hybridfree/eevblog-posts huggingface dataset:
How to unplug a molex flat cable connector [resolved] - Page 1
Forum section: electronics / repair

author: gevans
author_rank: Newbie
timestamp: February 19, 2015, 07:02:13 pm
content: I tested circuit boards in a company for 17 years, on the bench ,hundreds per day, and I have seen a lot of cable connector types, the most dreaded being from Molex, which act like they've been glued in.I am repairing a Hameg HM1507-3 oscilloscope, and have encountered a Molex type connector which baffles me.It is almost as if it is not intended to be unplugged, EVER.After pulling the "snap in cap" off with pliers, I pressed each contact in with a screwdriver and finally got it out, but this surely cannot be the way to do it, and this one in the second photo has only 4 pins...Any ideas anyone?

author: free_electron
author_rank: Super Contributor
timestamp: February 19, 2015, 07:56:07 pm
content: you need to press down the top plastic piece. HARDthat opens the clips and then you can pull out the flatcable.the flatcable has stiff wires. to insert : simply press it in, no need to press on the white piece

author: gevans
author_rank: Newbie
timestamp: February 19, 2015, 08:01:37 pm
content: Thank you, it works!

author: free_electron
author_rank: Super Contributor
timestamp: February 19, 2015, 08:08:11 pm
content: of course it works. you doubted me ?Agilent uses those too in their 34401 and lots of other machinery to go to the front panel.

author: tpecar
author_rank: Newbie
timestamp: April 29, 2023, 10:44:04 pm
content: For anyone that might be looking for a replacement connector of this type - as noted by gevans, this type of connector was also used in Agilent 34401.Based on its parts list, I've managed to determine it to be a Molex 52007 series connector, also called a "wire trap" connector. These were 2mm pitch, and came with the cap preinstalled - as noted, the cap isn't intended to be removed, but acts as a lever to push the spring contacts inside to release the (usually single core) ribbon cable.The original series is obsolete, but Molex still seems to produce compatible 52151 series.https://eu.mouser.com/c/connectors/headers-wire-housings/?q=wire%20trapAlso, some other eevblog post also referenced this type of connectorhttps://www.eevblog.com/forum/repair/yamaha-dm1000-digital-mixer-sourcing-obsolete-molex-connector/And there's also a 2.5mm pitch clone around, if anyone encounters themhttps://m.morethanall.com/product/index/btype_id/2/type_id/47/id/1633
How to upgrade Fluke 5100B？ - Page 1
Forum section: electronics / repair

author: mzspring
author_rank: Contributor
timestamp: January 17, 2025, 07:45:03 am
content: How to upgrade Fluke 5100BHow to upgrade Fluke 5100B to become a more stable standard source that can be used to calibrate 6.5-digit multimeters

author: coromonadalix
author_rank: Super Contributor
timestamp: January 17, 2025, 11:19:42 am
content: https://www.eevblog.com/forum/metrology/fluke-5100b-for-6-7-digit-dmm/meaning NO if it was doable we should had feedback or hear about it .... it is not enough for 6.5 digits

author: Runco990
author_rank: Frequent Contributor
timestamp: January 17, 2025, 07:12:25 pm
content: That's NOT happening. These units are ancient at this point. And of course, Ebay seller THINK they are still a valid option by the asking prices I have seen. I got mine for free years ago, along with all it's problems. I'd BARELY trust it on a 4 1/2 digit meters. I don't use it for meter calibration at all, but it IS handy for the odd voltage and frequency requirement.Consider it a cool old toy today.

author: bdunham7
author_rank: Super Contributor
timestamp: January 17, 2025, 07:46:42 pm
content: I've repaired, restored, tweaked and tuned a few of these and while I have used them for calibration purposes beyond what you might expect, it was always with a more precise meter in parallel and it was challenging, like using a micrometer aboard a boat in rough weather. There are a few improvable issues regarding stability, such as replacing a commonly faulty relay in one of the control loops and also carefully adjusting those loops. Calibration and adjustment of these are much more involved than just verifying the output accuracy. For best stability you need to let them warm up for hours on end--like overnight--and then let them stabilize after each output is selected, often for several minutes.And after you do all that, they are still nowhere near what you need for actual standalone professional calibration of 6.5 digit meters or even the better 5.5 digit models. These are 50ppm class devices and that's for DC on a good day. The AC part is 350ppm, which is actually pretty good, but stability on the higher voltages is problematic.

author: bbqws60
author_rank: Newbie
timestamp: January 18, 2025, 01:13:35 pm
content: The Fluke 5520 is priced at over 30000 US dollars to calibrate six and a half digits, while the 5101 is just a joke No matter how much it is modified, it is impossible
How to verify a PID controller board - Page 1
Forum section: electronics / repair

author: capocasa
author_rank: Newbie
timestamp: February 07, 2025, 05:41:08 pm
content: Hello!I have the attached PID controller board for coffee machines. It's a sort of simple device based on an atmega micro, a bluetooth board and some triacs to do the switching, and a temp sensor for the boiler.My issue is that after putting it into the machine, the bluetooth serup works but the water does not heat when it's supposed to.I am unsure how to verify the device works.My thinking is to verify the triacs using a transistor tester, and then connect it outside of the machine with secured cables and use a multimeter to check if the expectage voltage is output to the correct outputs.But before doing that, I'd love to know if you think I should be doing something else. Thanks!

author: Poroit
author_rank: Frequent Contributor
timestamp: February 08, 2025, 06:02:15 am
content: G'day capocasa,Have you checked the heating element is intact by measuring its resistance?

