Minor Repair HP3458A - Page 1
Forum section: electronics / repair

author: VK5RC
author_rank: Unknown
timestamp: November 21, 2015, 05:27:52 am
content: Hello, after having watched/read with great interest TiN's excellent repair of a "value" HP3458A, I bought a 3458 that needed just 'a bit' of love. I am not as game nor as experienced as TiN.The NVRAM in the 3458 (a Dallas DS1220 and DS1235 - now Maxim DS1220 and DS1230) has a 'built in' Lithium battery that has a service life of about 10 years, mine was 25yr old then gave a RAM fault warning (see below); which helped lower the price a little. It is quite an old machine with an early software version.It did come with a Calibration Sticker from 2009 and had a seal which came off shortly!

author: VK5RC
author_rank: Unknown
timestamp: November 21, 2015, 05:33:56 am
content: A day or two after receipt it also gave a fail of ACV calibration, my heart sank a little, but inside of the unit was covered with a fine black dust, which could well have caused some errors. So with not much to lose I gave the machine a modest clean using anti-static techniques , cotton-buds (Q tips) Kimtech wipes and IPA. A few hours later this fault was goneLots of Q tips in the bin!

author: TheSteve
author_rank: Unknown
timestamp: November 21, 2015, 05:46:02 am
content: Fingers crossed it is 100% now. I'd love one of these units but they scare the crap out of me, way too fussy.

author: VK5RC
author_rank: Unknown
timestamp: November 21, 2015, 06:15:56 am
content: I was going to have to ( as Jeremy Clarkson would say) 'take a brave pill' at some stage to replace the NVRAM that has the calibration data, as it was also very old.Before I was going to do that I wanted to back up the data.There are several ways this can be done.1. Use a Cal Ram Dumper Program that I think was written by Poul-Henning Kamp and modified by Mark Sims (see volt- nuts) "HP3458.exe"https://www.febo.com/pipermail/volt-nuts/2014-August/003598.htmlIt is contained within the excellent KE5FX program suite2. TiN has written a program that works with 64 bit Vista Windows, and he also has programs for raspberry Pi / Python program, Linuxhttps://xdevs.com/article/hp3458a_gpib/#summary.I have almost every version of Windows but Vista 64 and my programming skills are pretty poor so this wasout for me.3. Take the NVRAM out and read it directly, TiN has done this using the good value and widely available TL866 programmer.I will do this later.I went for path 1. initially so if I mucked up I would have something to recover, but using GPIB on a 3458 is a bit tricky I believe as the protocol (488.2) came after the 3458.My interface was a Prologix GPIB USB interfacehttp://prologix.biz/gpib-usb-controller.htmlwhich I use to interface some of my other gear ( a bit of a HP fan).I ran into a few problems, the Prologix would only talk to the 3458 if the Prologix powered up disconnected from the 3458 then connected. See 1st photo.The program of Mark Sims was written for a National Instruments GPIB 232 interface and the command END ALWAYS needs to be sent to the 3458 before hp3458.exe is run otherwise you will get photo 2.The KE5FX program suite has a GPIB configuration Tool that needs to be in Controller Mode, the GPIB address set and has a command line that will run the HP Basic Commands e.g. ID? and END ALWAYS.

author: TiN
author_rank: Super Contributor
timestamp: November 21, 2015, 06:28:17 am
content: Quote from: TheSteve on November 21, 2015, 05:46:02 amWorst part is that you can't give up on them, after spending all those money's and time on it too!VK5RCGet RPI, it's way more easier to muck with GPIB/Python then crappy windows environment (I'm win user big time, but there are things which *nix just does better).I also would love to have you jump in for some short noise testing, so we can compare meter's across.

author: VK5RC
author_rank: Unknown
timestamp: November 21, 2015, 06:31:14 am
content: @TheSteve; I did need to take quite few 'brave pills' as I read they can be very temperamental, I think a bit of dirt and a bit of a shake (transport) got it out of AC cal.@TiN I am not a good programmer! I get that feeling re Raps Pi but it will take me some time to catch up. I would love to join in in noise testing but I am at the bottom of a steep learning hill. Please be patient.Persistance paid off with a DOS / Command screen flying by of the cal data coming outAnd even nicer a "Check Sum OK" at the end. See photo 1.I also took a look at some 25yr old caps and the larger electrolytic was just a bit "bulgy" see photo 2 , so an order from Mouser, for some caps, some MilMax turned IC sockets (to resocket the NVRAM) , some Maxim (ex Dallas) DS1230 and DS1220 NVRAM. Of note that the new 1230s have an internal 'seal' that only connects the lithium back up battery after first power up, so you don'y have to be obsessed about production date. I am still awaiting the 1220.

