hybridfree/eevblog-posts huggingface dataset:
HP 8657B attenuator issues?...  - Page 1
Forum section: electronics / repair

author: Rax
author_rank: Super Contributor
timestamp: March 24, 2022, 05:44:50 am
content: Hi all,I got this HP 8657B for a bit over a song, and although it has recent calibration stickers, there indeed are some issues with it.Namely, the levels out are missing (no RF signal out) every 5dB of output level setting. Differently put, working my way down from a high level (say, +10dBm), I lose signal out when crossing from 2dBm to 1dBm, getting it back as I cross from -3 to -4, losing it again from -8 to -9, back again at -13 to -14, and so on. Given the attenuator is the one going in steps of 5dB, it's become my primary suspect. This is in module A10.Getting to it means removing A11 (audio board), which I still have to figure out how to do, but before I get into surgery mode, I was curious if anyone else has sun into this situation with this unit. I'm tempted to suspect A10U1 (an SN74LS273N), though I obviously have to check the (switching) logic levels on its legs.Thank you for thinking on this with me.

author: bdunham7
author_rank: Super Contributor
timestamp: March 24, 2022, 06:27:09 am
content: I've not yet had the pleasure of dissecting that exact unit, but you're on the right track for sure. The 8656 types have a mechanical attenuator that physically fails in its old age and needs grommets--those I've fixed. I don't know how the attenuator assembly on that unit is arranged, but if you get an audible click at the transition and the signal disappears entirely (or mostly) then it may be a mechanical problem and perhaps you can open up the A10 assembly and fix it. eBay sellerpart2goin Israel (who I've used and seems OK) has those attenuator assemblies, just in case.
HP 8660 4GHz Amp Assembly - Which Pins? - Page 1
Forum section: electronics / repair

author: NY2KW
author_rank: Regular Contributor
timestamp: March 11, 2020, 12:19:33 am
content: I would like to use a surplus HP 8660 signal generator 4 GHz Amplifier assembly. It has two supplies relative to ground, +20vdc and -10vdc. Only block diagrams available no schematic - I assume I will damage it if I apply the wrong polarity voltage to the supply pins? Any suggestions would be appreciated.

author: Miti
author_rank: Super Contributor
timestamp: March 11, 2020, 10:50:34 am
content: I don’t know the pinout of this amplifier but one thing you can try. With a multimeter on diode, touch the ground with the black lead and the pins with the red lead. The one that shows open is the positive power, the one that shows a diode is the negative.

author: NY2KW
author_rank: Regular Contributor
timestamp: March 11, 2020, 01:17:22 pm
content: I tried this and both pins were open with respect to ground, and when the DMM leads were reversed, both showed a diode voltage of 0.75vdc. I think that both pins have some kind of diode ESD protection.

author: Miti
author_rank: Super Contributor
timestamp: March 11, 2020, 05:58:43 pm
content: Then you can try using a power supply. Limit the current to 10mA and start ramping up the voltage from 0V to about 5V. One pin must limit to a lower voltage than the other.
HP 8664A Internal Frequency Calibration - Page 1
Forum section: electronics / repair

author: avvidclif
author_rank: Regular Contributor
timestamp: November 29, 2019, 06:31:41 pm
content: I have worn out a set of eyeballs trying to figure out how to calibrate the internal reference oscillator on this signal generator. Does anyone have any clues? I have one that is on freq and the other is off 62hz @ 1.5G. I realize that's almost nit picking but the other is less than 5 Hz off.

author: avvidclif
author_rank: Regular Contributor
timestamp: November 29, 2019, 11:10:26 pm
content: Disregard I found the adjustment hole on the back. Sheesh.That's what I get for trying to read the manuals instead of looking around.
HP 8713B does not start - Page 1
Forum section: electronics / repair

author: omega12
author_rank: Contributor
timestamp: August 10, 2025, 11:24:51 pm
content: Hello,After 5 or 6 years, I wanted to turn the HP 8713B back on, but it wouldn't start.The power supply unit at the back just flashed, but nothing appeared on the CRT.When I remove the A3 board, it starts up without any problems. I also installed the A3 board in another device, and this device also won't start with the board, so the fault lies with the A3 board.I measured the electrolytic capacitors and tantalum capacitors and everything is OK, but I have a short circuit on the IC U2. Replacing the IC did not help and the short circuit remained.Unfortunately, I don't have a circuit diagram for the lower board, only for the upper one.Can anyone please help me?Thank you.omega12

author: camellos
author_rank: Newbie
timestamp: August 11, 2025, 02:30:59 am
content: I’ve seen that happen when the breaker is right at its limit, even if the load looks light on paper. Sometimes it’s not about total wattage but about one circuit having a weak spot — a loose connection, corroded contact, or even a cable starting to heat up.When I’m troubleshooting these, I usually scan the panel and wiring with a thermal camera. It’s faster than poking around with a meter, and you can spot a hot breaker or cable in seconds. Last time I did this, the breaker was hitting 60°C under what looked like a normal load — swapped it out, problem gone.