author: capocasa
author_rank: Newbie
timestamp: February 08, 2025, 08:36:09 am
content: Hello!No but it works using the regular thermostat. Bit I'll remember I can do that, thanks!!
How would you repair those very thin copper contacts? - Page 1
Forum section: electronics / repair

author: HobGoblyn
author_rank: Unknown
timestamp: December 12, 2020, 02:56:21 pm
content: Have a cordless drill, one of the contacts on the switch has broken as per the attached photo (and you can see the circuit board where the contact touches).Also included a bad drawing showing how it fits in to the plastic switch.Is it possible to repair these things (make a new one out of something) or am I wasting my time trying?Thanks

author: Ian.M
author_rank: Super Contributor
timestamp: December 12, 2020, 03:29:42 pm
content: Its not copper, because it needs to be springy. Its probably made from spring temper phosphor bronze shim stock. Reproducing it would be really difficult, especially forming the contact tips so they don't scratch the contacts on the PCB. You might be able to patch it up by forming a new tab of springy brass of comparable thickness, and soldering it overlapped onto the base of the U, by tinning both surfaces and sweating them together.

author: HobGoblyn
author_rank: Unknown
timestamp: December 12, 2020, 03:52:04 pm
content: I thought it probably wasn't worth it, especially as I've since found the complete switch for £6 from China on ebay.Just don't like things to beat me

author: cncjerry
author_rank: Unknown
timestamp: December 12, 2020, 06:50:27 pm
content: it might be beryllium copper, BeCu. known to the state of California...by the way, cutting wood is known to the state of California...I've been able to glue it down onto aluminum and cut it with a very small end mill running in an oil bath. With very small nippers you might get close enough by hand. Given your goal is to repair, though, get the switch...ha.jerry
hp 08640-60506 schematics - Page 1
Forum section: electronics / repair

author: pelule
author_rank: Frequent Contributor
timestamp: September 01, 2015, 10:04:39 pm
content: I am searching service document and/or schematic of the hp 08640-60506 low noise amplifier.Any tip is welcome.

author: Stray Electron
author_rank: Super Contributor
timestamp: September 01, 2015, 11:31:00 pm
content: Is that a part of a HP 8640 Signal Generator? It sounds like it is based on the PN. If so, then the 8640 Service Manual should havesomeinformation about it.

author: pelule
author_rank: Frequent Contributor
timestamp: September 02, 2015, 08:48:30 pm
content: No, it is a low noise amplifier, 40 dB gain, for use in 50 Ohm applications from 20 Hz to 10 MHz, used f.e. for noise measurement.

author: jan.didden
author_rank: Newbie
timestamp: March 04, 2019, 12:52:24 pm
content: Hi, has this been resolved? I am also looking for tech documentation for this HP 08640-60506 Low Noise Amplifier.Jan Didden

author: GRA
author_rank: Newbie
timestamp: January 18, 2022, 07:15:46 pm
content: Does anyone know what the markings are on the Q1 and Q2 elements inside the HP 08640-60506 low noise amplifier?

author: jan.didden
author_rank: Newbie
timestamp: February 23, 2023, 06:33:58 pm
content: A kind soul send me the documentation pack, see attached.Jan
hp 1015 power board schematic - Page 1
Forum section: electronics / repair

author: raminrajabi
author_rank: Contributor
timestamp: December 07, 2021, 07:36:44 am
content: Hi,I wanted to repair my hp 1015 printer power board but I can't read the resistor value. Can anyone help me out to find the resistor value?the second was the transistor I can't find the equivalent part for it from bcxxx family.thanks,.

author: Lorenzo_1
author_rank: Regular Contributor
timestamp: December 07, 2021, 08:35:56 am
content: Could the transistor be a 2SC3202?

author: raminrajabi
author_rank: Contributor
timestamp: December 07, 2021, 08:41:58 am
content: yes, it is 2SC3202 but different manufacture. I have plenty of BC family in my junk parts so I wanted to use them if I can't find the equivalent part I have to order the 2SC3202.

author: raminrajabi
author_rank: Contributor
timestamp: December 08, 2021, 09:29:45 am
content: is BC635 can be replaceable with the transistor?

author: raminrajabi
author_rank: Contributor
timestamp: December 08, 2021, 10:43:20 am
content: I repaired the board with a 10-ohm resistor and c2235 transistor.
HP 10811A connector for 83752A/B synthesyzer - Page 1
Forum section: electronics / repair

author: jfphp
author_rank: Regular Contributor
timestamp: December 30, 2020, 10:02:55 am
content: Hello,In order to fit the high stability option -10811A- in an HP83752A/B synthesyzer I am looking for the mating connector of the motherboard . Thank you

author: wn1fju
author_rank: Frequent Contributor
timestamp: December 30, 2020, 01:32:48 pm
content: Looks fairly standard and should be easy to find on Digikey, Mouser, etc. once you measure the dimensions and look at the various datasheets.If you don't want to spend any money, you could always remove the connector from the motherboard and solder the 5 wires onto it.
HP 11036A AC Probe - Page 1
Forum section: electronics / repair

author: nicbul
author_rank: Newbie
timestamp: July 02, 2020, 10:24:41 pm
content: So I needed to re-terminate the connection between the triaxial cable and the probe head of the AC probe for the HP 410C VTVM. The probe was quite beat up and was probably getting tossed around for a couple decades at the surplus shop that I picked it up from. The tube is okay though!The grey 'boot' is where the faulty connection was so I needed to do some excavation of that material to make the repair. There was a void in there and I'm thinking the cable was actually able to move a bit. I would describe the boot as made of a medium durometer thermoplastic. The connections were made on the turquoise Bakelite piece and then the over-molded boot was made in some kind of two piece form.My original idea to recreate the boot was to print a mold and pot it with either RTV, a urethane, or an epoxy but this probe is meant to have a bandwidth of 700MHz so that may need some special consideration that I'm not entirely aware of!What kind of potting compound or material should I look for to remake this boot to ensure that I don't mess up the bandwidth of the probe?
HP 1220A - Repair Advice or resources? - Page 1
Forum section: electronics / repair

