Another blown Agilent 4263B

[Astralix]

Hi!

Thank you for these very informative run through of previous 4263B repairs. Really appreciate that work as it gave me some hints where to start and to look first.

I got ripped-off by an eBay seller (Unit removed from working test setup... bla bla bla) as not only he stated that the unit was working till the last day, but I now have evidence that the someone had the remnants of the accident that killed the unit carefully removed on the top layer.  But he forgot to do that on the bottom layer. Unfortunately I had the unit sitting on the shelf far too long to take any further actions besides repairing the unit.

Pictures of previous repairs in this forum already helped identifying, if the so cleanly removed trace under the Z6010 diode was a factory mod. No it wasn't it was carefully removed and cleaned to hide what happened.

But I have still two questions:
The Z6010 Diode below the connector B was blown on my unit and one of the 77G too. But around the blown Z6010 two traces have been vaporized and one through-hole has sort of exploded.
As your photos show, I need to replace the trace on the top side. But I cannot see where the through-hole connected before on the bottom side. All of the through-holes there look like they connect to the inner layer but they don't do so.




Any idea which of all the through holes do connect to that barely visible inner layer?

Current status of the unit is:
With all diodes removed and the trace to Hcur bridged to the 3 in parallel 100R resistors, the instrument does give stable readings, but they are far out of target. So a 560uF cap, tested for 530uF gives around 43uF on the 4263B and a 1% 100R metal film resistor gives 18M Ohm with X being far away from 0.

It is not really conclusive that, with such a big bang going through the inputs, only two traces and a 100R resistor on the Hcur Output had been damaged. Someone mentioned some 51R resistors on one of the hybrids. I will check these too. But I would be really glad if there are more suggestions and especially if there is an update on firmware, calibration software and whatever. Some of the threads on repairing these units are so old now, all the helpful links start to fade away...

Best of all
Astralix

[TERRA Operative]

I wrote a Python script that will do a self test and unlock both options automatically.

https://github.com/JaredCabot/HP-Agilent-4263B-Option-Unlocker

You'll find the latest firmware image there too. It can be written to the instrument via GPIB with the correct commands if one were to write a Python script to do so, but I think it's safer to just pull the socketed chip and stick it in a chip programmer.

As for the damage to your board, I'll take some photos from my instrument later tonight that might provide some clues to help you out.

Looks like no schematics are available AFAIK, but the service manual has some troubleshooting info and block diagrams that might help a little.

https://groups.io/g/HP-Agilent-Keysight-equipment/files/All%20HP,%20Agilent%20and%20Keysight%20instruments%20in%20folders%20by%20part%20numbers/4000%20to%204999/4263B%20LCR%20meter%2010%20Hz%20to%20100%20kHz

[Astralix]

Hi Jared!

Thanks!

My unit shows a date of February 2nd 2000 with firmware 1.06 with Options 001,002 installed. So the unit was bought with these options or someone already used your script? I cannot tell.
However the self-test seems interesting but isn't that available thought the menu as well? That one passes on my unit without any fault.

I have read the service manual and by that I understood the basic working principle. That manual also lead me to the conclusion that there must be more "down below" as I could trace the sinusoidal test signal from the opto-switch through the 100R resistors and then disappearing.

However, there are some open contacts around that one Z6010 Zener Diode that are unclear to me of where they should go.

[picburner]

Nice bang!
In my instrument all the points indicated by the black arrows are connected to GND (Chassis).
If you are still missing some other tracks, just ask.

[TERRA Operative]

Hi Jared!

Thanks!

My unit shows a date of February 2nd 2000 with firmware 1.06 with Options 001,002 installed. So the unit was bought with these options or someone already used your script? I cannot tell.
However the self-test seems interesting but isn't that available thought the menu as well? That one passes on my unit without any fault.

I have read the service manual and by that I understood the basic working principle. That manual also lead me to the conclusion that there must be more "down below" as I could trace the sinusoidal test signal from the opto-switch through the 100R resistors and then disappearing.

However, there are some open contacts around that one Z6010 Zener Diode that are unclear to me of where they should go.

Looks like you have the latest firmware and all options unlocked already, so no problems there.

Here are some photos of my board, it seems that the burnt anode side of that diode connects to the local internal ground plane.

Luckily the adjacent diode also connects to the ground plane at its cathode, so installing the diode from the undamaged hole at its cathode end and then connect the anode end directly to the cathode of the adjacent diode would get the job done.
See the drawing on your photo to see what I mean.

Hope that helps. I'll leave my instrument disassembled for the next day or two just in case you need more photos.

[Astralix]

Thank you all so much!

