Quick question about HP 3468A - Page 1
Forum section: electronics / testgear

author: c4757p
author_rank: Super Contributor
timestamp: February 17, 2013, 01:46:25 am
content: OK, I have a question about my "new" HP 3468A multimeter - this should be easy. If I leave it in DC V mode with probes attached but floating, it constantly switches between ranges: on the two lowest, very high-impedance ranges, the probe wires quickly pick up enough charge to bump it into the higher range. Then the low impedance at that range discharges them, and the cycle repeats. This doesn't happen with the probes disconnected because charge pickup is much slower.Should I be worried about wearing out the little relay with this happening, and disconnect the probes when not in use, or is it not a big deal? How long do the relays typically last under heavy use?

author: BravoV
author_rank: Super Contributor
timestamp: February 17, 2013, 04:41:54 am
content: Same feeling here when I bought it for the 1st time, but after few years, I adapted not to worry about it too much, beside it survives throughout those long years.But most of the times it becomes a habit that I always shorted both probes clipped together when not in used but powered on, don't know, maybe its just me, I feel like I'm going to have a mental breakdown to see the least significant digits keep changing all the time when not in used.Btw, have you replace it's RAM backup battery BT551 ?Edit: Posted this infos at other thread, attaching them here again to save you from drilling into the service manual just in case you have not done it.

author: c4757p
author_rank: Super Contributor
timestamp: February 17, 2013, 05:02:10 am
content: Thank you. Good to know it's not a problem.Quote from: BravoV on February 17, 2013, 04:41:54 amNot yet. I just got it a couple days ago and haven't had a chance to open it. I definitely plan to, though.I wish it had individual range buttons like the similar Fluke models from the time period - I'd like to be able to just stick it in the 30V range as soon as I turn it on. There's hardly a point to autorange when there is a single range that covers most voltages I ever encounter with 100 uV resolution. The little up/down keys are a pain in the ass, though.

author: BravoV
author_rank: Super Contributor
timestamp: February 17, 2013, 06:02:47 am
content: Quote from: c4757p on February 17, 2013, 05:02:10 amOne important thing to remember, don't let the RAM ever disconnected to the power source when replacing the battery or you will lose the calibration.Quote from: c4757p on February 17, 2013, 05:02:10 amI guess we will have to live with this old design, have to admit features wise it is beaten to death compared even to today cheapo dmm, one big feature I missed is nulling.But personally I think the biggest advantage of buying "working" old quality bench dmm is they're proven through time, and the best part is it's internal voltage reference is so well cooked that the drift is so small that re-calibration is not that demanding, at least at my unit.My 3468A probably more than 20 years old and now about 3 years since I bought it, with with last cal stamp dated about 8 years ago and still very accurate, fyi last year I checked it against my friend's 34401A (annually cert-ed) and its still on spot according to it's spec.Pics taken last year when I did measure low ohm resistor, and the resistor had been verified using 34401A.

author: robrenz
author_rank: Super Contributor
timestamp: February 17, 2013, 09:26:48 pm
content: I amnottrying to be a wise guy but the 34401A 1 year accuracy on 0.010 ohm is +/-0.004 ohm or +/-40% of value. The 3468 is only slightly less accurate at 0.010 ohm than the 34401A at +/-0.005 ohm or +/-50% of value. The 3468 is still a very nice piece of equipment and is way better than worst case spec since it agrees with the 1% resistor.

author: Unknown
author_rank: Unknown
timestamp: February 17, 2013, 09:36:04 pm
content: Yes, but the 34401A is on a yearly cal cycle. This gives confidence that it will meet its 1yr spec. The 3468A could have drifted out of cal in the 8 years since its last cal.I will usually set DMMs to a higher range or resistance when the leads are open. I find the relay chatter annoying and it will eventually wear down the relay, though probably not with typical hobbyist usage unless you leave it powered on 24/7.

author: robrenz
author_rank: Super Contributor
timestamp: February 17, 2013, 09:59:39 pm
content: Quote from: alm on February 17, 2013, 09:36:04 pmI completely agree. My point was neither meter even calibrated can verify that 1% 0.01 ohm resistor is in spec. Even if the resistor was only within 2% it would be 20 times more accurate than the worst case accuracy of the 34401A at 0.01 ohm.