author: omega12
author_rank: Contributor
timestamp: August 11, 2025, 07:21:37 pm
content: Hi camellos,I have now disconnected the connection between the lower and upper boards, and the device starts up without any problems.So the fault lies with the upper board, which must be the Fractal N board, because the reference board is located at the bottom. The fault could also be with the connection cable.When I have more time, I will carry out more tests, but at least now I know more precisely where the fault lies.Thanks, omega12

author: omega12
author_rank: Contributor
timestamp: August 15, 2025, 10:00:21 pm
content: SOLVED!C19 and C21 on the A3 Fractal-N board were faulty.The HP8713B is running again and will make me happy till the next repair.I will reprogram it to an 8714B tomorrow but only if i find the right command.omega12
HP 8713B does not start - Page 1
Forum section: electronics / repair

author: omega12
author_rank: Contributor
timestamp: June 10, 2025, 07:59:30 pm
content: After 5 years of non-use, the HP 8713B does not start and after switching on only the display and the LED on the CPU board flicker. In stand-by mode, the green and red LEDs light up, which is normal.When I remove the A3 board, the analyzer starts and error messages are displayed on the monitor.All 4 LEDs on the power supply are green if the A3 board is not in the VNA.I tested the A3 board in another VNA with the same problems/error.Has anyone experienced this?I have checked the electrolytic capacitors but all are ok.Does anyone have an idea what it could be?Thank you,

author: jwet
author_rank: Frequent Contributor
timestamp: June 11, 2025, 05:36:50 pm
content: On similar vintage HP equipment- check internal battery. NiCd's self discharge will flatten the backup battery. Its charged by Vcc when on, so often just leaving equipment on overnight will fix it. Turn down display intensity so you don't burn CRT etc. My 4195 would get cranky if I hadn't powered it up in a few months. (loneliness?). I would then look a the supervisor startup stuff. HP used TL770x parts for this usually.Good luck.

author: omega12
author_rank: Contributor
timestamp: June 21, 2025, 06:44:33 pm
content: Hello jwet,it´s not the battery, another 8713B also didn´t start with my defective board and my unit starts with a good board.I Have service manual for the little board on top but not for the board under it.I measure 7,5 Ohm on a trace and the tantals don´t load here and after i soldered NE 5532P out the short on the legs of the NE is still there, but without service manual, no chance to follow the trace.It must be something that gets older but i checked all Tantals and elko´s with ESR-Meter and all are ok.
HP 8714C RF network analyzer: No output - Page 1
Forum section: electronics / repair

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 30, 2025, 08:45:24 pm
content: Hello forum!This is kind of a continuation of another thread where I had an issue with the device freezing shortly after bootup, it turned out to be a improperly seated board interconnect.The current problem I am fighting is a nonexistent RF output, listed below is what I have checked so far:On A3 FRAC-N/REF module:- power supplies (good)- 100kHz test point (good)- 10MHz output (good)- FN output (varies with device setting properly)on A4 Source module:- most power supplies, some have test points some don't (appear good)- no signal on either REC-LO output or SOURCE outputI do not have the knowledge or experience to troubleshoot this RF circuit chain in my own, compounded by the fact that the service manual available from Agilent(now Keysight) is missing the block diagrams in the troubleshooting section. If anybody has a copy of this manual with those figures that would be very helpful! In the field troubleshooting kit HP included a backplane extender card so that you can access test points while everything is powered on, without it I have to solder wires to points in order to measure them.Based on my testing and the troubleshooting procedure, module A3 seems to work fine, but A4 will not generate a signal. Nothing looks obviously broken or gets hot. There are test points everywhere but no info on what is on them.
HP 8720A VNA Calibration Issue - Page 1
Forum section: electronics / repair

author: neuschs
author_rank: Contributor
timestamp: January 15, 2024, 06:40:52 am
content: Hi all,I purchased a HP 8720A for a good price because while testing it on site the RIFA caps blew.Shortly after repairing that - still waiting for a good measured calibration kit - I wanted to do some simple measurements. I used Rosenberger open, short and a mini circuits load. Everything works. I am happy. some reference attenuators look pretty good in respect to magnitude. (All polar/smith/phase plots had issues as expected due to wrong calibration standard models.)But from now and then - and only on S11 not on S22 calibration - the VNA decides to have 40dB of error after applying the calibration measurement corrections.Concrete step-by-step:0. Reflected Magnitude (uncal) looks as expected with a lot of magnitude errors1. Enter Calibration Menu2. Choose S11 Port Cal3. Measure Open, Short, Load4. Press Calibration Done5. 8720A "Calculating calibration coefficients ..."6. Reflected Power is a straight line (with an open or short connected) as expected reading 0dbSome times I redo the steps above and at No 6. I start reading - 40dB and worse.Do you think that could come from a degrading memory chip which some times work and sometimes not ?In case someone has any ideas on what to try or how to narrow down the issue, please respond !Kind regardsSebastian

author: TheSteve
author_rank: Unknown
timestamp: January 15, 2024, 04:23:41 pm
content: Cal kit making poor contact during calibration?

author: neuschs
author_rank: Contributor
timestamp: January 15, 2024, 08:41:07 pm
content: Hmm... I don't have connector gauges, but I will try to make microscope shots of the connectors and have a look.Edit: But the realtime measurement view looks fine while doing the calibration, so full reflection for short/open and high return loss for load calibration.

