Agilent/HP 54845A

[nidlaX]

I've seen this unit and other similar units on eBay this month. One of them showed a failure to communicate with the acquisition board in addition to the network password error, so my alarm bells were ringing. Hope you sort this one out!

[Tony_G]

I don't have enough of the shorter sma cables to do all 4 channels but could maybe do one at at a time

To me it seems like this is the best way to go - Can you try to isolate the sockets first and then the hard lines to see if one of those might be at fault?

TonyG

[Samogon]

Well you font need patches, your swaping of attenuators showes clearly that issue doesn't move with attenuator.

[smgvbest]

I've seen this unit and other similar units on eBay this month. One of them showed a failure to communicate with the acquisition board in addition to the network password error, so my alarm bells were ringing. Hope you sort this one out!

this one showed the failure and I can reproduce it by booting to DOS then starting windows on the scope.   if it starts normally no error about the acquisition board.   password was easy,  just boot to dos, modify msdos.ini (yes, ini files) and then reboot into safe mode and remove the passwords

I do have 3 working channels on it.  1,3 and 4 work,   2 seems dead,  1 wont' cal but works fine.

[smgvbest]

Well you font need patches, your swaping of attenuators showes clearly that issue doesn't move with attenuator.

that's what I'm thinking but an willing to try other suggestions

[Samogon]

Even in this state it is very very useful device.
And i glad it is can autoset and trigger even without being calibrated.
And i hardly remember when i was using more than two channels at the time.
Especially taking into account price of 1.5GHz probes
But for personal satisfaction fully working unit more pleasant no doubt.

[Tony_G]

There are several things that can be swapped and a couple of things that can't.

Swappable ones are the A/D Hybrids, Attenuators and hard lines. The ones that can't are the Hybrid sockets and, from looking at the manual, the board to board connector under the attenuator. I've never taken mine off so I don't know if that is the case.

You should be able to resolve where it is by swapping all of that around. I'm starting to lean to issues with those connectors.

TonyG

[Jwalling]

Silly question but did you try cleaning the sockets and making sure that all of the little pogo pins are moving freely?

TonyG

+1 on that. I've seen a number of 54835A/45A scopes that had a pin or two that would compress, but not spring back.
If you're not sure, you can move the sockets around as well.
I actually made a jig that would allow me to take apart the socket without the pins spilling all over allowing me to replace the bad ones.

[smgvbest]

I have to admit my eyes since iLasik suck for close up inspection.  I'll reinspect the pins.   since I had the hybrids out again I swapped CH1/2 hybrids this time and again same results.

looking at the diagram the hybrid socket looks like it's a pogo pin socket correct? so it's not soldered to the board but held in place by the top/bottom plates (hence the need for  something to retain the pins) since CH2 is dead at this point I could try on that one and remove the socket.

I guess it could even be possible the pads on the PCB may be in need of cleaning also.

yeh,  I rarely use more the 2 CH's but it really is the point of it.  I want it repaired.


FWIW,  I backed up the original CAL file in C:\scope\cal  and can restore that cal file anytime which I have done.  it restores it to all channel cal'd but CH2 still remains none functional.   CH1 even though it won't cal reads input perfectly fine across all timebases and vertical ranges so even though it fails ADC it is working.

[smgvbest]

Especially taking into account price of 1.5GHz probes
But for personal satisfaction fully working unit more pleasant no doubt.

the 54845A comes with the 1161A probe which are 500Mhz probes giving a system bandwidth of 1.5Ghz and going for an average of 60-70 each on eBay.   i picked up two with a offer of 100 and got them.   I must have felt confident this scope was fixable since I usually don't pick up accessories if i'm not sure something is fixable. 

[smgvbest]

ok, I removed the hybrid from CH2 and found some jewelers magnifying glasses to take a closer look.  I'm pretty sure I see several pins that are compressed.   
can those pins be fixed or would they have to be replaced?
anyone know if i have to replace them what I look for or have a spare socket I can buy from you?

[Samogon]

That is promising

[james_s]

I would try gently poking at them and see if they will un-stick. Be very careful not to damage them though, and take the usual precautions against ESD. Taking apart the socket would be a last resort for me, I can visualize something going BOING and tiny pins bouncing all over the room.

[Tony_G]

As James suggested, try poking them with a non-conductive plastic spudger (or something similar) and giving them a good flush with IPA.

I used a Precision Foam Swab (#SWP-25) from Caig Labs (makers of Deoxit). I find the SWP to be great for cleaning pins and surfaces because of the foam tip.

