hybridfree/eevblog-posts huggingface dataset:
HP 33120a Transformer Issue - Page 1
Forum section: electronics / repair

author: opamp2580
author_rank: Newbie
timestamp: October 01, 2022, 05:52:03 pm
content: Hello, I recently bought a used HP 33120a for cheap, because it wasn't outputting anything. I knew that that was most likely caused by a blow output fuse, which turned out to be correct. So its working now, but the output waveforms didn't look particularly clean. So I did some probing and discovered considerable ripple on the DC supplies. And it's everywhere- on both the outputs AND inputs to the linear regulators. I went ahead and replaced the electrolytic capacitors for the various supplies, but that had no effect on the ripple. So I checked the output of the transformer and it looks like its saturating. When I unplugged the transformer from the main board, the wave looks more or less normal. So I'm wondering if the transformer is in fact faulty. I've already looked for a replacement, but can't seem to find one, so I was also wondering if anyone knows what voltages the transformer is supposed to supply; the service manual doesn't specify, at least that I've been able to find... I might have to try to find a different transformer (or transformers) that output the correct voltage. I attached pictures of the output of one of the taps on the transformer (the red wire), as well as some examples of the ripple on the output of the regulators. Thanks!

author: alm
author_rank: Super Contributor
timestamp: October 02, 2022, 07:49:29 am
content: Did you check the bridge rectifiers? If one side is open, then it's effectively doing half-wave rectification, which produces more ripple.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: October 02, 2022, 11:06:11 am
content: HiTesting transformers can be a complex matter, but I would suggest that you disconnect the secondary loads and then check for the transformer temperature rise whilst on power over time, if it is saturating it will get very hot.Do you have the primary mains voltage tapings set correctly?G Edmonds

author: jonpaul
author_rank: Super Contributor
timestamp: October 03, 2022, 05:22:42 pm
content: 60 Hz mains frequency not rippleCheck for open return or earth in PSU or wiringj
HP 3312A button cap - looking for a spare one to complete restoration project - Page 1
Forum section: electronics / repair

author: rfdes
author_rank: Regular Contributor
timestamp: February 09, 2022, 02:52:51 pm
content: Hi -I am restoring a vintage HP3312A function generator and am missing one of the small square/tapered button caps on the front panel. I would appreciate it if anyone has an extra one that would want to part with to private message me with a price you would like for it.Thanks for your time.Jim
HP 3312A Frequency Drifting Downward - Page 1
Forum section: electronics / repair

author: Sipolandis
author_rank: Newbie
timestamp: December 28, 2024, 03:53:42 am
content: I acquired an HP 3312A Function Generator that works in all regards, except that the output frequency drifts downward about 100 Hz/second. Any pointers to the likely culprit?

author: Swake
author_rank: Frequent Contributor
timestamp: December 28, 2024, 09:58:22 am
content: As always start with checking out the power supplies thoroughly.You could also post the schematic to make it little easier helping you.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: December 28, 2024, 03:03:28 pm
content: The 3312 frequency is determined by Resistance Capacitance circuits. There is no crystal reference.Any of the controls including the front panel potentiometers are suspect. DIRT can cause this, so cleaning is a good first step.If you can leave it powered up for several hours safely, that may help also.Search for HP 3312 in the entire forum, there are numerous posts.Artek has good manuals for this unit, search for 3312http://artekmanuals.com/manuals/hp-manuals/

author: Manolo Mos
author_rank: Contributor
timestamp: December 28, 2024, 05:05:01 pm
content: I have this HP too. This defect is normal, is due to a mediocre design. The exact place of the component that provokes this drift in the small printed circuit, below, it was a metalic 8 pin circuit integrated. I don't remember which was. I'd don't use these instrument for frecuency precision works, it's clear it is don't made for this. Mine is keeped in a shelf, maybe someday goes to the electronic waste facility dump.

author: Sipolandis
author_rank: Newbie
timestamp: January 02, 2025, 09:25:27 pm
content: It's curious that this would be standard behavior for any HP gear. I have a couple of old vacuum tube signal generators that are rock solid. My best guesses are a capacitor that is drifting, or a thermally unstable transistor or IC. I can leave it on for several hours and it keeps drifting downward.
HP 3312a function generator - how to get covers off! - Page 1
Forum section: electronics / repair

author: TonyOldTimer
author_rank: Newbie
timestamp: September 30, 2020, 09:16:48 pm
content: I have noticed my previously acquired HP 3312a have a loose BNC connector. I was able to get the side rail (the one with the carrying handle) off. However, I was not able to get the top and bottom covers off. As far as I can tell, the covers are just formed thin aluminium metal painted gray, and held by 4 flat-head screws (two for each cover) to the frame. I have removed the four screws, and can even see the gray covers through the screw holes. I even used the holes of the bottom cover (see attached pic) as leverage against the frame, but it would not even budge. Are the covers held together in some other ways? Could the covers have been glued to the frame by the previous owner?Appreciate any pointers.

author: bdunham7
author_rank: Super Contributor
timestamp: September 30, 2020, 09:23:28 pm
content: On the backside of the unit there should be a single screw in the middle of each cover. Often they are covered by calibration seals if there are any. If you unthread that screw, it should pull the cover back as it goes and then you lift it off. If the screws come out, just pull the cover backwards manually.