author: neuschs
author_rank: Contributor
timestamp: February 01, 2024, 08:06:21 am
content: I exchanged some adapters in between and actually yes one of them seems to be just faulty. Even thought I can not measure any difference between this one or another one.
HP 8753A Repair  - Page 1
Forum section: electronics / repair

author: Timbo2020
author_rank: Newbie
timestamp: May 13, 2020, 08:33:05 pm
content: Hi all,Just joined this forum hoping for some help repairing my HP 8753A VNA.Bought recently at an equipment auction, last calibration says 2002 so I assume it failed before it's 2003 Cal.Seals were unbroken so it never got diagnosed and sat unloved for 17 years.Fan was clogged and seized with dust, now replaced and all cleaned out with compressed air.Power on now shows what I assume is a checksum error (although it's a bit out of focus), I guess the EEPROMs have forgotten what they were told in 1986.Is there an online depository of the software images so I might prog some new EEPROM's for it?Or any leads as to how to fix it?Thanks,Tim.

author: KE5FX
author_rank: Super Contributor
timestamp: May 13, 2020, 08:54:53 pm
content: Hmm, weird. The 8753A firmware should be up onko4bb.combut he's only showing the 8753C files, which aren't the same. I'll re-upload it there, and also attach it here.

author: Timbo2020
author_rank: Newbie
timestamp: May 13, 2020, 09:11:57 pm
content: Wow, that's awesome support :-)Many thanks.I'll get it loaded up and see what happens.I expect to be back on here in a week or so with the next problem..Tim.

author: energy_hunter
author_rank: Contributor
timestamp: May 14, 2020, 01:50:12 am
content: I fixed my HP8753D by replacing the EEPROMs found on ebay and from help from this forum. After replacing the EEPROMs on my HP8753D I then had to change a capacitor on the power supply. It was a bizarre problem but after powering on the VNA it would work once but then the display would be blank after a 2nd start. There seems to have been a power down problem/error catching routine that required a faster power down since the new capacitor was smaller than the previous one. This was hidden in the Firmware Upgrade instruction for the machine but I eventually found it and fixed my machine. Anyway, pls post your findings and hopefully we can help you out.

author: Timbo2020
author_rank: Newbie
timestamp: May 18, 2020, 12:05:17 pm
content: OK so I replaced the EEPROMS, programmed with known good firmware v1.0Whilst waiting for the chips, I realigned the HP1349A display with it's internal testcard. It's working great now, bright and focussed.I guess one good thing about a 35 year old machine that's been presumed dead on a shelf for 18 years, is that the display is only 17 years old :-)When I power on, with the new firmware, I get the same, one-line message as before.E S@M G@IL!1=PQPQPQPQPQPQPQPG>mI had guessed this was a checksum error message, thrown up by the boot loader?, but now it's focussed and readable, the message itself seems corrupted?Pressing "Preset", I get a small "HP" logo, then the one line message again.So the CPU appears to be alive and trying to run something...
HP 8753A S21 Noise from 300 KHZ to 1.1 GHZ - Page 1
Forum section: electronics / repair

author: outlawpsd
author_rank: Contributor
timestamp: August 25, 2022, 11:56:45 am
content: I was playing around with my 8753A which also has the 85046A test set and went to measure the transmission loss for a cable. I switched it to S21 and noticed that from 300 KHZ to around 1.1 or 1.2 GHZ the Log Mag plot was very noise, but pretty much flat after 1.1 GHZ. This is a new problem that just showed up and I ran some self test. Test 17 ADC Linearity failed. I have not torn into it yet but wonder if the teo problems are related? Just dont want to go down the wrong rabbit hole. If anyone has any suggestions on where to start please let me know. As far as I can tell S 11 measurements are fine and so are SWR.

author: outlawpsd
author_rank: Contributor
timestamp: August 26, 2022, 11:54:31 pm
content: Ran the Receiver Noise Level test from the onsite service manual. A came out fine at 15uU but B came in at 502uU @ 3kHz. I reran it at 10Hz per the manual and A again came out fine. B was at 500uU for 1/3 of the test and then dropped down to 15uU for the last 2/3's. Im guessing someone put too much power into it and it's now deaf in the lower range? Any idea's where to focus in on?
HP 8753E - not working - Page 1
Forum section: electronics / repair

author: piotekp90
author_rank: Contributor
timestamp: October 21, 2018, 08:54:49 pm
content: I have acquired non starting HP 8753E with good visual condition. After turn on the power supply, fan start, LEDs on post power supply board are on, on front panel some LEDs are on. The display is blank and only reaction is when I press the green "Preset" button the LEDs on front panel are off and when I released the button they are on again. I have checked the power supplies voltages on post power regulator and they are ok. Do you have any idea what is wrong? Does anybody have the dump of firmware for this analyzer.

author: KE5FX
author_rank: Super Contributor
timestamp: October 21, 2018, 08:57:44 pm
content: Quote from: piotekp90 on October 21, 2018, 08:54:49 pmMight just be a display problem. Is there a VGA output or other alternative video output you can try?If the EPROMs have been dumped, they may be up on ko4bb.com (check the 'Manuals' section).

author: piotekp90
author_rank: Contributor
timestamp: October 21, 2018, 09:35:01 pm
content: I connected the external display to VGA output but there is nothing . I have checked ko4bb and xdevs.com but I not found the dump.

author: TheSteve
author_rank: Unknown
timestamp: October 22, 2018, 12:31:14 am
content: Looks pretty dirty inside. I'd consider pulling the cards and cleaning each of them. At the same time look for any signs of bad capacitors, burnt parts etc. No need to mess with the actual RF parts yet. Practice ESD safe handling/cleaning techniques of course.

