Problem removing HP3478a cover - Page 1
Forum section: electronics / general

author: uprightsquire
author_rank: Contributor
timestamp: February 21, 2013, 01:51:20 am
content: I've recently picked up a 3478a, and thought i should check the backup battery voltage, however I can't remove the top case panel. The top-center rear screw seems to turn infinitely in cw and ccw directions (obv an issue), but the cover won't budge. Is there another screw that needs to be removed to remove the top cover?I've removed all the screws I can find and the bottom and side covers come off easily. Am I missing something obvious or do I need to drill that screw out?I can probably test the voltage from the bottom, but its either good, or flat, so im more interesting in changing it out and that has to be done from the top...Cheers.

author: EEVblog
author_rank: Unknown
timestamp: February 21, 2013, 01:58:20 am
content: Just two screws on the back, and one on the bottom, that's it. Case should slide off.Dave.

author: uprightsquire
author_rank: Contributor
timestamp: February 21, 2013, 02:24:18 am
content: Just very frickin stuck3.00V on the nose. It looks to be the original battery.I'ts crazy dusty inside. Does anyone have any tips for cleaning this sucker out?

author: nukie
author_rank: Frequent Contributor
timestamp: February 21, 2013, 03:19:47 am
content: Voltage does not dictate the capacity level of Lithium cells. If its more than 10years old I say change it if you put it into service. The longer you drag the higher chance you forget about it.Microbattery.com has the battery for a few bucks, its a small sum compared to a calibration service. It's up to you, your choice.

author: uprightsquire
author_rank: Contributor
timestamp: February 21, 2013, 03:33:40 am
content: I plan to, I am thinking that it might be the original (Eternacell. Thoughts?). Interestingly (perhaps), the battery does not have the solder tabs as I was expecting, it has pins:Also: see dust.

author: BravoV
author_rank: Super Contributor
timestamp: February 21, 2013, 04:08:12 am
content: Quote from: uprightsquire on February 21, 2013, 03:33:40 amWow .. so dusty !Check here on 3478A backup battery replacement and read the note on replacing it, just never let the cmos ram get disconnected from power source during the replacement or goodbye calibration ->Inside HP 3478A, a German site thru google translate

author: EEVblog
author_rank: Unknown
timestamp: February 21, 2013, 04:47:30 am
content: That's a lot of dust!Just shot a quick teardown of my 3478A, will edit and post it now.Dave.

author: uprightsquire
author_rank: Contributor
timestamp: February 21, 2013, 04:56:40 am
content: Neat!I'm thinking of getting in there (disconnected from power) with the round brushy vacuum attachment. Not sure what other option there is. It really is very dusty.Bit more examination revealed that the rail the top cover slides on is slightly dented, which stopped it from sliding.

author: TerraHertz
author_rank: Super Contributor
timestamp: February 21, 2013, 05:43:02 am
content: A vacuum cleaner with a long pointy nozzle, and a separate brush - like a narrow long-haired paintbrush - tends to work better. It's often necessary to actually scrub at the settled grime to get it off, especially in the crevices between parts. A vac-cleaner hose brush is too big, you can't angle it under things, and while trying you might hit fragile parts with it. Also because of it's size, the plastic body, and the air movement it might cause static discharge problems.If you have a compressed air gun, start with that to get about 80% of the dust and fluff out. Then start scrubbing. Just hold the vacuum nozzle near where you're brushing. Keep yourself grounded to the instrument case, but don't worry about static on the brush hairs. They don't have enough charge holding capacity to do any harm.

author: uprightsquire
author_rank: Contributor
timestamp: March 01, 2013, 12:30:10 am
content: Thanks TerraHertz, that cleaned it up nicely.Just replaced the battery. Used hot air to avoid issue with grounded iron. Snipped off old battery leads, needed new solder melted onto old leads to get the old solder to melt, then they pulled right out. not the most ideal method, but had no real issues.