PCB  :-DD :-DD :-DD
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Miti on April 22, 2026, 02:14:52 am
Just curious, why so much space between the 45 degree segments and the vertical and horizontal ones? If you look at the VFD display on 34401 they are much closer. I’m guessing mechanical limitations?
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on June 03, 2026, 04:16:47 am
Just curious, why so much space between the 45 degree segments and the vertical and horizontal ones? If you look at the VFD display on 34401 they are much closer. I’m guessing mechanical limitations?

In short, yes.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on June 03, 2026, 04:21:09 am
Just a quick update: we're now testing the production prototype.
The supplier change set us back a bit, but we're almost there now.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: the Chris on June 03, 2026, 04:31:16 am
Thanks for the update. Looking forward to it.

Strickly speaking, I haven't been unhappy with the brightness of my 34401A, but once my 34410A arrived last year, I could see that the 01A is noticeably dimmer. Now that a 34411A with a nearly-new display joined the two others, I definitively want to treat my 34401A to one of those LED displays.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on June 03, 2026, 04:41:39 am
Thanks for the update. Looking forward to it.

Strickly speaking, I haven't been unhappy with the brightness of my 34401A, but once my 34410A arrived last year, I could see that the 01A is noticeably dimmer. Now that a 34411A with a nearly-new display joined the two others, I definitively want to treat my 34401A to one of those LED displays.

The original Agilent 34401A VFD was quite bright when new. In fact, they added two current limiting resistors in the latest revision of the display board to reduce the brightness. The Chinese clone VFDs currently available on eBay and AliExpress are noticeably dimmer. The brightness of our LED display is somewhere between the original Agilent VFD and Chinese replacement clones.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Smile2016 on June 03, 2026, 09:32:10 pm
Great! Agree the red "ERROR" would probably look really cool. I might struggle a bit to squeeze in a small resistor there to make it work though. I also tend to prefer slightly bolder fonts, but that’s just a personal preference.

Any idea what the overall BOM would come out to, & the selling price & availability?
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on June 04, 2026, 04:07:31 am
Great! Agree the red "ERROR" would probably look really cool. I might struggle a bit to squeeze in a small resistor there to make it work though. I also tend to prefer slightly bolder fonts, but that’s just a personal preference.

Any idea what the overall BOM would come out to, & the selling price & availability?

Expected availability is in about two weeks and it will be priced at $69.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on June 04, 2026, 04:13:40 am
A few photos for you to enjoy  :D

This is the first unit featuring the upgraded dual color LED display, and it's now available on eBay. Sold

Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on June 11, 2026, 05:33:12 am

Preorders are now open! Shipping is expected to start on June 25, 2026.

https://hubequip.net/products/hp-agilent-34401a-vfd-to-led-display-replacement-led-conversion-preorder
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on June 18, 2026, 03:50:57 am
The dual color LED display replacement for the HP / Agilent 34401A is finally ready, and we started shipping orders today!

Hubequip website: https://hubequip.net/products/hp-agilent-34401a-vfd-to-led-display-replacement-led-conversion (https://hubequip.net/products/hp-agilent-34401a-vfd-to-led-display-replacement-led-conversion)
eBay: https://www.ebay.com/itm/325714571683 (https://www.ebay.com/itm/325714571683)
eBay listing for UK buyers: https://www.ebay.com/itm/327219091572 (https://www.ebay.com/itm/327219091572)

Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on June 18, 2026, 07:51:01 pm
I'd like to point out that the new 34401A LED display is a true drop in replacement.
No additional wires need to be soldered to the display board, making the installation process quick and straightforward.

Simply desolder the original VFD display along with its mounting brackets, then solder the new dual color LED display in its place.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: willinsau on June 23, 2026, 12:38:32 pm
Are all firmware revisions compatible with both early and late versions of the 34401A VFD display assembly?
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on June 23, 2026, 02:14:34 pm
Are all firmware revisions compatible with both early and late versions of the 34401A VFD display assembly?

Yes, the LED display is fully compatible with all three display board revisions as well as all firmware versions.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: kblue on June 23, 2026, 07:03:22 pm
Out of curiosity are there any advantages with this conversion? As far as I know the VFD version is available in large quantities.

Best wishes!
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on June 23, 2026, 07:27:53 pm
Out of curiosity are there any advantages with this conversion? As far as I know the VFD version is available in large quantities.