author: Larry_Bridge
author_rank: Newbie
timestamp: December 23, 2022, 04:32:15 pm
content: Hey BabyI have an 8753E with the same problem.Were you able to repair your 8753E?Please help me to repair my device.Thank you

author: Stray Electron
author_rank: Super Contributor
timestamp: December 23, 2022, 08:22:47 pm
content: Quote from: TheSteve on October 22, 2018, 12:31:14 amI would start by pulling all of the circuit cards and cleaning their edge connectors and their sockets and then reseating them and seeing that helps. AFTER doing that, pull the cards and clean and reseat all of the socketed ICs. While you have the cards out, LOOK at the capacitors but don't get ahead of yourself and start replacing any of them unless they are VERY obviously bad. Take one step at a time or else, when something fails, you'll have no idea what you did that caused it."Practice ESD safe handling/cleaning techniques" <<< Pay heed!Get a manual and be sure that all of the cabling is plugged into the right connector. Some of these have many cables and it's easy for someone to plug one into the wrong connector. Hopefully no one has been inside of this one before. But if the seals are broken then there is no telling what kind of simple (or not so simple!) screwup that they may have made.Probably THE first repair that I would make would be to replace the RIFA caps.
HP 8753ES Phase Lock & Source Issues - Page 1
Forum section: electronics / repair

author: cyma
author_rank: Newbie
timestamp: September 26, 2022, 12:19:39 pm
content: I recently purchased an HP 8753ES network analyzer. What I failed to realize is that the seller had combined 3-4 bad units into a single one and given all of the problems to me. I can deal with some of these (bad port coupler, bad switch) but I'm struggling on two of them. One is a sampler (A6) which nominally works but is 20 dB down. The other is the source which fails to allow the machine to do a phase lock (A3).I'm pretty sure that some part of the source is bad, in part because the person who put this machine together kindly labeled all of the failed components.Symptoms:1) The S11 is erratic below 1.2 GHz and between 2.7 and 3 GHz. Otherwise it tends to be reasonably stable(ish).2) When I replace the phase lock board (A11) from another working unit, I see the same results, but the erratic behavior from 2.7-3 GHz disappears.3) When I replace the source (A3) with a source from a 3 GHz unit, it creates other problems, but the erratic behavior from 0-3 GHz disappears.I get a variety of error messages at various times as shown below:I have taken the cover off of the 08763-60146 and checked that the connections between the various boards work. They seem to all be okay. I am really at a loss as to how I should troubleshoot this. It seems apparent that something is wrong with the source (A3) but that it may not be completely dead as we are getting (at least nominally) return loss measurements at most of the frequencies. Looking for suggestions of what I should try or how I can better diagnose this issue.I have looked into a new source, but these things run 3.5K and that's not quite what I had in mind.By the way, the port coupler was not only blown, the connection going into the device was completely melted and shorted inside of the tube. I have never seen anything like this. There must have been some serious power going into this device.
HP 8757D firmware - Page 1
Forum section: electronics / repair

author: ffranzini
author_rank: Contributor
timestamp: May 09, 2020, 04:45:06 pm
content: This is my first post, it is not a good start for me but i really need help!!!I just got a fault on one of the eprom (U7) of my HP 8757D , is completely unreadable... , the other one (U27) is fineI tried to search but i didn't find anything on the net, someone here have the dump of the EPROMS of this analyzer?My release is 6.2 but also version 6.1 should be ok.Thank youFrancesco

author: ffranzini
author_rank: Contributor
timestamp: June 26, 2020, 07:48:01 pm
content: For anyone interested to HP 8757D Firmware version 6.2I got the complete firmware from a very kind Japanese person, my 8757D is back to lifeand to make the firmware available to everyone interested i already uploaded it on KO4BB site, right now is on the upload queue and i suppose will be available to download in few days.Big thanks to who addressed me to the right personBest RegardsFrancesco

author: rplabs
author_rank: Contributor
timestamp: October 31, 2022, 06:04:30 pm
content: Hi,I used the version from the KO4BB site, probably the one uploaded by you on a 8757C but it seems to not pass the Self Tests.My unit came with 3.2 and I wanted to upgrade it to D model and 6.2 version.Are you sure the files are OK? Or do you have other version to test it on my C model?I programed the EPROMs with a TL866 programmer and verification was OK. Your files were in Intel HEX format and the TL866 software seems to detect it correctly.
HP 8903 won't complete power-on test - Page 1
Forum section: electronics / repair

author: ianbatty311
author_rank: Newbie
timestamp: May 26, 2022, 03:48:10 am
content: Hi, folks,A friend of mine has an HP 8903 with a missing CPU board which he has just replaced.At power-on, all the front panel LED segments light up.The four status LEDs on the CPU board flash, although Charlie reckons that one goes off and stays off.The instrument does not appear to become active.I think that(i) the various LEDs lighting shows that the microprocessor is beginning the Power On Self Test (POST), but(ii) the micro is not completing the POST.If this was a PC desktop, I'd expect to get a beep pattern when the POST halted as an indication of what was wrong.so....1. Am I on the right track with my idea of an incompleted POST?and2. If I'm right, is there any way of working out what is stopping the POST from completing? Is the non-lit LED on the CPU board a clue?Any hints gratefully accepted from Down Under.Ian.