author: TonyOldTimer
author_rank: Newbie
timestamp: September 30, 2020, 10:17:52 pm
content: @bdunham7,Yes, you are absolutely right. How on earth am I to miss those two screws hidden under those yellow labels!Thanks.
HP 3312A Function Generator - Page 1
Forum section: electronics / repair

author: wally
author_rank: Newbie
timestamp: December 30, 2023, 11:25:51 pm
content: Hi all,After a few decades, I turned on the HP 3312A,after a few seconds smoke came out, and from the smell I realized that a capacitor had probably exploded.I opened the HP and found that the paper capacitor in parallel with the power socket had exploded.Although it is not very important, I would like to put in a new one, but I cannot see the capacitance value.What I can see is:PME 271 Y 522 GPF 40/085/56I think it works as a noise suppressor.I tried to see the various manuals on the net, but I couldn't find thevalue of the capacitor, can you help me?happy new yearwally

author: enut11
author_rank: Super Contributor
timestamp: December 31, 2023, 12:08:04 am
content: Value is not critical. 0.047uF should be OK provided it is rated for 240vAC operation or about 630vDC.Do not replace it with the same brand as these are notorious for exploding. The body cracks and moisture gets in to short the capacitor elements.

author: pqass
author_rank: Super Contributor
timestamp: December 31, 2023, 02:45:13 am
content: As per the service manualhere, it is C601 on the last schematic (4th-last page of document).The BOM listing on page 6-11 has C601 as: "CAPACITOR-FXD .02uF +80-20% 600WVDC CER"Also, I checked my 3312A and it's not a RIFA but an ordinary ceramic cap. See attached.Since it's across the mains, it should be safety ratedX2.

author: RFDx
author_rank: Regular Contributor
timestamp: December 31, 2023, 03:38:39 am
content: Quote from: wally on December 30, 2023, 11:25:51 pm22nF, 250VAC, Class Y2 (although it's connected across the mains).https://www.alldatasheet.com/datasheet-pdf/pdf/973468/KEMET/PME271Y522M.html

author: Paceguy
author_rank: Regular Contributor
timestamp: January 01, 2024, 02:32:38 pm
content: Yes, stay away from those RIFA caps, they are bad news.

author: alm
author_rank: Super Contributor
timestamp: January 01, 2024, 04:17:13 pm
content: Which RIFA caps? As far as I know they currently make both paper and polypropylene dielectric class X/Y caps. Their polypropylene caps should be just as reliable as those of any other manufacturer.
HP 3312A service manual for late serial numbers? - Page 1
Forum section: electronics / repair

author: precaud
author_rank: Frequent Contributor
timestamp: November 24, 2020, 11:19:19 pm
content: My trusty 3312A suddenly has symmetry and frequency that are way off. It's serial prefix is 2901A. I downloaded the op/service manual from Keysight, and the boards do not match. Their manual is for much lower serial numbers (1432A). Downloaded a couple more from the usual sites and they're the same as the Keysight version. It doesn't have "manual changes" pages.Does anyone have a PDF service manual for it that applies to serials 2901A? Or the manual changes page(s) that apply?

author: precaud
author_rank: Frequent Contributor
timestamp: November 25, 2020, 05:09:42 pm
content: More specifically, I could use the schematic for the Tuning Amplifier and Integrator section of the A2 board. In the old manual it is Figure 7-2. And the component layout would help too. The A2 board was significantly redesigned in the later 3312A versions.

author: wn1fju
author_rank: Frequent Contributor
timestamp: November 25, 2020, 05:20:26 pm
content: I thought I might be able to help because I have the 3312A manual I purchased from Artek Manuals. However, that seems also to only apply to 1432 series. There are a few change sheets at the back, but again only for early versions. The only later version that is mentioned is for series 2501A and that just talks about some cabinet part number changes and the addition of metric hardware.You might e-mail Artek Manuals and see if they have some later manual changes.

author: nfmax
author_rank: Super Contributor
timestamp: November 25, 2020, 05:55:49 pm
content: I have an actual -hp- printed copy of what seems to be the same manual, serial numbers 1432A01246, part mber 03312-90004. The the print date is March 1990, which would be very late in the production run. The 3312A is in the 1989 HP catalogue, but it's gone from the 1994 edition. I doubt that they ever re-printed the manual, probably just issued errata or updating sheets.

author: precaud
author_rank: Frequent Contributor
timestamp: November 26, 2020, 01:40:46 am
content: Thanks guys. Yeah, the Keysight PDF has numerous asterisks in the schematics saying "see change sheets", but the change sheets weren't included!I found and fixed the problems today.
HP 3314A Power Voltage Selector Repair - Schaffner - Page 1
Forum section: electronics / repair

author: VK5RC
author_rank: Unknown
timestamp: June 09, 2019, 08:33:50 am
content: A HP 3314A has been one of my bench Freq Gen - with a bit of a bug that it would only work on 100 and 120V - not our 240V line voltage. I guessed it was a transformer issue - ie too hard so never looked into it till recently. The Schematic from HP.https://www.keysight.com/main/gated.jspx?lb=1&gatedId=805471&cc=AU&lc=eng&parentContId=3314A:epsg:pro&parentContType=pt&parentNid=-536900193.536896858&fileType=VIEWABLEis for the earlier versions that have 2 separate switches.Mine is of the later series with "soft-touch" buttons and what I nick name the "tumbling dice" all in one IEC connector, fuse holder and voltage selection switch. There is not a lot of room in the back of a 3314A so tracing out the circuit was a PITAThe voltage selector Cam activates several (2-3) of the 5 switches contained within this unitPhoto 1 - the outside view of the unitPhoto 2 the switches - with the cam removed and my labelling of the switches A to EPhoto 3 the Cam removedPhoto 4 Rob-CAD _ the switch connections and switches that the Cam activates in which positions, approximate resistance when the Active to Neutral resistance is measuredPhoto 5 the Schematic NB Switch labelled F is really switch DThe issues in my unit were- The Black Cable wasn't connected to the assembly- Several of the Switches weren't connecting when pressed down by the cam - a bit of judicious bending was requiredBe careful not to push the cam in too hard - this flattens the switch levers - they will then either stay "ON" - pressed forward or not reach the contact when the Cam pushes - ie stay "OFF"If I have made any mistakes - please let me knowHope this is of some help to othersRobPS This unit has one of HP better Easter EggsEdit error in labelling switch D in schematic - labelled as F
HP 3314A sine-wave short discontinuity - Page 1
Forum section: electronics / repair

