Difficulty finding bipolar electrolytic capacitor replacement for CRT TV - Page 1
Forum section: electronics / repair

author: CRTguy23
author_rank: Contributor
timestamp: March 06, 2025, 10:42:51 pm
content: In my Toshiba (Model 27A33) 27" CRT TV, there is a bipolar electrolytic capacitor that tests bad with a value of 6.8uf/50V. This capacitor is in the vertical deflection (section that controls vertical screen geometry) circuit. There aren't many options available for replacements. Digikey and Mouser have one option as a replacement but it specifies that said capacitor is specifically for audio and is only rated for 1,000 hours at 85C,Nichicon UDB1H6R8MHM1TOHere is a link to the service manual page that shows a schematic of the vertical deflection circuit in the Toshiba 27A33 and shows said capacitor as "C442", (Toshiba 27A33 Service Manual)Another site called "Arcade Parts & Repair" has a replacement but I'm not sure how good it would be,6.8uf-50v-non-polar-capacitor-105c-radial-df-5An Ebay seller has a new old stock replacement for sale by the Brand "Teapo",Teapo replacement capWhich option would you go with? Would it be safe to create my own electrolytic bipolar capacitor by combining two polar capacitors to get the value I need? I'm very interested in making my own but would want to be absolutely sure it's safe and that it would work well.

author: benj38
author_rank: Frequent Contributor
timestamp: March 06, 2025, 10:55:32 pm
content: It is perfectly fine do do it yourself by connecting two capacitors of double the capacitance in series with their two positive (or two negative) terminals tied together. In fact, some manufacturers actually say so explicitly.While you can find 14uF capacitors, they are quite rare, so go for two 16uF 50V capacitors which are easy to find. The slight increase in capacitance should not be an issue.

author: floobydust
author_rank: Super Contributor
timestamp: March 06, 2025, 11:12:04 pm
content: The cap is likely for the vertical output stage, so it needs to be close in value (tuned w/yoke) and tolerate high ripple current as well.I would use a film cap instead of an electrolytic. Depends on how much room you have. Consider (from Digi-Key):KemetR606.8uF 63VDC 18x10mm, 15mm pinsPanasonicECQ-E2685KFbigger if it will fitCDE685MMR100K6.8uF 63VAC 100VDC still 26x18.5x9mm, 22.5mm pins kinda big maybe.

author: CRTguy23
author_rank: Contributor
timestamp: March 06, 2025, 11:13:29 pm
content: Quote from: benj38 on March 06, 2025, 10:55:32 pmThanks. I just watched a video of someone creating a bipolar capacitor () and they wired a 1 M ohm resistor in parallel to the newly created bipolar capacitor to evenly distribute the voltages. Does this sound like a good idea? Is it necessary?

author: CRTguy23
author_rank: Contributor
timestamp: March 06, 2025, 11:50:59 pm
content: Quote from: floobydust on March 06, 2025, 11:12:04 pmThanks. I made an error. You are correct that said capacitor is in the vertical deflection circuit. Would there be any potential drawbacks and/or safety issues in using a film capacitor for this purpose instead of an electrolytic bipolar capacitor? Have you tried what you are suggesting in a CRT before?

author: bdunham7
author_rank: Super Contributor
timestamp: March 07, 2025, 12:24:37 am
content: Quote from: CRTguy23 on March 06, 2025, 11:13:29 pmThere are so many fundamental errors in that video that I'm not entirely sure it isn't intended as comedy. I encourage everyone to watch it as I found it to be quite hilarious.As for substituting film caps for bipolar electric, the main issue is that the ESR may be considerably lower. IDK what effect that will have in your particular circuit, but I'm guessing you'll be OK. One other thing, is the rating 50VDC or 50VAC? If it is AC, then you need a 100VDC rated cap not 63. The CDE 685MMR100K thatfloobydustlinked would probably be a good choice if you can fit it in there.

author: garrettm
author_rank: Frequent Contributor
timestamp: March 07, 2025, 12:40:38 am
content: Quote from: CRTguy23 on March 06, 2025, 11:13:29 pmGenerally, yes; but in your case, no. Series connected electrolytic capacitors should have balancing resistors across each capacitor to avoid over-voltage at any one capacitor due to charge imbalances in the string. For two anti-series connected electrolytics, you just need each capacitor to be rated for the full voltage. So in your case, 50V rating is sufficient.If ringing or other unwanted behavior occurs with a film capacitor replacement you can add a dampening resistor in series with one of the leads. Probably something on the order of 0.1 to 3 ohms would likely do the job, but a critical dampening analysis would tell you the exact value to use.

author: CRTguy23
author_rank: Contributor
timestamp: March 07, 2025, 12:43:57 am
content: Quote from: bdunham7 on March 07, 2025, 12:24:37 amLOL, good to know about the video. I'm not sure if the voltage rating of the original bipolar capacitor of 50V is for DC or AC. Do all bipolar electrolytic capacitors operate on AC? I should be able to fit the cap you suggested in the board.

author: CRTguy23
author_rank: Contributor
timestamp: March 07, 2025, 12:47:15 am
content: Quote from: garrettm on March 07, 2025, 12:40:38 amIf I did add a dampening resistor, what wattage would I want it to be rated for?