author: strawberry
author_rank: Super Contributor
timestamp: May 26, 2022, 08:37:47 am
content: if CPU/ROM is ok it will talk to GPIB

author: Tony_G
author_rank: Super Contributor
timestamp: May 26, 2022, 06:42:50 pm
content: The flash pattern of the test LEDs on the controller board is important during startup. According to the service manual the order, for a successful startup, should be:Indeterminate for about 1/8 second( ),( ),( ),(1) for about 1 second.(8 ),(4),(2),(1) for about 2 seconds.(8 ),(4),(2),(1) with (1) blinking indefinitely until a key is pressed.The actual checks begin at #2 in the list above.During startup of the 8903B, all lights on the front of the panel should light up and stay that way till the unit is ready to run (this can take a surprisingly long time, not minutes long but more than long enough to seem like startup has hung).If you don't get to #4 then the test LEDs should provide information where the startup failed. Again, according to the service manual the order of these tests are:Front-Panel Annunciator CheckROM CheckRAM CheckInstrument Bus Parity CheckKeyboard CheckGrab the service manual and take a look at sections 8-27 & 8-28, from there you should look at the troubleshooting section in BD1 and follow up with the appropriate service sheets.TonyG

author: Runco990
author_rank: Frequent Contributor
timestamp: May 28, 2022, 01:32:26 am
content: Did you check the power supplies for correct voltages and especially ripple? The unit can hang if it's excessive. I had to change the main filter caps in mine. One was going bad, so I did the lot.Unit then booted and works to spec.ALWAYS check power first!
HP 8903A - Clean up and moving the BNC jacks to the front - Page 1
Forum section: electronics / repair

author: gdnichols31
author_rank: Regular Contributor
timestamp: November 22, 2020, 12:55:41 am
content: I started taking it apart to clean it.First PicThe over all shot so I can remember how to put it back together.Second PicAll the cards out, stacked in the order they came out.Third PicEverything (almost everything anyway) disassembled and clean!I was going to stop cleaning here and start putting it back together, but I thought It would be a good time to move the BNC connectors to the front panel. I was thinking it wouldn't take much more time.The only problem was the input and output coaxes were run behind the plotter and monitor BNC connector board. The only way to to get the cables out was to remove the motherboard from the chasis. So much for not taking too much time! I didn't get a pic of the cables running behind the connector board, sorry.
HP 8904A - Front Panel Replacement LEDs? - Page 1
Forum section: electronics / repair

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: May 17, 2024, 02:50:46 pm
content: Anyone know where I can find replacements for the LEDs on the front panel of the 8904A?Thanks!- Wil

author: rfengg
author_rank: Regular Contributor
timestamp: May 17, 2024, 08:30:25 pm
content: Aren't these standard 5mm RED and Yellow LED's?a)https://www.mouser.com/ProductDetail/Kingbright/WP56BID?qs=58z0TXQGVSSigALogKJCBg%3D%3Dor evenb)https://a.co/d/clpXEMH

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: May 17, 2024, 08:38:31 pm
content: Quote from: rfengg on May 17, 2024, 08:30:25 pmWell, they're not red... more of an orange-ish yellow. But I'm not sure if they're "standard"... gonna have to pull it apart and see I guess.And they're 3mm at most... nowhere near 5mm.- Wil

author: rfengg
author_rank: Regular Contributor
timestamp: May 17, 2024, 08:40:13 pm
content: Looked at some pics online , and they do look a bit orangy in some pics and red in others.....but anyways looks more like red.BTW, if you bias a red led too high, they do have an orange tinge......

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: May 17, 2024, 08:42:49 pm
content: Nope.

author: rfengg
author_rank: Regular Contributor
timestamp: May 17, 2024, 08:50:50 pm
content: Yes, your pic shows them orangish indeed.....here's one from another site.....anyways, are you bothered too much about the color?Here's one at Mouser which has a red lens but has a orange-red emission.https://www.mouser.com/datasheet/2/776/BL_BJE5V4V_AT-3074580.pdf

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: May 17, 2024, 09:01:27 pm
content: Quote from: rfengg on May 17, 2024, 08:50:50 pmNah, I don't care about the color... one of them is smashed and I just want it to work. It would be nice if all four were the same... just because I'm OCD. This weekend, I'm going to pull the cover off and measure one of them more accurately. Thanks for the links!- Wil

author: Lstkartagi
author_rank: Contributor
timestamp: May 17, 2024, 09:29:09 pm
content: The 8904A service manual including parts and schematics is online:https://www.keysight.com/us/en/assets/9018-40471/reference-guides/9018-40471.pdfhmm, but I don't see the LEDs at first glance.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: May 17, 2024, 11:24:25 pm
content: Yes, I looked in the service manual first and didn’t find anything.- Wil

author: xrunner
author_rank: Super Contributor
timestamp: May 17, 2024, 11:35:24 pm
content: Quote from: Wil_Bloodworth on May 17, 2024, 02:50:46 pmI have one of those units. They are just 3mm yellow LEDs nothing special. Available pretty much anywhere LEDs are sold.