author: c4757p
author_rank: Super Contributor
timestamp: February 18, 2013, 03:17:20 pm
content: Quote from: BravoV on February 17, 2013, 04:41:54 amUpdate: The battery measures 3.04V - should I bother replacing it, or is it good for a while longer?

author: SeanB
author_rank: Super Contributor
timestamp: February 18, 2013, 04:06:47 pm
content: When was it made? That is a better measure than voltage, they get a little dicy after 15 years. You never know when it will be EOL and drop voltage over a period of a few days.

author: c4757p
author_rank: Super Contributor
timestamp: February 18, 2013, 04:12:53 pm
content: Ah, OK. Forget 15 years, the most recent date code I can find in this thing is 83 (none visible on the battery itself) and no signs of a replacement ever having been done. I guess I will change it.

author: Unknown
author_rank: Unknown
timestamp: February 18, 2013, 04:19:31 pm
content: I concur. These batteries generally last well beyond their expiration date, but how much is anyone's guess. Like Sean writes, the battery might be good for another couple of years or another couple of days.

author: SeanB
author_rank: Super Contributor
timestamp: February 18, 2013, 04:25:25 pm
content: Probably best. I have a chime clock from Maplin ( bought 20 odd years ago and I took all they had ( 4) as spares) which was using a huge Eternacrll as chime drive which I put in 2 years ago to replace the AA cells that only did a year. Last monthit died, but still shows over 3V, just an internal impedance in the kilohm range. I had placed a 1000uF capacitor in parallel with it and this helped with it lasting. Hard to date the cells, but I suspect they were made in the 90's, date coded 152/7BA.

author: c4757p
author_rank: Super Contributor
timestamp: February 18, 2013, 05:10:01 pm
content: I'm trying to figure out what kind of battery to use as a replacement. The original one seems to be pretty much unobtainium now. Forgive me, I'm clueless about batteries. Can I just divide the capacity by the load current to get the expected life (bounded by the specified shelf life, of course)? And what is the load current like for a 1980s SRAM chip?There are 950 mAh button cells available - could these really source 10 uA for 10 years? I like the idea of making a custom battery holder that holds two in parallel for painless replacement in the future.

author: BravoV
author_rank: Super Contributor
timestamp: February 18, 2013, 05:27:10 pm
content: That is long life, low drain and with very flat discharge Lithium battery, the only known reliable manufacturers that I'm aware of are :- Panasonic BR series ->http://www.panasonic.com/industrial/batteries-oem/oem/primary-coin-cylindrical/cylindrical-type-br.aspx- Maxell ER series (Lithium Thionyl Chloride Battery) ->http://biz.maxell.com/en/product_primary/?pci=9&pn=pb0004- TadiranQuote discharge curve from Maxell ER series, see how long it's life, but the voltage will drop like a stone once its time to die.Personally mine is on "emergency" state too, and planning to buy one of these above.

author: BravoV
author_rank: Super Contributor
timestamp: February 18, 2013, 06:06:13 pm
content: Quote from: c4757p on February 18, 2013, 05:10:01 pmThat is not a SRAM, its an ancient 256x4 bit static cmos ram with part no 5101L (google it for it's datasheet), when in low voltage data retention/standby mode, the minimum Vcc is at +2 volt and consumes only 10uA@2 volt, while working the max Vcc = 7 volt, so even with 3.6 volt battery should be fine instead of 3 volt.

author: EEVblog
author_rank: Unknown
timestamp: February 19, 2013, 09:12:05 am
content: Quote from: c4757p on February 17, 2013, 01:46:25 amThat is a known wear issue on the HP3458A.Dave.

author: c4757p
author_rank: Super Contributor
timestamp: February 23, 2013, 01:30:05 am
content: There - replaced the battery (Tadiran TL-5104/P). The original battery has an impedance around 120 Ohm, which seems very high to me. No problems at all - sure feels like delicate surgery, though, when there's no way in hell you can afford to have it calibrated if you screw up...

author: BravoV
author_rank: Super Contributor
timestamp: February 23, 2013, 03:11:47 pm
content: Quote from: c4757p on February 23, 2013, 01:30:05 amPlease share the detail process what you've done in that surgery, and appreciate if you could share some photos.