author: the Chris
author_rank: Regular Contributor
timestamp: August 23, 2024, 06:52:22 am
content: I've recently observed that my HP 3314A exhibits a slight discontinuity between the end and start of a new sine-wave period. This is also visible in the FFT as sidebands at 1/2 and 3/2 of the main frequency. The screenshots show a comparison with a proper output from an UTG1022X(-PA).Did anyone have had something similar and located the origin or has a guess where to look at first on the PCBs?

author: wn1fju
author_rank: Frequent Contributor
timestamp: August 23, 2024, 01:18:28 pm
content: I have had two HP 3314A's. One exhibited what you are seeing and one did not. Guess which one I kept? None of the calibration adjustments got rid of the one with the distortion.Take a look at the triangle waveforms and see if there's a "blip" at the corners. The sine waves are generated from the triangle waveforms via a custom hybrid IC. I would think if the integrator generating the triangle waveforms isn't perfect, the "errors" will propagate through as distortion on the sine waves. Then again, perhaps there were slight differences in the precision of the hybrid sine-shaper IC that HP produced.There has been a discussion on eevBlog about ringing on the triangle waveform for the 3314A. People were speculating that it was a mix of board layout and parasitics that affected the capacitance in the integrator.

author: the Chris
author_rank: Regular Contributor
timestamp: August 23, 2024, 01:48:45 pm
content: Thanks, makes sense. Seems to be a good starting point. I'll check the triangles, but I think I saw something there as well, just not so obvious.BTW: love your website, I visit it regularily.

author: MathWizard
author_rank: Super Contributor
timestamp: August 25, 2024, 08:13:40 am
content: So looking at that nice old machinehttps://www.eevblog.com/forum/testgear/hp-3314a-function-generator-teardown-explanation/So say something like the "hybrid sine-shaper IC" really is faulty. With all the advances in IC's, and all the fast FPGA's and A/D chips and whatever else is off the shelf.....how hard would it be to homebrew some replacement for chips in these older digital machines ?Even if it's a lot of work and money, I bet there's people that would do it for fun.
HP 3326A Failing DC offset calibraton - Page 1
Forum section: electronics / repair

author: Zenwizard
author_rank: Regular Contributor
timestamp: September 30, 2024, 03:34:17 am
content: I have an HP 3326A on the bench that I would like to get up and running. I am currently thinking that a few of the small signal relays have gone high resistance and am curious if any one else knows a starting point.The unit will pass all self testStart up self calibration will error with error 193 Dc offset failureIf both channels are set to more than 1 volt of DC off set both positive or negative calibration will complete with no issues.Setting DV off set to 0 does function correctly. So when the unit has aligned its self all is good and working It is just the initial power up configuration is failing alignment.Has any one run in to this before and any ideas on where to start?Zen
HP 3326A Two Channel Synthesizer  repair  - Page 1
Forum section: electronics / repair

author: TerraHertz
author_rank: Super Contributor
timestamp: July 03, 2021, 05:10:36 am
content: I picked this up for US$80 and it arrived yesterday. It was sold as "powers on and has ERROR 192." Which from the manual is "ACAL 192 Amplitude CALibration. An amplitude calibration is unsuccessful and the HP 3326A is unable to calibrate internal circuits."So far I'm just doing the usual clean up and righting minor mechanical issues. I'll update this thread as repair progresses, but for now a few photos and a request. The unit's front power button is missing, switch shaft snapped off. (Deja vu, buttons again...)For the broken switch the service manual gives just a HP part number 3101-2748 and manufacturer code 28480. Which unhelpfully looks up as "HP head office Palo Alto CA." Great.Anyway, does anyone recognise the switch from the last picture below? Gooargle isn't helping with the PN.The burned and open track on the power supply PCB in pic 4 was for +15 Raw, so no +15V rail. No wonder it couldn't cal! Whether that's due to some fault load, or just a track designed a little too thin for its normal loading, remains to be seen. If tracks get warm, over time they can delaminate from the PCB, so suddenly they have very little heat dissipation and get red hot.Overall, after a cleanup it's pretty nice. Hopeful I can get it working easily.

author: TerraHertz
author_rank: Super Contributor
timestamp: July 03, 2021, 02:25:06 pm
content: Purely mechanical and probably boring. Fixing the two bent BNCs from the front panel.The photos are self-explanatory I hope.

