HP34401A - Original capacitors? - Page 1
Forum section: electronics / testgear

author: ra-ma
author_rank: Contributor
timestamp: February 15, 2020, 08:23:52 pm
content: I got a HP34401A some weeks ago. I'm pretty happy as it looks and works well.As far as I see the DMM is from 1992. As I learned that capacitors should be exchanged after a certain time, can anyone help me to find out how old these are? From the solder joints on the bottom I can't judge if the caps have been replaced. I can't see any leakage or damage. Does anyone know if the ones on the pictures are original? Thank you.

author: Yansi
author_rank: Super Contributor
timestamp: February 15, 2020, 08:28:32 pm
content: If it ain't broke, don't fix it, damn.

author: Specmaster
author_rank: Super Contributor
timestamp: February 15, 2020, 08:57:43 pm
content: I totally agree, don't touch it if it in't broke, leave it alone.those filter caps all look perfectly OK to me.

author: amc184
author_rank: Regular Contributor
timestamp: February 15, 2020, 09:37:04 pm
content: The capacitors that are in there are the same manufacturer (Nippon Chemicon) and series as any other 34401A, so they're almost certainly original.These are good quality capacitors, but will still have a finite life. This could be 30 years, or it could be 60 years, a lot of this will depend on the environment it was operated in before you owned it, and how close these capacitors were used to their ratings in the design. Both unknowns to you probably.There are a couple of risks if you don't replace them and they degrade; they may not work as well, and they may leak. Not working as well isn't a big deal, it might just force you into replacing them. Having them leak electrolyte is the worst case. The electrolyte in these capacitors is corrosive, and when it leaks it will eat away tracks and component leads (a bit like an old battery, but not as bad). Correcting this is potentially a much bigger repair than replacing the capacitors in the first place.There are risks when replacing the capacitors as well; it's pretty easy to damage a multilayer PCB when you remove the old capacitors. How are your rework skills?All up, you should balance the risk of the old capacitors causing damage versus the risk of damaging the PCB during rework.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: February 15, 2020, 09:39:49 pm
content: I would also tend to agree. I’ll replace any RIFA cap, but there is none in the 34401A. I replaced all the Electrolytic caps in my 6632A that is about the same vintage, just to find out all the caps I pulled are within spec in capacitance and ESR while I was cleaning up.I own two 34401A, one from 2009 and then he other from 2012, the thing to look out for are uneven VFD display brightness if you leave it on constantly, and calibration if you want to ensure it is within spec.Given the age of your meter, the component are well aged and should not drift much. If there is no cal history, I would suggest you to get it cal to be certain of its accuracy.

author: TD
author_rank: Contributor
timestamp: February 15, 2020, 09:44:41 pm
content: Maybe he wants to stock up on the parts that could cause issues down the line. I to stock up on parts and part types that are known to have issues. I have two 34401's, no cap issues yet. I've only had them for a little over a year. I recommend looking for any thread or videos were the replacement of 34401 caps are being replaced.

author: HighVoltage
author_rank: Super Contributor
timestamp: February 15, 2020, 10:20:55 pm
content: I have many 34401A, old and new and the electrolytics are perfect, even after so many years.No need to exchange them, unless you have a problem.

author: bitseeker
author_rank: Super Contributor
timestamp: February 16, 2020, 03:10:12 am
content: Those look like original caps to me. No need to worry about them. This series of meters is not known for having issues with capacitors. I had two very early versions, two more recent ones now, and a 34410A. They're all fine. Take a look through the forum and you'll see other equipment that are notorious for capacitor leakage, but this isn't one of them.As amc184 said, you're putting the equipment at risk going through the replacement process. It's just unnecessary unless yours has a problem.

author: ra-ma
author_rank: Contributor
timestamp: February 16, 2020, 07:23:53 am
content: Quote from: amc184 on February 15, 2020, 09:37:04 pmYes, that's exactly the decision I have to take. I really want to prevent the capacitors to start leaking, whenever that might be...Thanks!

author: Yansi
author_rank: Super Contributor
timestamp: February 16, 2020, 11:43:38 am
content: Nippon Chemicon caps are pretty unlikely to leak. (In fact, I've never seen one that leaked).

author: mariush
author_rank: Super Contributor
timestamp: February 16, 2020, 12:01:07 pm
content: As most manufactures, they are not perfect.They had some series of capacitors which are known for leaking or degrading even when not used.In particular the KZG series and I think KZJ (but not sure, saying it from memory), both ultra low esr electrolytic capacitors with a water based electrolyte.I've seen Asrock motherboards (but Asrock's not to blame, they were just one of the last manufacturers that still used electrolytic capacitors on budget boards, now everyone uses solid capacitors) still in original retail boxes that sat as spare parts for a year or two that had KZG series capacitors in the VRM circuit.Happened to Nichicon as well, with similar very low / ultra low esr series like HM and HN around 2004 where they failed (again, from memory, I think rumors were they used too much of a particular chemical along with the electrolyte which made them go bad prematurely).Otherwise Nippon Chemi Con and Nichicon and Rubycon and Panasonic are fairy safe and reliable... if the bottom looks good and the top doesn't seem to crack, they should be fine.

author: Cubdriver
author_rank: Unknown
timestamp: February 16, 2020, 11:41:03 pm
content: HP and the like typically used high quality components in their instruments - these aren't consumer electronics that are built to a price point that we're discussing here. Given that, other than parts that are known to be problematic as a whole (such as the surface mount electrolytics used in 2000-ish Tek TDS scopes, for instance), I am disinclined to shotgun parts in them simply because <reasons> if they are otherwise functioning correctly.I recently got a pair of old nixie DVMs from my favorite surplus place out in CA - they're siblings, both made by HP in mid-late 1969, and both sport most recent cal stickers from 1990, so I surmise that they've been out of service for nearly 20 years, likely stored in a warehouse somewhere. Both were initially powered up in short bursts, starting at about 15 seconds per minute on and then with slowly increasing on times - 20 seconds, then 30, then 50, then a minute at a time with a minute or so rest in between (I don't have a variac out there) to permit the long dormant caps to reform if they could, until I felt they could stay on without damage. One buzzed and flashed random things when turned on, never getting any better; the second settled in and seems happy as it was received, and eventually stayed on all through the night several times during my stay. Both have since shipped home and spent some time on the bench. The good one appears to be good straight out of the box - DC readings agree very closely to other meters, and the resistance readings are very close to the decade box settings. It still needs to be opened and wrung out, but I'd feel comfortable at present using it. The buzzy one has a dead filter cap - sticking another in parallel with the dead one got it operational with accuracy similar to that of its sibling. IT will be getting a new filter cap. I plan to open the other up and check ripple, but if it is in spec than it will NOT be getting any new caps.I have several other 30+ year old instruments still running on their original electrolytics, too.TL/DR - Unless there are known failures that are endemic to the particular breed, I replace parts in my gear when they go bad.-Pat

author: james_s
author_rank: Super Contributor
timestamp: February 17, 2020, 01:50:04 am
content: The only capacitors I shotgun are SMT electrolytics and random Chinese brand electrolytics. If you have good quality reputable brand parts that are in good shape leave them alone. One of my pet peeves is when somebody wholesale changes perfectly good high quality parts just because they're old and installs cheap crap.