Best wishes!

It's up to you VFD or LED. The only thing to consider is that the replacement VFDs on the market are all Chinese clones
and their long-term reliability is a bit of a question mark.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on June 23, 2026, 07:30:27 pm
The LEDs will start out brighter, and IMO easier to read.  Plus they will not fade over time.  NOS VFD units are old and probably leaky, new clones are of suspect quality and longevity.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on June 23, 2026, 09:17:15 pm
I've replaced 3 VFD's with @dimmog's LED panels. They've all been fantastic...and only one of the VFD maybe needed replacement. ;)
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: willinsau on June 24, 2026, 12:07:12 pm
what's the version of your 3 meters?
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on June 24, 2026, 02:42:34 pm
what's the version of your 3 meters?
I replaced two 53132A screens, and one K2010.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on July 01, 2026, 03:58:18 am
@dimmog, any chance you're going to do an LED screen for the 34410A / 34411A?

Thanks,
Josh
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on July 02, 2026, 02:08:12 am
@dimmog, any chance you're going to do an LED screen for the 34410A / 34411A?

Thanks,
Josh

As I mentioned before, the 34410A display isn't just a regular VFD. It has its own built in MCU that drives the VFD display, so making an LED replacement would mean reverse engineering the communication between the main board and the display. That's a pretty big project and takes a lot of time.

On top of that, the 34410A just isn't as common as the 34401A or even the Keithley 2000, so it's hard to justify all that development work.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: felixd on July 07, 2026, 06:41:49 pm
Доброго ранку @dimmog.

Greetings from Poland.

Do You have those displays somewhere in EU to send from or are You sending all of them directly from USA?
My question is how "best to buy it"?
eBay?

I need 3-4 pcs.

I have 4 34401A.
Firmwares:
- 11-5-2
- 10-5-2
- 10-5-2
- Oldest HP with 3-1-1

Will your Display fit all of them?


Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on July 07, 2026, 06:51:00 pm
Доброго ранку @dimmog.

Greetings from Poland.

Do You have those displays somewhere in EU to send from or are You sending all of them directly from USA?
My question is how "best to buy it"?
eBay?

I need 3-4 pcs.

I have 4 34401A.
Firmwares:
- 11-5-2
- 10-5-2
- 10-5-2
- Oldest HP with 3-1-1

Will your Display fit all of them?

All our displays are sold exclusively from the US. I think the cheapest way to purchase would be directly through our website hubequip.net

There are three revisions of the HP / Agilent / Keysight 34401A display board. While there are some differences between them, the dual color LED display is a true drop-in replacement and is fully compatible with all revisions and requires no modifications for installation.

Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: felixd on July 08, 2026, 11:05:37 am
Done.
3 pcs  :box:

Cheers.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Hydron on July 08, 2026, 12:40:22 pm
Now we just need 34420A (yes I know volume likely isn't there)
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on July 08, 2026, 09:40:46 pm
Done.
3 pcs  :box:

Cheers.

Thanks for your order! Dziękuję!
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on July 08, 2026, 09:49:06 pm
Now we just need 34420A (yes I know volume likely isn't there)

We're thinking about it.  ;D
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Hydron on July 08, 2026, 10:15:58 pm
Well at least it should only involve changing symbols/annunciators from the 34401A design - schematic of the display board is identical from the quick review I did yesterday.

I just bought a 34420A so very interested in the option of not spending $150-200 on some super shady ebay VFD if it turns out it needs one (don't get my hands on the unit until I next go to the states unfortunately).
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on July 08, 2026, 10:31:15 pm
Well at least it should only involve changing symbols/annunciators from the 34401A design - schematic of the display board is identical from the quick review I did yesterday.

I just bought a 34420A so very interested in the option of not spending $150-200 on some super shady ebay VFD if it turns out it needs one (don't get my hands on the unit until I next go to the states unfortunately).

Yes, the display board is the same, and our LED board is compatible. The only difference is that the last digit is replaced with some annunciators.

My thoughts right now are that if the LED display for the 34401A sells well, it will help finance the production costs of the 34420A display project.



Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on July 08, 2026, 11:52:12 pm
@Cyclotron, didn't you also just get a 34420A that probably needs a new display? ;)
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Cyclotron on July 09, 2026, 12:38:04 am
@Cyclotron, didn't you also just get a 34420A that probably needs a new display? ;)

I did get a 34420A on Monday, and I'm a fan of dimmog and the team at https://hubequip.net/

My unit has a very nice-looking VFD. That's not to say I wouldn't replace it with an LED.  I'm curious how that might impact the ambient noise in the system.
I know one of my backlight changes on a scope from CCFL to LED made a huge difference to the noise floor.

@dimmog, if you guys do a 34420a, let me know; I will probably buy one regardless. Out of the colors I have, I prefer the more cyan color, I think it's. Though I wonder what doing a white LED would be like with a change in the filter screen.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Hydron on July 09, 2026, 12:48:59 am
I snagged the second unit from the eBay listing cyclotron got his from. No pics specifically of the second unit, so there's a chance mine has a vfd in worse shape, hence the interest (note it's not arrived yet and I need to pick it up next time I'm state side).

As for the other models, I got a 34401A clone vfd to replace my tired one before these were available, otherwise I'd have grabbed one to try.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on July 10, 2026, 05:20:59 pm
Thanks RJ for the very nice and detailed review of our new LED display for the 34401A!

https://www.youtube.com/watch?v=tegAA70d5U0 (https://www.youtube.com/watch?v=tegAA70d5U0)
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on July 10, 2026, 11:41:59 pm
Ordered mine today.  On sale - who could resist?
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on July 23, 2026, 02:27:14 pm
@dimmog.

Just a suggestion here.  Avoid using DHL eCommerce as a shipping option please.  2 weeks and the package has not yet arrived.  They just do not seem to give a damn about getting things delivered.  Just use USPS for deliveries to Canada in the future please.  Thar's what DHL do, after shuffling it around half the states in the US and keeping at their depot in Chicago for 3 days.

I can drive to Miami from where I am in under 24 hours.  Two weeks?   :palm:


Anyway, looking forward to getting it before passing away.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on July 23, 2026, 02:46:57 pm
DHL Express is great, but the slower services suck. I recently received a package with regular DHL, and it just sat for 8 days at a warehouse before DHL decided it should continue on its journey. DHL Express on the other hand, gets anywhere within a couple days.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on July 23, 2026, 02:55:23 pm
I agree on DHL Express.  I generally get my PCB orders shipped via DHL express and they are usually in my eager (big) hands within 3 days from China.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on July 23, 2026, 03:50:14 pm
@dimmog.

Just a suggestion here.  Avoid using DHL eCommerce as a shipping option please.  2 weeks and the package has not yet arrived.  They just do not seem to give a damn about getting things delivered.  Just use USPS for deliveries to Canada in the future please.  Thar's what DHL do, after shuffling it around half the states in the US and keeping at their depot in Chicago for 3 days.

I can drive to Miami from where I am in under 24 hours.  Two weeks?   :palm:


Anyway, looking forward to getting it before passing away.

We ship using the carrier selected by the buyer at checkout.
Several shipping options are available, and we added DHL eCommerce as the lowest-cost option after it was requested by a number of customers.

Well, now I'm curious. If DHL eCommerce is so terrible, what made you choose it in the first place?  :)

Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on July 23, 2026, 03:51:41 pm
Probably a combination of old age and impatience.  ;) ;)  :-DD
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on July 23, 2026, 03:56:05 pm
Well, now I'm curious. If DHL eCommerce is so terrible, what made you choose it in the first place?  :)
You got me there.  I honestly did not even look at the options.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on July 23, 2026, 03:57:17 pm
Probably a combination of old age and impatience.  ;) ;)  :-DD
Essentially  :palm:
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on July 23, 2026, 04:02:20 pm
Well, now I'm curious. If DHL eCommerce is so terrible, what made you choose it in the first place?  :)
You got me there.  I honestly did not even look at the options.

Fair enough. We've all been there. That's how DHL eCommerce keeps getting customers.  ;)
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on July 30, 2026, 01:25:15 pm
Just an update.

The package finally arrived on Monday.  Really nicely documented and the display looks very nice (Not yet installed).  I'm very happy with the product.  Thanks Dimmog.