author: MadTux
author_rank: Frequent Contributor
timestamp: December 27, 2023, 09:40:23 pm
content: Couple of my HP3326A boxes have developed trouble with PSU lately, Opamp directly inhibiting 3kOhm pullup on Darlington transistor is shit design IMO.Darlington transistor gain has likely degraded over the years in some of my boxes, makes PSU unreliable and 3326A shutdown and restart at random. One got so bad, that it even didn't reach +15VDC on bench.All regulator transistors tested fine with curve tracer, with some variation in gain, though.Solution was to power the board externally with 5x HP361x PSU and put PNP inhibition drive transistor between LM1558H Opamp and Darlington transistor and decrease pullup on +15V down to 660Ohm. Transistor is some kind of 2N2907 in weird EBC config from front, bulk purchase from china+15VDC is rock solid now, -15VDC and +5VDC gets same fix applied soon.Diodes the other way round, in my shoddy drawing
HP 3330B Automatic Synthesizer A35 power supply board damage - Page 1
Forum section: electronics / repair

author: Cubdriver
author_rank: Unknown
timestamp: July 21, 2022, 07:19:09 am
content: Hi All -I was recently given an old HP 3330B Automatic Synthesizer, and was told a capacitor had burned up inside, and damaged a board. I've poked around inside and found the damage - C13 - called out in the parts list as a 0.1 uF, 100 V ceramic capacitor (don't recall EVER seeing a a ceramic cap fail so spectacularly!) on the A35 board in the power supply section. It appears that a repair effort was made and that a burned trace was jumpered and a new ceramic cap bodged in, but there's still an ugly burned crater on the board.Board overall:Detail of damage:The A35 board is in the small isolated cage at the rear center of the chassis, under the flat aluminum cover with two oblong holes:Board partially removed from card cage:Does anyone have a 3330B, and if so, would you please take a picture of that area of the A35 board and post it here so I can see what it originally looked like? Thanks.-Pat

author: wn1fju
author_rank: Frequent Contributor
timestamp: July 21, 2022, 11:59:48 am
content: See attached photo. I hope you appreciate this - my 3330B was at the bottom of a stack of about 10 heavy pieces that I had to move away. Oh, my aching back!!!

author: Cubdriver
author_rank: Unknown
timestamp: July 21, 2022, 02:40:33 pm
content: Perfect! Thank you very much for making the effort to pull and photograph it! (Why is it that the instrument you want is almost always at the very bottom of the stack?)I have a bad feeling that this thing is going to have some serious issues - I’ve never seen a ceramic cap go out in a blaze of glory like that - you’d think there had been a dipped tantalum one there.Once again, much appreciated!-Pat
HP-3421A Service Manual is required. - Page 1
Forum section: electronics / repair

author: youngwug
author_rank: Contributor
timestamp: April 20, 2020, 02:23:33 am
content: There is one HP-3421A that does not turn on (+15, -15, +5V is dead).The measured value of C708 where oscillation is occurring inside the capacitor is 495(0.205).C708(25V, 470uF) was replaced.And when you turn on the power, +16.9V is measured in TP700, +7V in RT700, and +6.6V on top, regardless of S502(Switch).However, +15V, -15V, and +5V cannot be measured.I suspect the U702(LM393N, Dual Differential Comparator), but it is not easy to analyze because there is no circuit diagram.If the “Wakeup Logic” on the left side of the figure can be related to S502, the problem is complicated, so I need a schematic.Please tell me where to buy the service manual schematic(pdf or jpg).

author: wn1fju
author_rank: Frequent Contributor
timestamp: April 20, 2020, 11:04:40 am
content: http://www.hpmuseum.net/collection_document.phpSearch on page for 3421A.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 20, 2020, 11:37:01 am
content: some links3421A with only one ROM talkshttps://groups.io/g/VintHPcom/topic/27149599?p=Created,,,20,2,0,0::recentpostdate%2Fsticky,,,20,2,0,27149599hp museum service manual attacheddo a 3421a search, will be easier to find what you needthks @ wn1fju never saw this website.

author: youngwug
author_rank: Contributor
timestamp: April 20, 2020, 10:16:46 pm
content: coromonadalix & wn1fjuThank you so much.It's best.
HP 3437A parts - Page 1
Forum section: electronics / repair

author: Jester
author_rank: Frequent Contributor
timestamp: September 07, 2022, 11:19:48 am
content: I like using these old HP chassis for projects, I picked up a 3437A and have no need for the internals. I have no idea if they are working or otherwise, but might be useful to someone trying to fix one. So if you need something just ask, price is free (you pay shipping)
HP 34401 probe fits very tightly - Page 1
Forum section: electronics / repair

author: tkamiya
author_rank: Super Contributor
timestamp: December 03, 2021, 05:42:05 pm
content: Hi.....I have something like 8 HP 34401 (not all of them are mine) and third-party probes. All of them fit very tightly/snugly into terminals on 34401. That is, as if outer diameter of the insulation on banana plug is too large. Is this the way they fit? I don't own a genuine probe by HP. Some of them are just tight, but most of them are so tight, they are hard to pull them out. What I have are eBay specials.Have anyone experienced this?

author: TheSteve
author_rank: Unknown
timestamp: December 04, 2021, 04:29:28 am
content: I think you need better quality probes

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: December 04, 2021, 10:58:17 am
content: Usually mine are too loose HA!Sometimes a little white thermo grease (for mounting transistors on a heat sink) helps. Just a little. I know it is not conductive but does not matter.Wally

author: tkamiya
author_rank: Super Contributor
timestamp: December 04, 2021, 02:44:26 pm
content: You mean to say eBay probes aren't quality? Ad said "made of high grade material in China." Supposedly they are compatible with HP, fluke, Agilent, etc, etc, etc

author: Hamelec
author_rank: Regular Contributor
timestamp: December 04, 2021, 04:06:55 pm
content: ..had the same Issue.Used a reamer to fix it 10 Years ago.See Service Note as attached.

