Best Electrolytic Capacitor to Recap an Oscilloscope? - Page 1
Forum section: electronics / testgear

author: ResistorRob
author_rank: Regular Contributor
timestamp: April 28, 2020, 10:26:36 pm
content: I have 2 vintage oscilloscope that have issues related to old/defective electrolytic capacitors.Can someone tell me what I should be looking for in replacement caps? I obviously know about capacity, voltage, temperature, and going with a name brand. What I don't know is the secondary specs like ESR. If someone has a specific series of capacitor I should use that would be amazing help. As an example Panasonic sells like 10 different series of capacitors. I can eliminate a few, but I'm not sure how to select what I really need. I only want to do this once and have it last at least 5-10 years, so cost is not a factor. I'm really good at soldering and safety procedures, so I just need to know what to buy.

author: electricMN
author_rank: Regular Contributor
timestamp: April 29, 2020, 12:07:42 am
content: Look at the capacitors you're taking out and get the datasheets for them. Then find equivalent replacements if you can't get the originals.

author: rsjsouza
author_rank: Super Contributor
timestamp: April 29, 2020, 01:09:52 am
content: Just a few of my observations along the years. I am pretty sure you will find other opinions around.If cost is not a factor, in general you are looking at the highest working temperature versus number of rated hours. Also, polymer or tantalum capacitors usually have a longer lifetime. In some cases you may need to carefully look at the ESR so you don't blow any diodes at power up. Also, sometimes you need to fit a capacitor in its alotted space, so the dimensions are important - IME ultra small capacitors always compromise on one or more of the prior specs above.In certain spacious places you can also reduce the stress on the capacitor by using a higher voltage part.One additional detail is that, in certain places, it may be tempting to replace a lower value electrolytic with a MLCC (they can potentially last forever). However, the circuit may be designed to work with the inferior frequency response of the electrolytic and therefore nowadays I only replace them with the same approximate type (sometimes poly or tantalum).

author: Soulfetish
author_rank: Newbie
timestamp: April 29, 2020, 07:06:45 am
content: What's the make? I know that Tektronix of a certain vintage (465 comes to mind) use radial electrolytics with a unique mounting footprint. Someone designed a universal PCB adapter to allow you a lot of flexibility in choosing the best currently manufactured replacement. Below is a link to an example sold on ebay (no affiliation) if you need it:https://www.ebay.com/itm/Capacitor-Adapter-Tek-Tektronix-7000-Series-Recap-6-square-1-triangle-adapter/272799971348

author: Miti
author_rank: Super Contributor
timestamp: April 29, 2020, 11:02:47 am
content: In the power supply I always use Nichicon PW series, they never failed me. I’ve also used them to recap the main board of a Tektronix 2445B. In general I only use Nichicon and Rubycon in all my important repairs.

author: ResistorRob
author_rank: Regular Contributor
timestamp: April 29, 2020, 10:45:39 pm
content: Quote from: Soulfetish on April 29, 2020, 07:06:45 amPhilips PM3065BK Precision 1474The Philips I wanted for years. I got a brochure for it back in the 90's and was really expensive. (I still have the brochure) I still love the look of it, and while it works okay the waveforms aren't as accurate as they should be. I'm working on restoring it, and want it in perfect condition.The BK Precision was my grandpas, and he gave it to a few weeks before he passed away. He knew I was the only person in the family who would appreciate it. Definitely has some issues. He thought it needed new caps on the power supply. I tested the voltages and they are in spec, but barely. I did a lot of troubleshooting and can't seem to find anything else wrong. He worked for NASA, so I'm not going to second guess a rocket scientist and try that first.Quote from: Miti on April 29, 2020, 11:02:47 amThank you! This is the kind of information I needed. Any idea what Rubycon series would be equivalent to the PW series?

author: tautech
author_rank: Super Contributor
timestamp: April 29, 2020, 11:43:35 pm
content: Cap replacement is not too complex when it's apparent what type of sub-circuit they're used in which typically is somewhat simple to deduce when we have a schematic.PSU's are generally under the most stress but old caps can leak most anywhere.I try to break circuits into types, say if SMPS, caps will need to be low ESR and it's wise to use higher heat ratings also.Linear PSU's OTOH are less demanding of cap performance and low ESR here can be a mistake as initial cap charge at turn ON can exceed rectifier surge ratings if insufficient headroom wasn't factored into the original design.Today we often have better cap choices than the OEM had especially in compactness and higher voltage ratings so to provide better voltage headroom and therefore longer life. But sometimes you need to check the BOM and get datasheets especially to check a replacement has sufficient ripple rating.

author: Mp3
author_rank: Frequent Contributor
timestamp: April 30, 2020, 03:52:22 am
content: Quote from: Miti on April 29, 2020, 11:02:47 amYup, Nichicon PW is great stuff. Lately, I've been pretty much ONLY using United Chemi-Con though. I still use Nichicon PW as my first preference after EKY or KWB series. Been really happy with them.

author: helius
author_rank: Super Contributor
timestamp: April 30, 2020, 04:51:09 am
content: Quote from: tautech on April 29, 2020, 11:43:35 pmAnother situation where low ESR is a mistake is at the power input of a low-voltage device with a remote power supply. The power lead inductance can cause harmful ringing without the C+R acting as snubber.

author: james_s
author_rank: Super Contributor
timestamp: April 30, 2020, 05:31:06 am
content: Quote from: Mp3 on April 30, 2020, 03:52:22 amI've found Panasonic to be good as well.Really most of the reputable brands are fine. I avoid the very cheapest stuff and I look at the rated lifespan.

author: tautech
author_rank: Super Contributor
timestamp: April 30, 2020, 05:59:10 am
content: Quote from: helius on April 30, 2020, 04:51:09 amQuite so, and you sometimes see this remote bulk capacitance on a long power rail some distance from the PSU. The caps are usually not large, say a few 100 uF at most and technically they provide rail decoupling yet the obligatory 0.1uF decoupling ceramics on each IC are used too.

author: Mp3
author_rank: Frequent Contributor
timestamp: April 30, 2020, 06:31:22 am
content: Quote from: james_s on April 30, 2020, 05:31:06 amGood point, Panasonic is great for making lots of high reliability options in just about every size you need, but I usually pick them only when I have to since they tend to sound like garbage in audio applications. If you're not working on something that needs to be heard, Panasonic is totally fine. Totally subjective, though, but I know others who work on audio stuff share my sentimentsEvery time i need to buy caps and UCC or Nichicon doesn't have the cap i need at the lifespan/heat tolerance i want, i go for Panasonic every time.

author: W3KW
author_rank: Contributor
timestamp: December 12, 2022, 10:10:14 pm
content: I found this video very helpful:https://youtu.be/lrXCVg6T-ek-a Tek 2235 scope.The comments section had a shopping cart for Digikey. Merely click on the link, find suitable replacement caps for out of stock parts (there were maybe 4) which digikey makes super easy to do, and purchase. Wow. Super helpful. If someone has a shopping list put together for the 465, 465B, 2246, or 2465B, please share it on this thread. The author of the above YouTube video even labeled the part numbers in the list for super convenient inventory and part location. Thank you, sir!If I need to put parts orders together on my own for those scopes, I’ll try to post the shopping cart link in a thread on the eevblog.Thanks in advance if you’ve got one and can share it!WesW3KW