Now for the bad part, which is 100% my fault for choosing DHL eCommerce.  DHL extorted another $26 from me before they would deliver the package.  If I'm not mistaken, that's $52 for shipping that took 17 days. :-// :palm:  :wtf:

Moral of the story NEVER, EVER choose DHL eCommerce if you are shipping from the US to Canada or you will likely have a really bad experience.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on July 30, 2026, 04:46:22 pm
Now for the bad part, which is 100% my fault for choosing DHL eCommerce.  DHL extorted another $26 from me before they would deliver the package.  If I'm not mistaken, that's $52 for shipping that took 17 days. :-// :palm:  :wtf:

Moral of the story NEVER, EVER choose DHL eCommerce if you are shipping from the US to Canada or you will likely have a really bad experience.

Just a small gift for you should be arriving soon. I don't want you to look at that display for years to come and remember the bad shipping experience every time you use it.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on July 30, 2026, 05:12:31 pm
Just a small gift for you should be arriving soon. I don't want you to look at that display for years to come and remember the bad shipping experience every time you use it.
Well, thank you, but really unnecessary.  I usually don't associate things that way.  The product is 100% and has nothing to do with the shipping.  Very detailed instructions BTW.  That's a real breath of fresh air!
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on July 31, 2026, 07:46:35 pm
Gift received.  Thanks!  Much appreciated.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on August 08, 2026, 05:04:21 pm
I had a few minutes this afternoon to put my new TRI-COLOR display in.

I put a piece of Kapton tape over the ERROR annunciator.

What do y'all think?



Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on August 08, 2026, 05:15:53 pm
I had a few minutes this afternoon to put my new TRI-COLOR display in.

I put a piece of Kapton tape over the ERROR annunciator.

What do y'all think?

I can't say I expected that but it works! :)
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on August 08, 2026, 07:46:35 pm
Yeah, even looks better than that in person.

Awesome display!
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on August 08, 2026, 07:59:57 pm
Nice! You could also get film for that purpose in whatever color you want: https://www.aliexpress.us/item/3256807011367857.html (https://www.aliexpress.us/item/3256807011367857.html)

I have like 5 colors of that, but I haven't used any of it yet.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on August 08, 2026, 08:06:53 pm
Oooh!  I'll have to get some of that.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Zucca on August 10, 2026, 02:20:36 pm
Nice! You could also get film for that purpose in whatever color you want: https://www.aliexpress.us/item/3256807011367857.html (https://www.aliexpress.us/item/3256807011367857.html)

I have like 5 colors of that, but I haven't used any of it yet.

Send me half inch in red, in 15 years when dimmog is done with the 34410a I want the ERROR red.  ;)

Well spotted Josh!
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on August 10, 2026, 03:35:03 pm
Send me half inch in red, in 15 years when dimmog is done with the 34410a I want the ERROR red.  ;)

Well spotted Josh!

The only thing I can say right now is that the film won't be needed.  ;)
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Zucca on August 10, 2026, 05:12:44 pm

The only thing I can say right now is that the film won't be needed.  ;)

If it is a dream do not wake me up.

F yes.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Hydron on August 10, 2026, 05:51:19 pm
Picking up a 34410A in a couple of weeks, auction photo showed good VFD but if that's not the case then I'm lining up for one too (same deal with 34420A).
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on August 10, 2026, 06:42:56 pm
I had a good VFD but this is WAY better.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Zucca on August 10, 2026, 06:54:55 pm
I had a good VFD but this is WAY better.

and dangerous.... once you upgrade one device all the other pristine and new VFDs on the bench look like shhhh....
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on August 10, 2026, 06:57:06 pm
and dangerous.... once you upgrade one device all the other pristine and new VFDs on the bench look like shhhh....
Hah!  This whole sport is dangerous!
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on August 10, 2026, 07:29:22 pm
That's no joke. I had two good 53132As with good VFDs, and they both got replaced. The 2010's VFD was also fine, and that got replaced (and what a difference!). If he made screens for the 2700, I'd get one of those too.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Hydron on August 10, 2026, 08:20:21 pm
Why are they an upgrade from a good VFD? Other than eliminating burn-in anxiety that is.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: KungFuJosh on August 10, 2026, 10:23:24 pm
Why are they an upgrade from a good VFD? Other than eliminating burn-in anxiety that is.