author: JoeShmoe
author_rank: Newbie
timestamp: December 05, 2019, 02:50:08 am
content: I have not posted onto a forum in quite a long time, so please forgive me if this sounds awkward.I have an HP 1220A without any probes, I only have the wall adapter.I plugged it in, nothing displays on the screen no matter which buttons I have pressed or knobs I have turned, no beam or anything. I believe the power unit is faulty and I was wondering if anyone can help me confirm my hypothesis. Using my multimeter I tried to check for voltage across multiple resistors, diodes, and two pins(one labeled 12v- and another 12v+). I didn't get any read outs. I tested continuity on the wall adapter and it seems to work fine, the fuse also is still continuous.If any more information is needed, I would be happy to provide photos and readings, or clarifications.

author: bob91343
author_rank: Super Contributor
timestamp: December 05, 2019, 04:43:59 am
content: What wall adapter? The 1220A runs directly from 120 V power line I believe. Is there a power pilot lamp? How about graticule illumination? Do you measure some continuity across the line voltage plug?Read the manual. It tells you how to set up the unit.
hp 1345a strange issue - Page 1
Forum section: electronics / repair

author: Xtremexp
author_rank: Regular Contributor
timestamp: January 18, 2025, 09:33:14 pm
content: hello all,I got a hp 1345a display and it got very strange issue. It displays the vectors quite well but the characters are scrambled . The characters that are displayed are random. To debug, I disconnected the data interface and display goes to calibration mode. in calibration mode, the texts are also scrambled, for an example, at the top it should display "Y=2048" but it shows Y]... so I believe this issue is from display itself.Had anyone faced similar issue and solved the problem?

author: wn1fju
author_rank: Frequent Contributor
timestamp: January 19, 2025, 01:37:58 pm
content: Just a guess, but...I've repaired several of the 1345A displays. The most common failure are the 2.2 uF tantalum capacitors (usually yellow cylindrical) on the A1 xyz amp/stroke board. One or more shorts out and takes out one or more of the low voltage power rails (+/-15V). Clearly not the case with your unit.But once, when I was trying to repair a 1345A, I started lifting one end of each tantalum until the short went away. I replaced the shorted cap and the 1345A sprang to life. However, I saw behavior like you are getting - distorted characters. Turns out that I forgot to solder all the leads of the good capacitors that I had pulled up. Once I did that, everything worked perfectly.So perhaps you have an open tantalum capacitor.

author: Xtremexp
author_rank: Regular Contributor
timestamp: January 19, 2025, 05:33:13 pm
content: Quote from: wn1fju on January 19, 2025, 01:37:58 pmThanks for the direction. I opened the unit and looked around it. It seems that someone already has worked on it. I see "BAD" sticker on "U5" PROM (character generator). Do you think it might be bad U5 PROM, if thats the case then I do not have any option as I do not think we can find PROM data now. what do you think?

author: wn1fju
author_rank: Frequent Contributor
timestamp: January 19, 2025, 07:02:48 pm
content: I guess a bad U5 might make more sense.In my bad capacitor case, the display was sort of jittering. Your display appears stable, just wrong. So my original capacitor guess could very well be wrong.
HP 16500B Pattern Generator (16520A) will not load files - Page 1
Forum section: electronics / repair

author: pnv57
author_rank: Contributor
timestamp: April 08, 2020, 06:18:20 pm
content: I recently added a pattern generator and expansion (16520A and 16521A) to my HP 16500B, and a big draw for me was the fact I could build programs for the pattern generator on my PC, then load them up via floppy disk. When I tried to load the file (via the merge function in the listing editor) it says "File not found". I can save the listing to the disk, but I get the same error when I try to load it back. The file clearly exists, I can see it in the hard drive browser, and I can load it back onto the floppy and onto my PC. I'm on the latest OS (3.14/3.13 for the mainframe, 3.03 for the pattern generator), I tried 2.03 (2.00 for the pattern generator) as well. In addition, I tried to load the pattern generator 1.00 software from the C mainframe and the 2.00 software from B v2.03, and then edited the files to make them appear as the 3.03 version. None of this worked. I have a 16500A as well to try to test it with, except the front floppy drive is misaligned currently, and I am working out how to realign it. The service manuals don't appear to be much help either, as they don't explain how anything works, other than vague block diagrams. Has anyone else run into this before? Any suggestions?
HP 1663A logic Analyzer not starting up after flash ROM update. - Page 1
Forum section: electronics / repair

author: imac
author_rank: Newbie
timestamp: February 03, 2021, 08:00:14 pm
content: My HP 1663A logic Analyzer does not start up after the flash ROM update. The power up self test runs okay and after that a grey screen with some strange signs.Is there a way to re-run the flash ROM update at startup?

author: imac
author_rank: Newbie
timestamp: February 03, 2021, 08:02:34 pm
content: The update was okay.

author: imac
author_rank: Newbie
timestamp: September 28, 2021, 06:28:59 pm
content: Is there anyone that have a dump of the eprom U14 01660-80004?

author: fzabkar
author_rank: Super Contributor
timestamp: September 28, 2021, 08:53:12 pm
content: Could we see your flash dump and update files?

author: imac
author_rank: Newbie
timestamp: September 29, 2021, 07:51:35 pm
content: Here is the 3.01 sw for the OShttps://www.keysight.com/se/en/lib/software-detail/instrument-firmware-software/1660aas-series-operating-system-software-version-301-sw568.htmlI don't have any dump of the eprom.