author: c4757p
author_rank: Super Contributor
timestamp: February 23, 2013, 06:16:44 pm
content: Well, the process was simple in theory. I found the point where the two power sources are connected with diodes, and soldered in a third diode, then soldered wires to the diode and a nearby ground point. I used a power supply plugged into a UPS to provide power - I didn't have any batteries with terminals I could solder to, and I did have a UPS available. I slowly turned up the voltage to make sure nothing went wrong, and made sure the voltage at the diodes rose, so I knew it was powered by the supply. Kept an eye on the power supply's ammeter (with the current limit set to 10mA) and a voltmeter connected across that rail the whole time. Desoldered the battery from the PCB, then soldered in the Tadiran. Realized it didn't fit, so I swore profusely, then bent the leads around to make it fit. Then I disconnected the power supply, put the can back on, and realized that even though the battery looked like it fit, it was still blocking the damn can. Swore profusely again, this time in two languages, because I had to very carefully bend the leads and tape over them to keep them from shorting to anything, and finally got it to fit. I put a spacer of hot glue under it and taped it down to the PCB. (Making sure all the glue and tape were only over the digital section - I don't know if the glue has any electrical effects that might interfere with measurements at high precision. Who knows what the dielectric constant of El Cheapo hot glue sticks is..) Then I put it all back together and started it up to verify I didn't ruin it.No pictures because I'm not particularly proud of how it looks...It's in there pretty securely, but looks pretty redneck. Just imagine a battery about 50% too long with its leads bent all over the place, taped down to a PCB...

author: SeanB
author_rank: Super Contributor
timestamp: February 23, 2013, 07:01:14 pm
content: You have to do it at times, though I am a fan of double sided foam tape for those battery packs.

author: BravoV
author_rank: Super Contributor
timestamp: February 24, 2013, 08:04:36 am
content: Thanks, btw just curious on the battery replacement, did you deliberately buy an oversized one ? Also could you close the metal shield ?

author: c4757p
author_rank: Super Contributor
timestamp: February 24, 2013, 10:24:46 pm
content: I measured to make sure it fit. Itdidfit, I just didn't really think about how hard it would be to fit it in properly and anchor it so it wouldn't move, and also fit whatever I used to do that. The shield closed fine after a few repositionings of the battery.

author: BravoV
author_rank: Super Contributor
timestamp: February 25, 2013, 03:47:00 am
content: Quote from: c4757p on February 24, 2013, 10:24:46 pmI can imagine that must really tight fit, anyway glad to hear its done, and prolly you don't need to worry for the next 20 years or even more with that oversized battery.

author: c4757p
author_rank: Super Contributor
timestamp: February 25, 2013, 03:52:14 am
content: Good, that's the plan. I do not like messing with backup batteries - I am happy only when the battery long outlasts the instrument itself...

author: willb
author_rank: Regular Contributor
timestamp: February 27, 2013, 08:50:12 pm
content: I just replaced my battery in my 3478A today. I wasn't sure on the age of the battery, so I did it to be on the safe side.Here is the battery I used :http://www.alliedelec.com/search/productdetail.aspx?SKU=70197006It was the only place and only battery I found in stock that would work and ship to Canada. Anyhow, I powered up the meter and used a Weller Pyropen to solder the new battery. The whole process was painless. I soldered pieces of 22ga wire on the battery tabs and fixed the battery in place with some double stick tape and a zip tie. I turned the meter around once the battery was in place and soldered the wires to the PCB. 20 minutes later I had my meter back in service.

author: Dave
author_rank: Super Contributor
timestamp: February 28, 2013, 12:34:53 am
content: c4757p, could you measure the dimensions of the original battery? I need to replace batteries in two meters and I want to buy the right batteries for the job.

author: c4757p
author_rank: Super Contributor
timestamp: February 28, 2013, 01:14:23 am
content: Very nice on the 3478A. Looks like there's a bit more room to move things around - and that hole you put the cable tie through was convenient indeed!Dave, of course! I'll grab the measurements tonight.

author: willb
author_rank: Regular Contributor
timestamp: February 28, 2013, 02:10:33 am
content: Those holes were indeed very practical! Made everything so easy and clean.Aren't the batteries the same in the 3468A and 78A?? The one I used fit absolutely beautifully in my meter. I don't think the old battery was original, but the dimensions of the old vs the new are the exact same. Attached is the old battery.

author: c4757p
author_rank: Super Contributor
timestamp: February 28, 2013, 02:41:01 am
content: It looks identical. Mine IIRC was blue (could be black, now that I think about it) but was otherwise the same shape, size, and brand.

