I'm new to this group and hope I'm posting in the correct location - I apologize if it's the wrong location.

I recently acquired an Agilent 54831M scope with a known problem: channels 2 and 4 don't switch to 50ohm mode.

From research, it seems the input amplifier is blown.The channels seem to work fine in high impedance mode using a scope probe, but I'm uncertain if the amplitude is correct as I question my signal generator.

I know the chips are no longer made, so my questions are:

if I leave the scope in this condition, will the two bad channels affect the high impedance mode or are the two paths isolated?

If the scope can remain in this state, will I be able to calibrate it so I know my measurements are reasonably correct?

Does a reputable source exist to purchase used chips so I can replace the two bad channels?

Also, this is my first scope with an operating system. This has caused some confusion and concern. The scope currently has Win95. My guess: someday the printer drivers will not work with modern printers, so I'll be forced to update the OS; or the hard drive will crash. This means the scope software will be erased, does a source exist where I can find the software to reinstall if needed and can I upgrade to Win10?

I haven't heard from anyone about my message and wanted to reply in hopes it moves to the top of the list.

no, bad 50 ohm will not necessarily affect your 1M input. But it depends where the damage has occurred in the front end
if the 1M signal show up OK, then you have your answer

no, you will not be able to calibrate the scope. The cal procedure (which is automatic) will fail .

why dont you run the scope self tests (extended self tests) and see what you get? these scopes have a fairly comprehensive and detailed self test.

I dont think a chip is dead in the front end because in that case the 1M would have failed.?
There is very good chance that (if only the 50 ohm is dead) the scope is easily repairable, based on my past experiences with other scopes with similar problem.
first you need to open the attenuator shields on the acq board and see what it looks like...

Win10?? heh...forget about it. The best you can do is to upgrade to win98. Possibly winxp but some people say the drivers work
and some say they dont, I am not sure but I have seen people saying they have upgraded to winxp. Of course not with the stock motherboard and cpu, that has to change.
These scopes never came out with winxp.?

I can't help with the bulk of your post, and I don't really know the 54831M, however, I can give you the general advice I use for all sorts of these older OS-based devices.

If the system was built and designed for Win95, there's next to no chance that Win10 would work on it. Think about the class of PC's that ran Windows 95. That would have been approximately 1995-1997. Some of these hardware devices have long R&D times, so that could be shifted a bit. Microsoft ended extended support for it in 2001. The main issue is the lack of compatible chipset drivers and custom drivers for the connected (PCI?) hardware.

Sometimes HP/Agilent/Keysight provided update kits for their boxes. You'll need to do some research to see if this is the case.

Sometimes HP offers an "OS Restore" CD that allows one to bring one of these units back from the dead. Check into that.

Last, but not least, I'd highly suggest pulling the HD out of the unit, and imaging it using "dd" (or ddrescue) on a linux box. This will make a bit for bit copy of the disk, which can be re-written to a newer, and probably faster disk. I've upgraded my 16900 logic analyzer to use an SSD, which really increases the performance of the box. There's no reason why you shouldn't be able to return to "current state" later if you've got that image.




YOU NEED TO BE VERY CAREFUL THAT YOU SELECT THE RIGHT DESTINATION DISK (ie, make sure it's a file on a disk, so "of=./54831M.bin" is included in the command line) OR YOU CAN TRASH A HDD EASILY.

If you don't already have access to a linux box, burning a USB livecd stick, and just booting off an existing modern computer will get you the temporary access you need.

This is an incredibly useful skill to know.

I hope this helps!

Keith

Amirb,

responses in-line

On 9/6/2020 10:53 AM, amirb wrote:

Win10?? heh...forget about it. The best you can do is to upgrade to win98. Possibly winxp but some people say the drivers work
and some say they dont, I am not sure but I have seen people saying they have upgraded to winxp. Of course not with the stock motherboard and cpu, that has to change.
These scopes never came out with winxp.

Similar discussions are being had on/off with the HP 16900 logic analyzers on EEVBLOG, which ships with WinXP. HP supported Win7 on some HW revisions of the units. Some people have replaced the motherboards, installed Win10, and installed a much newer version of the software.

I'm not sure it would really affect the usability of the units. I find WinXP with my new SSD card and install, plenty usable. And I connect over the network, and use software on a modern Win10 machine anyways.

But it sure is fun to mess around with!

I do like the idea of merging state-of-the-art HW and "updating" the units, even if it's not "original" hardware. It's amazing that we can even get some of this stuff to work! There is a certain level of preservation that also comes with updating these units like this. Removing 20-year old hardware and using modern pieces in its place is one way of doing this preservation. For the "antique" lovers, I can understand where that might be seen as sacrilegious, and often, the "polish" of the finished product is less than perfect. I still think it's cool!!

Keith

Overall, the scope won't calibrate, but the two healthy channels will look calibrated after the procedure fails. The two bad channels will not work properly on the 1Meg input impedance after the failed calibration.

