Just bought HP 3456A, anything I should check? - Page 1
Forum section: electronics / testgear

author: BillWojo
author_rank: Regular Contributor
timestamp: September 07, 2014, 06:24:36 am
content: Just won a HP 3456A on Ebay for 76 bucks, should be here next week. Anything I need to check or be leery of? The SN is 2201A14265 so it's a later one. Showed it powered on and said buttons worked, for what ever that's worth. After reading up on them here it seems like a pretty rugged unit with a good reputation for retaining it's accuracy.I'm trying to figure out what the EXP under the last digit is for on the display. I believe it means exponent, maybe used for the math functions? This has way more features on it that I'll ever use but it's just to cool. I just hope it all works.I'll report back when it arrives.BillWojo

author: SArepairman
author_rank: Frequent Contributor
timestamp: September 07, 2014, 07:22:47 am
content: yea, if there is electrical line behind the wall your gonna cut open to fit it on your bench

author: calmtron
author_rank: Regular Contributor
timestamp: September 07, 2014, 08:49:06 am
content: SArepairman is correct, it's deeeepAlso, probably not relevant in this case, but there's a crystal that should be replaced for maximum performance if using a 60 Hz unit on 50 Hz mains and vice versa, seethis thread.

author: Wytnucls
author_rank: Super Contributor
timestamp: September 07, 2014, 10:36:07 am
content: EXP allows you to enter a number using exponential:https://drive.google.com/file/d/0B49s4UAFZUvVVmJNWVhYbHhONEk/edit?usp=sharing

author: saturation
author_rank: Super Contributor
timestamp: September 07, 2014, 01:04:14 pm
content: Welcome to the 3456a 'club'. I have 4.EXP is when the LED readout values as engineering exponent, such -3, -6, -9 for milli, micro and nano etc.,That's a good serial number and one of the more prolific for sale that I've found, the 2201A series.I would download and read the user/service manual back to back, both to operate the unit effectively and be familiar with its electronics.It has a linear PSU inside, and could benefit from a modified capacitor reforming procedure using an ammeter and a variac just to be safe, it could save you from having to replace any aged filter capacitors on the PSU. See voltage limit methods for the theory:http://www.nmr.mgh.harvard.edu/~reese/electrolytics/Warm it up for 60+min then do the self check routine.Enjoy.

author: BillWojo
author_rank: Regular Contributor
timestamp: September 07, 2014, 03:49:00 pm
content: Thanks everybody! Yea, it's big. Since I'm setting up a little lab in the corner of my basement I'll just design around this to fit in. It will keep my Tek 465M scope company along with my old PD power supplys.Saturation, you gave me a lot of good info, I already downloaded the manuals and have started reading through them. A lot of it is over my head but I do absorb some of it. And what I don't understand I know is there for future reference. So you have 4 of these, not saying a word, I used to be that way with motorcycles, now I'm down to just 3. Subject to change of course.As far as a variac goes, I have a small unit that starts out at 60VAC and goes up from there. Of course the seller has already plugged it into 120VAC. When I get this, I'll open it up and look for leaky and bulging caps and anything loose. Hopefully all goes well.Since I don't have anything to verify it's accuracy I'll probably pick up a DMMCHECK Plus as it's better than nothing. Any voltnuts live in the southern NJ or Phila area?Thanks guys and keep it coming.BillWojo

author: David Hess
author_rank: Super Contributor
timestamp: September 07, 2014, 07:11:50 pm
content: I would check the date code on the memory backup battery since it is responsible for maintaining the calibration data. If it is old, then I would look into the procedures necessary to change it without losing the calibration data.I would also visually check the aluminum electrolytic capacitors in the power supply and the power supply voltages for ripple which will give some indication of their state.

author: MarkL
author_rank: Unknown
timestamp: September 07, 2014, 11:02:48 pm
content: Quote from: David Hess on September 07, 2014, 07:11:50 pmThe 3456A doesn't have a memory backup battery. (An advantage, in my opinion.) Calibration is performed via a series of 10-turn pots underneath the front terminal cover.

author: David Hess
author_rank: Super Contributor
timestamp: September 07, 2014, 11:24:31 pm
content: Quote from: MarkL on September 07, 2014, 11:02:48 pmThat was my mistake. I was thinking of the 3457A.

author: BillWojo
author_rank: Regular Contributor
timestamp: September 08, 2014, 12:10:49 am
content: Well thanks to this awesome forum I was able to do a little research on this unit before I purchased it. The SN indicated that it is a later unit and the later units seem to not have the same problems with the ROM chips. Also it appears not to be fan cooled, another big plus in my book. Will definitely be looking at the PS though. Can't wait to get it.BillWojo

author: saturation
author_rank: Super Contributor
timestamp: September 08, 2014, 03:21:40 pm
content: You're welcome, BillWojo. The 3456a was the first in the line of voltmeter designs using the newer dual? slope technique invented by HP that is now a common procedure used by many DMM for good accuracy in ADC conversion. You can find more about the generations of DVM from HP journal and old discussions in the eevblog archives. Essentially you get an AC-DC voltmeter and ohmmeter with accuracy ~ > of the 34401a but without the cost, and its easier to DIY service.Only the users portion of the manual is essential, the electronics is just for curiosity and reference in case of a failure.Yes, the unit has a large perimeter, but its easy to stack.IIRC DMCheck only gives confidence to 5 digits vs the 6.5 digits of the 3456a.I have 4 units as I expected some to fail in subsequent years, and I calibrated them one per season, to watch the drift pattern. I also bought them over a 2 year time span when I could win a working unit for <= $60.IMHO the older these units get without some basic care or use such as when sold on eBay, the more likely the PSU or other old parts fail [ commonly leaving it stored unheated until sold, then subjecting it to thermal shock by a test boot in a warm room]. Redundant units make for a spare parts repository. To date, 3 remain continuously working but one blew a filter cap within a month of purchase.When monitoring circuits, I normally leave many voltmeters on test points so all 3 3456a are always in use, as well the HH DMMs.Quote from: BillWojo on September 07, 2014, 03:49:00 pm

author: petieken
author_rank: Contributor
timestamp: September 08, 2014, 09:38:45 pm
content: I also received a 3456a from ebay last week. Serial starts with 2825A, the version with silicone buttons. Sold as: "pulled from working environment".Of course upon arrival it didn't work, readings were all over place. Self test gave errors on all tests except 1-3. After opening the unit I found C8 cap on the power supply board colored black like it was burned. After replacing that cap and checking the other rails with the DMM and scope everything is running fine and stable now.I've been reading through the manual to learn about the math, registers and other functions, and I'm really impressed with this DVM so far.

author: saturation
author_rank: Super Contributor
timestamp: September 09, 2014, 12:00:05 am
content: I'm glad you got it repaired in short order, its very common in old gear for simply the PSU filter caps to go, makes for easy repair. The more heinous problem is abuse of the DVM inputs e.g. overloads, this is a most involved repair.I once got a view of a whole pallet of DVMs unloaded from a US government site. In mothballs for years. Now this is a sad picture but it shows you how popular this DVM was and what condition they are usually found before sale.For details on the 3456a seen the HP Journal April 1981.www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1981-04.pdfEnjoy.Quote from: petieken on September 08, 2014, 09:38:45 pm