It's most obvious in the K2010 (2000, 2015, etc.). The original VFDs have very small digits. Look at this comparison of the same meter.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: HairyWombat on August 22, 2026, 01:31:28 pm
So I have a 34401A with dodgy COTO relay and iffy front rear switch.
Ordered the hideously expensive COTO from Mouser AUD $63.23 (US$45.32) unhappy about the drop to 500VDC on principle.

Its about this time I found and promptly ordered Dimmog's awesome looking replacement display, many thanks for the prompt postage.
Dimmog asked if I could post photos.

Found a parts only unit from Japan for AUS$402 delivered with tax.
It turns up perfect, no COTO or switch issues, few scratches and filthy, VFD was a bit dimmer than the faulty unit..... righto.
In go a set of upscaled caps, and Dimmog's display, it looks awesome, I will get it calibrated on Monday and the original patient I am now not sure about.
More parts units on order   :D

[attach=1]
[attach=2]

I had a lot of trouble getting a good photo as the brightness flares my Samsung phone camera, had to stuff with the settings.

I thought along BillyO's suggestion of the Kapton tape but on the Shift icon with green silicon tape.
It didn't work and made little difference except slightly dimmer.
Will get some coloured tapes as I want red for error, now not sure if I will change Shift.
It does look good and an instant no fear of leaving the meter on.

[attach=3]

https://drive.google.com/file/d/1HUY8m8VEbScooaV8SM7pKAhtDy1uYlnI/view?usp=sharing (https://drive.google.com/file/d/1HUY8m8VEbScooaV8SM7pKAhtDy1uYlnI/view?usp=sharing)
Also while in the phone camera settings I enabled super slow mode which shows the multiplexing nicely.
Sorry for the poor quality, it got reduced badly during transfer.

Very happy with it, thanks Dimmog and will be ordering a couple more soon.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on August 22, 2026, 05:54:28 pm
In case anyone is wondering what's inside the display.

Here it is.

Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: HairyWombat on August 23, 2026, 05:00:13 am
I was curious, thanks.
Tiny, do you load them yourself?

Send me half inch in red, in 15 years when dimmog is done with the 34410a I want the ERROR red.  ;)

Well spotted Josh!

The only thing I can say right now is that the film won't be needed.  ;)

So does this mean you are planning to do a batch with the error in a red led?
If so whats the ETA on availability.

Yeah scrap that, I read back and can't be done on the 34401A display
Sorry for the 01A 10A confusion, without glasses 1's and 0's don't get along
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Hydron on August 23, 2026, 10:02:16 am
I note "10A" rather than "01A" there - might be referring to that meter, which has a very different display fitted.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: Cyclotron on August 23, 2026, 01:11:02 pm
I note "10A" rather than "01A" there - might be referring to that meter, which has a very different display fitted.

That is the way I read that. I have a 34410a that needs a display.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on August 23, 2026, 06:47:53 pm
I was curious, thanks.
Tiny, do you load them yourself?

Each LED is a 0201 package, measuring only 0.65 × 0.36 mm.
A package this small is beyond manual assembly. It requires a pick-and-place machine.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on August 28, 2026, 03:15:19 am
Thanks to Dave & Dylan for mentioning our 34401A Dual color LED display!
I bet Dylan will want to do the upgrade once you get the 34401A  :)

https://www.youtube.com/watch?v=B30W9j2LsIY&t=832s (https://www.youtube.com/watch?v=B30W9j2LsIY&t=832s)
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on August 28, 2026, 03:24:15 am
I left a positive comment too.  I really will get that upgrade for my 2015 THD once I get the time to do the job.  Got some travel to do in the mean time...
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: dimmog on August 28, 2026, 03:39:06 am
I left a positive comment too.  I really will get that upgrade for my 2015 THD once I get the time to do the job.  Got some travel to do in the mean time...

Thanks!
When you're ready, just message me. I have a discount available for EEVblog forum members.
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: BillyO on August 28, 2026, 03:40:37 am

Thanks!
When you're ready, just message me. I have a discount available for EEVblog forum members.

Awesome!
Title: Re: HP / Agilent 34401A VFD to LED Display Conversion
Post by: HairyWombat on September 01, 2026, 02:53:31 am
Just got my meter back from being calibrated and while having all meters setup took this shot as a comparison.
[attach=1]

The top 34401A has a good bright and even VFD
That 2001 VFD could be better.
Overall the brightness is good and works well with other displays.

Auto phone camera settings so the image is brighter than reality.