author: tkamiya
author_rank: Super Contributor
timestamp: December 04, 2021, 04:34:19 pm
content: thanks for the bulletin. That clears my problems. Thanks again.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 04, 2021, 05:34:19 pm
content: Never saw this bulletin

author: tooki
author_rank: Super Contributor
timestamp: December 04, 2021, 08:23:21 pm
content: Quote from: Hamelec on December 04, 2021, 04:06:55 pmHow the heck is the service note branded Agilent yet copyrighted 6 years before Agilent was created? Surely they didn’t just go and replace “HP” in old documents without updating copyright dates?

author: Gyro
author_rank: Super Contributor
timestamp: December 04, 2021, 08:31:29 pm
content: When is a 4mm banana plug not a 4mm banana plug?... When it's a <0.155" banana plug!

author: tkamiya
author_rank: Super Contributor
timestamp: December 04, 2021, 11:54:00 pm
content: Wow.... I didn't expect an official response like this existed. So, the problem is the copper sleeve, not the plastic part? Just confirming.
HP 34401A current fail - Page 1
Forum section: electronics / repair

author: abdul
author_rank: Newbie
timestamp: September 03, 2019, 08:47:34 am
content: Hello i need help to repair HP34401A selt test pass but it fails when measuring current for both AC & DC till 1.2 Amps ok after that its showing excess for example if we give 1.3Amps it shows 2.7Amps. I changed IC U201 still same can any one help me to solve this problem

author: Yansi
author_rank: Super Contributor
timestamp: September 03, 2019, 08:48:59 am
content: Fucked up current shunt, maybe?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 03, 2019, 10:01:18 am
content: Internally the 100 mV range is used to measure the voltage at the shunt. So it the 100 mV range working correct ?

author: abdul
author_rank: Newbie
timestamp: September 03, 2019, 10:47:05 am
content: Thanks

author: abdul
author_rank: Newbie
timestamp: September 03, 2019, 10:48:00 am
content: Thanks to all

author: HighVoltage
author_rank: Super Contributor
timestamp: September 03, 2019, 11:56:49 am
content: What is the resistance between the current terminals in the different current range modes?
HP 34401A, Error 602 - Page 1
Forum section: electronics / repair

author: diewindowsdie
author_rank: Newbie
timestamp: October 21, 2015, 06:26:16 pm
content: Hi guys!Received my HP 34401A from ebay seller today. Full self-test reports error 602, which is RAM read/write error. I have also checked main functions - DC voltage/current, AC voltage, continuity test, frequency, resistance - and everything seems to work fine (except for out of calibration maybe, can't check that). So my question is - why a multimeter actually needs a RAM? It is only for programming-related stuff? What is the consequences on leaving it as-is in terms of being able to perform basic measurements?Thanks.

author: bitseeker
author_rank: Super Contributor
timestamp: October 21, 2015, 10:48:22 pm
content: The logging function likely uses the RAM. Also, any temporary settings would go into RAM. The calibration values would be stored in non-volatile memory, so no worries there.For basic measurements, you're probably fine. I'm not sure about the math functions, though. Give them a try.

author: free_electron
author_rank: Super Contributor
timestamp: October 22, 2015, 01:13:46 am
content: the 34401 has like half a megabyte of ram. you have to remeber there are 3 CPU's in that thing ... plus 3 asics plus 2 flash roms plus an eeprom ...

author: Ordinaryman1971
author_rank: Frequent Contributor
timestamp: December 18, 2019, 07:40:02 pm
content: I wonder if anybody solved one of those errors?

author: Ordinaryman1971
author_rank: Frequent Contributor
timestamp: December 26, 2019, 04:49:25 pm
content: To answer my own question the solution is to change the RAM. It's 256K, 32k x 8.
HP 34401A Error 612 - Page 1
Forum section: electronics / repair

author: BobH0001
author_rank: Newbie
timestamp: March 16, 2024, 12:56:11 am
content: I have a HP34401A that will not read resistance correctly and is throwing Error 612. Attached are the readings from the current source circuit.U201 is suspect and I see that is a common failure. I just wondered about anything else to check before replacing U201.Thank you all..RegardsBob H

author: floobydust
author_rank: Super Contributor
timestamp: March 16, 2024, 02:30:45 am
content: Welcome to the forumsZener CR203-A appears to be dropping more than 5.1V (18V rail-5.1V=12.9V but you measure 6.942V) so I say the part is not working or maybe a bad connection. 1902-1565 is BZX84-C4V7 though, a 4.7V zener so I think it's typo to be 5.1V. Very early models there was a Service Note and change of the part I faintly recall.Regardless, you are showing a 11.06V drop. As a result Q202 is biased off. The +/-18V rails, are they OK? They are regulated so I'd expect them to be close.Usually the transistor string gets damaged or the JFET Q211 if the meter gets zapped on Ohms function.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 16, 2024, 10:41:52 pm
content: Hello,I also suggest to first check the +18V rail, and CR 203-A, before changing U201.It's most probable, that CR203 ist toast, as U201-B obviously outputs >14V, which means that its supply is 15V at least.If I remember correctly, these 5V1 of CR203 had been changed, (to 3V3), so that depends on the version of your 34401A.Do you measure reasonable values in the different 2W Ohm ranges?I expect , that not only the 10M range or higher is defective, like Err. 612 suggests.In the appended schematic, I have written down the nominal voltages for my working unit, 10M range with an external 10M resistor attached.The printed boxes show values for a defective U201.Frank

