Help: my Infiniium MSO 8K seem to fail digital position test - Page 1
Forum section: electronics / testgear

author: F1GWR
author_rank: Regular Contributor
timestamp: October 06, 2025, 05:13:04 pm
content: Anyone owning an Agilent MSO8000 series (not DSO) could perform a simple test on his scope for me? In the scope Infiniium application, use Utilities menu/Self Test/Key & Knob Test and let me know the color resulting from rotating the right mostvertical position encoder (digital section): see first picture.Inmy testall buttons turn red >>> yellow >>> green after two stops except the said one that only turns red to yellow (never green). I desoldered the 16 positions encoder and the one next to it with same reference number. With a continuity tester I don't have any difference between the two. So what?My firmware is v5.40.Couldn't find any similar encoder (photo 2 and 3) with Google Lens or by roaming in the electronic suppliers sites.One thing to note: when I bought this scope the shaft was broken and I glued it back with cyanoacrylate. Now suspecting encoder circuit contamination; but if that was the case the two neighbours should test differently.Therefore my question (before I exchange the two encoders placement and reassemble the whole rig): are the other Infiniium 8K resulting in the same test result for that digital vertical position encoder?

author: nctnico
author_rank: Super Contributor
timestamp: October 06, 2025, 05:26:08 pm
content: IME these encoders are quite crappy. Turning them round for a while can clean them but they can keep working intermittently.

author: F1GWR
author_rank: Regular Contributor
timestamp: October 06, 2025, 05:35:13 pm
content: Quote from: nctnico on October 06, 2025, 05:26:08 pmAgree. Not premium quality at first sight. Done what you said after flushing IPA with a spray.I suppose you don't own an MSO to perform the said test?

author: nctnico
author_rank: Super Contributor
timestamp: October 06, 2025, 06:28:42 pm
content: Quote from: F1GWR on October 06, 2025, 05:35:13 pmNo, but I had a similar one through my hands not so long ago with bad (erratic) encoders. Ideally I would have changed the encoders but I didn't manage to find compatible encoders for that model. Cleaning with IPA is OK I think. I wouldn't use any kind of contact spray for sure; IME that causes damage long term.

author: F1GWR
author_rank: Regular Contributor
timestamp: October 07, 2025, 07:25:19 am
content: Quote from: nctnico on October 06, 2025, 06:28:42 pmAgree if used alone. But if you abundantly "wash" the contact spray with IPA afterwards it would be OK.If still no answer for this autotest from anyone on this list, my next step this afternoon will be to swap the two encoders, reassemble the scope (which is a pain in the a...) and perform a new autotest to see if the default migrated with the encoder location or not.

author: nctnico
author_rank: Super Contributor
timestamp: October 07, 2025, 09:13:28 am
content: I'd test the board while it is not inside the oscilloscope. This also allows to measure signals to the encoder. But you should be aware the scanning frequency is quite high (in the kHz ballpark IIRC) and the encoders are scanned in some kind of matrix so you'll see all kinds of signals. But you mention the encoder was damaged. It is possible it is cracked on the inside; I'd expect the problem to move along with the encoder.

author: F1GWR
author_rank: Regular Contributor
timestamp: October 08, 2025, 07:43:32 pm
content: So tonight unmounted the two neighbor encoders (including the "failing" one), and re-soldered the good one into the "digital position" location. Even got worse: the auto-test stayed red when rotating (not even yellow nor jittery arrows).Therefore checked where the encoder pins for each encoder connects in the circuit: on two SMD shottky diodes marked B3L (FSS24). Looking closer one diode CR26 was missing. This locationhasto be populated because the neighbor encoders all have two companion diodes (see CR13 and CR14).Solution is: one diode fell off the circuit!

author: nctnico
author_rank: Super Contributor
timestamp: October 08, 2025, 11:31:58 pm
content: That is a good find! Unfortunately it is not uncommon for Agilent equipment to have bad solder joints of chips causing all kinds of issues / erratic behaviour. However, I have not seen diodes dropping from a board. Perhaps it is a good idea to check the rest of the components for bad solder joints. But these are hard to spot though, even with a strong magnifier.

author: free_electron
author_rank: Super Contributor
timestamp: October 09, 2025, 12:38:48 am
content: Those encoders were made by J-Noble in Japan.https://www.noble-j.co.jp/en/products/discrete/encoder/They suffer from fretting in combination with the silicone lubricant in them which results in tiny metal flakes that create false contacts and make the lubricant conductive.Desolder , wash in ultrasonic with a cleaning solution made form 50% distilled water and 50% IPA.Peel back the metal cap to inspect.Apply a very thin coat of Fader Lube F5 (Caig Labs) on the track.The axle itself can have a bit of Fadergrease or Krytox GPL204 or GPL205 (PTFE in PTFE. Ditch that silicone crap)

author: F1GWR
author_rank: Regular Contributor
timestamp: October 09, 2025, 02:52:46 pm
content: Thank you for your contrib. Unfortunately the very model of encoder is not manufactured anymore.In fact I did something similar for the suspect encoder: sprayed many times IPA into the slot opening (you can't open the can of the encoder without breaking the retaining tabs).As rotation was a bit scratchy after that, introduced with a thinned toothpick a small quantity of ball bearing grease "Graisse Belleville" (avoided those lithium or carbon loaded which may be conductive and also silicone which is abrasive), while checking in the tiny slot while rotating the four spring contacts (two outer and two inner) that they could not be misaligned while moving the toothpick around.But as already said the encoders weren't the cause of the failure.

author: free_electron
author_rank: Super Contributor
timestamp: October 09, 2025, 03:41:56 pm
content: Quote from: F1GWR on October 09, 2025, 02:52:46 pmThey were custom designs for HP/Agilent. Been in use since the 546xx series ( long before infiniium came along)Noble makes a lot of custom parts. In the 54601 and 54645 they made the whole circuit board for the frontpanel. But those were mainly passive boards. No active circuitry.The color of the axle indicates if it is a clickless or one with detents. it also indicates number of pulses/revolutionI've opened enocders , but you are right : the tabs break relatively easy.Belleville makes PTFE grease : Calorahttps://graisse-belleville.com/produit/graisse-perfluoree-boite-1kg-calora

author: F1GWR
author_rank: Regular Contributor
timestamp: October 09, 2025, 04:58:47 pm
content: Quote from: free_electron on October 09, 2025, 03:41:56 pmInteresting the history of these components.The flavor I used as a grease is the "PERFECT spéciale roulements" I bought for my milling machines and lathe ball bearings replacement. After checking their site, unfortunately contains lithium, which was not mentioned on the container:https://graisse-belleville.com/produit/graisse-speciale-roulements-carton12cartouches400g.But had already reassembled the scope; running the front plate test everything is nominal. If later and by chance I suspect some kind of current leaks I can always return and replace the grease by a standard one...And the Infiniium app behaves as it should.So as we say over this side of the pond: "il ne faut pas être plus royaliste que le roi" or "le mieux est l'ennemi du bien" (Google Translate -or Deepl- is your friend)

author: free_electron
author_rank: Super Contributor
timestamp: October 09, 2025, 06:48:15 pm
content: You should be fine. the lithium in lithium-grease is not really conductive. not at low voltages.I speak french. No need for "traduction"