HP 4276a LCZ meter repair.

[TERRA Operative]

So, I got myself another bit of test equipment.
This one is a Yokogawa/HP 4276a LCZ meter, and it is huge, 2.5U or so high,, 19" wide...

I fired it up last night and hit the self test button, and was gifted with a few more errors than I was hoping for...

37, 38, 39, 41, 42, 43, 44, 45

Does anyone happen to know what these errors actually are? Maybe I need to dig deeper into the service manual, but all it seems to say is that they are related to the analogue section. No other info.

I also found that the brushless dc motor in the cooling fan is dead and been disconnected by the previous owner, so I'll replace it with a standard 12v San Ace brand 60mm fan.

And, the backup battery has leaked everywhere too, as is tradition. It's a 2.4V nicd, so I'll probably remote mount a couple nicd AA batteries to keep further mishaps a little more contained.
The battery is only used to save the front panel settings when you turn the machine off, so no calibration memory was lost like happens with the 3478A multimeters.
The main problem is one of the card edge connectors for the digital board is corroded pretty bad from the battery juice, but I'm sourcing a NOS exact replacement for that.

So, the first plan of attack is to clean up the battery residue and replace the card edge connector, and figure out what those error codes mean, hopefully some are magically resolved with the disappearance of the old card edge connector...

Second step is a full capacitor replacement, all electros are getting ditched, and a few dodgy looking poly caps too.
It looks like all the electrolytics are United Chemicon, many being SM series, an obsolete 85degree rated general purpose type. They'll be replaced with 105degree rated caps of an equivalent series and same brand.

Third step is to recreate my own Option 001 board to give me built in DC bias output.
The service manual has schematics, BOM and PCB layout so it should be relatively easy, pending the sourcing and substitution of obsolete silicon.


I'll add more photos when I'm back home tonight.

[TERRA Operative]

One step closer...

I popped past Akihabara on the way to work today and grabbed a replacement backup battery.
500yen for a 300mAh 2.4V (2x AAA nicd) pack.

A small cable tie or double sided tape should have this mounted somewhere a bit safer for the longevity of the PCB...

[jfphp]

Silly, but, before the test,  did you connect a mesurement interface to the 4 BNC connector ?

[TERRA Operative]

Hahaha, oh wow. I blame the fact I was playing with this thing at 2AM for that little oversight...

With the kelvin clips connected, it passes all tests! Good call! 


Well, with that sorted, we just need to order capacitors and the edge connector.
And until they arrive, here's a bunch of pictures of the unit as it stands.

• First pic: Lid off
• Second pic: Old fan with cut wires. You can see the hybrid module to the left, that's the motor controller. Also the empty space to the right is where the Internal DC Bias module will go.
• Third pic: The leaky battery and corroded card edge connector.
• Fourth pic: Battery juice on the motherboard. It doesn't seem to have got into the traces at first glance, Once I get the card edge connector out, I'll know for sure.

[TERRA Operative]

Continuation of pictures:

You'll notice that on the Digital and Analogue PCB's, that the different sections are delineated and labelled, makes understanding the circuit and troubleshooting a breeze.
I wish more equipment was labelled like this!

• First pic: The corroded card edge PCB, it seems to be not toooo bad, I'm hoping a careful clean and application of Deoxit will bring it back to an ok condition.
• Second pic: Digital PCB (with the corroded edge connector.
• Third pic: Analogue PCB, all looks good except for the next pic:
• Fourth pic: Two poly caps have some sort of corrosion or something on them. These are cheap, so I'll stick some decent Panasonic ones in as replacements

[TERRA Operative]

And last of all (Forum restrictions on file sizes....)

• The power PCB. This'll get all new caps, just like all the other PCB's. It's otherwise in really good condition for it's age.

[SilverSolder]

Beautifully made piece of equipment.  Nice find!

[TERRA Operative]

Alrighty, I desoldered the battery and edge connector to assess the damage.
Fortunately, it looks like the PCB is mostly unaffected! Minimal black on the traces and no corroded through traces anywhere, and only minimal damage! 

I've given it a clean with isopropyl alcohol and then dish soap for now, but I'll give it a little bit of vinegar then a good rinse in distilled water then isopropyl alcohol to get rid of any remnants.

[TERRA Operative]

Continuation (Forum limits on images...)

Interestingly, the card edge connector seems to be only affected at the actual fingers, I can't see any damage where the legs touch the PCB..

I'll also have to polish the card edge on the daughter card (The picture is after a wipe with alcohol). I'll have to get one of those fiberglass pens, or maybe a melamine sponge will do it?
In either case, a treatment with vinegar and rinse as above, and a good coat of deoxit is on the cards.

[TERRA Operative]

Got a bit more stuff done on the weekend.

