HP Signature Sets - Page 1
Forum section: electronics / repair

author: wanderer404
author_rank: Newbie
timestamp: January 24, 2025, 06:54:55 am
content: Hi all,I’m repairing a HP 4726A LCZ meter. The digital troubleshooting section refers to reading HP Signature Sets using a HP 5004A. I’m assuming these are basically unobtainium. Is there a way of calculating the signature sets without one?Regards,Chris

author: Tony_G
author_rank: Super Contributor
timestamp: January 25, 2025, 06:20:06 pm
content: I think there is a Tektronix Logic Analyzer that can do the analysis - 308/380 something like that.I also seem to remember an HP Journal article that covers the "math" they used to create the signature. You could probably implement that as a plug-in for a Saleae or something similar.Finally, 5004 & 5005 are available on eBay but they are somewhat pricey (US$150 and up) - You might want to post over onhttps://test-equipment-for-sale-wanted-or-exchange.groups.io/g/mainto see if anyone has one they want to sell.TonyG

author: abeyer
author_rank: Frequent Contributor
timestamp: January 25, 2025, 06:28:59 pm
content: People have also recreateddevices to read them. (not necessarily much cheaper than ebaying the original ones, though)The bigger challenge might be finding the codes you expect, as I've heard say that some devices changed signatures even between different runs of the same device if there were minor design changes, so you needed to ensure you had the correct table of codes to match your specific devices, and not just a scan of someone else's off the internet.Quote from: Tony_G on January 25, 2025, 06:20:06 pmI think at least the high-level details were inthis one.

author: tggzzz
author_rank: Super Contributor
timestamp: January 25, 2025, 10:44:12 pm
content: Quote from: wanderer404 on January 24, 2025, 06:54:55 amCaveat: I last looked at signature analysers when they first came, i.e. ~45years ago. I recall all they could do is tell you whether the signals on a node werepreciselythe same as those in a known good "golden" device. If there was any deviation, they gave zero information about what might have caused it.Hence they are only useful to tell a repair technician which module to replace. I was never in that position, so I never had occasion to use a signature analyser. I doubt you are in the position of being able to replace a moduleIn any old instrument, the strategy is to carefully look at all components and switches, to see if there are any gross failures. If not, then check all the power supplies are correct, both voltage and ripple (electrolytic capacitors are a standard problem, and don't forget the RIFAs!). Beyond that, intuition and understanding the specific schematic and are useful

author: wn1fju
author_rank: Frequent Contributor
timestamp: January 25, 2025, 11:45:34 pm
content: I concur with the previous posts. There is a chance that the signatures published in whatever version of the service manual you have will not be correct. Although I try to download free manuals whenever I can, I also do occasionally purchase hardcopy manuals from various sources. Almost all of these have had change sheets which modified the signatures. These change sheets are hardly ever found in downloaded manuals.I actually have an HP signature analyzer which I have used from time to time. I don't think it had much use in finding a defective IC. It mostly just verified that the digital side of the equipment was working and I should focus my attention elsewhere.

author: tggzzz
author_rank: Super Contributor
timestamp: January 25, 2025, 11:57:27 pm
content: Quote from: wn1fju on January 25, 2025, 11:45:34 pmYes.Perhaps I should have worded my reply "tells a repair technician which modulenotto replace". But even that presumes that a failure in module X won't cause a changed signature in module Y.

author: MarkL
author_rank: Unknown
timestamp: January 26, 2025, 06:01:35 pm
content: Sigrok has a signature analysis protocol decoder:https://sigrok.org/wiki/Protocol_decoder:Signaturewhich is supported on tons of different hardware.I have an HP 5006A signature analyzer, and I share others' experiences here that it has never really helped me troubleshoot failing equipment down to component replacement. It can help sort out which sub-systems are working, but usually that's already self-evident.I've used it most often to check the validity of EPROMs on old equipment to look for bit rot, which I found in a couple of cases. You need to have the exact right revision of the service manual for your hardware and firmware.

author: wanderer404
author_rank: Newbie
timestamp: January 29, 2025, 12:06:33 am
content: Thanks all!I think my first step will be to see how validly the signatures read using SigRok and a Saleae clone. I'll keep an eye out on fleaBay to see if any dedicated readers come up with reasonable postage to Aus (which is usually more than you pay for the device).

author: RolandK
author_rank: Regular Contributor
timestamp: January 29, 2025, 07:37:00 pm
content: Good luck with the sigrock - just building it is a nightmare. But there seems to be a build script somewhere, which collects all dependencies.The newest version may be able to use the clock signal of the zerologic LA. Perhaps from others, too. If not - good luck. The sampling deeps must be able to capture the whole signature. If the LA does not sync with the clock signal you need at least 4x more sampling deepth.But: on the 4274a / 4275a the signatures is just a 16 bit width counter on 16 datalines. The whole signature is allways 2^16 cycles long. Every following bit has the half frequency and you can see any short. You can just use a scope or any parallel logic analyzer. Each bit has a clean square wave signal with half the frequency of the previous. If the ratio is any other, eg. 1:3 or asymetric you have a short between two bits.eg:010101010011001100001111just 2^16 bits long.

author: ZGoode
author_rank: Frequent Contributor
timestamp: January 29, 2025, 07:56:29 pm
content: Quote from: wanderer404 on January 24, 2025, 06:54:55 amWhat kind of symptoms are you seeing in your 4276A? I recently repaired a 4277A, which is nearly identical as far as I'm aware so I can try to help out. Terra Operative has also worked on the 427xA series of LCR/LCZ meters extensively.