author: fzabkar
author_rank: Super Contributor
timestamp: September 30, 2021, 08:15:07 pm
content: I can see how the files are structured. There is a 0x200-byte header after which is the actual payload. The payload is delivered in 0x100-byte blocks, with the first big-endian word being the byte count for that block. All blocks except the last have a byte count of 0xFE (= 0x100 - two bytes for the count).If you were to provide a flash dump, I could verify whether the payload has been unpacked correctly. What surprises me is that there doesn't appear to be any checksum.I have attached the unpacked files, as I see them.
HP 16700/16702 Power supply repair - Page 1
Forum section: electronics / repair

author: dxl
author_rank: Regular Contributor
timestamp: September 04, 2021, 08:41:10 pm
content: Hi,i've got my hands on a HP16702A Logic Analyzer. Unfortunately, a few seconds after power on the Power supply died. It looks like there's a small standby power supply in these units. An unknown TO220 Mosfet(?) bursted, so i can't read any part number anymore. I've attached a Picture of the PCB with the missing part. Does anyone know, what this part is?What is strange is that Pin 2 connects to GND, and Pin 3 connects to the small standby transformer. I would have expected it the other way round.

author: bob91343
author_rank: Super Contributor
timestamp: September 04, 2021, 11:02:28 pm
content: Perhaps an IRF840 or similar part.

author: FrodeM
author_rank: Contributor
timestamp: April 25, 2024, 08:04:56 am
content: Not sure if you figured it out, but it's a TOP227Y integrated switch and regulator. You can see the schematics around this part here:https://bitsavers.org/test_equipment/hp/167xx/Celestica_7000_Aux_Power_Regulator_Schematics.pngNote that 360V might not be correct. I have since figured out that the high-voltage side that source all of this is generated by a boost-converter regulator, not just rectified power-grid voltage. It is more likely something like 400V, but I have not measured it. Also make sure to check D7 down at the main board, this is by far the weakest link in the main current-path of the PSU.
HP 16702A does not recognize mouse - Page 1
Forum section: electronics / repair

author: nikodem
author_rank: Regular Contributor
timestamp: July 22, 2020, 10:57:40 am
content: I have recently acquired an "untested" HP 16702A logic analyzer mainframe, planning to repair it if it's not DoA. And it's not (except a blown-out cap in the mains filter).Now i try to boot it to make some more elaborate self-test, but it does require a mouse, in order to boot its GUI. I have connected a PS/2 mouse, but it does not reckognize it (there is no problem with a keyboard). Does HP-UX need any particular type of a pointing device?Thank you in advance for you help

author: oPossum
author_rank: Super Contributor
timestamp: July 22, 2020, 11:36:32 am
content: Adding a couple of pull-up resistors may get it working.https://www.eevblog.com/forum/testgear/hp-16702a-mouse/msg374967/#msg374967

author: nikodem
author_rank: Regular Contributor
timestamp: July 22, 2020, 12:19:52 pm
content: Quote from: oPossum on July 22, 2020, 11:36:32 amThank you, but unfortunetely my unit has Rev.A of this board with no place for pull-ups (see image). Do you think, that just pulling up data and clock lines will be sufficient? I'll try to do that (maybe in the mouse, not in the 16702a).EDIT:I've added the resistors (1k) to data and clock line in the mouse but it did not help. I've ordered another mouse in order to see if it will work or not.

author: z80tw
author_rank: Contributor
timestamp: July 26, 2020, 09:57:58 am
content: A regular PC mouse won't work on HP16702x logic analyzer,better to try an Agilent mouse,I found this Agilent mouse worked on my 16702B( and PC) very well(I no longer have the 16702B),it's an USB optical mouse with high resolution.

author: Gerhard_dk4xp
author_rank: Frequent Contributor
timestamp: July 26, 2020, 11:40:59 am
content: On my 16702Ba Microsoft IntelliMouse 1.2A works. It still has a ball.Other identifiable text strings: PN X04-72167 Product ID 63618-OEM-0290854-7 5199 (probably date)There were other mice that looked similar with the same green PS/2 plugthat did not work.Cheers, Gerhard

author: oPossum
author_rank: Super Contributor
timestamp: July 26, 2020, 01:26:50 pm
content: I use a Kensington model K72215 with my 16702A and 16702B.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 26, 2020, 01:51:31 pm
content: Same thing for another insrument, some mouse brands dont work well, you hae to find the right one, got an intellimouse too and a logitech they work very well
HP 1670D LA broken trim - mystery plastic - Page 1
Forum section: electronics / repair

author: TerraHertz
author_rank: Super Contributor
timestamp: June 11, 2021, 02:48:52 am
content: A while ago I bought a cheap HP 1670D logic analyzer. For reasons not worth going into. Shipped from the USA, it wasn't packed well (what a surprise.) All the minor damages were easily repairable, until I got to the last one...The plastic edge trim around the front of the machine. It was cracked in two places.Then I discovered that HP used some quite tough but brittle plastic, that does not soften with any solvent I've tried. MEK, acetone, polystyrene glue... nothing. Worse, the MEK has a bad effect, making the surface shrink, resulting in nasty looking surface crazing. See last pic.I'd just assumed of course MEK would work, jigged up the pieces and squirted MEK into the crack. Some flowed onto the outer surface of the plastic. The cracks developed some time after this failed attempt to glue it.Does anyone know what this plastic is? Is there any known solvent for it? There's no type identifier markings I can see.Probably the only method of repairing the breaks would involve heat welding it then surface profiling the mess. But for that I'll need some of the same type and color of plastic. I don't suppose anyone has an unwanted one of these trims, broken or not?Oh btw, the missing knob is since repaired.