author: BobH0001
author_rank: Newbie
timestamp: March 16, 2024, 11:13:13 pm
content: Thank you both for the information.I am reading 18.9V supply.The forward drop for CR203 looked normal so I only replaced U201.After replacing U201, CR203 anode is now reading 13.7Selftest is now passing, auto-ranging is working and a few resistance readings I took look normal now.Tomorrow morning I will do additinal testing to confirm full functionality.I have never worked on one of these meters so I am grateful for your time! (and documented readings Frank!)Regards,BobH
HP 34401a switching modes by itself? - Page 1
Forum section: electronics / repair

author: _rushin_or_draggin_
author_rank: Regular Contributor
timestamp: February 27, 2025, 10:06:17 pm
content: Hello all,I am working on a mosfet biasing circuit and I believe it’s self resonating. Anyway I went to check the voltage of the gate with the 34401a and it immediately switched to the resistance mode. It does this every time when I try to measure the gate.When I measure a DC source it does just fine. I was wondering if the potential EMI could be switching the modes or if I have a serious issue elsewhere. All self tests pass.Thanks!

author: bdunham7
author_rank: Super Contributor
timestamp: February 27, 2025, 11:08:54 pm
content: That's very odd. Can you try manually setting the 1000V range on the 34401A and also try reversing the test leads? Is there a lot of common mode noise or HF there? Can you look at that gate with an oscilloscope?

author: _rushin_or_draggin_
author_rank: Regular Contributor
timestamp: February 28, 2025, 12:43:40 am
content: I will have to recreate the original case as I stabilized the mosfet already. But I can definitely say there was a lot of oscillation when I checked with an oscilloscope. Also, I was using a GwInstek GPS-1850D PSU for my gate bias and as I was increasing it the relays would click, so potentially a high voltage transient?But I was NOT touching the gate bias as I was measuring the gate voltage. Again I’ll have to recreate it (maybe even with a function generator and sweeping to see if it trips the 34401a…but not sure if that’s a great idea). So far the dc voltage and the resistance modes are still good. Just a very weird scenario

author: floobydust
author_rank: Super Contributor
timestamp: February 28, 2025, 03:29:47 am
content: If it's the older front panel board 34401-66502 with the NEC MCU, the keypad scan/decode is handled with an 'HC194 and high value (100kΩ) pullup and diodes. It might have an EMI sensitivity for false key presses.The NEC MCU PMOS fades with age, which could cause it as well.The newer FP board using 87C51 I think it has 6kΩ internal pullups so not as high Z. There are no ESD/EMI caps on the keypad for either FP board.I don't think we figured it out on the blog here what causes the 34401a phantom keypresses.Phantom switching from ACV to Ohms:https://www.eevblog.com/forum/testgear/agilent-34401a-switches-from-acv-to-resistance-measurement/mentioned a bit here:https://www.eevblog.com/forum/repair/34401a-with-fault/msg4760888/#msg4760888
HP 3450A inguard power supply troubleshooting  - Page 1
Forum section: electronics / repair

author: valley001
author_rank: Frequent Contributor
timestamp: June 11, 2020, 04:18:21 am
content: Hello all,I have another HP 3450A here, this unit also displays overload constantly. Problems were revealed when checking the inguard power supply voltages. I have known good A52, A53 and A54 boards, swapping those in has no change. I think this sort of narrows it down to the components mounted to the chassis (A100 Q1-3, C1, CR1, T1, etc). I have posted the schematic from the manual available online, along with the voltage readings I am getting (referenced to inguard ground). As you can see voltages are way out. Rather than guessing and going nuts with the soldering iron I am interested in your input on which component/s might be most suspect based on the voltages. Thanks all.1: -5v TP: -7.8v2: +5v TP: +600mv3: - 35v TP: -34.7 V4: -17v TP: -17V5: +17v TP: +460mv6: + 34v TP: +22V7: +10v TP: +3.4V

author: Vicus
author_rank: Regular Contributor
timestamp: June 11, 2020, 06:46:09 am
content: Take a step back and measure voltage after the bridge rectifier. It seems linke the +-17V is independent from other voltage. Start from here.

author: floobydust
author_rank: Super Contributor
timestamp: June 11, 2020, 04:55:28 pm
content: The regulators have a lot of dependency on each other.The +5V and -5V uses +17V and -17VThe +17V uses +34VThe +34V uses +10V (ref) and -17VI think the +17Vreg is what I would first go after. It should still come up a bit even if the 34V is low at 22V. Voltage at Q7-B should be around 18.4V; if the current-limiting Q6 is stuck on, there may be a short on the 17V rail loading down the regulator. That would give a constant voltage across current-sense R14 1.8ohms.The +10V REF supply is another bird to fix, I don't have the schematic. With the 10V low, it would cause the 34V to be naturally low by the same ratio.With gear this old, I'll replace all electrolytic capacitors before troubleshooting because AC ripple can give the wrong DCV readings and you go on a wild goose chase. Check the off-board filter capacitors.P.S. wow it has two trimcaps to null the Inguard power supply transformer capacitance. Such details.