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: May 18, 2024, 03:26:09 am
content: Sweet! Thank you!- Wil

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2024, 04:16:32 am
content: i have that too, i think they look a little smokey or something. dirty yellow
HP 8920A NewScope CRT to LCD retrofit display - Page 1
Forum section: electronics / repair

author: kj7e
author_rank: Frequent Contributor
timestamp: December 12, 2023, 03:19:53 am
content: I have been eyeing the NewScope LCD retrofit kit for my HP 8920A for a few years. Finally pulled the trigger, it was ordered Thursday and arrived Monday. The instructions were spot on and the results are fantastic. Great contrast and brightness, very crisp and now dual tone, white and green display. I think the "one hour" time estimate is a bit optimistic, took me about 2 hours total.http://www.simmconnlabs.com/1401/10001.html

author: TheSteve
author_rank: Unknown
timestamp: December 12, 2023, 04:28:53 pm
content: That certainly does look nice. I'd so like to do it but the CRT in my 8920B is still like new.

author: kj7e
author_rank: Frequent Contributor
timestamp: December 12, 2023, 11:28:36 pm
content: Yeah, I went back and forth because my CRT was in decent condition, reasonably bright with minimal burn in. Glad I did the LCD update, way brighter with a clean and crisp display and the two color display is really nice. Numeric readings and traces are in white now, here is a better example.

author: TheSteve
author_rank: Unknown
timestamp: December 13, 2023, 09:25:33 pm
content: Maybe I'm just nostalgic as I fell in love with the 8920 in college. Everything else in my lab is LCD(or VFD). I converted several VNA's to LCD but the green CRT in the 8920 seems a little special. Of course if it was to die, dim or burn-in I'd replace it pretty quick with the LCD

author: W3KW
author_rank: Contributor
timestamp: October 01, 2025, 03:07:35 am
content: I'm starting my LCD display swap. My CRT looks brand new, but the new-scope display is just too nice to pass up. Talk about surgery! Wow. It's like a chassis off restoration. It's very intimidating and intrusive. The rigid signal "cables" make me very nervous. I'm afraid of damaging one in the process and being out whatever I paid for this thing. It was not cheap but looks fresh off the HP line! Just gorgeous.The foam insulation on my speaker mount failed and the speaker almost fell out when I took the case off. Be careful there. I resecured mine using four dabs of silicone glue. It's easily reversed if the plates need to be separated at a later time.Once in the machine, I discovered I have the version with two batteries. Off to Digikey for another. The part number is P270-ND. It's a BR-2/3AE2SP 3V 2/3A Lithium Battery.The manuals are downloadable for free at the Keysight website and are like-new digital copies. Very nice!

author: watchmaker
author_rank: Unknown
timestamp: October 01, 2025, 10:41:12 am
content: This was my "Red Green Show Possum Lodge" solution, although two sided tape instead of duct tape. I could not bring myself to tear the thing open. Just turned the CRT down all the way.
HP 8920A TLC (proactive PS recap and more) - Page 1
Forum section: electronics / repair

author: kj7e
author_rank: Frequent Contributor
timestamp: January 02, 2024, 02:47:36 pm
content: After replacing the CRT with the NewScope-0Jr LCD (https://www.eevblog.com/forum/repair/hp-8920a-newscope-crt-to-lcd-retrofit-display/msg5217075/#msg5217075), I was motivated to freshen up the old 8920A. Recapped the power supply, changed out the memory card battery and replaced the original OCXO for one with much lest aging drift.I found some new old stock OCXO's as used in the optional reference board on eBay, see here:https://www.eevblog.com/forum/repair/ocxo-pin-out-ofc-1813-1106-aka-corning-mc857x4-004w-used-in-hp8920ab/After letting them cook on the bench for a few weeks watching them age, I had one clear winner. The warmup time was faster, less overshoot, faster settling and about 10% the aging drift as the others. So I swapped this OCXO in.The memory card battery is not crucial, if it dies you wont loose you cal data, just saved automated test programs and setup presets. I took this opportunity to replace the memory card battery anyways, it will be good for another 10 years+The weak link in these units is the power supply, which are impossible to find. So I thought it better to recap it now before I ended up with an issue causing a more complicated repair. The hardest part was lifting the PCB off the plastic pins on the aluminum frame. There is a tab you press in on each pin while lifting the PCB up slightly, but have to do them all at the same time, just a little at a time. I've included a cap BOM PDF attached here. The power button rod can be very fragile and again unobtainable so take care here and follow these instructions;Use the following sequence to remove the Power Supply:1.Remove the Input assembly (see figure 8, "A23 RF Input Assembly," on page 77).2.Pull the POWER switch shaft forward from the power supply, then pull it out back toward the rear of the Test Set.3.Remove the screws and molex connector.4.Slide the power supply out from the bottom of the Test Set.I found using a long thin blade screwdriver to gently pry the power button shaft forward off the switch while pulling the shaft forward made removal easy. Then slide the shaft back into the supply to gain room to remove the shaft up and away from the front panel.So now with the new LCD display, Power Supply caps, Memory battery and a more stable OCXO, its good to go for another 20 years.
HP 89410A (89441A) is stuck during bootup - Page 1
Forum section: electronics / repair

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: August 27, 2019, 06:35:01 pm
content: My regularly used HP 89411A DSA (rebadged 89410A) refused to start up today.It is stuck on the bootup screen with all keyboard indicator lights off and no response to keypresses. HP-IB connection is dead too.Restarting with "Return" pressed does not seem to make any difference.Last time it powered up and worked just a few days ago fine.Any idea what the next startup step would have been for a happy unit? Anybody had a similar issue?CheersLeo

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: August 28, 2019, 01:10:55 pm
content: Replaced coin cell battery and got a bit further. It locks up straight after bootup - seemingly with a critical MCU exception.PSU voltages are fine. All PCBs were reseated. Firmware re-installed too.Any suggestions?Leo

author: Tomorokoshi
author_rank: Super Contributor
timestamp: August 29, 2019, 03:24:11 am
content: I don't have one of those, but I did research them once.Do you have the 89410-90103 Service Guide:https://www.keysight.com/en/pd-1000002367%3Aepsg%3Apro-pn-89410A/vector-signal-analyzer-with-w-cdma-capability-dc-to-10-mhz?pm=PL&nid=-32439.536881642&cc=US&lc=engIt looks like that error is referenced on page 1-8, with debugging information starting on page 1-10.