author: james_s
author_rank: Super Contributor
timestamp: June 11, 2021, 04:44:55 am
content: It may be PC-ABS, I've tried gluing that with solvent without much luck, especially when it gets old and the plasticizer leaches out. I'd try cyanoacrylate rather than solvent, you can fill in cracks and gaps with baking soda and then soak them in a bit more glue and it forms a rock hard material. If you manage to get it all back together you can spray paint it so it looks good.
HP 1710A Oscilloscope manual - schematics - Page 1
Forum section: electronics / repair

author: ehobby
author_rank: Contributor
timestamp: February 02, 2021, 01:51:50 am
content: Hi,I have been looking for a scan of the manual for the HP 1710A oscilloscope for a long time and have not found one. Some have suggested that I look at the 1710B but it has board and schematic differences. Let me know if anyone has a scan/pdf of the manual, or are willing to loan me a manual to scan, pdf and OCR. It is just hard to believe nothing exists for the 1710A.ThanksTony
HP 1725A Oscilloscope, 275Mhz - Page 1
Forum section: electronics / repair

author: cemelec
author_rank: Contributor
timestamp: July 17, 2021, 10:38:33 am
content: About 3 years ago I bought (very cheaply) a defunct HP 1725A oscilloscope. This was never intended to be my main oscilloscope, but I have great respect for well made vintage test gear, and you don't get much better than HP of yesteryear.In its day this would have been pretty high end, and with a 275Mhz bandwidth and other features (e.g. 50 ohm input capability) it would still be of use to me.Anyway I got it working of sorts, the main fault is that many of the contacts in the timebase switch wafers are broken. If I recall there are 5 (maybe 4?) such boards on the TB switch. I managed to kind of repair them with phosphor bronze strip - see photo - but switching TB is still unreliable. When going, it works pretty much perfectly, voltage and timebase very accurate.Long shot - I'm wondering if anyone else has ever fixed one of these, especially the above mentoned switches, and has any tips or advice. As for actually getting spares, I think I've more chance of winning the lottery.Many thanksCharles

author: lowimpedance
author_rank: Super Contributor
timestamp: July 18, 2021, 10:32:17 am
content: Unfortunately a parts donor will be the only option for original contacts. Any HP CRO from that series will do I think.Those hand made contacts look good, perhaps some polishing and a bit of contact grease may help with reliability.

author: tggzzz
author_rank: Super Contributor
timestamp: July 18, 2021, 11:04:58 am
content: I would look carefully at the PCB part of the switch.My 1740 became erratic because the outer rim of that black plastic piece rubbed the circuit board and eroded the PCB track from the switch contacts to the rest of the circuit. Solution was obvious: solder a very thin piece of wire across the gap, ensuring no solder migrated onto the switch contact.

author: cemelec
author_rank: Contributor
timestamp: July 18, 2021, 12:13:46 pm
content: Thanks, but actually the PCB boards are all in pretty good shape, in fact the whole unit is, its just those contacts. I've even been contemplating 3D printing a replacement with easier to mount contacts, but maybe there comes a point where time is better spent elsewhere....Charles
Hp 17400A amplifier info wanted - Page 1
Forum section: electronics / repair

author: Roman oh
author_rank: Regular Contributor
timestamp: June 25, 2023, 06:45:42 am
content: Hi, guys,Just picked up a very cheap HP17400A amplifier - hoping to use it as low level preamp for an experiment I am doing. But I have no data and not much comes up on the usual manual sites. Does anyone have any info on this?Roman

author: factory
author_rank: Super Contributor
timestamp: June 25, 2023, 12:07:24 pm
content: Doubt a free manual will turn up for this, it's a DC input module for either the 7402A or 7404A oscillographic (chart) recorder, there are a couple of 17400A manuals on ebay in the US, then you would need the fancy input connector (also found on ebay)orsomething to replace it with.Pages from 1976 catalog attached.David

author: Roman oh
author_rank: Regular Contributor
timestamp: June 25, 2023, 01:06:40 pm
content: Thanks for that much, at least. That helps a bit. One reason. Grabbed this was because i happen to have a few of those fancy connector mates in my “assorted connectors” bin!

author: factory
author_rank: Super Contributor
timestamp: June 25, 2023, 02:42:33 pm
content: Not the same module, but one of the 17401A manuals on eBay has a part of the circuit diagram showing the mainframe connections, looks to need +15V, -15V +48V, -48V, two separate grounds? , signals of 440Hz & 2.4kHz and has two outputs.P.S. I have some HP DVMs that also use that input connector.David

author: Roman oh
author_rank: Regular Contributor
timestamp: June 25, 2023, 10:21:04 pm
content: David,Thanks, that’s going to be a big help!Do you need a spare connector?Roman
HP 1740A Oscilloscope Help ... Voltage Amplitude is Exactly 10x too Small - Page 1
Forum section: electronics / repair

author: Pork
author_rank: Contributor
timestamp: May 29, 2020, 03:00:56 am
content: So my HP 1740A is displaying the voltage exactly 10x too small.If the volts per div is set to .1 and the probe is connected to the 1V Cal, I get a one division reading (same for both A & B).The amplitude of the reading is exactly 10x smaller than it should be and I can't seem to correct it.HelpWhat I know:Probe is a Tek P6122 (10x)1V Cal has been set to .500 volts with a Fluke 177 DMMDepressing the blue 10x button on the scope increases the width of the signal.Depressing the tan 5x button increases the amplitude by 5x.