I got a delivery of capacitors from Digikey so they all went in, except I missed the one cap on the display/front panel board , so I'll hit Akihabara for that...

I also replaced some fuzzy poly caps on the analogue board. I'm not sure why only these two went fuzzy, maybe thee were susceptible to something in the air from the leaky battery or maybe they just did it over time? Not sure, but they were replaced with new Panasonic caps.

And thirdly, I scraped back the solder mask where the battery goop had got underneath.
Luckily it seems there is only very minimal damage underneath, one trace is a tiny bit tarnished, and just the pads for the battery and the exposed square around the word 'battery' in the ground plane.
I could probably leave the solder mask off as in the photo as the copper is tinned, but I bought some of the UV cure solder mask goop from ebay, so I'll give it a go and see if I can make a complete mess of things.

All going well, I should have the replacement edge card connector delivered in the next few days too.

[TERRA Operative]

Got delivery of the replacement card edge sockets today. I only need one, but they came in a set of three, so I'll keep the others as spares.

Also got some distilled white vinegar, something that isn't the easiest thing to come by in Japan (although rice vinegar is everywhere), but Amazon saved the day.
I was able to clean up the corrosion on the card edge and gave the motherboard PCB a treatment, followed by distilled water and finally isopropyl alcohol.
It looks like someone has had a scratch at some of the fingers in the past, but they came up pretty good regardless. A bit of a polish with a melamine sponge soaked in vinegar got them shining pretty good.
Now I just have to wait on the solder resist to arrive from ebay.

I also went and bought some bits and pieces from Akihabara for the DC Bias option, still got a few more coming in the post and a few more bits to order.
It's a bit of a pain to find obsolete semiconductors sometimes, but I have tracked down everything except HP part number 1854-0523.
If I could get a hfe reading for that transistor, it'd make cross referencing so much easier. It appears to be a HP custom part made by Motorola, so there is no standard part to directly cross reference to.
I don't really want to pay over a hundred bucks for 10 shipped from ebay either, I only need one!

So far I have found the following ratings:
NPN Silicon TO-39 case
P_d = 1W
F_t = 150MHz
V_ce = 160V
I_c = 0.5A

The search continues.

[PartialDischarge]

Hi,

Can you check the interior of the bnc connectors?
In my 4277 I have to short the GNDs of LCUR LPOT HCUR HPOT, otherwise it gives errors on self test using the same test leads.

The bncs go to ground with capacitors except one according to the schematics.

[TERRA Operative]

It looks the same as mine, I'll add photos of my BNC's tonight.

Strange that you need to short the BNC's like that, the metallic front panel should do it....
Can you disconnect the test leads and the shorting wires and do an ohms test between the outer shields on the BNC jacks?
I wonder if the BNC jacks aren't making good contact somehow or the capacitors/diodes are busted.

[coromonadalix]

Are your cables custom mades or are they the originals one included with your lcr ?  the cable shields must be at ground levels or the ground body of the lcr, and the inner bnc pins must go to the circuit ?

But on the first photo,   the bnc's ground body is on the metal plate already and you have capacitor and diode going to the body ? they dont serve any purposes ?  ground body vs ground body ?


You need this device for your tests : HP 16089A, B, C or D model

You have this link for your test device appartus :
http://bee.mif.pg.gda.pl/ciasteczkowypotwor/HP/16089A,%20B,%20C,%20D%20Operation%20&%20Service.pdf

https://doc.xdevs.com/doc/HP_Agilent_Keysight/HP%2016089A,%20B,%20C,%20D%20Operation%20&%20Service.pdf

[PartialDischarge]

Are your cables custom mades or are they the originals one included with your lcr ?  the cable shields must be at ground levels or the ground body of the lcr, and the inner bnc pins must go to the circuit ?

The cables are standard LCR cables, TERRA has the same ones, and with them he doesn't get any errors on self-test but I do. I have to short the grounds to get rid of the errors. However the manual kind of states that there has to be a short in ground at the DUT level. So all this puzzles me.

But on the first photo,   the bnc's ground body is on the metal plate already and you have capacitor and diode going to the body ? they dont serve any purposes ?  ground body vs ground body ?

Although not apparent, those bncs are isolated, and the connections are as per schematics. See attached pics.

Has the lcr been tampered before you buy it ?

Nope, cal stickers intact

[coromonadalix]

the short at the dut is for shielding purposes as you know,  sometimes they call it the 5 th wire, the nearest of the DUT is the better as i just read.

Normally an good lcr  must have an zero adjustment while you short the kelvin leads together.

The HP 16089A, B, C or D model   is the official dut test device adapter for your lcr as i said, if you dont use the good leads kit it may give you thoses errors

Are you able to zero the leads ? if yes   I would not be afraid to use it with your shorts the way you did it, if the read values are good, just as always to be sure to have an discharged capacitor

And maybe find on ebay an similar test device  but they are pricey ...