author: Dave
author_rank: Super Contributor
timestamp: February 28, 2013, 04:56:21 pm
content: Judging from the picture, I assume that is a 2/3 AA battery (33mm or 1.3" in lenght). Is this the correct size?It could also be a 1/2 AA battery (25mm or 1" in lenght). Which of the two should I buy?

author: c4757p
author_rank: Super Contributor
timestamp: February 28, 2013, 05:13:46 pm
content: Ah crap, I forgot to get the measurements! Here, I just did now: Length 32.5mm (29.4mm excluding the + bump), diameter 16.3mm.

author: Dave
author_rank: Super Contributor
timestamp: February 28, 2013, 05:19:52 pm
content: No worries.2/3 AA it is. Thanks!

author: tribbles
author_rank: Newbie
timestamp: March 02, 2013, 06:07:35 pm
content: I have a 3468a and the battery in it is a SAFT LX1634. Is that an original or has it been replaced? If they replaced it they did a good job looking at the board and joint.

author: c4757p
author_rank: Super Contributor
timestamp: March 02, 2013, 07:50:50 pm
content: Well, it's not the same type mine had, but it's just a battery - they certainly could have swapped for a different one at some point.

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 02, 2013, 11:11:53 pm
content: Quote from: tribbles on March 02, 2013, 06:07:35 pmI also have a 3468A with a SAFT LX1634 in it. Looks original to me. I just ordered a BR-2/3A to replace it. (Digikey P226-ND)edit: I documented the replacement procedurehere

author: Dave
author_rank: Super Contributor
timestamp: March 19, 2013, 02:50:26 pm
content: I replaced the batteries in both my multimeters this weekend, but was only 50% successful at doing so.I first tackled my 3468A and successfully replaced the battery. I kept the RAM alive by tack soldering a temporary AA battery pack to the leads of capacitor C550.After I finished working on this meter, I tested it and everything appeared to be in order.Feeling confident, I cracked open my 3468B. This time around, I decided to also take some photos of the process.I soldered in the temporary battery pack, took a picture, and immediately desoldered the lithium battery. Just as I was holding the lithium battery in my hand, I noticed one of the AA batteries sitting NEXT to the battery holder. At that point, I wanted to bang my head on the bench. You can see the result of my stupidity in the images below.Now I have to find a way to recalibrate my meter. Hopefully I can find some help at my uni.

author: bingo600
author_rank: Super Contributor
timestamp: March 19, 2013, 07:53:22 pm
content: Quote from: ModemHead on March 02, 2013, 11:11:53 pmThanx for the nice description & pics.This inspired me to finally change the battery in my HP 3478A in the weekendI'll use my Propane solder unit , and a spare 3v3 litihum diode-ored to the ram supply.I even think i'll keep 230v mains on , while performing it./Bingo

author: c4757p
author_rank: Super Contributor
timestamp: March 19, 2013, 08:12:35 pm
content: Quote from: Dave on March 19, 2013, 02:50:26 pmOh, no!That's not going to be easy. I hope you can find help.

author: ModemHead
author_rank: Frequent Contributor
timestamp: March 19, 2013, 09:28:28 pm
content: Quote from: bingo600 on March 19, 2013, 07:53:22 pmGlad you found it useful. Should be no problem, just double-check everything, don't get sloppy with the iron, and make sure your back-up power is actually connected before snipping! (@Dave I too hope you can find some help...)

author: bingo600
author_rank: Super Contributor
timestamp: March 21, 2013, 01:21:39 pm
content: I did change the battery in my HP 3478A successfully today.https://www.eevblog.com/forum/beginners/changing-battery-in-a-hp-3478a-can-i-use-a-3v-lithium//Bingo

author: george graves
author_rank: Super Contributor
timestamp: April 13, 2013, 10:03:46 am
content: I wonder how hard it would be to add a backlight a 3468A.

author: skipjackrc4
author_rank: Regular Contributor
timestamp: April 13, 2013, 02:50:49 pm
content: Quote from: EEVblog on February 19, 2013, 09:12:05 amAre the relays replaceable? I have one and had the same concerns.

