How to replace battery in Agilent 54621A Oscilloscope? - Page 1
Forum section: electronics / repair

author: vicroberts
author_rank: Newbie
timestamp: February 17, 2016, 03:38:14 am
content: I have an Agilent 54621A scope that is about 12 years old. It still works perfectly, except that I have started to get a low battery warning each time I run the unit on. (This is a memory backup battery.) I checked the service manual and found that the battery is a CR2354 and it's mounted on the motherboard. I purchased a CR2354 and opened the case today. The battery is easily visible and accessible on the bottom of the MB, but I can't see how to remove it. It does not appear to be soldered in, but may be attached to the MB with double sided tape.Does anyone have experience replacing these batteries. I do not want to try to pull it off the tape, if he is really held by some other means.Vic Roberts

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: February 17, 2016, 05:23:34 am
content: Seems that this scope has auto-configuration of it's settings (Calibration) so,it's not so complicated to replace the battery.

author: vicroberts
author_rank: Newbie
timestamp: February 17, 2016, 06:58:04 pm
content: The problem I have is physically removing the battery from the motherboard. Reconfiguration of the scope is not the issue. The battery does not seem to be in a traditional button cell holder, plus there is what looks like some double sided tape between the battery and the MB. I don't want to force the battery away from the tape until I know that is what should be done.

author: vicroberts
author_rank: Newbie
timestamp: February 17, 2016, 10:35:09 pm
content: I now believe that the battery in the Agilent 54621A is a CR2354/HFN instead of the basic CR2354. The CR2354/HFN has solder tabs welded to the battery. See the attached datasheet. The two tabs on the battery are soldered to the motherboard so a battery holder is not used. I've ordered two of the CR2354/HFN from Mouser, and after they arrive I'll take the motherboard out of the scope, unsolder the old battery and solder in the new one.

author: vicroberts
author_rank: Newbie
timestamp: February 17, 2016, 11:10:40 pm
content: Based on the tab design, the battery is most likely the CR2354/GUFN, not the CR2354/HFM. The GUFN is not available, but the CR2354/GUN has the same tab configuration, but without the yellow insulation ring. See attached file, which shows both the GUN and the GUFN.

author: jimdeane
author_rank: Regular Contributor
timestamp: February 18, 2016, 05:54:05 pm
content: Is there enough room to solder in a battery holder? Would make future replacement easy. That's what I did with a handheld amateur radio when its battery died.

author: vicroberts
author_rank: Newbie
timestamp: February 18, 2016, 08:59:42 pm
content: Thanks. That's a good idea. However, I won't know if I have enough room until I get the motherboard out of the unit, and I may need a battery holder with the same footprint. The original battery has lasted for more than 10 years, so I don't expect to have to replace this one in the near future.

author: sheakev
author_rank: Newbie
timestamp: May 24, 2020, 09:56:41 pm
content: Just ran across this post wondering how the OP replaced the battery. Just picked up one of these scopes and I am getting a low battery warning.

author: hanakp
author_rank: Regular Contributor
timestamp: February 25, 2021, 01:49:51 pm
content: I had the same problem with Agilent 54621A I picked from a surplus sale, but I didn't feel like disassembling half the scope to desolder the old battery. Plus, I plan to hold on the scope for a long time and I didn't want to repeat the process again in 10 years or so. So I devised a much better way to replace the battery:1. I cut the positive pole tabs with sharp pointed pliers (be careful not to damage the super-thin PCB traces nearby). Then I bent it away from the PCB.2. I rocked the battery back and forth until the negative pole pin (which is hidden under the battery) broke off from fatigue damage, it took about 2 minutes. There was double-sided adhesive tape under the battery, but it was so shriveled up after the years it offered little resistance.3. I soldered in CH03-2032 battery holder for standard CR2032 coin cell, it's sold under part number 122-0110-GR at Mouser. I then used automotive-grade double-sided tape to glue it onto memory chips nearby. This holder has the advantage it's fully enclosed in plastic and so it won't short anything even if it falls off. Also, it has a switch which must be obviously in the ON position.https://cz.mouser.com/ProductDetail/122-0110-GR/And don't forget to check out this thread if your scope doesn't boot after the replacement:https://www.eevblog.com/forum/repair/agilent-54622d-dead-after-battery-replacement/

author: SilverSolder
author_rank: Super Contributor
timestamp: February 25, 2021, 02:01:34 pm
content: I just soldered in a battery similar to the original. If it only has to be done once every 12 years or so, I can live with soldering it!

author: bob91343
author_rank: Super Contributor
timestamp: February 25, 2021, 09:14:21 pm
content: I have a similar problem. My 8594L (?) spectrum analyzer has an inaccessible battery. It's on a small board buried within the unit. The board is held in place by plastic spacers that refuse to be removed. Before I break something important, I'd like to know the procedure.The spacers appear to be nylon, about 1/4" in diameter or maybe they are hexagonal I forget. The ends are shaped and snapped into holes in the board but have strongly resisted my attempts at removal. I may have damaged one or more spacers so far.I gave up for the nonce but if anyone can help, I would appreciate it.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 25, 2021, 09:45:26 pm
content: If it is the kind of spacers I'm thinking of, I usually squeeze the ends together with pliers and lift a corner of the board. You can also try a ring of heat-shrink to squeeze them, it works in some cases.

author: Greybeard
author_rank: Frequent Contributor
timestamp: December 14, 2021, 07:21:16 am
content: Does anybody know, which kind of data is stored in the battery buffered RAM?Any calibration data that can't restored by user cal?

author: Hamelec
author_rank: Regular Contributor
timestamp: December 14, 2021, 07:10:39 pm
content: Be careful with the HP8594/8595 or you will lose your calibration data !!!Manual backup/restore before is possible, have a look into the manual.Or use a second backup batterie soldered to the PCB board (using 2 wires and a resistor) during replacement of the original one.

author: SilverSolder
author_rank: Super Contributor
timestamp: December 15, 2021, 08:48:36 pm
content: Quote from: Hamelec on December 14, 2021, 07:10:39 pmFor the Agilent 54621A Oscilloscope, I had no ill effects from removing the battery and soldering in a new one. The user calibration process took care of everything.

author: Greybeard
author_rank: Frequent Contributor
timestamp: December 15, 2021, 09:04:09 pm
content: Quote from: SilverSolder on December 15, 2021, 08:48:36 pmYour battery was completely dead (0.x V)?

author: Hamelec
author_rank: Regular Contributor
timestamp: December 15, 2021, 09:34:44 pm
content: sorry, HP8494/8495 >> should be 8594/8595

author: SilverSolder
author_rank: Super Contributor
timestamp: December 16, 2021, 12:16:03 am
content: Quote from: Greybeard on December 15, 2021, 09:04:09 pmWell, it was certainly 0V when unsoldered from the board!It took me maybe 10 minutes to solder in the new one.

author: tonykids
author_rank: Regular Contributor
timestamp: December 16, 2021, 09:09:12 am
content: Quote from: hanakp on February 25, 2021, 01:49:51 pmThanks hanakpI repalced my battery the same way like you.Got this 54622A at $60 as my first Oscilloscope,perfect