And you surely have tested the input diodes and the capacitors ?

My Fluke pm6304 uses 2.5 mm banana jacks 24 inch long, not bnc shielded cables, it does work very well, i do an zero test at startup and stay reliable all day long.

[PartialDischarge]

the short at the dut is for shielding purposes as you know,  sometimes they call it the 5 th wire, the nearest of the DUT is the better as i just read.

Normally an good lcr  must have an zero adjustment while you short the kelvin leads together.

The HP 16089A, B, C or D model   is the official dut test device adapter for your lcr as i said, if you dont use the good leads kit it may give you thoses errors

Are you able to zero the leads ? if yes   I would not be afraid to use it with your shorts the way you did it, if the read values are good, just as always to be sure to have an discharged capacitor ;
And maybe find on ebay an similar test device  but they are pricey ...

I didn't bought the official adapter cause for my application I need a bnc connector to the DUT, and I will build that myself. The leads do calibrate fine in open/short, and measurements are good, but its the different outcome TERRA has that puzzles me and points that "something" is different, I would like to know what that is

And you surely have tested the input diodes and the capacitors ?

Not yet, test pending

[TERRA Operative]

Here's the photos of what I've got on the back of my BNC's

Looks like one of the ceramic caps is chipped, might have to look into replacing it maybe.


According to the manual (Pages 6-16 and 6-17) the diodes (number 64) cross reference to 1N4936, and the capacitors (number 63) are 0.022uF, 100V ceramics.
See the last pic for the connection details.

[PartialDischarge]

Well, those are some different values and components, also my LPOT gnd goes directly to earth

[TERRA Operative]

Yeah, might be worth buying some new caps and diodes and reverting it to factory spec, then see what the self test says.
Could be as simple as someones sticky fingers poking things here and there...


[EDIT] Wait a sec, you said you had a 4277A, it looks like it actually is a bit different to the 4276A......

Looks like yours is somewhat correct. Looking from the rear, it has 4x 1N4936 diodes with two 390pF capacitors (63 and 64), then the tab connected directly to the chassis for the third from the left, and finally a 3300pF cap (65) on the far right.
I'd test and replace those diodes and caps as needed to start with and see what happens. Also, be doubly sure the kelvin clips are wired correctly.

It seems like the test cables/test jig needs to be connected, but 'open' as in no DUT and the kelvin clips not touching each other, as detailed where I highlighted in the last image.

What happens if you just put two jumper wires from the center of the BNC's to the center of their respective BNC's?

[PartialDischarge]

Looks like yours is somewhat correct. Looking from the rear, it has 4x 1N4936 diodes with two 390pF capacitors (63 and 64), then the tab connected directly to the chassis for the third from the left, and finally a 3300pF cap (65) on the far right.
I'd test and replace those diodes and caps as needed to start with and see what happens. Also, be doubly sure the kelvin clips are wired correctly.

It seems like the test cables/test jig needs to be connected, but 'open' as in no DUT and the kelvin clips not touching each other, as detailed where I highlighted in the last image.

What happens if you just put two jumper wires from the center of the BNC's to the center of their respective BNC's?

Yes mine is a bit different, and is according to schemtics. If I jumper the center BNCs (2 and 2) it still gives the errors, I have to short the gnds.

Anyway, OT but this is the jig I'm building to have one bnc out, still missing cables...

[TERRA Operative]

Cool. Once my unit is operational, it'll be onto building the test jigs.

What do you get if you run the self test with only the center pin of the two left jacks connected to each other, and only the two right jacks connected to each other at the same time?

[PartialDischarge]

What do you get if you run the self test with only the center pin of the two left jacks connected to each other, and only the two right jacks connected to each other at the same time?

errors, I think i've tried every possible combination

[Tomorokoshi]

For the fun of it this capacitor may work:
https://www.digikey.com/products/en?keywords=399-14059-ND

Although perhaps I went overboard in trying to find something that had low inductance. It's a bit cheaper than this one:
https://www.digikey.com/products/en?keywords=338-3880-ND

Here is my first attempt at an adapter for the HP 4194A. It's a bit of a hack job, and there are several changes to make, but for what I needed it worked well and compensated out very nicely. The next revision will have shorter connections with less inductance, and there will probably be several variations to deal with combinations and polarities of the connectors.

[TERRA Operative]

Replaced the capacitors and diodes on the BNC jacks today.
I found one diode was never soldered properly... If you look back at the images in post #17, you'll see it there.  Good QC there HP!

I decided to go ahead and just replace the lot, I don't know the history of these 'user facing' parts and they are cheap anyway.


I also got some UV cure solder mask paint from ebay delivered the other day, so I'll make a transparency mask to match the motherboard pads etc and see how much of a mess I can make things....