author: grumpydoc
author_rank: Super Contributor
timestamp: April 13, 2013, 03:37:58 pm
content: QuoteIf the display is similar to the 3478 I think basically impossible

author: Wh1sper
author_rank: Regular Contributor
timestamp: July 10, 2013, 10:59:25 am
content: Hello HP3468A owners.I have this one, too.Often I change from Volts to Resistor Measurement and back.What's sometime happen is that no value is been shown.I didn't found another solution than power off an power on again to awake the DMM.Is this a known behavior to you, or it's just mine? Its ROM inside date around '97 as I remember right.(Please apologize for not introducing myself first, I will catch it up soon.Greetings

author: mianchen
author_rank: Regular Contributor
timestamp: August 07, 2013, 09:23:19 pm
content: Thank you everyone in this thread. After reading this thread, I've successfully replaced my battery for the HP3468A with a1/2 AA Tandiran SL350Pwhich is what I could get from Farnell UK at the time.I guess it must be easier than putting in a 2/3 AA. With a half AA, you have a lot more room to work with and the leads are easier to solder in compared to solder tabs I think.Before I did anything, I had a bit of oh @!&* moment when I accidentally shorted the battery - I realised that within 5 seconds. There was no spark, flame etc. and the temperature of the battery did not increased noticeably, if at all. But the voltage of the battery went down to 3.2V (3.6V nominal, 3.7V when I first tested it). It gradually came back to 3.65V after 10 minutes or so. I wasn't sure how much damage I did to the battery, and didn't think straight, used it to replace the old battery inside the HP meter.Now when I think about it, I start to worry about the longevity of this new Tandiran - Should I be worried? should I get another one to replace this??Any comments are welcome, TIA

author: Fsck
author_rank: Super Contributor
timestamp: August 07, 2013, 10:46:00 pm
content: Quote from: willb on February 27, 2013, 08:50:12 pmAs an addendum Allied also has ones with presoldered tabs with 2 leg positive terminal:https://www.alliedelec.com/search/productdetail.aspx?SKU=70197007haven't seen a lot of 3457a interiors, but the battery in mine has 2 legs on the positive tab, also makes it easy to identify +/- for us morons.

author: bronson
author_rank: Regular Contributor
timestamp: January 31, 2014, 11:00:55 am
content: Sorry to revive this old thread but @Fsck I'm surprised to hear your battery has two leg positive. My 3457a has the plain one-leggers.Mine was made 3rd week of 1987,http://www.hpmuseum.org/collect.htm#numbers). Is yours newer or older?FWIW, this is what I ordered:http://www.mouser.com/Search/ProductDetail.aspx?R=BR-2/3AE5SPNvirtualkey65800000virtualkey658-BR-2/3AE5SPNAlso, is it really necessary to use a butane soldering iron? Seems like a typical grounded soldering iron would be fine as long as the multimeter is unplugged and a temporary battery is shunted in...?

author: AMR Labs
author_rank: Frequent Contributor
timestamp: March 04, 2019, 04:29:53 pm
content: Hi BravoV,I wanted to ask where did you purchase those gold color banana plugs that also allow wires to be connected to their end like that? Or at least, what are these called? Not sure they are the same used to connect speaker wires, maybe.I realize this is an old post but knowing you are still very active on the forum on other threads, though I just ask here to keep this thread on topic. Not even sure how these are called, tried several possible names but so far was not able to get any meaningful results. Want to order a pair or two for my own 3478/3468 DMMs.Thanks.Quote from: BravoV on February 17, 2013, 06:02:47 am

author: BravoV
author_rank: Super Contributor
timestamp: March 06, 2019, 02:17:01 am
content: Quote from: AMR Labs on March 04, 2019, 04:29:53 pmYes, you're right, its just ordinary banana plugs for audio amplifier/speaker wires, and mine are similar to these below, an example random result from googling "gold banana speaker".Forgot where I bought it, maybe from local shop, usually those audiophoolery shop sell these, and they're quite cheap.They're quite handy as test probes for thru hole components that have long legs, the top bolt can be opened quite wide, and can clamp quite securely on those DUT's legs, something like this below.Also if you're lazy to find the like DMM test leads, or they're hiding some where, they're quite handy too.

author: AMR Labs
author_rank: Frequent Contributor
timestamp: March 06, 2019, 03:05:48 am
content: Thanks for the info BravoV. Found these on ebay which I think are similar to yours:https://www.ebay.com/itm/401033352392Yes I agree they are very handy to test leaded components without using regular test leads, exactly why I wanted them. And also avoid the additional inductance and resistance.Thanks again!