The failed 50ohm inputs are 99.9% due to bad input hybrids, it doesn't take much of DC to blow the input (even the 50ohm resistor is integrated). It appears there is a chinese guy on EBay, selling these hybrids (expect a chunk of PCB with the chip soldered? on it). I did not buy any and don't know anybody that did, so the risk is all yours if you decide to go for.?

Or you may want to hunt for another 54831 as a part mule, this is what I did and now have spares for the rest of my life.

I saw the eBay listing when I first looked into this problem; and appreciate the link.

It's not necessarily buying a bad chip, it's the trouble of replacing them only to find they are defective or some knock off that doesn't work correctly.

In any case, I was hoping someone had a reputable source that they could point me to. If I could calibrate the two broken channels, I don't see a reason to need 50ohms because I can just use a 50ohm coax terminator if need be.

As for a backup OS CD, I'll look into it, but had planned to image the hard drive. My fear is: keeping Win98 (or even if I could get XP) would eventually eliminate connecting a printer to it or even save files to a USB stick.

I don't know what modifications have been done to this scope, but it has USBs, and was told a SSD was installed.

Since USB wasn't out in 98, I assume a board was replaced or something got installed.

Hello,

please beat me if I am wrong, but I can remember Win98SE had some kind of USB stack.


Tam

With best regards
Tam HANNA

Enjoy electronics? Join 15k7 other followers by visiting the Crazy Electronics Lab at

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I haven't had a chance to look for an OS restore yet, but I will. I still plan to image the hard drive, possibly regardless if I find a CD or not.

The more important question is how to deal with the two blown input amplifiers. If the two channels won't calibrate correctly for high impedance, it seems logical to fix the channels, not use them, or use them knowing the measurements will be wrong.

I'm willing to gamble on buying used ones, but spending money on having them replaced with possible fake/junk ones is the larger issue.

Does anyone know which other pieces of equipment these were used in, or any reputable places to buy them?

The DSO8064A/MSO8064A/DSO8104A/MSO8104A uses the same acquisition board. That being said, they are way more expensive then the 54831M. All the 54831M, 54831B, 54831D, 54832B and 54832D also uses the same acquisition board.

The first thing I would try before ordering anything else is to find the real issue. As had been said, when the 50 ohm doesn't work, it's usually blown. One test I would do before ordering any part is measure the input impedance of the faulty channels. I agree with Ovidiu and Amir, 99% chance the input termination is blown, but I would verify it first. You can also follow Keysight calibration procedure. Usually, in the service manual, there is a flow chart that links a specific failure to the hardware issue.?

Keep in mind that a 54831M is worth about 700USD (even though seller are selling twice too expensive), so before spending 200$ for replacement parts, I would look carefully at eBay listing. I bought mine last year for 800USD with probes and it passed all self test and self cal.

When you say the calibration fail, does all channel fails or only the 2 faulty? Because if all channel fails, there is a second issue somewhere.

The other thing is your OS. I don't want to say it's impossible, but... Changing the OS in any of these product is extremely hard, even more with these older units. Windows95 and Windows XP works on totally different architecture. The only thing that could help you is the 54832B had a windows XP version. If you can find an image of a 54832B image, it could work. There is a big step up from W95 to XP, mostly for the USB drivers, but the step from XP to W10 wouldn't give you much. As suggested, one of the best upgrade you can make is to use an SSD instead of that drive.?
If the OS is a major concern for you, I would look for a DSO8064A instead.

Today I measured the impedance on all four channels and they all measure 1M to ground when in 1M mode and 50 ohms to ground when in 50 ohm mode.

I tried a calibration. It ran through channel 1 just fine, but channel 2 caused an error message: Acquisition failure in cable connected test. After selecting 'OK', I got a Windows error (or at least I believe it to be): Ag5483x - this program has performed an illegal operation and will be shut down.

Unfortunately this causes the calibration screen to close and the scope program to close.

I also ran a a self diagnostics and everything passed except: Test probe board and Test scope self tests

I assume test scope self test is a result of the Test probe board failure.

Due to the 50ohms measuring fine, does this mean the problem is elsewhere?

did you run the complete (or extended) self tests?
can you post a picture of all the test results?

Hmmm I'll need to check which self test I ran, but I attached the pictures of the messages I referenced before.

ok, that's the test I was talking about. Have you tried running it several times or in a loop like 3-4 times? This is important as these scopes sometimes
have intermittent failures that does not happen in every test
if it always passes except that probe board, I think you can disconnect the probe board for now if you are not using any active probes
and try the tests again.
It appears that all the major parts of your scope are fine and I am beginning to think that your problem is likely a software or hard disk problem really
a fresh reinstall and perhaps a new SSD might resolve the issue . For instance if suddenly the scope cannot read/write a byte from/to the calibration files on the D: drive
because of a HDD error, it will throw up this illegal instruction error and quit (happened to me on a 54845A)

I hope you're correct and the IC chips are fine. I forgot to reiterate that two out of four channels don't have a wave when in 50ohm mode - channels 2 and 3.

I'll look at the manual to find which is the probe board so I can disconnect it, but won't this cause the self test to fail since it won't see it?