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: August 29, 2019, 07:57:19 am
content: I seem to have revived it by erasing its NVRAM.Hold [ . ] and [ 0 ] pressed while simultaneously cycling the power. It's not in the service manual so was a pretty lucky guess.Leo

author: amiq
author_rank: Regular Contributor
timestamp: September 04, 2019, 12:24:30 am
content: Do you have copies of the firware prior to 9.05?

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: September 04, 2019, 07:41:06 am
content: Quote from: amiq on September 04, 2019, 12:24:30 amNo, are they any better than the latest?Leo

author: amiq
author_rank: Regular Contributor
timestamp: September 04, 2019, 09:31:39 pm
content: I doubt it. I'm just trying to bring to life an older unit that needs an older firmware release. I guess I'll have to get in touch with HP to see if they will dig out the appropriate version for me.
Hp 8970B Error 18 - Page 1
Forum section: electronics / repair

author: ffranzini
author_rank: Contributor
timestamp: November 22, 2021, 10:14:14 pm
content: After some debug I located the Fault on A11 second converter, 1.75 Ghz oscillator was not working, this cavity oscillator is very simple, voltage on the circuit were ok, unfortunately the original transistor HP 1GS1-4210 in TO72 Package seems to be totally unknown.I tried to find some candidates to replace the original transistorBF1552N5179BF1612SC787BFW30 (Vceo 10v only, on the circuits will be 15V !!)The only one working is the BFW30, initially i was concerned because on this application is way out of spec, but considering that is German made by Siemens should be ok forever.With direct replacement the frequency was completely out of spec, 150 Mhz lower, no way to adjust it because the oscillator was not working above 1680 Mhz.Looking on the small PCB of the oscillator i guessed that one big pad was the capacitor to roughly tune the frequency, I started to remove small part of the pad and i saw the frequency going up.Removing good part of the pad the oscillator now is perfectly centered, I can fine tune it's frequency with the screw and error 18 is gone and everything is working !!!I think that the HP engineers were really smart, with a very simple solution it is very easy to compensate for different transistor characteristics, they also added few extra not connected pad, if you need more capacitance you have only to connect the right one to the main pad.You can see on the attachment oscillator PCB and my work made by handThank YouFrancesco
HP Agilent 1670XX Boot Fix - Page 1
Forum section: electronics / repair

author: calmissile
author_rank: Contributor
timestamp: November 11, 2017, 07:57:48 pm
content: Moderator, please move this to the appropriate thread if appropriate.I was unable to do an Ignite (fresh install) of the HP 16702A software. I was using Ver A..02.90.0For anyone that finds they cannot do anything and the analyzer seems to be all screwed up, give this a try.I don’t know all the details yet, but I do know what fixed the problem with the 16702A. Based on the results of all the experiments, I came to the following conclusions:1. The Ignite process appears to not change the configuration data that is stored on NOVRAM (EEPROM) in the analyzer.2. Apparently the NOVRAM got corrupted at some point and created all the problems that I experienced for several days.3. The analyzer would not see the external CD-Rom and prevented me from reading the CD-Rom and could not do an install (Ignite)4. When the CD-Rom was connected, it also prevented seeing the main Hard Drive.5. Best I remember, I had to disconnect the CD-Rom and then booted the CD-Rom with the ver 90 software.6. The install was all screwed up with all kinds of errors having to do with allocation of space on the hard drive. It always ended up crashing with errors I am not smart enough to understand.7. What I did was interrupting the boot process (CD-Rom disconnected), and used the Configuration Menu to make some changes. I suspect that the configuration changes were made to the NOVRAM on the LA.8. Here is a snippet of what I had to enter using the configuration menu. I found it on the internet with a search….Are your 16700's BIOS settings correct? Sometimes users will select "DEFault" BIOS settings in an attempt to fix a problem, however these settings are incorrect.To restore the proper BIOS settings after selecting DEFault settings, begin by interrupting the boot process (hit Esc repeatedly when powering up) and entering the COnfiguration menu (type "co"). The type the following commands:au bo on (turns Autoboot ON)lc 100/h (sets LAN Config to 100/Half_dx)pa pri sescsi.6.0 (sets primary boot path to SESCSI.6.0)pa alt sescsi.1.0 (sets alternate booth path to SESCSI.1.0)res (RESets or reboots the machine)If the hard drive is good and contains a working image, the analyzer should boot normally at this point. To restore the hard drive to its factory default state, see: My 16700-series logic analyzer has become unstable or erratic, delivers unexpected results, or is otherwise not working properly. What steps should I take to resolve this?9. Here is the link that saved my butt..http://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=376054&nid=-11143.0.00&id=376054

author: artag
author_rank: Super Contributor
timestamp: May 24, 2024, 05:38:20 pm
content: This link is dead. Does anyone know where a document describing the boot rom commands can be found, please ?

author: RomDump
author_rank: Regular Contributor
timestamp: May 24, 2024, 11:56:42 pm
content: Quote from: artag on May 24, 2024, 05:38:20 pmWhy Won't My 16700-Series Analyzer Boot Properly?
HP / Agilent 3312A 16V on power led - Page 1
Forum section: electronics / repair

author: TNTdesigner
author_rank: Newbie
timestamp: July 18, 2020, 01:18:47 pm
content: I When i turn my 3312A on the 17V and -17V are fine, but the generator did't start, after some probing around I fount I had 16.2V on the power on led. I suspect the 1820-0203 linear amplifier but I can't find any datasheet for it. Does anyone have a goed datasheet for this part or a newer replacement part number for this part ?