From another thread about this unit, I read that there may some 51R resistors fail on these amplifier boards. There are two identical ones inside and I pulled them both and compared part by part and transistor pin by pin.
They are completely identical. So no luck here.


Then I cleaned up the solder points on the A1 board and soldered the hybrids back in their places. While again verifying all solder joints with magnifying glasses and cold light, I found a HC04 chip with what looks lie a little chimney...
I checked the TTL Manual from 1991 and there are no drawings mentioning such a chimney or venting hole... 


I hanged the HC04 for a NOS one I had in stock and...


Perfect! All measurement values are on spot compared to my trusty old HP 4257.

Only thing I have to wait for, are the diodes. When they arrive, the unit is as good as new. I need to find a calibration lab that can handle the thing, but as the values are very close too my 4257 it is probably good enough for me, the last calibration of the 4263B is only 4 years old.

[TERRA Operative]

Good work!

If you do find a cal lab that can actually perform the calibration and adjustment and not just a simple verification, try to coerce a copy of the HP calibration software from them.
A number of us are desperate for it, and I want to port it to Python.
(Keysight simply refuse to provide any support for these instruments at all).

You can't adjust this or any of the other related units (high resistance, milliohm, capacitance, etc meters) without the associated software.

I'm almost at the point of trying to reverse engineer the firmware to recreate the adjustment software from scratch.

[Astralix]

1) Getting the cal disk
I hope there is a way to find that software. I heard it is a BASIC program, what will enable me to modify it a bit to use my calibrated Schlumberger 7081.
Just guessing, but I can imagine that all the small cal labs that own the software nowadays do pay their rent, bread and butter from software like this. And I can understand that they do not give it away for free.

2) Getting a calibration
But I'll also check the other way. I feared that calibrating an 8.5 digit unit like the 7081 costs big money but learned that it only is around 300€. I can afford 300€ every few years to have a reference multimeter to calibrate everything against.

3) Missing Pods / Calibration Pods
The cal-pods for the 4263B are also very rare and then go for big money each. That is another thing we have to replicate. There are now second sources of pods for Celvin cables and other types. But I haven't seen any OSL pods. With the pods around 100€ a piece I can image to just buy three, recycle the cables for other instruments and make an OSL myself. I would opt for using just simple metal shield cases and drilling matching holes myself for these BNC adapters. But I haven't seen these special BNC plug with the missing outer ring or the little handle anywhere. Also, I can imagine what Open and Short will look like, but what is the load made of?

However, the unit works super nice with second source Celvin cables with BNC. The defective parts are only protection and one logic chip what should leave the calibration of the unit completely unaffected. Only the little parasitic capacitance of the diodes will currently be missing until the replacements have arrived.

[TERRA Operative]

I actually have a design that works great for the resistance and open/short standards. I replicated the HP design closely enough.

https://www.eevblog.com/forum/buysellwanted/wtb-hp-16361a-1khz-dut-box-for-adjustment-4261a/msg5597771/#msg5597771


As for capacitance standards, I have a design rattling around in my head to make my own air capacitors as per the HP design too.
I don't know what the HP ones look like inside, but I can guess...
The trick will be measuring and adjusting them... The resistance standards were easy to measure with my 6.5-digit 34461A multimeter, but I'll need a nice accurate capacitance meter for the capacitance standards, but I need to calibrate my capacitance meters to be able to measure my air capacitors to calibrate my capacitance meters... circular catch-22 problem...

[Astralix]

That is cool!

What a nice work! I definitely will make these myself, too. But I'll be stuck at the same point as you are. Needing a calibrated LCR for measuring C to calibrate the LCR...
However, if you have some time to wait, I'll contact my preferred Cal Lab and check if they can do 4263B and then we talk about how I get some tested reference C to your location.

Maybe, we connect via PM to exchange some details.

[TERRA Operative]

Sounds good. I have a few spare bare PCB's of my 4-wire standards linked above, so we could maybe do a trade, or something. (They are small and hence cheap to order anyway).

[mawyatt]

Somehow missed this project, like the direct BNC connections with 3D printed levers, nice

We have a Hioki IM3536 (8MHz) that was purchased new a couple years ago and been in our lab in the same spot since, also a Tonghui TH2830 (100KHz) purchased new just before the IM3536 and also in same spot since. The lab operates with 25C and 42~45% RH 24/7. Also 3 KS34465As, DMM6500, SDM3065X and a HP34401A and AG34401A.

We can offer some measurements if you wish. An option might be to use some small value Caps like Polystyrene, Mica and NP0/C0G for measurement, then shipped. The latter types are available and not too expensive in 1% types up to 0.1uF.

Anyway, nice project

Best