HP 3468A Battery Replacement - Page 1
Forum section: electronics / testgear

author: elverado
author_rank: Newbie
timestamp: May 06, 2016, 10:05:02 pm
content: Hello all,I recently acquired a HP 3468A in great shape from eBay for about $80 shipped. One reason I jumped for it: it was stickered for calibration completed in 2014 and passes self test with no issues. I built my own set of silicone wired Kelvin clips and excited to be able to measure with such accuracy for so cheap.I'm just a hobbyist (Audio, logic ICs and Arduino projects etc) and don't care about full-digit accuracy, so whatever it's set at now is more than fine for me. But am aware of the lithium 3v ROM retaining battery and its need for replacement and would like to do that before it fails. After a careful peek under the hood I see what appears to be the factory ROM battery (matches other pics I've seen as 'original batt') - from 1982 or so based on the serial number to date calc found on this site. Thanks to this forum and a great blog post by Mr. Modemheadhttp://mrmodemhead.com/blog/gallery/posted-galleries/hp-3468a-battery-replacement/I ordered a Panasonic 2/3A lithium battery and am ready to solder in the diode/2AA temporary battery and swap it out.My question for the group is: do Ineedto also buy a butane soldering torch for this operation? I don't like buying junk tools and don't like buying tools that'll be used once and sit. It seems a good one is $50-60 on amazon. If I do any soldering on a car or in the garage I've used an extension cord with my Weller WES51 and do just fine.I know to be sure of success I should be totally floating, but curious as to opinions here. Worst case scenario if I loose CAL I'll get myself a DMMCheck and do the front panel DC/Resistance calibration the best I can (knowing AC would be a challenge and possibly not possible).Thanks,Neil

author: Satch
author_rank: Contributor
timestamp: May 06, 2016, 10:21:28 pm
content: Neil, as rather a newbie to this myself, I was glad to see your question. I refer to myself as electronical. I work commercial industrial electrical maintenance with a bit of electronics thrown in. I read read the blog post you mentioned but also saw some comments there from readers who failed at it. So getting a better idea of how to do this while avoiding pitfalls is of interest to me.

author: elverado
author_rank: Newbie
timestamp: May 06, 2016, 11:34:21 pm
content: After some other digging online I just came across an idea that is either brilliant or likely to lead to tons of frustration ... unplugging the iron while hot and hoping for enough retained heat to solder the battery to the the PCB. I'd plan to heat the big battery lead end first, then unplug iron and join battery positive to pcb. Just an idea I came across after posting but would love to hear others. (or warnings of impending peril)

author: bitseeker
author_rank: Super Contributor
timestamp: May 07, 2016, 12:39:55 am
content: A few options to the gas soldering iron:1. Use a battery-powered soldering iron.2. Use a USB-powered soldering iron plugged into a battery power pack.3. Plug the DMM into a UPS with sufficient battery capacity to complete the operation. Disconnect the UPS from the outlet.4. Disconnect the DMM from the outlet, thus floating the meter. The battery pack that Modemhead used will power the RAM during the operation. However, that does mean that you'll only have one power source keeping the RAM alive after desoldering the lithium cell.5. Plug the DMM into an isolation transformer. This may still be problematic depending on how the isolation transformer outlet is wired and how the affected portion of the PCB is referenced.Option 1, 2 or 3 would be preferable to 4 or 5.

author: elverado
author_rank: Newbie
timestamp: May 07, 2016, 01:47:19 am
content: Thanks bitseeker! I did it with the DMM floating as you suggested and succeeded!! I did have a bit of a scare though - the connection to the LCD is a lot more delicate than I would have thought and I managed to break a pin off if it. My heart was racing as it fell right next to an IC and nearly let the magic smoke out! I temporarily added a small solder blob in place of the missing pin and the remaining nub is enough to have it work. I'd suggest leaving the ribbon cable (looks like an old IDE hard drive cable) alone as I had room to solder around it. I also used micrograbbers instead of soldering in the temporary battery pack.All in all it wasn't a hard procedure but did feel a bit like diffusing a bombI have some pictures and will upload soon to help others, but no real surprises. Thanks to Mr Modemhead for the detailed fix. Only other thought is that the diode I happen to grab did introduce a 1.5v voltage drop but still ended up over the required 2v and worked fine.Other slightly unrelated note if youre looking at these: look for ones that are ugly from stickers and sharpie markers and not engraving. Isopropyl Alchohol and a qtip removes the marker, goo gone handles the stickers. Then a toothbrush with a peroxide whitening toothpaste. My new DMM from 35 years ago looks brand new.

