HP 54111D oscilloscope probe input trouble

[bristpi176]

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. Failed
Bought 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.

[wn1fju]

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 suggest
you 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 direct
connection, 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 for
the 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 not
for 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 are
little 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 my
54111D/54112D to working condition.

[bristpi176]

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.

[bristpi176]

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? 

[wn1fju]

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 that
are 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 game
with 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 has
been 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 was
fixed 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 might
eventually need them if something obvious (e.g., are all the internal cables properly connected?) doesn't present itself.

[bristpi176]

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.