HP 54111D oscilloscope probe input trouble  - Page 1
Forum section: electronics / testgear

author: bristpi176
author_rank: Contributor
timestamp: December 29, 2019, 05:40:02 pm
content: Hi guys,I have an HP 54111D digital scope that won’t show any input from the probes. Here’s what I’ve done so far.Scope passes power up self check. Checked all wire and cable connections. Pulled and replaced cards looking for corrosion. None found.Followed test procedure to check and attach jumper to calibration port to get 0.800v output.Bought new 500mhz probes and attempted to calibrate them by the service manual procedure. FailedBought original HP probes from eBay. Still won’t calibrate.No input comes over the probes on channel 1 or 2. I don’t have the skill to go much farther without somewhat of a roadmap of what to look for. Any suggestions would be appreciated.

author: wn1fju
author_rank: Frequent Contributor
timestamp: December 29, 2019, 07:10:06 pm
content: I'm a bit confused by your description. When you hook up a signal to, say, the channel #1 input BNC, do you see anything on the 54111D? I suggestyou not confuse matters with oscilloscope probes just yet - simply try to get a signal directly into the scope. If you can see a signal with a directconnection, but not with an external probe, then the probe is no good (that is a lot better than having a bad scope!).Behind each of the four input BNC jacks are four input pods. These have attenuators/switches driven by solenoids as well as some electrical parts forthe input preamps, etc. If you are seeing no signals, I would surmise that the input pods are dirty and need a cleaning. This can be done, but it is notfor the faint of heart. You have to meticulously disassemble everything and clean it with alcohol. You need to do this in a clean area because there arelittle springs and clips that can fly across the room if you are not careful. I once saw a web page that shows how to do it (I can't locate the page now).And there is also an HP Journal that has a pretty good description of the pods. Google around. I've cleaned several of these pods and it restored my54111D/54112D to working condition.

author: bristpi176
author_rank: Contributor
timestamp: December 30, 2019, 04:22:58 am
content: Thanks. I’ve had channel 1 attenuator out but not disassembled. I saw a page where a guy took his apart and cleaned them as well. Sounds like a project for New Year’s Day. I’ve really got nothing to lose since it doesn’t work anyway and sending it out for professional repair would cost more than it’s worth.I did try to feed a signal directly into it from a function generator and got nothing as well.

author: bristpi176
author_rank: Contributor
timestamp: January 02, 2020, 10:32:13 pm
content: I cleaned all the attenuators and managed to get channel 2 and trigger 4 working. Channel 1 and trigger 3 are still out. Any more ideas on how to track this down?

author: wn1fju
author_rank: Frequent Contributor
timestamp: January 03, 2020, 02:08:58 am
content: You might try, for instance, switching the input pods for channel #1 and channel #2. You want to see if it is the pod or the board(s) behind the pod thatare faulty. In other words, does the fault follow the pod change or not.If I remember, the channel #1 and channel #2 pods and circuitry are the same, so switching is permissible. I'm not sure you can play the same gamewith the two triggers, however.Also, try doing a two-key reset (power on holding the top and bottom function keys down) and then run the extended self-tests. My experience hasbeen with the 54112D, not your 54111D, but the two are quite similar. And mt unit's self-tests pointed to D/A problems on two of my channels (that wasfixed with new D/A chips). I expect the 54111D diagnostic tests to be similarly thorough.ArtekManuals has the complete service manual set including the Component Level Information Package (CLIP) containing the schematics. You mighteventually need them if something obvious (e.g., are all the internal cables properly connected?) doesn't present itself.

author: bristpi176
author_rank: Contributor
timestamp: January 06, 2020, 02:03:51 pm
content: Thanks again for the help. I’m going back in in a few days to do the parts swap. I’m hoping to stumble on a parts machine that isn’t selling for its weight in gold. Nothing that fits that bill on eBay right now.