author: Satch
author_rank: Contributor
timestamp: May 07, 2016, 11:33:01 am
content: Good job Neil. The micro grabbers were a nice touch and a bloke needs to mind the diode volt drop too. Thanks for reminding us. And please do share those photos. I have looked at this model and would perform the surgery as a matter of necessity just to avoid any issues

author: mmagin
author_rank: Frequent Contributor
timestamp: May 07, 2016, 07:18:52 pm
content: My solution with my 3478A battery replacement was to run it with an isolation transformer + a IEC cord I'd clipped the ground pin off of. (Yes, generally considered a terrible thing to do, but for this...) The key thing, as far as the process, I think to check was to use my handheld DMM to verify there was no connection (or very very high resistance) between the soldering iron tip and the battery contacts before starting the actual replacement.But I had also tacked a 2xAA battery pack with diode somewhere closer to the static ram, because I wasn't going to trust AC power

author: bitseeker
author_rank: Super Contributor
timestamp: May 08, 2016, 02:25:30 am
content: Good job! I have several 3478A in my repair/refurbish/resale queue. They'll get new batteries too.

author: Helix70
author_rank: Unknown
timestamp: May 08, 2016, 11:15:03 am
content: Why can't I ever find these for $80?Well done.

author: Satch
author_rank: Contributor
timestamp: May 08, 2016, 11:19:20 am
content: Quote from: Helix70 on May 08, 2016, 11:15:03 amI was thinking the same thing. Every time I look at one of these or a Keithley 199 or 195 in any kind of decent condition they are always twice that much. Agreed, well done.

author: elverado
author_rank: Newbie
timestamp: May 08, 2016, 03:24:22 pm
content: Quote from: Helix70 on May 08, 2016, 11:15:03 amNot sure you know that I am in the US and these are USD. But still they seem to average closer to $150 for Buy It Now. I monitored a lot of listings and ended up bidding on one that had a shipping price gouge built in - $30 to ship. So that likely scared off a lot of people as it tends to do to me. Usually shipping is $15 or so ... and shipping anything of any weight like this it factors greatly into the price. So I bid about $25 initially and then had a few other bidders I played against. Then dropped a $50 bid with 2 secs to go and got it.Edit: I just noticed the flags next to usernames so I see you're in the US too; new to forum and still learning you're not all AussiesLooking at the 'sold' listings of eBay I don't think my price was too far from average. There are a lot of these out there (usually from tech surpus companies) and not a lot of buyers in my estimation. I figure if a company is buying for a lab they want warranty and newer manufacturing years than this - so I think we have a buyer's market for people building home labs.

author: bitseeker
author_rank: Super Contributor
timestamp: May 08, 2016, 10:38:45 pm
content: Shipping is expensive. When you see a vendor list $15 to anywhere in the US, either the rest of the cost is built in to the base price or the seller ships a high volume and gets a much better rate than the norm. When I sold my HP 34401A last year, which weighs about the same as the 3478A, the shipping was around $35 because the size of the package overrides the weight.$80 is a really good price for one in good, working condition. Even $100 would be a good deal. As you said, they usually go for around $150 in that condition.Why that much? Well, work the numbers in reverse and you get the following for a 3478A in complete and good working condition:$150 sell price ($30 shipping)-$18.00 eBay fees-$ 5.52 PayPal fees-$35.00 ground shipping-$15.00 feet & tilting bail (these are missing more often than not)-$ 6.00 new battery----------$100.48 net before any other costsNext, subtract the price of the original DMM, before refurbishing. Let's say you could get it for $50 and didn't need to do any repairs to the electronics beyond the battery replacement. The cheaper you can get it, the most profit for you, but also the less likely it doesn't have some kind of problem.That leaves you with $50.48 to buy and install the feet and batteries, take photos, create the eBay listing, answer questions, and finally package and ship it. Oh, and that assumes that you don't have to buy any packing materials.Now you see why most of these things are sold by recyclers who do as little as humanly possible when posting their stuff on eBay. Anything beyond turning it on costs too much.

author: Satch
author_rank: Contributor
timestamp: May 09, 2016, 12:30:12 am
content: bitseeker, great post. I knew there had been quite an uptick in eBay seller fees but man, I see why they try to get creative sometimes with the carriage, fees, and other ways to make a profit. If not for the completely random nature of buying off eBay I would ge one but you could make a 150 mistake with the stroke of a key. We'll see.