author: berik
author_rank: Newbie
timestamp: December 24, 2024, 02:44:47 pm
content: The 1820-0203 should be very similar (if not identical to) a LM301A.Why did you suspect the 1820-0203 op-amp if I may ask?

author: berik
author_rank: Newbie
timestamp: December 25, 2024, 12:21:28 pm
content: According toBench Briefs 4th Quarter 1987,the 1820-0203 can be replaced by a UA741HCdatasheet

author: wn1fju
author_rank: Frequent Contributor
timestamp: December 26, 2024, 05:48:22 pm
content: Doesn't make much sense to me. What do you mean, 16.2V on the power LED? That LED goes from ground, through the LED, through a 1K current limiting resistor and then to the -17V1 rail (via another 10 ohm resistor). When operating, one side of the LED should be 0V and the other side should be about -2V.When you said that the 17V and -17V voltages are correct, be aware that according to the schematic, there are multiple variants. For instance, there is a -17Vline, a line marked -17V1 and a line marked -17V2. The V1 and V2 lines come off of the main -17V through inductors. So you need to verify that the inductors are good and you have all the voltages marked on the schematics. Same thing for the +17 and its multiple copies. Only after this should you start to suspect faulty opamps.
HP / Agilent 34970A: Faint display solved. - Page 1
Forum section: electronics / repair

author: Sören_Marodören
author_rank: Contributor
timestamp: July 20, 2024, 07:13:21 pm
content: Some months ago, I purchased an Agilent 34970A Data Acquisition unit.(More about this unit can be read here:https://www.eevblog.com/forum/repair/hp-agilent-34970a-error-614-easy-fix-for-one-unit-at-least/)When I received the unit, I noticed that the display (Vacuum Fluorescent Display - VFD) was dim or faint. When taking the unit apart I could see that the VFD was replaced at least once. So, someone had tried to fix this problem, but with no success. (The instrument is manufactured at the beginning of 2009 and the new VFD is from 2017.)Luckily, I had another 34970A that I could switch front panel with. Interestingly, the front panel from the working 34970A also got a faint when connecting to this unit.After some measurement it turned out that the filament voltage was faulty and not at the level it shall be. Firstly, the controlling Op-Amp (LM393D) was replaced but with no improvements. Secondly the dual MOSFET, MMDF1NO5E was replaced to an IRF7303. (See attached picture from schematics.)This last change made the VFD bright and clear.This problem was also an easy fix.I don’t know if there are other 34970A with faint display that can be fixed in this way. But it is always worth a try.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 21, 2024, 01:03:30 am
content: you may have got a more recent vfd ....since the problems was not vfd wear ...
HP Agilent 6050A Electronic Load Mainframe repair - Page 1
Forum section: electronics / repair

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 11, 2021, 08:30:45 am
content: Hi,I just bought an HP 6050A Electronic Load Mainframe that was described as:For parts or not working“Untested, No Warranty or Returns, Item As Is; Issue(s): Unit does not power on.”You can look at the pictures on eBay. eBay item number:274833496729Do you want to guess why the unit won't power up?It will be a few weeks before I receive the unit.Regards,Jay_Diddy_B

author: Jwalling
author_rank: Unknown
timestamp: September 11, 2021, 09:00:11 am
content: They were using 120VAC?

author: ddrl46
author_rank: Regular Contributor
timestamp: September 11, 2021, 10:03:44 am
content: Probably the top cover not being screwed on all the way causing the interlock to remain open.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 20, 2021, 11:06:02 pm
content: Quote from: Jwalling on September 11, 2021, 09:00:11 amYou are almost right. I am using 120VAC and the unit was configured for240VAC operation.I don't know about the interlock. I open the unit and I found one of the blades had come off a fan.When I turned on the unit I could hear the fans, I though that the LCD module was bad. I checked it before I found that it was configured for 240VAC.I will probably change both fans.Best regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 23, 2021, 12:33:51 am
content: Hi group,I changed both fans in the 6050A electronic load mainframe. The fan is described as rectangular/rounded 172mm x 150mm and 38mm thickness.I selected NMB part number 5915PC-12T-B30-S00 available from Digikey P13606-NDThe replacement fan is a perfect fit and works great.Regards,Jay_Diddy_B

author: Jwalling
author_rank: Unknown
timestamp: October 25, 2021, 09:48:38 pm
content: Need any loads for it?https://www.ebay.com/itm/154669190507?Great price... No affiliation.
HP / Agilent 8114A High Power Pulse Generator 100V/2A Service Manual? - Page 1
Forum section: electronics / repair

author: Mike112
author_rank: Newbie
timestamp: February 05, 2020, 04:04:12 am
content: Hey guys, anyone know if there is a service manual for the 811xx family of pulse generators out there? I have a 8114a that now has timing board issues, ive spent hours on it and am now just throwing darts. Thanks

author: ttbelectronics
author_rank: Contributor
timestamp: September 22, 2020, 09:52:57 pm
content: I have a unit that someone removed many parts from the power supply, I got the power supply running but one section the voltages are only half of what suppose be.Any members have the part number for VR501 and VR509?Thanks.