#82 - Agilent E3646A dim display repair

[@toastedcrumpets]

Would never have thought a dim VFD is a biasing issue. Nice detective work! Another failure mode to double check for.

[@ydonl]

Brilliant! I would guess less than 1% of techs would even ask the question about a dim VFD display. We rely on assumptions too often!

[@SirBunghole]

Always pays to have access to a known good unit. Well done.

[@OrbiterElectronics]

I see a FL video.. I watch, enjoy & like 👍

[@saarike]

Excellent video for that kind of problem! Display itself can be weak of course. Nicely solved problem.

[@Chris_Grossman]

It's always nice to have a working model fot comparison!

[@davecc0000]

Brilliant diagnosis. I would have missed that.

[@SidneyCritic]

That's some good detective work. Now I wonder if Signal Path blew his VFD for the wrong reason.

[@toastedcrumpets]

Any chance you can link to the Signal Path video?

[@feedback-loop]

I think he really had a bad VFD since the replacement was bright.

[@davidwhite9751]

Very interesting video; second time I've watched it. As @SoddingaboutSi remarked, it is suprising that you could see anything at all with the bias out so much. I am working on a receiver with a dim VFD (plate, filament and bias voltages are all good), and had been thinking about replacing the 5V6 bias zener with a different value to get the VFD to conduct more current. As the plate voltage is negative, I would have to lower the zener value, but there may no be enough room. I think the lowest zener value is 2V4.

[@eldenchang]

WOW! What a nice repair. I have repaired many of these Agilent PSU and never thought about checking this bias voltage. Thanks for sharing.

[@stevenyamada70]

Thank you for post all these repairs, it help to see your troubleshooting steps. Very Nice !!!

[@HelmutTschemernjak]

Very cool repair, thank you for sharing this with us. Sometimes even simple repairs can make us happy.

[@TestEquipmentAnonymous]

Good to know and check for. As always, thanks for sharing!

[@zx8401ztv]

We are so used to vfd displays wearing out, that zenna diode is a possible trap. Hopefully it was a one off and your unit behaves itself :-). I watched one of your old videos on repairing/calibrating an old techtronix power supply. Your diagnostic skills are impressive :-D It's too easy to jump to conclusions and be wrong, ive been wrong lol.

[@Ozzy3333333]

Excellent, tearing into my e3633a now for the same issue, thanks!

[@jacoblindquist1152]

Brilliant video, great work.

[@andymouse]

Wow, I would have bet good money on a tired VFD, biasing would not of entered my mind...until now...cheers.

[@MrDubje]

Thank you again for your work. Your videos are a great help in the repaircommunity, I'm sure.

[@gordonwedman3179]

That is good information to pass along to everyone. Thanks for making the video and please keep up the good work.

[@ovalwingnut]

😲 Fantastic discovery!!!! Never crossed my mind to try switching them. At least checking the VFD supply. Very impressed. 9 out of 10 gray beard "techs" loved this video. The 10th was on jury duty and unavailable for comment 🤗 Cheers ❤

[@mymessylab]

Theese are the often uncovered faults that make you save money. Smart observations. 👍

[@originalmianos]

Excellent. So easy to miss unless you have seen the issue before or have a second one.

[@PapasDino]

That's a great tip to salt away for the future! Thanks!

[@vincei4252]

Wow! That is awesome sleuthing. I swear I would not have even thought to try swapping them and just assumed that I had a dud VFD. However, a story from my recent past. I bought a 8566B from one of the larger used equipment vendors on eBay. The shipped price was so low I decided to buy it for parts in case I needed them for my working unit. I get the thing (one day shipping!) turn it on and there's garbage on the screen much worse than in the listing. I measured the power supplies and nothing seemed amiss. After thinking extensively on it I take the display cable from my existing working unit and swap that in. Boom, unit works, is in way better condition than the one I bought 4 years ago which was crushed and had its screen smashed by UPS and the guy I bought it from that didn't package it properly. Nice work!

[@danishnative9555]

That's an unusual failure. I have seen these fail for loss of cathode emission. Not much hope for those. Good troubleshooting work.

[@rpbale]

Great video. Thanks

[@billspencer8540]

Thanks for sharing.

[@jp040759]

EXCELLENT topic. Now I wonder if I trashed a CD player with bad VFD display that could have been restored. I did not know about the DC bias of the filament voltage. I took the initial DMM readings as you did and didn't know to go further. Thanx.

[@masoudmontazery907]

Good luck sir....

[@largepimping]

I've replaced VFDs with cheap ebay replacements 2 or 3 times in old HP/Agilent gear... never even gave this a thought! Fortunately in my cases, the VFD was really shot. Anyway, thank you (as usual/again) for a very informative video.

[@feedback-loop]

Unfortunately there are no ebay replacements for this model.

[@amirb715]

very good observation indeed. thanks! and congrats on the new camera :-)

[@TheDefpom]

I will have to watch out for that fault, thanks.

[@TheDefpom]

I’ve repaired the encoders in a video, it was very easy to do.

[@Futschikatores]

Great work as always. Btw I did not notice the 4k because i am watching youtube on 720p 30fps :)

[@SoddingaboutSi]

Very interesting. So basically the Cathode was an anode! Surprised you could see any display at all!

[@andr27]

Nice, as always

[@TKomoski]

Nice to see you back again, would you have the part number of the encoder from Digikey. I have the same problem with my power supply and it would be nice to fixit. Shahriar from The Signal Path cleaned the encoder but he didn't show it. Great channel always enjoy your quick fixes look forward to the next *_CHEERS_*

[@feedback-loop]

I believe these encoders fit: TT Electronics EN16-H20AF15 or Bourns Inc. PEC16-4015F-N0024

[@TKomoski]

@@feedback-loop Thanks Alex

[@laoluu]

Who knows what an Agilent service station would have charged? 5 cents for parts, 50 $ for work.

[@bfx8185]

This is great , may be most of the people changed the display without any reason.

[@_PovertyLabs_]

4k wow that's just great for us ...but sadly for you it means you have to make more videos :-)

[@xDevscom_EE]

Nice video, been too long :)