HP 3478A – Recommendations for RIFA, Electrolytics & Backup Battery Rep - Page 1
Forum section: electronics / testgear

author: octal
author_rank: Contributor
timestamp: July 24, 2025, 08:42:08 pm
content: Hello everyone,I recently acquired two HP 3478A digital multimeters in somewhat good cosmetic and operational condition. Before putting them into regular service, I’d like to replace the known‑to‑fail RIFA mains‑filter capacitors and, while I’m inside, upgrade all of the electrolytic caps. I’d also like to fit a new backup battery for the calibration SRAM so I can keep these units running reliably for years to come.What I’m looking for:- Mains‑filter (RIFA) capacitorsOriginal spec: X2, 0.022 µF @ 275 VAC (approx.)High‑quality, safety‑rated replacements available from Mouser (manufacturer and part number suggestions appreciated)- Electrolytic capacitorsThe service manual lists four (maybe five) caps on the main board—values range from a few µF up to 100 µF.I’d love recommendations for low‑ESR, long‑life electrolytics (Nichicon, Panasonic FJ/KW, Rubycon, etc.) with Mouser part numbers.- Calibration‑SRAM backup batteryI believe it’s a 3.6 V lithium cell (half‑AA size?), soldered into a holder or directly to the board.Suggestions for the correct voltage, capacity, and mounting style, plus Mouser ordering info.My goal is to pull all of this together into one parts order and service session, so any “one‑stop” Mouser BOM links or kits would be incredibly helpful.I have found a lot of contradictory and approximative information all over the web and really don't want to miss the modification.Thanks in advance for sharing your favorite replacement parts, part numbers, and any installation tips!octal

author: 11mrjones
author_rank: Contributor
timestamp: July 24, 2025, 09:43:06 pm
content: I followed this to overhaul 2 3478's without issue. Ordered the parts from digi per video.I think the youtube poster is a regular here.https://youtu.be/e-itiJSftzs?si=bHFfqw8p6RMXaED1

author: octal
author_rank: Contributor
timestamp: July 25, 2025, 08:02:13 am
content: I already saw this video but he don't give the part numbers he bought. Also he says "low esr" for electrolytic, but this is too fuzzy.I just wanted to know if someone (electronics guy, as I'm not) has done real research in Digikey or Mouser catalog and can share with us the parts numbers.

author: J-R
author_rank: Super Contributor
timestamp: July 25, 2025, 08:13:00 am
content: Quote from: octal on July 25, 2025, 08:02:13 amDigiKey link is in the video description...

author: octal
author_rank: Contributor
timestamp: July 25, 2025, 08:18:00 am
content: Quote from: J-R on July 25, 2025, 08:13:00 amoh my badI didn't see itthank you very much.

author: octal
author_rank: Contributor
timestamp: July 25, 2025, 08:21:20 am
content: The RIFA capacitors are out of stock(wouldn't be difficult to find an alternative now that I have the electronic specs).The Lithium battery BR-2/3AE5SPN is not available at DK or Mouser FR, this part is reserved to US marketI'm really tempted by removing all this crappy battery and remove the SRAM and replace it with a small MCU that would emulate the SRAM and store the cal values in internal flash/eeprom or just check if I can drop a simple FRAM like Cypress FM16W08.Still need to find an equivalent

author: krish2487
author_rank: Frequent Contributor
timestamp: July 25, 2025, 10:47:32 am
content: Maybe start by searching the forum for the said modsThere are plenty of posts about these topics..https://www.eevblog.com/forum/projects/3478a-fram-modificationfor starters... and a super nice member by name@Dan Nwho posted his fram mod pcb to oshpark. and then you have the scripts for backing up and restoring the cal ram contents using gpib.and another post by the same guy in the youtube video, name is Jared but user handle is @TERRA Operative - super nice and extremely fast in respondingabout modding the 3478a to use oled displays instead of the stock lcds.. and then plenty others like it..just search around in the forum first and you might find all your questions already answered. :-)

author: octal
author_rank: Contributor
timestamp: July 25, 2025, 09:03:24 pm
content: Well,found references available from Mouser.for ElectrolyticsEKZN500ELL331MJ20S Aluminium Electrolytic Capacitors - Radial Leaded 50V 330uF 20% Tol.EKYB350ELL332MM25S Aluminium Electrolytic Capacitors - Radial Leaded 35VDC 3300uF Tol 20% 18x25mmEKYA630ELL102ML25S Aluminium Electrolytic Capacitors - Radial Leaded 63VDC 1000uF Tol 20% 16x25mmI think I'm missing the big capacitor close to the backup battery, will need to open my multimeter (don't have it at hand) and check the ref tomorrowfor RIFAR413F11000000M Safety Capacitors 1000pF 300volts 20%R413I222050T0K Safety Capacitors 300V 0.022uF 125C LS=15mm AEC-Q200Unfortunately for the battery I can't find any replacement. They are all out of stock, or either US market only and thus not available at France.I checked even other brands and even batteries with wires, can't find any quality replacement batteryI found the Panasonic one from one seller at France but in packages of 25 unit min, I can't buy a single unit