Earlier I opened it, and should have taken pictures (but I can open it again and will need to in order to disconnect the probe board). From what I was told, and could see, the hard drive was replaced with a SSD (looked like some connector hacking occurred to make the connection.? A CD ROM is also installed, but not connected; nor could I see a way to connect it. I'm curious whether the software CD is inside the drive, but at the moment, can't open it.

It looks like the motherboard may have been replaced because the capacitors look new and there doesn't seem to be connections for the 3.5" drive in front or the CD ROM.

I'm not sure I'm quite ready to say that there are no hardware problem, but it could be a software issue.

One of the thing you could try is to boot on the recovery partition and recover your OS. Prior to do this, you should make a copy of your HDD on a secondary drive. I don't mean a copy paste of windows, I really mean a duplicate drive. I did it using UBCD, it's quite easy and is definitely worth it (be careful not to wipe the scope HDD)! Of course test your duplicate. Then just boot on the recovery and try to run the cal in recovery, it might work. If not, recover the primary partition. If this doesn't work, reinstall the scope software, I doubt that it will work, but it's simple enough that it's worth trying.

You only have the Probe board that fail at the moment, I'm a bit surprised, I would have expected something closer to the ADC. I think you should follow the troubleshooting procedure in the service manual to find the issue.? It could very well be a unconnected cable. When I received mine, I had a similar issue (I had traces on all channels) and the issue was a connector plugged at the wrong place.?

I would be curious on seeing what the wave looks on the defective channel. Is it that the ADC is saturated, is it that the display overlay shoots nothing or something else. What happens when you try to measure something on that waveform? On other waveform?

Just a quick update.

Last week I removed the cover to look around and saw (what I thought) was the cable to a SSD, but it seemed connected in a haphazard way.

Today I powered it for the first time since placing the cover on. The boot up beeping could be heard, however, the screen remained white. Also, although I'm uncertain whether this was the case before, channels 1 and 4 had the 1M and 50ohm illuminated whereas channels 2 and 3 (the "bad" channels) didn't have anything lit.

I'm going to remove the cover and look at the cable that I touched to see if something got disconnected.

Also, as for what the scope displays when taking measurements in 50ohm mode (prior to the white screen issue), channels 2 and 3 (the "bad" channels) display a flat line as if nothing is connected to the inputs. Maybe, but I'm uncertain, the line bounces a bit when something is first connected. When in 1M mode, the channels work fine.

The only questionable anomalies I saw: on all channels, when I select auto measurement, and measure a square wave from a function generator, the horizontal portions of the wave are thick. I think if I take measurements after initial booting, the lines are thinner, but I can't say for sure at the moment. Also, the lease concerning issue, the square wave on the front of the scope (to calibrate the probe) isn't producing a signal.

As for the thicker horizontal lines as stated above, I've never used a high frequency, high sample rate scope, so maybe this is normal for such a scope. I'm use to Tektronix 100MHz scopes.

I guess by SSD cable you mean SATA, I'm surprised, if I remember right, those units where IDE. So???

For the white screen it's most likely an unplugged cable. You can also try to use the VGA output, but I'm not sure if you need to enable it in BIOS first...

It is normal that only channel 1 and 4 lights up. It's not because both of them are working or not. It simply in it's initialization process. Same goes for the 1M and 50 ohm LED, both are only for the initialization, don't worry about that, mine does that too! So don't worry!

That thick line is normal, higher bandwidth mean higher noise, so get use to it! It's closer to the reality too (unless it is out of proportion, then it might be the scope).?

The calibrator output is on the same circuit then the AUX out that generates the calibration pattern. So if it doesn't output anything, it might mean the calibrator is defective. If that is the case, you won't be able to do the self cal and you won't be able to fix the two other channels (you might fix them but you need to calibrate them at least one for them to be usable).?

If the ADC were blown, you wouldn't see a line at all or it would be saturated, so that's good. You notice that when you plug something to them, there is a little bounce. depending on what the bounce looks like it might mean several things:
1- if it's just an impulse, it's either caused by coupled capacitance or by the long ground cable
2- if it's continuous and doesn't change if their is a signal or not, it's probably just detecting the probe as an antenna. In that case, you probably have a blown component, hard to say which one.
3- if it's continuous and change depending on signal, it is probably a bad amplifier. It could also be bad calibration factor. With your possibly defective calibrator, I would bet on that. If the calibration factor got corrupted at some point and the calibrator doesn't work, it could very well be simply that. You say you have other Tektronix scope? Use them to verify the output pattern of the AUX out when calibrating a channel and make sure it works properly.?

Considering your 50 ohm impedance is fine, it is unlikely that anything is blown on your signal path. Maybe, you could do this simple test. Plug 2 (1 functional, 1 defective) channels of your scope together to the FGEN. Output a square wave or a triangular wave. Both channel should be on 1M and same configs. Are they match? Then switch the functional channel to 50 ohm and store the waveform. Switch it back to 1M and display the save waveform. Switch the defective channel to 50 ohm. Does the functional channel and the save waveform match? There should be no amplitude or phase mismatch.