HP 8714C RF Network Analyzer freezes shortly after bootup - Page 1
Forum section: electronics / repair

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: July 06, 2025, 07:21:49 pm
content: Hello forum peeps!A couple of weeks ago I picked up a HP 8714C network analyzer for a very decent price in the hopes of playing with it a bit and then flipping it for a small profit.I don't actually have the means to do a proper performance check on the unit, but up until today everything seemed to be working as it should. I was getting ready to test a couple of filters when the analyzer froze up on me.I had previously toyed around with it for quite a while without issue, now It wont go more than 30 seconds before becoming completely unresponsive to front panel input. I am trying to identify a pattern to the freezing, but the only observation I have so far is that it happens faster when you are messing around in the menus. I let it sit after bootup without touching it and it went several minutes, whereas when I try to access menus it freezes shortly after.Not knowing hardly anything about this device but having played around with a good number PCs my first instinct in a DRAM problem. The analyzer will pass all bootup self tests, I am not able to do any of the self tests in the service menu before it freezes.I am not sure what the best course of action would be from here, I think the DRAM is removable, I could try swapping it out.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: July 10, 2025, 12:31:55 am
content: I swapped the ram stick with another one that I had on hand, which happened to be the exact same part. No change to the behavior.As I suspected earlier I can let it sit on the bench after booting indefinitely and it will not freeze, only when I start messing with things will it freeze. To me this feels like the processor is unstable under load? I assume most of the heavy signal processing is done in an ASIC or DSP chip, rather than the CPU?I am not sure what to check next, unfortunately due to the design of the 8714C I cannot access the CPU board when it is installed and connected to the backplane, which will make troubleshooting very difficult.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: July 20, 2025, 08:39:59 pm
content: I checked the power supply voltages and did a visual inspection, nothing seemed wrong except for a couple of RIFA caps, the ones that like to blow. Interestingly the power supply is not original, it is an Agilent branded one from 2004, perhaps the power supplies had a high failure rate? a power supply from the 90s would kind of be in the "capacitor plague".There is a 3.0V lithium battery on the CPU board, it still measures 3 volts but I don't know how old it is. Since I intend to eventually sell this 8714 I would like to replace it, however I don't know what would happen if the battery is removed, would stored calibrations and settings be lost?

author: Tony_G
author_rank: Super Contributor
timestamp: July 21, 2025, 02:31:07 am
content: I have one of these on my shelf here (I now use an 8720C) but I've never had any problems with it - Looking forward to seeing what you find out on it just in case...Good luck,TonyG

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 13, 2025, 07:11:23 pm
content: It has been a bit, I have played with the 8714 on an off for the last couple of weeks, it has not frozen like it did before, perhaps there was a backplane connector not fully seated?I want to make sure that the unit has basic functionality, is there a good way to do this with simple equipment and parts? I have scopes, cables, and BNC fittings. I am a novice when it comes to RF, I have a fundamental understanding and I am learning.I found this device at a bargain and jumped at the opportunity, but to be honest I don't have the skills to properly use it or even a real practical use for it, so my intention is to ultimately sell it after having confirmed basic functions.Thanks in advance!

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: August 13, 2025, 09:47:29 pm
content: Do you have open short and load? First thing to do would be to let it do its own calibration. Then analyze some cables from the in to out then cables with open end and 50 ohm load.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 14, 2025, 07:47:39 pm
content: I let it do a cal with open short and 50 ohm load, it did not seem to encounter any errors.I dont know what to expect when testing cables but all I ever get is lots of noise on the screen, regardless power settings or connections to the ports. Sometimes changing the power level will shift the offset of the trace a little.

author: omega12
author_rank: Contributor
timestamp: August 15, 2025, 10:05:58 pm
content: Hi,"but all I ever get is lots of noise on the screen" - This is not good.You should have nothing on the screen without measuring cables connected.Can you post some pictures of the screen?omega12

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 15, 2025, 10:16:17 pm
content: I took two photos with a two foot cable between the input and output, one at 0dBm and one at 10dBm.

author: omega12
author_rank: Contributor
timestamp: August 17, 2025, 08:02:40 pm
content: Hello,When you connect the input and output with a cable, you should see a straight line.Remove the front panel and measure whether the 10 MHz is there and, if so, measure the other signals as well.I once had a defective output and had to replace U1.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 17, 2025, 10:09:47 pm
content: Thanks for the reply and advice omega12.Unfortunately this will have to wait a week or so, I am travelling. I will look forward to digging into it when I get back though!

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 24, 2025, 02:07:22 pm
content: I tested a couple of signals on the cables between modules. The frequency was set to CW mode at 10MHz.The 10MHz does not look good, but I am not sure. The signal marked FN has an odd ~4MHz modulation, not sure if this is normal either.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 25, 2025, 08:13:31 pm
content: I checked both U1 and Q1, they test fine out of circuit.There are loads of test points on the board, but you cannot access them with the card power up since it has to be inserted into the backplane. perhaps I can try running external wires to some of them.

author: omega12
author_rank: Contributor
timestamp: August 26, 2025, 10:19:39 am
content: Did you checked the output of Port 1?Set the output level to 0 dbm and look if you have the 0 dbm at port 1.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 26, 2025, 02:30:31 pm
content: What do you mean port 1? There is nothing labeled port 1.Module A3 has A3J1 and A3J3 on the front, or the front panel has a reflection/RF out port and a Transmission/RF in port.

author: TheSteve
author_rank: Unknown
timestamp: August 26, 2025, 03:15:48 pm
content: Quote from: Alex_Baker on August 26, 2025, 02:30:31 pmAs it isn't a full 2 port machine they don't label the ports 1 and 2. In this case he was asking if you see RF on the reflection/RF out port.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 26, 2025, 04:28:23 pm
content: In regards to output on the reflection/RF out port, there is no apparent RF signal detected by an oscilloscope. There are some periodic small pulses but otherwise just a bit of noise, regardless of power setting.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 27, 2025, 12:26:27 am
content: I traced out the 10MHz reference circuit and measured voltage test points. I remeasured the 10MHz output with a better setup, it is shown in the attached image, this looks much better.I don't believe there is a problem with the 10MHz reference in module A3.

author: omega12
author_rank: Contributor
timestamp: August 28, 2025, 09:14:42 am
content: Yes, 10 MHz is ok.If no RF output on the reflection/RF out port, than you should check this unit.On my unit U1 was faulty, so check the amplification chain till the output.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 28, 2025, 05:26:40 pm
content: U1 where? A3, A4, or A5Each module would have its own U1.

author: Alex_Baker
author_rank: Frequent Contributor
timestamp: August 29, 2025, 01:40:46 pm
content: Would it be beneficial to start a new topic to troubleshoot the no output issue? I don't want to spam the forum with topics but the title of this one is no longer applicable to the problem at hand.I suppose I could also change the title, but then the first few messages would not make sense to a new viewer.