HP 4276a LCZ meter repair. - Page 1
Forum section: electronics / repair

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 22, 2018, 03:59:57 am
content: So, I got myself another bit of test equipment.This one is a Yokogawa/HP 4276a LCZ meter, and it ishuge, 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, 45Does 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.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 22, 2018, 06:55:12 am
content: 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...

author: jfphp
author_rank: Regular Contributor
timestamp: October 22, 2018, 09:25:26 am
content: Silly, but, before the test, did you connect a mesurement interface to the 4 BNC connector ?

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 22, 2018, 02:35:12 pm
content: 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 offSecond 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.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 22, 2018, 02:38:50 pm
content: 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

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 22, 2018, 02:40:03 pm
content: 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.

author: SilverSolder
author_rank: Super Contributor
timestamp: October 22, 2018, 07:12:37 pm
content: Beautifully made piece of equipment. Nice find!

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 25, 2018, 04:29:32 pm
content: 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.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 25, 2018, 04:34:58 pm
content: 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.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 29, 2018, 12:58:07 am
content: 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.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 29, 2018, 06:00:30 pm
content: 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 casePd= 1WFt= 150MHzVce= 160VIc= 0.5AThe search continues.

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 07, 2018, 08:42:51 am
content: 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.

author: TERRA Operative
author_rank: Super Contributor
timestamp: November 07, 2018, 08:47:54 am
content: 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.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 07, 2018, 10:51:16 am
content: 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 modelYou have this link for your test device appartus :http://bee.mif.pg.gda.pl/ciasteczkowypotwor/HP/16089A,%20B,%20C,%20D%20Operation%20&%20Service.pdfhttps://doc.xdevs.com/doc/HP_Agilent_Keysight/HP%2016089A,%20B,%20C,%20D%20Operation%20&%20Service.pdf

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 07, 2018, 11:01:17 am
content: Quote from: coromonadalix on November 07, 2018, 10:51:16 amThe 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.QuoteAlthough not apparent, those bncs are isolated, and the connections are as per schematics. See attached pics.QuoteNope, cal stickers intact

author: coromonadalix
author_rank: Super Contributor
timestamp: November 07, 2018, 11:18:02 am
content: 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 errorsAre 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 capacitorAnd 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.

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 07, 2018, 11:45:28 am
content: Quote from: coromonadalix on November 07, 2018, 11:18:02 amI 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 isQuoteNot yet, test pending

author: TERRA Operative
author_rank: Super Contributor
timestamp: November 07, 2018, 02:57:24 pm
content: Here's the photos of what I've got on the back of my BNC'sLooks 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.

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 07, 2018, 03:43:30 pm
content: Well, those are some different values and components, also my LPOT gnd goes directly to earth

author: TERRA Operative
author_rank: Super Contributor
timestamp: November 07, 2018, 04:14:55 pm
content: 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... 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?

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 09, 2018, 08:08:28 am
content: Quote from: TERRA Operative on November 07, 2018, 04:14:55 pmYes 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...

author: TERRA Operative
author_rank: Super Contributor
timestamp: November 09, 2018, 08:12:08 am
content: 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?

author: PartialDischarge
author_rank: Super Contributor
timestamp: November 09, 2018, 08:30:28 am
content: Quote from: TERRA Operative on November 09, 2018, 08:12:08 amerrors, I think i've tried every possible combination

author: Tomorokoshi
author_rank: Super Contributor
timestamp: November 09, 2018, 04:49:46 pm
content: For the fun of it this capacitor may work:https://www.digikey.com/products/en?keywords=399-14059-NDAlthough 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-NDHere 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.

author: TERRA Operative
author_rank: Super Contributor
timestamp: November 24, 2018, 06:59:17 am
content: 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....

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 01, 2018, 02:36:48 pm
content: Time for an update.I have made the two extender boards needed to work on this unit.The big one is to lift the main cards out of the unit to enable adjustments and measurements while the unit is active.The small one is the same but for the DC output option board I am building.I also went and socketed the ROM chips etc. so I can easily copy the contents of the ROM chips for future use if these fail or suffer from bitrot etc.I used turned pin sockets for reliability, and replaced the older style leaf spring sockets too. I might get around to those two in the middle if I feel like it..Third picture is of the DC output option board I'm building so I can apply a DC offset to the capacitor under test.The unit has the ability to be connected to an external supply, but this board makes it all internal to the unit and hence programmable and able to be automated.I managed to source and cross reference all the parts and I used the schematic and PCB layout from the service manual to replicate it as closely as possible, so hopefully it works.......

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 01, 2018, 02:46:19 pm
content: Quote from: Tomorokoshi on November 09, 2018, 04:49:46 pmI might give something like that a go once mine is working, although these can be had for a reasonable price, and seem to be a clone of the HP types.https://www.aliexpress.com/item/TH26001A-4-Terminal-Test-Fixture-for-LCR-Meter/32676362733.html

author: precaud
author_rank: Frequent Contributor
timestamp: December 02, 2018, 01:00:00 am
content: Nice work. I've been using a 4276A which I brought back from the dead 10 or so years ago. It gets a lot of use, especially via GPIB control.I picked up this fixture a few months ago.http://www.testequipmentdepot.com/bk-precision/accessories/test-fixtures/4-terminal-test-fixture-tl89f1.htmIt's a dead copy of the HP 16047A including all of the inserts, and works fine. I'm thinking of selling my genuine HP and getting another one.The one you linked to is cheap but the contacts are recessed too deep for testing pulled parts with short leads.