author: VK5RC
author_rank: Unknown
timestamp: November 21, 2015, 06:50:46 am
content: The old electrolytic came out and still tested OK see photo1 as did its brothers photo2 but as I was mucking around inside i was going to do it al at once.Edit ; Add the photos D'Oh

author: VK5RC
author_rank: Unknown
timestamp: November 21, 2015, 07:18:21 am
content: More Brave Pills , pulled out the NVRAM , MillMax sockets and new NVRAM in , cycle power (switches on RAM) and all is working!Awaiting DS1220!Need to start learning RASP Pi / Python

author: TiN
author_rank: Super Contributor
timestamp: November 21, 2015, 07:37:41 am
content: I don't think lot of brave pills needed for digital side repairs thoughAs of being good programmer, I had a good laugh on that phrase. I'm not good, most of coding things I just googled upIt's just looking that hard, but actually after you tried, it just works. Well, sorta, just keep trying till it does

author: VK5RC
author_rank: Unknown
timestamp: November 21, 2015, 07:46:47 am
content: @TiN I needed brave pills to take the cover off! HiHiStill some more to come re the 3458 but I wish to say a big thanks toTiN; great effort on getting your 3458 to work and for sharing your efforts via xdevs.com as well as EEVblog forumDave; great blog and forum, well moderated. DrFrank et other volt nuts, thanks.Poul-Henning Kamp and Mark Sims and KE5FX, a great resource.I think I need to quit my day job so I have more time!

author: TiN
author_rank: Super Contributor
timestamp: November 21, 2015, 08:10:21 am
content: QuoteBetter don't, you will need all that cash to buy more precision resistors, voltage references and ultra-low noise parts to test your 3458A

author: VK5RC
author_rank: Unknown
timestamp: December 12, 2015, 05:39:13 am
content: EVENTUALLY some DS1220 arrived to replace the 1990 original, finding DS1220Y proved to be very difficult and Maxim caution as the DS1220AD takes 150ms to get up and running after power on.Pulled the old DS1220Y-150 out and initially it was not being read by the TL866 Arrrrrrggghhhhh. Put in the good milled sockets.All else fails, sleep on it, and in the morning the programmer could read it, ? a Windows issue/ reboot helped.I had found as possible replacementsMaxim DS1220AD-150+maxim DS1220AD-150+INDST M48Z02-150P.Whiie the covers were off, I reprogrammed all three, all three work and the 3458A appears equally happy with all three. Cal count maintained.An old Schaffner IEC EMI filter due for replacement next.

author: VK5RC
author_rank: Unknown
timestamp: December 12, 2015, 05:44:36 am
content: PS after the failure to read the DS1220Y, a bit of Googling found that the Willem programmer can drop the voltage to Vcc a bit too much and a bit of bodge wiring can help, I was getting about 4.6V at Vcc with the TL866, (the 5V from the USB minus one transistor drop).http://www.ezoflash.com/willem_info/forum.php?show=topic&topic=1180128342

author: VK5RC
author_rank: Unknown
timestamp: December 19, 2015, 07:00:03 am
content: A bit of careful drilling had the old riveted in Schaffner EMI filter out, a bit of sticky tape around the place to catch swarf.I used one of Schaffner's newer higher filtering model, 6A should be adequate. From my reading it seems to be some older models with a paper filter cap that cause trouble,The old one had the earth lead soldered on for some reason I don't understand.All works OK now.

author: TiN
author_rank: Super Contributor
timestamp: December 19, 2015, 08:01:19 am
content: I had earth lead soldered on 3245A as well, but not on 3458A. I did same anyways. 3245A also have springy fingers on chassis frame sides, to have good contact with external aluminum covers. Perhaps 3245A more sensitive to external EMI/RFI, as it does not have guarded enclosure for its analog guts.

author: VK5RC
author_rank: Unknown
timestamp: December 19, 2015, 08:08:54 am
content: Interesting, mine looked original.I have a Rasp Pi, reading about getting it to talk to a USB-GPIB interface, not helped by the fact I know nothing about Linux and its structure and Python, oh well you have to learn sometime!

author: TiN
author_rank: Super Contributor
timestamp: December 19, 2015, 09:44:20 am
content: Google knows a lot about it, so should be not much problemsI just setup second Pi using latest image Jessie, worked okay following all steps inguide. Perhaps that would be useful for you.

author: VK5RC
author_rank: Unknown
timestamp: December 19, 2015, 10:21:37 am
content: Thanks TiN, that looks very helpful.My main electronics area, my "shack", has only one PC connected to the net, wirelessly, and is some distance from my internet modem, so I haven't connected my RPi to the net yet, I will have to bodge/make a small 5V PSU for the mini display I am using with it (about 15x10cm) to use it next to the wireless modem for the short term.In the longer term I think I will get a wireless switch for the shack.