HP 3455A, Partial Teardown - Page 1
Forum section: electronics / testgear

author: 0culus
author_rank: Super Contributor
timestamp: November 17, 2018, 06:20:30 pm
content: So as I posted in TEA last week, I bought an HP 3455A for a cool $160 shipped. It arrived, and I finally had some time to take it apart and have a peek at the innards to make sure nothing was amiss. Posted these pics in TEA, but this thing is so pretty inside I thought it deserved it's own thread!Fortunately, with use, the buttons seem to be freeing themselves for the most part. Still a couple sticky ones that I'll have to disassemble the panel to fix, but that will have to be done later and in a cat-free environment.I was frankly amazed at how clean inside this unit is. The boards look clean and unmolested. The line filter doesn't look like the exploding kind in that other thread. The AC board is the RMS and not the averaging board. Not pictured is the strap which covers the calibration ports on the analog lid; it is present, but I took it off for the picture. The engineering that went into this unit is really quite something, especially with the lengths they went to shield the analog circuitry from the outside world.Bonus pic of the 3455A and my Fluke 87 agreeing pretty much exactly on output from a DC power supply.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 18, 2018, 02:59:24 am
content: I would change the line filter right away, dont take any chances ......... it's nice to see this "old" kind of electronic design / assembly ...

author: 0culus
author_rank: Super Contributor
timestamp: November 18, 2018, 03:54:58 am
content: Quote from: coromonadalix on November 18, 2018, 02:59:24 amHow would you get the old one out without damaging anything? It seems to be riveted in place.

author: SeanB
author_rank: Super Contributor
timestamp: November 18, 2018, 09:43:40 am
content: 3.2mm drill bit, a vacuum cleaner to handle the chips and work carefully. Replacement is put in with small screws and nylock nuts, of appropriate size and style to match the rest of the unit, or what you can get locally.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 18, 2018, 03:23:16 pm
content: Exactly if you do it carefully you will succeed, you could put some green paint tape protection ...... or put back some rivets too to make it look original, i do that sometimes, and clean the solder and flux residues with isopropyl alcohol, to protect any writings on the panel, ... you could not tell it was changed.

author: alm
author_rank: Super Contributor
timestamp: November 18, 2018, 03:35:04 pm
content: I've indeed put masking tape on the inside of the rivets and then drilled them out on similar instruments without having any chips fall inside the instrument.

author: 0culus
author_rank: Super Contributor
timestamp: November 18, 2018, 06:30:08 pm
content: So is there a recommended brand? I looked on mouser and of course saw a huge variety. Obviously it needs to match the specs of the original for current, etc.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 19, 2018, 02:31:21 am
content: normally nowadays they are rated 15 amps at 120vac, most brands are fine, never heard any blowing line filter from a long timeSince you're from usa Digikey Mouser Electrosonic etc etc ... should not cost an arm loll

author: alm
author_rank: Super Contributor
timestamp: November 19, 2018, 02:59:26 am
content: I believe filters for higher current ratings tend to have smaller inductors, so I wouldn't upgrade the current rating without reason. It's generally the caps that die, so upping the current rating isn't likely to increase reliability.

author: 0culus
author_rank: Super Contributor
timestamp: November 19, 2018, 04:28:12 am
content: Quote from: alm on November 19, 2018, 02:59:26 amI want to match what it has, not upgrade to a higher rating.I'll see if I can't just get a bunch of them since I'm sure this is neither the first nor the last time I'll need to replace a line filter.