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 02, 2018, 04:34:37 am
content: Ah nice, I like the look of the BK Precision one, it comes with the extra test clips too.I might have to put an order in sometime soon, and add a logic probe and pulser to the order that I've had my eye on too.

author: PartialDischarge
author_rank: Super Contributor
timestamp: December 02, 2018, 07:47:23 am
content: Quote from: TERRA Operative on December 01, 2018, 02:36:48 pmThis option is extremely useful for LEds and diodes, or transistors

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 19, 2018, 04:59:34 am
content: Just a quick update.I have finished recreating the DC offset option board!I managed to cross reference all the parts to modern parts with the exception of the LF13331D analogue switch and the AD7530LN DAC.It seems there might be modern equivalents to the LF13331D, but finding an equivalent to the DAC was proving a little difficult, luckily I could find those chips for not too ridiculous pricing...Once I'm back from holidays, it's onto replacing the damaged soldermask that I removed from the motherboard and then reassembly and testing of the unit.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 19, 2018, 10:45:55 am
content: Very good work herecongratsI tried an dc option board for fluke pm6304 lcr, i still have the board draftings, bought many parts, but had a hard time having to size the parts on it, i did not have the same physical size for many stanges values resistors, i had a hard time finding the same precision.Project on hold indefinitely

author: Kosmic
author_rank: Super Contributor
timestamp: December 20, 2018, 03:30:59 am
content: Wow good job with the option board!

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 27, 2019, 12:28:24 pm
content: OK!Finally got some time to get some more stuff done.I've tweaked all the front panel switches (flipped the leaf spring in them) to make them press smoothly again, and I've replaced the corroded edge connector socket on the motherboard.All the electrolytic capacitors have been replaced with United Chemicon caps along with a few other bits too as needed.I decided not to replace the solder mask that I removed to clean up the self disemboweled backup battery. Two reasons, one - I don't want to potentially seal any goop in, and two - I can't be bothered...It's all tinned traces under the solder mask, so it'll be fine as is, and I won't see it inside there anyway.I also installed the new battery, cable tied a long way from the PCB (Top right of the image). All I need to do now is to install a plug on the standard wiring to adapt my new fan in and get some 30mm #4-40 screws to mount it.Oh, you can see my DC Bias Option board installed at the lower left too.Once I have the fan installed, it'll be time to turn it on and see if it still works...Then on to calibrating voltage levels and whatever else I can with the gear I have here.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 28, 2019, 02:55:13 pm
content: Well, I got it all fired up tonight, and no smoke was emitted!It is all spot on with the voltages, except one small issue.I found that while my Option 001 board worked first try (!!!), I couldn't quite dial in the calibration on the voltage output.The picture below is as close as I could get to the 9.99V +/- 0.002V I set on the front panel (as per the instruction manual).Turns out the adjustment pot (FS Adj) has a 29K resistor in series, and I substituted a 28.7K, where I should have substituted a 30K, A quick test with a pot dialed to 30K in place found the FS Adj trimpot was almost spot on the required 9.99v just a hair off the center point. (This could be due to me using a 6.2V zener diode for the vref rather than the HP specified 6.3v unobtanium one).So, off to Akihabara tomorrow to get some 30K 50ppm resistors. I might pick up some 10-turn pots too to allow for finer adjustment on the three trimpots on the Option Board (I have single turn ones there now).Oh, that little plug you see dangling in the back of the unit is for the fan, It is all wired ready to go, I just gotta get some #4-40 screws that are 1 1/8" to 1 1/4" long (about 30mm) to mount it... Akihabara only has 16mm long screws in #4-40, so I'll have to check the local hardware store before I resort to eBay.

author: SilverSolder
author_rank: Super Contributor
timestamp: January 28, 2019, 03:57:26 pm
content: I love how you made your own extender and option boards! Very cool project.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 29, 2019, 01:19:30 am
content: Ha thanks!I'm just amazed that it worked first try (well beyond one resistor, but besides being 0.035v off....)Next step after finishing this is to calibrate it properly, or as properly as I can with what I have available..The old HP 16074A Calibration R-L Standards don't pop up so often for sale, so I might have a go at making a few of the modules in the near future as best I can.

author: TERRA Operative
author_rank: Super Contributor
timestamp: January 29, 2019, 05:01:59 pm
content: Alrighty, after installing a 30K resistor (Found some 1% 50ppm tempco resistors in Akihabara) and some Bourns 30 turn trimpots (100ppm tempco) I got it all working perfectly and calibrated.You can see where the 30K resistor (R1-8) is located near the top right of the schematic below.If anyone has one of these LCZ meters, I have some spare gold plated PCB's and one set of the two NOS chips needed (AD7530LN and LF13331D, but they are available from utsource.net for a not too unreasonable cost).PM me if you want a board, I'll send one for the cost of postage plus say USD$25 (gold plating and edge card connector processing etc adds some cost..) with a bunch of resistors and transistors and stuff included. The two chips will cost extra and are first in, best dressed.

author: TERRA Operative
author_rank: Super Contributor
timestamp: March 17, 2019, 04:02:38 pm
content: So I fired it up after reassembling the whole unit and it seems to work perfectly.I don't have the equipment to fully calibrate it yet, but it seems pretty close to my Keysight 34461A and Der-ee DE-5000.Next step is to buy some attachments, and maybe start looking into building the 16065A External Voltage Bias Fixture, for testing up to 200V (Or maybe more if I poke things right), good for testing caps for tube amps etc....Long video on the whole process to come soon....

author: TERRA Operative
author_rank: Super Contributor
timestamp: March 18, 2019, 07:38:51 am
content: The video of the whole process is now live!https://youtu.be/kX8WMw0BK7w

author: SilverSolder
author_rank: Super Contributor
timestamp: March 18, 2019, 01:07:39 pm
content: Great video! The section on fixing Bill West switches was worth the price of admission alone...