author: valley001
author_rank: Frequent Contributor
timestamp: June 13, 2020, 10:35:04 pm
content: Q2 was toast. Replacing it brought all the voltages up to where they should be. A100 C1 tests (out of circuit) as 10uf on my little component tester (should be 8500uf), but I dont think that is accurate. It tests another know good 8000uf cap low also. I'm going to recap it anyway though.Swapping out the master timing board brought it out of overload but it is not reading properly and two digits do not illuminate. Going to balance the amplifiers next and troubleshoot the display. Thanks all.
counter HP 5351A HPIB failure - Page 1
Forum section: electronics / repair

author: hnjmkl
author_rank: Regular Contributor
timestamp: May 29, 2020, 06:17:27 am
content: HP5351A does not work HPIB, replacing the MK3870 piggybak (U5) is very expensive, I would first try to verify the correctness of the EPROM content by comparing it with the hexadecimal code of a functioning one, if anyone has it and can communicate it to me thank you, I live in Italy.
HP 3455A DMM Intermittent Power-Up - Page 1
Forum section: electronics / repair

author: Bimmerdude
author_rank: Newbie
timestamp: March 02, 2021, 06:22:13 pm
content: Greetings to all....I have an old school 3455A DMM that has an intermittent power-up issue. In most cases, it powers up just fine. Unfortunately, there are a few instances when you power-up the DMM, the display goes blank as well as no response from the front panel push buttons. Once you cycle power, it comes on like nothing's wrong. I've checked the power supplies (+5VDC and +12VDC) on the A1 board. Both are good (even when the DMM is acting up). Used the flowcharts and ended up on the outguard troubleshooting procedure diagram (figure 8-H-26, pages 8-131 and 8-132). When I'm at step 8 (is the signature 401F when each key is pressed), some of the keys do not display 401F. I then follow the no direction and end up at "is the signature at A1U51 pin 2 42AP?", the answer is yes. In lieu of switches S2, S7-S9, S13, S15-S22 and cable A2W2, it has me check out A1U50 and A1U57. These two IC's check out good.Any suggestions? I'm stumped at this one. Throwing money in the wind, I did swap out the A3 board with a known good one with no success.I'm lost on this one. Any suggestions?Thanks,Daniel

author: Kleinstein
author_rank: Super Contributor
timestamp: March 02, 2021, 08:10:57 pm
content: Quite a few of the older meters can have problems with the data transfer part. The 3455 service manual is still very detailed. It may be worth checking the waveforms for the data channels between the 2 sides of the isolation. It could be a boarderline wafeform.

author: wn1fju
author_rank: Frequent Contributor
timestamp: March 03, 2021, 11:52:32 am
content: I've had a few 3455A units with similar start-up problems. In most instances, the problem is in the inguard circuit which is not completing its auto-cal and/or measurement process. The outguard microprocessor just sits there waiting for that completion and the machine hangs.In one instance, there was a problem on the A/D daughter-card. In another case, the problem was with one of the switching FETs that caused two voltages to be simultaneously applied to the measurement. But in your case, which is intermittent, I would suspect what I found with the last one of these I fixed. Namely, the power supplies on the inguard board. Look at all the voltages carefully with an oscilloscope - not just a voltmeter. In my case, the voltage feeding one regulator had terrible 120 Hz ripple on it and the voltage dipped below the required regulator input voltage. Thus, the regulator would drop out, the inguard measurement wouldn't complete, and the 3455A just sat there blank. A new electrolytic cap cured all.
HP 3455A startup errors non-integer then cal code errs-where to start debug? - Page 1
Forum section: electronics / repair

author: ChuckDarwin
author_rank: Regular Contributor
timestamp: December 23, 2024, 08:47:50 pm
content: Acquired dead, signs of previous repair work, living on my 'someday' shelf for a few years, first time inside the 3455A. Got from power with no display to booting and displaying errors by replacing A1C14 (tant blew with fireworks), start-up related: A1U48 & U5 and then most of the large electro caps on A1 and A10 as several tested below their rating and others had excessive ripple. At present, on every power-up I see displayed: "-99.9992", then cycling the TEST button cal errors "9" en "5". The Service Group Summary pages (8-199.b) note that the display of an integer number indicates and Auto-Cal failure and "if only a non-integer number is displayed, the failure is in the logic circuits". I have what appears to be both types of errors, starting with the display of a non-integer number. Should I take this to be a logic error first and start debugging there, or is the non-integer number likely to be part of the cal 9 (ohms) failure and start debugging for code 9?
HP 3456A DCV Zero Internal Charge Adjustment-won't adjust - Page 1
Forum section: electronics / repair

author: Testtech
author_rank: Regular Contributor
timestamp: September 10, 2025, 04:04:25 pm
content: I am working on three 3456A instruments, and all seem to exhibit the same behavior.Ref: Paragraph 8-F-18; DCV Adjustment, steps i-l. All of the previous steps completed and apparently normal. Digits set to 6, and N CYC INT set to 100.I am unable to make the R147 (zero without analog filter) adjustment have any effect on the displayed zero count. The subsequent R148 (zero with analog filter engaged) adjustment does adjust for a zero count.These meters are otherwise functional, no error codes, and the individual ranges are adjustable to spec.Looking at the input to the input amplifier a change can be observed in the waveform, seeming to indicate some charge injection to that node. This waveform varies with R147 adjustment.Any previous experience with this problem or thought are appreciated!

author: Kleinstein
author_rank: Super Contributor
timestamp: September 10, 2025, 06:29:03 pm
content: R147 and R148 should adjust the charge injection from AZ switching. To me it is a bit odd that the filter should make a significant difference.In the service manual I have (PDF copy), the zero adjustment is via R150.R147 and R148 should both together minimize the charge pulses. One would likely need a scope at the input to adjust, not just the meter DC reading. Ideally one would also test with not just 0 V but also at a different voltage. One may have to compromize here.

