Replacing electrolytic capacitors with ceramic? - Page 1
Forum section: electronics / repair

author: Orihalcon
author_rank: Contributor
timestamp: October 09, 2024, 09:44:29 pm
content: Hello all,I'm working on refurbishing some VCRs that originally used relatively low capacitance electrolytic mini capacitors as part of the Video/RF signal right after the video head before the RF signal is decoded. The capacitors in question are all 10uF or lower.I am wondering if there are is any reasons NOT to "upgrade" those electrolytic capacitors to ceramic (or some other capacitor type) other than cost?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 09, 2024, 11:08:14 pm
content: So, signal coupling capacitors?Distortion and microphony are the main downsides. Distortion might not matter, depending on how they're being used (active clamp DC-restore per line/frame?), but microphony has the interesting effect that you'll see horizontal luma bars when tapping on the circuit (or there's enough ambient audio).The ideal choice here is tantalum, actually. At least, electrically speaking -- but their cost (in general, plus externalities, i.e. Ta is a conflict mineral) may be sufficient reason to stick with electrolytic.Or film, but large values in low voltages are prohibitively large; film just can't be stretched as thin as ceramic can, without succumbing to thinning or pinholing.On the upside, they see very little if any ripple current, or heat, so shouldn't need replacing unless they were poorly made in the first place. (Seals can go leaky, electrolyte can corrode, etc..) This is one place where an ESR test (in circuit should even be reasonable) is preferable over a general "replace everything" policy. Anyway, modern electrolytics will be good for at least another couple decades at room temperature, so it's not like you're dooming the unit by replacing like with like.Tim

author: factory
author_rank: Super Contributor
timestamp: October 10, 2024, 12:57:55 pm
content: What is the age of the VCRs? Are they surface mount or through hole parts? Is the board covered in fine traces and/or a multilayer PCB?Certainly smaller values can dry out with age, leakage (peeing) can be a major problem, it doesn't matter is the seals are rubber or plastic, they degrade with age & fail, even well known brands fail in this way.In my experience stuff from the late 80s & 90s seem to be worse than much older parts.David

author: MathWizard
author_rank: Super Contributor
timestamp: October 10, 2024, 05:31:44 pm
content: What about electrolytic caps that are 0.1-1uF ? I've never bought any EC's that small, so I've always just used those green coated, higher voltage Mylar caps, or ceramics in any circuit/repair.IDK if small 0.1-1uF EC's were ever cheaper than large ceramic's, but yeah I guess it depends on the circuit, and the pro/cons for each type of cap.I'm still just talking about under 1uF caps, not +1uF multi-layer ceramics, but are small EC's getting rarer though ? I haven't worked on that many repair's, but I feel they are getting less common. So are the other types getting better at what an EC can offer, or maybe it's the types of circuits used these days match better with ceramics.One of these days I need to compare so caps side by side on a scope, and see IRL.

author: Orihalcon
author_rank: Contributor
timestamp: October 12, 2024, 01:46:27 pm
content: Thanks for the replies!They may very well be signal coupling capacitors, but unfortunately my knowledge of circuits is rather limited haha. There are 3 of them - all 2.2uf 35V bipolar, through hole electrolytics, I'd say 4mmx5mm radials. They are very short because of the low clearance between the video drum and the PCB. Oddly enough, the service manual online doesn't have a board schematic I think maybe because it's either incomplete, or they never really intended this board to be serviced and just swapped out along with the video head if it ever needed to be swapped. It is directly attached to the video head and is labeled "cylinder drive" though it is obvious that all the signals from the heads come through this board first as all contacts from the video head go through this board first. The board after this in the chain is the Head Amp.The VCR is a Panasonic AG 1980 and it's from around the 2000's.To get enough clearance to get the old capacitors out, I actually have to desolder the head from it. I've done swaps with 2.2uf bipolar electrolytics that are 4mmx7mm, but that extra 1mm often gets very close or sometimes actually touches the head drum on top which is grounded and I don't like the idea of that somehow causing issues. I also have to bend the leads rather sharply at the exit of the capacitor to get them to sit low enough to fit at all which isn't ideal.I attached a picture of the PCB in question - they used surface mount ceramic caps on other parts of this board, so I'm thinking they wanted electrolytic capacitors there for some reason even though they are quite low value in the scheme of things - could be a cost saving thing though if tantalum has similar filtering/coupling characteristics as electrolytics.As for why I am changing these at all, I've found that playback on the machine with EP tapes (which uses a different set of heads than SP and probably a different 2.2uf capacitor) gives relatively frequent sparkles/comets on random frames on playback, and by replacing those with new capacitors, that image noise resolves completely. I did a test with some 2.2uf bipolar MLCC capacitors and that also got rid of the issue in a short test, but I don't really know the properties of MLCCs vs bipolar electrolytics to know that this is an ideal choice for this situation.Consideration was also given to just mounting these on the underside of the board or possibly laying down the 4x7mm electrolytics I have on their sides, but I'm worried that laying those capacitors down horizontally over other traces that carry all of the unamplified video information right after the heads has potential to introduce signal noise to those other traces?

author: fzabkar
author_rank: Super Contributor
timestamp: October 12, 2024, 10:30:08 pm
content: Service manual:https://elektrotanya.com/showresult?what=Panasonic%20AG%201980&kategoria=All&kat2=All

author: Manolo Mos
author_rank: Contributor
timestamp: October 13, 2024, 09:35:03 am
content: In this Panasonic head unit does not worth to replace capacitors, or at least I've never found a bad capacitor, but there is a typical fault: Dry joints in the connector and the main IC. Nothing else.Relation between capacitors and image sparkles? I don't know.Check dry joints.