TonyG

[smgvbest]

Here's a small update.
I tried cleaning them again and no change.   i used a non-conductive screwdriver to push on them and not much boing in them.
I re-read the service manual as it does talk about removing them.  i followed it very carefully and it does emphasize if you remove the 2 screws holding it to the board carefully you may not have to remove the acquisition board and I did not need to but did notice one thing.  one of the heat sink screws is stripped so it doesn't snug down one side of the hybrid as tightly as the other.   that might be the missing link here and part of the problem.

anyways, so gave it a try and I am happy to say the pins are held captive in the socket.  you can flip it and they do not come out.   Now, with it off the board i cleaned both the pins (both sides) and the PCB contacts.  there is some improvement in the pins but still not as much boing as others.

now the flip side of this is CH2 is showing signs of life.  it's not triggering but I do now see a signal on it and I can adjust the vertical scale as well as time base which is far better than it was.  it still fails the FISO test but passes all others.   there's signs of life here. 

since I haven't been able to find anyone with spare parts for this scope I am considering a parts unit to help.

[james_s]

That's certainly promising and suggests that there is/was indeed a problem with the contacts. There are a number of ways to repair the stripped hole, but you have to be careful as some of them can make things worse if you screw it up. You may be able to tap the hole for the next size up screw, maybe even use a self tapping screw. Another option is fill in the hole with metal epoxy and then drill and tap it. If there's nothing on the other side, you could drill it through and put a nut on the back. Yet another option is drill it out to press-fit an threaded insert, with a bit of CA or Loctite that can be a very strong repair. Which, if any of these is feasible depends on the tools you have access to and how you are at machining.

[Jwalling]

If you get to the point that you're sure it is a pin problem, and you can't fix it, you can open up the socket and replace the pins that need replacing. I would recommend you make a jig like mine.
Note that my jig states to put the side of the socket facing the chip down (toward the jig) for a very good reason. You'll never get it back together as the pins won't align with the plastic of the socket - I found out the hard way the first time I attempted this! 

I have a bunch of sockets harvested from scrapped 54810A series scopes (the 54542A series also used the same type of socket). If you need one, I could send it to you for the cost of postage. This will give you a source of pins to use in your socket.

[smgvbest]

I did do the same now to CH1 which is reporting the stuck bit on the ADC and in this case there was no change to CH1
I may pull it again and recheck it.   if nothing else the apprehension is gone in removing the socket.

[james_s]

Is this thing known to be a problematic design? I wouldn't have expected so many problems with sockets and connectors. You might try a bit of Deoxit D5 on the pins and pads, that stuff is almost like magic.

I was getting a stuck bit error on my recently acquired TDS784C and it turned out to be bad solder joints on one of the DMUX ASICs. It can be very challenging to track down issues like this, especially intermittent ones because there are *so many* connections between parts and it only takes one of them to throw a wrench in the works.

[smgvbest]

I know of 4 repairs on these
Signal path
Tony_G
dasaro
myslef

each of us has had some issue with the socket but others have solved problems in cleaning them.  mine seems to go further though or I"m not cleaning we'll enough.  I'll try deoxit it also.

[Tony_G]

Add Jay into that as well and it makes 5.

I think the pins are gold plated so it might make sense to use Deoxit Gold rather than the standard one.

In my case though I must have had only minimal issues because I just cleaned with IPA.

Also it looks like the connectors just screw down - You might want to take Jay up on his offer for one or two and see if they make a difference.

TonyG

[Jwalling]

Add Jay into that as well and it makes 5.

I think the pins are gold plated so it might make sense to use Deoxit Gold rather than the standard one.

In my case though I must have had only minimal issues because I just cleaned with IPA.

Also it looks like the connectors just screw down - You might want to take Jay up on his offer for one or two and see if they make a difference.

TonyG

The sockets are different, so the ones I have are only good for harvesting pins. There's a lot more contacts on the 54845A hybrid and the chip is larger as well.

[Tony_G]

My apologies - Didn't get that from your post - Clearly reading comprehension isn't my strong suit...

It might still be worth swapping the connectors on the 54845A if they haven't been categorically identified as the fault (though it sounds like it's pretty much a given now).

TonyG

[smgvbest]

I'm in the mind it's the sockets as well and in an effort to find ways to spend a bonus check I picked up a second 54845A which should be here tomorrow.   I'll have donner parts then to swap.

i suspect the first issue on the second one is power supply related so I'll start from there.   just wish they wouldn't strip the LS-120's out of these things.
it's also a VIN25 with serial in the 3838 range.

I'll probably re-list the one 54845 or part it out after I've checked all the Hybrids and Attenuates and such.  If nothing else if I list the whole thing I'll include what I know to be wrong with it

edit:
I did reclean CH2 socket with and no improvement on CH2.  Still same Fiso error

[Tony_G]

Ok, I can't wait to get the next update...

How'd it go with the donor sockets?

TonyG