author: Testtech
author_rank: Regular Contributor
timestamp: September 10, 2025, 08:58:33 pm
content: Thanks Kleinstein,The manual I was using does not include the padding procedure. I have found the later manual, and will give it a try.
HP 3457a - Broken input finger grips - Page 1
Forum section: electronics / repair

author: breadboard
author_rank: Newbie
timestamp: March 09, 2022, 10:43:01 pm
content: I have an HP 3457a with broken finger grips on two of the front inputs. Electronically, the inputs work fine, just the plastic finger grips are broken. The input terminals look like they are pressed into the front panel, and aren't replaceable like some other HP/Agilent/Keysight meters.Does anyone know of a replacement for these grips?
HP 3457A - Powered up and saw POST Error and then the magic smoke - Page 1
Forum section: electronics / repair

author: cbelcher2020
author_rank: Newbie
timestamp: August 07, 2023, 04:06:36 pm
content: My ultimately reliable HP 3457A Meter finally had it's first failure, not bad for 30 years? Powered it up, saw a POST error out of the corner of my eye. Went to get some water and came back and no power, main fuse was blown. Smell told me tantalum cap but my nose pointed me to the general area of that Schaffner Line Filter or the transformer on the Common Chassis PS. All checked out? Opened up the Floating Common PSU side and started poking around. Found a dead short on the -15V output. There it was, I knew that smell all to well. C922, big black ring around the entire package and wide open.All it's identification mostly unreadable, schematic and HP parts list said there was several others used in this chassis. On the hunt to see if I could find one or more of the others. Found several of them, Sprague 35V 1uF Tantalum's.That lead me to:Reference Designation: A11C807HP Part Number: 0180-0291CD: 3Quantity: 3Description: Capacitor - Fixed 1UF +- 10% 35VDC TAMfr Code: 56289Mfr Part Number: 150D105X9035A2-DYSFound a modern Vishay Sprague part:Manufacturer Product Number: 150D105X9035A2BE3Description: CAP TANT 1UF 10% 35V AXIALDigi-Key Part Number: 150D105X9035A2BE3-NDShould be here today, also picked up Line Filter since everyone says they've had issues with them failing. It's open, I'm getting all that tantalums replaced! I want this to last another 30 years.Keep everyone abreast if this solves it.Fuse part number if you need one:Don't use this in 220 or 240v regions!Fuse for 95 to 132Vac Operation:.2 AT HP Part Number 2110-0235 or equivalent, HEaton Bussmann MDL 2/10 Time Delay glass fuseDimensions 6.4x31.7mmDigi-Key Part Number: 283-3393-NDManufacturer: Eaton - Electronics DivisionManufacturer Product Number: BK/MDL-2/10-RDescription: FUSE GLASS 200MA 250VAC 3AB 3AG

author: cbelcher2020
author_rank: Newbie
timestamp: August 08, 2023, 01:05:20 am
content: She lives. New Line Filter, all new caps.Working like a champ. My babies back.

author: alm
author_rank: Super Contributor
timestamp: August 09, 2023, 08:42:19 pm
content: Congrats on the repair and thanks for sharing the outcome.

author: Swake
author_rank: Frequent Contributor
timestamp: August 11, 2023, 09:10:35 pm
content: That soldered spade connector on the line filter is a pain to remove.I'm swapping them out as soon as I discover them. Same issue as the stand alone RIFA caps.
HP 3458A 8051 on ADC Board - Atmel v. Intel versions - Page 1
Forum section: electronics / repair

author: martinr33
author_rank: Frequent Contributor
timestamp: December 14, 2017, 09:15:26 pm
content: I read the code from both an Intel chip, and an Atmel chip.The code is identical. Therefore, there is no benefit to upgrading to the Atmel version. Like I did... although the exercise did prove the point for me.Thought I would post this to save others the effort.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: December 14, 2017, 09:23:31 pm
content: Well, it's an 8051-Core. So they more or less have to be identicalBut good to know that both chips work. Allows to choose the cheaper chip/the one still in production - If I remember correctly, Intel stopped making 8051-Micros.

author: Scopetechniques
author_rank: Contributor
timestamp: November 22, 2019, 08:41:37 pm
content: I had an older A3 module that had 80C51 Rev 1 code on it and was able to install Rev 2 code and it works.I don't know what the changes were to go from Rev 1 to Rev 2.FYI the REV 1, REV 2 is what is reported when you execute REV? and the 3458A returns 9,1 or 9,2 (assuming you have latest main processor firmware Rev 9).--Victor
HP 3458A Error 206 after Socketing U132 - Page 1
Forum section: electronics / repair

author: Olivia
author_rank: Regular Contributor
timestamp: June 05, 2023, 08:25:18 am
content: Hello there,This is the second thread/part on the repair of my HPAK 3458A.Just to bring everyone up to speed: My 3458A is a HP device, being built around 1999-2001.The digital board iteration is the version with only one ROM IC.The electrolytic Capacitors on A4 and A6 have been replaced recently.The only perishables left inside were the Dallas NVRAMs.After desoldering and socketing the U132 NVRAM, I turned the instrument back on and was greeted with a "HPIB Failiure" Error.I did use ESD-Rated tools and a protective mat on which the pcb laid during desoldering.If anyone knows what the source of the Error 206 might be, please let me know.CheersOle

author: alm
author_rank: Super Contributor
timestamp: June 05, 2023, 01:20:57 pm
content: Did you try reseating the fiber optic cables that connect the boards?

author: Olivia
author_rank: Regular Contributor
timestamp: June 05, 2023, 06:45:27 pm
content: I did not...While the instrument works, the only error is the 206 HPIB Failiure.The whole ordeal was done in two parts:Part 1: Replacement of all electrolytics (A4 and A6)Part 2: Desoldering of A5U132 and soldering of a fitting socket in its place.Between part 1 and 2 were multiple weeks and i did run the Meter in between.