author: tautech
author_rank: Super Contributor
timestamp: May 29, 2020, 09:43:21 am
content: https://www.eevblog.com/forum/testgear/hp-1740a-help-voltage-amplitude-is-exactly-10x-too-small-243474/Please don't double post or the moderators will get right up you.

author: Simon
author_rank: Unknown
timestamp: May 29, 2020, 10:37:27 am
content: Please don't double post or we (moderators) have all the users getting "right up us" about it. There is nothing more annoying for anyone to take the time to reply to a post only to find there is another one with more discussion on it than the one you posted on and what you took the time to write had already been written.
HP 1740A Repair (Low Voltage PSU) - Page 1
Forum section: electronics / repair

author: gigipaplayed
author_rank: Newbie
timestamp: August 08, 2022, 11:55:39 pm
content: Hi everyone,i am an electronics engineering student, humbly asking for someone's help. Here i will put ALL the resources i have (and those that you ask me) to repair this old scope with some informations i gathered probing things here and there. I do not have any ESR meter so i cannot tell if any capacitor has ESR issues (but i do have a four channel scope and 2 multimeters to probe things with). The ONE AND ONLY low voltage power supply that does not work properly is the 120V, reading about 7V with HV horizontal and vertical scale, and 53V when nothing is connected, so i assume that the problem it's not elsewhere other than A16. Everything else is pretty much spot on other than the 43V being 42,8V, which is pretty okay i guess.CR1 looks to be okay on every diode, C3 capacitor is reading quite high, almost 180DC. I tested all diodes related to BJT's but only Q3 B-C junction and Q4 B-E junction seem to not be readable by my Voltmeter diode test. Could this really be the explanation of my problem? If so, could you help me understand why? (if those transistors are broken why should my voltage drop so low...)

author: m k
author_rank: Super Contributor
timestamp: August 17, 2022, 07:32:40 pm
content: If Q4 and ext. Q2 are closed the ground connection goes only through R2 and R8.To change that the base current of Q4 must be enough to open the transistor and then open ext. Q2.Local Q2 is the one for the task and Q3 is denying it, if needed.Lift a leg or remove a component to be sure what the situation really is.

author: andy3055
author_rank: Super Contributor
timestamp: August 18, 2022, 04:21:57 am
content: Do you have the 147.5 volts at the output of the bridge rectifier CR1? If not, isolate the load side and make sure it is there and go from there.
HP 1980B Oscilloscope repair - Page 1
Forum section: electronics / repair

author: micho
author_rank: Newbie
timestamp: August 19, 2019, 02:45:08 am
content: Hi,I was given an 1980B to have a look at it. Someone tried to repair it before and lost some screws. Also messed up the voltage rails by plugging one connector backwards. And lost almost all of the screws that secure bottom boards to the chassis.I got it to turn on eventually. But only thing it does, is all front panel lights are on. And if I press Beam find there is a very faint green glow that appears on one side of the CRT. So something is working.After 8 hours of troubleshooting, I got to a point where I am almost 100% sure that the problem lies on the "processor board". Troubleshooting charts also followed me to this board. I checked around the processor board and one of the masked ROM chips (U18) was boiling hot, where the other one was cool (U17). They are pair and even when I swapped them, the problem followed with a chip. It is an Intel P8355 part.What do you think?Is there anyone on the forum that has a parts unit and would be willing to sell me those ROMs?

author: MarshallPlexi
author_rank: Contributor
timestamp: November 15, 2024, 08:34:24 am
content: Any updates on this? I’m having a similar issue.

author: Poroit
author_rank: Frequent Contributor
timestamp: November 16, 2024, 05:47:07 am
content: G'day Micho,There is a similar topic running in Test Equipment.
h/p 204 Oscillator battery P/Supply conversion to AC question. - Page 1
Forum section: electronics / repair

author: Paceguy
author_rank: Regular Contributor
timestamp: December 28, 2024, 12:43:53 pm
content: Hi, I have this battery option h/p 204 with dead batteries. Has anyone here converted a h/p 204's power supply from battery operated to AC only?. I looked at the service manual and see that there are two different part numbers for the power transformers but no voltages are shown on the schmatics. Can I use the original transformer in my conversion project? The power supply for AC only operation looks very simple and straightforward. Advice to how to go about it would be much appreciated. Thanks in advance!

author: m k
author_rank: Super Contributor
timestamp: December 30, 2024, 03:14:26 pm
content: There are few versions.For example 204C is quite a bit more transistorized than 204A.

author: edavid
author_rank: Super Contributor
timestamp: December 30, 2024, 03:24:52 pm
content: Yes OP, tell us what version you have.If it's a 204C or 204D, I answered this question in a previous thread:https://www.eevblog.com/forum/testgear/oscillator-not-working-right-(hp-204c)/msg1226009/#msg1226009P.S. Please stop writing h/p, that is just confusing.

author: factory
author_rank: Super Contributor
timestamp: December 30, 2024, 04:35:24 pm
content: Quote from: m k on December 30, 2024, 03:14:26 pmIt's not going to be a 204A, as the OP mentions a power transformer, something the "A" version doesn't have.It must be either a 204B, C or D.Attached below is the conversion someone else did to the 208A I have.David

author: TimFox
author_rank: Super Contributor
timestamp: December 30, 2024, 04:38:26 pm
content: I have an -hp- 403b voltmeter that used a string of Ni-Cd rechargeable batteries with an internal charger.It could be run from the AC line or on the battery power, but the batteries were required to derive the internal supply voltages on AC-power mode.The batteries were dead, so I replaced them with a series string of several TL431 shunt regulator circuits (with fixed resistors) to replace the battery sections between voltage taps, operating from the original charging circuit.There was plenty of space in the battery compartment to hold the TL431s on perfboard.
HP 214B Pulse Generator Parts  - Page 1
Forum section: electronics / repair

author: JFPhy
author_rank: Contributor
timestamp: August 06, 2025, 01:27:26 am
content: I snagged this from University years ago and I’m just getting around to opening it. I noticed these resistors are falling apart (from old age or from being zapped?). The manual has a number listed to them but is this ohms, kohms, Mohms? Also, the color coding does not agree with the written value. Any idea of what could be going on here. I tried to measure a few but they are definitely shot and do not agree with the color code or the written amount.The schematic can be found on page 108 (6, P/O A2 Timing Board)Any help would be greatly appreciated.-Josh

author: JFPhy
author_rank: Contributor
timestamp: August 06, 2025, 01:51:04 am
content: Disregard my blindness. I see that the color coding does match up. But, I am still annoyed by the lack of units on the others that are burnt as I cannot see a color code.

