Agilent 54622D self-calibration failed

[ajin]

I got a bad-looking 54622D with a dead battery last year. After battery replacement, I attempted to run self-cal, but it failed and complains PATH DELAY. After reboot, it complains Instrument Uncalibrated. The scope can pass the self-test though. I checked the power rails according to the service manual and they seem to be just fine, except the power supply restarts occasionally(maybe it was overheated?). I also tried to reset the NVRAM but it remains the same. Maybe some signal paths that is needed for calibration is not functioning? I plan to get myself a RS232 cable and try to get some boot logs.

Anyone have ideas or schematic of this scope?
Thanks!

[fmashockie]

Some scopes use an NVRAM chip to store calibration data.  However, that chip needs battery power to hold that data when the instrument is powered off.  So if the battery died, you've likely lost the calibration data.  I did find the service manual online for you here https://docs.rs-online.com/96f1/0900766b800301c5.pdf

[ajin]

Thanks fmashockie, That's the service guide I used to check power rails.  This is pretty useful, but it did not mention how to solve user-cal issues and it simply ask me to replace the motherboard. It seems that this series of scope can be calibrated using user-cal. However, the main issue now is that it can't perform user-cal.

[fmashockie]

I have the HP version of this scope. To run the self calibration, there's a switch in the back of the unit that needs to be changed to perform the self-cal. I believe it's the same for this Agilent scope. Did you switch that cal switch in the back to 'unprotected' before running the self-cal? Because delay path sounds like it is waiting for that switch position to change

[ajin]

Hi fmashockie, I did switch it to unprotected before I perform user-cal. If I forgot to do this, it would thrown out error about the switch. but I did notice that the switch had bad contact, it's possible there's something eroded inside the switch. Maybe I can try to replace the switch.

[Runco990]

I've seen a few of these scopes on ebay that look like they came out of a coal mine for sale.  Not like anyone wipes ANYTHING down to sell these days.  My point is, how does it look on the INSIDE?

The self cal deals with small voltages and fast signals.... ANY conductive "Dirt" on the main board can interfere with that.  Perhaps try cleaning the board first.  You MAY have slight conductivity problems.

[ajin]

Thanks Runco990, there's black "dirt" on the plastic case, which I'm not sure it is conductive or not and. I think cleaning the board with acetone should be helpful.

[ajin]

By the way, I have tried to run self test and user-cal today. Just like before, it passed the self-test but failed user-cal. However, I managed to record a video and you can see it below. Maybe this can provide more information for you. If you find something interesting, please reply this post.

Link to the video: https://www.bilibili.com/video/BV155411q7TU

Thanks!

[fmashockie]

Okay I definitely see what you mean now.  I assumed it was failing immediately upon you beginning the self-cal.  But after watching your video, it seems like it is able to get through a good deal of the calibration before it fails. 

I tend to agree with Runco990 that taking it apart to perform a visual inspection and cleaning would be a good idea.  But if you've replaced NVRAM battery, you've probably already looked inside a bit.  It still wouldn't hurt to do it again.

It's interesting that the user cal appears to fail as soon as the scope attempts to do a single snapshot measurement.  Or at least that is what it looks like from the video.  It might be worth it to you to give that front panel board a thorough cleaning.  Those boards seem to get dirty very easily and can cause all sorts of issues.  Yours looks in particularly poor shape with lots of missing knobs.  In my experience, very complex fault symptoms tend to have a simple solution or explanation - such as a dirty contact on a switch or rotary encoder.  I would start there first.

Also, it wouldn't hurt to make sure all your power supply voltage rails are within spec. 

[ajin]

Well...The knobs were pulled off by me since they're pretty dirty and I need to clean them. The side of the motherboard shown in the video was just fine, but I'm not sure about the back side since the power supply near was full of dust. And I believed the thick dust have caused the malfunction of the supply. I noticed the power supply restarts unexpectedly, especially when it's more humid here. It's possible that the dust become more conductive when they "react" with the water in the air. So I will buy some 530 electronic cleaner to clean the board. By the way, will 530 cleaner(basically acetone and organic fluorine compound, i guess it's Fluoroalkanes) cause damage to the plastic part of rotary encoders?

[Greybeard]

Never use acetone for plastic parts...

[fmashockie]

I am not too familiar with this brand of contact cleaner called 530.  As Greybeard said, acetone can be aggressive against plastics.  I use Deoxit which does not list all of its ingredients on the can, but it does say mineral spirits and difluoroethane are part of the mixture. 

[ajin]

Dioxit...it's a similar product to WD40, right? If so, I'd like to use WD40 to clean the rotary encoders and 530 to clean the circuit board.

[fmashockie]

I don't know how similar WD40 and Deoxit are.  Deoxit makes a wide range of products.  I use the D5 and F5 formulas.  The original WD40 is not specified for use as an electronic contact cleaner.  But I'm sure the WD40 brand does make a contact cleaner version.  So you have to be careful there.

Again, the product you originally mentioned (530) could be just fine for electronics.  I've just never heard of it before.

[ajin]

So I managed to clean up most of the dust on the motherboard and PSU with acetone yesterday. In fact, the back of the motherboard and the power supply was really dusty. Then I tried to tried to power it up and try to run user-cal. Just like before, it passed self-test but failed in user-cal and complained path delay. Afterwards, I reviewed the video I recorded before and I found that the scope's trigger was rising edge and the trigger source was external source just before user-cal failed but nothing was shown on the screen. I guess there's some sort of signal generator and the scope redirected it into the external trigger source by relays near the ext. trig BNC. So I wonder is it possible that some of the relays failed and caused user-cal failure? Again, I will appreciate if someone can provide the schematic of this scope.

Thanks!