author: garrettm
author_rank: Frequent Contributor
timestamp: March 07, 2025, 12:58:29 am
content: Quote from: CRTguy23 on March 07, 2025, 12:47:15 amGood question. Depends on the current through the capacitor. If I knew more about the circuit, I could be more specific. But likely a normal 0.25W resistor would be sufficient. The dampening resistor is only used to add a small amount of loss to mimic an electrolytic cap, so power dissipation should be low. Let's assume the current through the cap is 100mA AC RMS. Then 0.1^2 * 3 = 0.03 W = 30 mW. In this case even the largest value I suggested (3 ohms) isn't dissipating much power. But since the power is proportional to the current squared, power dissipation quadruples each time the current is doubled. But even 200mA results in 120 mW which won't cause the resistor to get too hot. So its likely a standard 0.25W carbon composition or metal oxide resistor will do the job fine.

author: CRTguy23
author_rank: Contributor
timestamp: March 07, 2025, 01:04:25 am
content: Quote from: garrettm on March 07, 2025, 12:58:29 amThanks. I did provide a link to the this TV service manual in the first post if you want to look at it. It is a schematic of the circuit this capacitor is operating in which is the vertical screen deflection (screen geometry) circuit.

author: andy2000
author_rank: Frequent Contributor
timestamp: March 07, 2025, 03:01:45 am
content: I doubt that capacitor needs to be anything exotic. You can get a good idea of how much ripple current it need to take by looking at the physical size of the original. 6.8uF, 50v should be pretty small (around 5-6mm diameter, and ~10mm long give or take). If it's a lot bigger than that, then more care will be needed selecting a replacement.It's hard to go wrong with using a film cap for the replacement if it will fit. Lower ESR shouldn't be an issue in that circuit. Yes, they may have taken the ESR of an electrolytic into account when designing the circuit, but in all the years I've been repairing electronics, I've never run into a situation where replacing an electrolytic with a film cap failed to work. The main reason they didn't use a film cap originally is most likely cost and size. That electrolytic from Digikey will also probably be fine. The 1000 hour rating is at 85 degrees. Normally capacitors run much cooler, and last orders of magnitude longer. 85 degrees would be too hot to touch! Avoid Teapo, it's a crap brand which will fail.

author: benj38
author_rank: Frequent Contributor
timestamp: March 07, 2025, 08:20:01 am
content: Quote from: floobydust on March 06, 2025, 11:12:04 pmGiven the crappy tolerances of electrolytic capacitors I doubt the difference between a printed value of 8uF and 6.8uf will make any difference.That said, a film capacitor, if it fits, is a good idea.Quote from: bdunham7 on March 07, 2025, 12:24:37 amAll non-polar electrolytic capacitors' voltage ratings that I have seen are DC not AC. See for example:https://www.mouser.com/datasheet/2/231/XC-600180-1174900.pdf

author: bdunham7
author_rank: Super Contributor
timestamp: March 07, 2025, 02:46:01 pm
content: Quote from: benj38 on March 07, 2025, 08:20:01 amI've seen VAC ratings on older models and on motor start capacitors.https://www.cde.com/resources/catalogs/PSU.pdfThey can have both an AC and DC rating, the AC rating could be about 70% of the DC rating or less, depending on whether it was limited by peak voltage or ripple current. A VAC rating is only valid if you know the frequency and in most cases 50/60Hz is either specified or implied. Bipolar capacitors used in audio applications like speaker crossovers typically only provide the DC rating and you have to figure out for yourself if it will be overstressed in your application.

author: benj38
author_rank: Frequent Contributor
timestamp: March 07, 2025, 03:58:02 pm
content: Quote from: bdunham7 on March 07, 2025, 02:46:01 pmLet me clarify my statement a bit more.First I was not referring to motor start capacitors, or fluorescent ballast capacitors, etc. I was referring to whatever one may find on a TV's PCB. But indeed, my statement as it was given was too encompassing, and I welcome your correction.Even taking into account motor start capacitors, every non-polar electrolytic that I have seen, if it has a voltage number printed on it (like 50V) with no other indication whether it is AC or DC, the voltage given is a DC rating. In other words, if the printed value is an AC rating, it will clearly indicate so by either saying "AC", or "~", or a frequency given (or implied as you wrote).

author: bdunham7
author_rank: Super Contributor
timestamp: March 07, 2025, 04:30:00 pm
content: Quote from: benj38 on March 07, 2025, 03:58:02 pmAnd I was referring to, among other things, TVs old enough to not have a PCB.But in this case, if you look at the schematic you'll see that the capacitor in question is designated as "UHT", presumably meaning Ultra High Temperature. And it has failed. IDK how big it is but I suspect that it handles a relatively large ripple current and a generic bipolar or one constructed from two regular caps may not work well.

author: floobydust
author_rank: Super Contributor
timestamp: March 07, 2025, 06:12:18 pm
content: Looking at the set's schematic, the cap is not (as I guessed) involved with vertical deflection - I was thinking of C408 1,000uF 25V that part usually gives vertical problems like non-linear or squished and not enough V deflection.C442 6.8uF 50V BP Rubycon? UHT series is tied to the horizontal output but I'm not sure what it's doing with the discrete buffer amp and drive Q410.I'd still be OK putting in a film cap there that can take high ripple current, instead of an electrolytic.

author: CRTguy23
author_rank: Contributor
timestamp: March 07, 2025, 08:52:24 pm
content: Quote from: floobydust on March 07, 2025, 06:12:18 pmThe main issue I'm having with the TV is that the picture looks like an hour glass shape where it's slightly bowed in at the sides. I've owned this exact model before and it had the same issue. I thought that maybe the bipolar cap C442 might be the culprit. I ordered capacitor replacements yesterday for the TV and I ordered the bipolar electrolytic cap from digikeyUDB1H6R8MHM1TOas well as this polyester film capacitor you recommended,685MMR100K. I might just experiment with both and see how they each affect the picture. I also ordered replacement electrolytic caps for the rest of the board. There is only about 20.