author: picburner
author_rank: Frequent Contributor
timestamp: August 06, 2025, 04:21:53 am
content: In the section of the schematic shown, all resistors have values expressed in Ohm and belong to the E96 series, therefore with a 1% tolerance.Resistors R513 and R514 (53.3 Ohm: you can't see the dot, but the space between the two "3" indicates it's there) belong to neither the E96 nor the E192 series.53.6 Ohm resistors are mounted on the pcb instead which, since they don't appear to be burned, do not represent a problem.Be careful, as there are other smaller resistors on the pcb that are also burned.

author: winfieldhill
author_rank: Contributor
timestamp: August 06, 2025, 11:59:51 pm
content: You may want to consider using a modern MOSFET switching circuit to replace the 214B HV output-drive functions. My pulse circuit can deliver 200 to 500-volt 50-ohm Zout pulses with 15ns risetime, up to 5 amps, just like the 214B, but higher voltages. It uses an ON Semi gate driver with two FCP650N80Z 650-volt SiC MOSFETs. Here's an article to be published in the next edition of The Art of Electronics, x-Chapters, 2nd edition.

author: winfieldhill
author_rank: Contributor
timestamp: August 13, 2025, 12:01:42 pm
content: I'm sorry, the FCP650N80Z 650-volt SiC MOSFET, a favorite of mine, is not a 650-volt SiC transistor, it's an 800-volt Super-Junction MOSFET. These are more robust than SiC parts, yet have very low Crss capacitance, about 5pF.Sadly, ON Semi is discontinuing this excellent Fairchild part, it's on Last Shipments.

author: factory
author_rank: Super Contributor
timestamp: August 14, 2025, 10:00:08 am
content: Think he needs to determine why the attenuator is cremated first.Quote from: winfieldhill on August 06, 2025, 11:59:51 pmAnd maybe you'd like to explain how you think it's going to create pulsesthatare higher than the power supply rails, not sure why you would want to modify this anyway, just build something separate for that.David
HP 239A OP-Amp substitution to restore unit - Page 1
Forum section: electronics / repair

author: jseefried
author_rank: Newbie
timestamp: December 26, 2022, 09:40:37 pm
content: I was recently working on a dead HP 239a and the Op-amps (U1, U2) for the oscillator section and the amplifier were both bad. I did much research and took the opportunity to test some combinations for replacement:1) replaced both U1 and U3 with TI OPA-1655 op amps, ok performance with the LM1458 in U22) replaced the U1,U3 with TI OPA-1655 AND U2 with an NE5532 dual, no real improvement3) replaced U1, U3 with TI NE5534 and then put LM1458(factory) back into unit, good performance and .001% (measured with HP8903B & Tek DA-4084)4) replaced U1, U3 with TI NE5534 and then put a TI NE 5532 (dual) into unit, slightly HIGHER THD @ .009%So it appears the best combination is U1 and U3 are TI NE5534 and U2 LM1458 (VERY similar to the Tektronix SG505 design), in addition the NE5534 are a direct pin for pin replacement, so you can socket the new devices for easier work.Hope this will help anyone searching to replace the old HP round can OP-Amp which are unobtainable any more.PS also replace the caps in the power supply with 1,500 low ESR Audio grade nichicons.

author: RichardM
author_rank: Frequent Contributor
timestamp: December 27, 2022, 09:14:20 am
content: Great to know. I have a stock unit that works. The best THD I measure on my HP35660a is 0.007% at 1kHz. I might print this out and tape it to the top of my unit for future reference.Cheers

author: alanep
author_rank: Contributor
timestamp: December 28, 2022, 11:31:52 am
content: I think the HP239A was the predecessor to the low distortion oscillator used in the HP339A Distortion Measurement Set. So, the oscillator sections are very similar in both i.e. they both use HP part number 1826-0487 op amps for the critical sections. From my checks, the 1826-0487 is a selected Harris HA2-2625 op amp which is different internally to the NE5534 e.g. the HA2-2625 has a higher slew rate but is more noisy than the NE5534.HP used some quirks of the HA2-2625 in their circuits e.g. in the HP239A, CR21, CR22 & R27,R28 on pin 8 of U1 act as a clamp preventing extreme output overshoot whilst the amplitude control network stabilizes the output. I'm not sure what these components would do to pin 8 of a NE5534 if it were substituted? Given your measurements, I guess it works... The Tektronix SG505 has a clamp circuit around the second integrator NE5334 (U1401) but it is completely different to that used in the HP239A.

author: precaud
author_rank: Frequent Contributor
timestamp: December 28, 2022, 12:57:13 pm
content: 10+ years ago some guys over on DIYAudio.com did a deep dive into the HP 339A. The opamp of choice to replace the one from Harris is the LT1468. The circuitry connected to pin 8 needs to be removed. The update made a noticeable improvement in mine.
HP-239A Oscillator Adjustment - Page 1
Forum section: electronics / repair

author: RichardM
author_rank: Frequent Contributor
timestamp: March 18, 2022, 06:33:05 am
content: Hi All,I have an HP-239A that works well and the THD measures low also. I thought I might try and calibrate the device as per the service manual section 5.11 (attached) but I am unable to get the frequency wwithin tolerance. At 10kHz I am always high and the best I can do is 10,069 Hz which is +- 10Hz as per specification. At 100kHz it is even worse and measures 92,296Hz. If I adjust C5 to match 100kHz my 10kHz becomes 10,916Hz.Does anyone have experience in adjusting this device ? I note there is provision for an additional capacitor C45 (0-22pF) to adjust to 100kHz but that still won't solve my issue at 10kHz. I have no problems adjusting the gain per the manual.Any suggestions welcome.

author: wn1fju
author_rank: Frequent Contributor
timestamp: March 18, 2022, 12:23:13 pm
content: Perhaps one or more of the range capacitors or digit resistors in the frequency feedback network have drifted. You could try to measure them in-circuit (with the power off) if suitable switch combinations can easily isolate them.I just tried the adjustment on my unit. Mine doesn't have the C45 padding capacitor installed. By adjusting C5, I was able to get the two readings as 10,005 Hz and 99,890 Hz. The values do change depending upon whether the aluminum cover plate is installed (about 5 Hz at 10K).

author: RichardM
author_rank: Frequent Contributor
timestamp: March 18, 2022, 08:26:18 pm
content: Thanks for the advice. C45 also isn't installed on my unit.
Successful HP 3101-2046 DPDT Switch Repair! - Page 1
Forum section: electronics / repair

author: ZGoode
author_rank: Frequent Contributor
timestamp: January 31, 2024, 05:00:23 pm
content: I had a broken DPDT switch on my HP 4277A LCZ meter that unfortunately I could not find a replacement for on Ebay or Digikey. There were no comparable/compatible replacements that I could find, particularly since these are nonshorting switches. Since the only part that was broken was the plastic lever toggle bit, I decided to design and print a replacement toggle using Fusion360 and the SLS printer we have in the lab. My replacement part was printed using PA12 nylon and then finished to a nice glossy black using a propane torch. It works great, and feels pretty much identical to the original switch.

author: ZGoode
author_rank: Frequent Contributor
timestamp: January 31, 2024, 05:02:23 pm
content: more photos of the repair!

author: SeanB
author_rank: Super Contributor
timestamp: January 31, 2024, 08:43:25 pm
content: Can you post the file, in the HP parts thread, so that this can be used by others as well. Nice work on making the new body.

author: ZGoode
author_rank: Frequent Contributor
timestamp: February 01, 2024, 08:53:37 pm
content: Yeah, I can do that. Can you link to that thread?
HP 3310A Test Points - Page 1
Forum section: electronics / repair

author: jdragoset
author_rank: Frequent Contributor
timestamp: April 28, 2019, 12:07:38 am
content: I have one with triangle bias (first adjustment after +10 volt supply) card A1 TP 11 not there.Have a spare board wit TP 11, and marked a spot to test TP 11.I can share pix if any interest.Jim
HP 33120 ERROR - Page 1
Forum section: electronics / repair

author: tatfuture
author_rank: Contributor
timestamp: October 09, 2019, 08:13:50 am
content: HP 33120 TEST All PassHP 33120 TEST All Pass, but turning on the power, the more sine the flickering changes, the more the picture please helpSYNC changes with the frequency when adjusting the freq

author: tatfuture
author_rank: Contributor
timestamp: October 09, 2019, 08:17:03 am
content: Please guide where to find

author: tatfuture
author_rank: Contributor
timestamp: October 09, 2019, 08:21:44 am
content: checked all the components on the PCB look good - please help me

author: tatfuture
author_rank: Contributor
timestamp: October 09, 2019, 01:27:06 pm
content: Please !!! Help me !!!

author: duak
author_rank: Super Contributor
timestamp: October 10, 2019, 07:25:53 pm
content: tatfuture, do you see any waveforms or changes in voltage with the oscilloscope on the +18V and -18V?I don't have a manual or schematic. Are there other DC power supply voltages you can show us?What does the output signal look like on the oscilloscope when the horizontal timebase is set to slower speeds, say 10 ms and 1000 ms/cm?

author: mr.fabe
author_rank: Regular Contributor
timestamp: October 10, 2019, 10:55:57 pm
content: Quote from: duak on October 10, 2019, 07:25:53 pmNow you do...https://ese.wustl.edu/undergraduate/Documents/lab_support/HP_33120A_Function_Generator_Service.pdf

author: tatfuture
author_rank: Contributor
timestamp: October 11, 2019, 07:44:43 am
content: Thank you duakPlease give me more guidance - thank you

author: tatfuture
author_rank: Contributor
timestamp: October 11, 2019, 07:50:37 am
content: Thank you mr.fabePlease give me more instructionsProbably broken zener CR709 I do not have (DIODE-ZNR SMB 3.3V 5% 1W- 1SMB5913B) I am looking for equivalent zener

author: mr.fabe
author_rank: Regular Contributor
timestamp: October 11, 2019, 08:00:00 pm
content: Check the transistor at Q718 and the surrounding components.

author: feedback.loop
author_rank: Frequent Contributor
timestamp: October 12, 2019, 04:37:28 am
content: Perhaps, this video might help.

author: tatfuture
author_rank: Contributor
timestamp: October 15, 2019, 02:42:44 am
content: Thank you feedblack.loopjust as this video measures voltage Q718 is also 17.7 V but measuring transistors are good both-capacitor also good ..?