[solved]Replacement capacitor, same brand & value, but 3 leads?? - Page 1
Forum section: electronics / repair

author: Gen-8bit
author_rank: Newbie
timestamp: November 30, 2024, 06:50:42 am
content: Hello from the PNW, I really need some help here;I'm in the process of fixing my Zenith ZF-171 luggatop. I need to replace both Malleroy 780μf, 75 Vdc capacitors on the power supply board, which seem to be extremely difficult to find. The only ones I came across were found on thiseBay auction: #https://www.ebay.com/itm/193860551121&ved=2ahUKEwj11vvmgoOKAxVFDzQIHQsXGa0Qjjh6BAgbEAE&usg=AOvVaw3gEAgal-_sXAVrvEYSI507.As these at the time seemed the only ones I could find, and I was a bit impatient, I didn't pay attention to the fact they had a third lead attached on the top and down the side of the capacitor.Well, I'm now stuck with those and need to make them work somehow, so here is the prize question: What is the extra lead wire for and how can I plug it on the board in place of the normal two lead ones? I did some research but that didn't help much. Some say it's for physical support, others say it's the negative lead and two positive leads, then again it's allegedly two caps in one. What is it now?If the top lead is negative, can't I just clip off one of the two bottom leads and fit it like a standard "two legged" capacitor?

author: Haenk
author_rank: Super Contributor
timestamp: November 30, 2024, 08:26:06 am
content: Other than for looks, I would not use this decades old capacitor, at all.If you don't care about the looks just replace with a modern capacitor, like 1000uF 100V (might want to go to a even higher voltage). Use a part from a well known company (Nichicon, Chemicon and so on.), you might want to show us the PCB where it goes in, but I assume anything will work. A "standard" part might be better seuited than a "low ESR for switching power supplies" model.If you want to keep the vintage look, hollow out the old cap and hotglue the new one into it. (Careful not to short out anything etc. pp.)

author: coromonadalix
author_rank: Super Contributor
timestamp: November 30, 2024, 12:14:16 pm
content: same answer as previoussome open the cans to put more recent ones in them just to keep the look intact ...my friend rebuild lamp radios and do this trick

author: Gen-8bit
author_rank: Newbie
timestamp: November 30, 2024, 05:13:09 pm
content: As mentioned before, I'm stuck with a 10pack of these and they were the only ones with the exact values, so I might as well just use them. I don't care about looks, I would even kludge two different caps together to make one with close enough values, if I had the right ones. I just want to get this thing fixed, and working.I'm fully aware that they are old, but they're new stock, so I trust that they will last at least for a little while. Which capacitor style am I dealing with anyways? Is it really ++ with - on the other end? Or is it +- and the third wire for structual support only? See attached picture of the location they're supposed to go.

author: Dave Wise
author_rank: Regular Contributor
timestamp: November 30, 2024, 05:27:24 pm
content: It's not 75V, it's 7.5V . (Or 7,5V depending on where you live.) I would sketch a partial schematic, and if I was satisfied that there was no compelling reason to keep the exact original capacitance, I'd throw in a couple of new 1000uF parts of whatever voltage > 7.5V that fits the pad spacing.

author: factory
author_rank: Super Contributor
timestamp: November 30, 2024, 05:37:27 pm
content: It looks to be a typo in the first post, the auction link in that post links to the 7.5V ones, I wouldn't use them either, they look like those crappy epoxy seal things that crack & leak electrolyte everywhere.But looking at the PCB there parts that are burnt too, replacing just the caps will probably not fix it.For the capacitors I would just use some good quality ones from Mouser/Digikey(not from auction site or Chinese selling sites), buy the next value up e.g. 820uF or 1000uF, uprate the voltage to get similar physical size & lead spacing to the originals.David

author: BILLPOD
author_rank: Frequent Contributor
timestamp: November 30, 2024, 07:24:01 pm
content: Good Morning Gen-8bit, I'm also curious what the 3rd lead is for, but no one seems to know. But the original was 7.5 Volts, not 75, as Dave Wise has noted. Get an LCR meter and measure capacitance and ESR between all possible lead configurations on those replacements you have. Even if you don't use them on this project, you can put them in your stock and eventually you will find a use for them.Be sure and mark them with their specifics. I'm sure the manufacturer's specification sheet will give you everything you need.

author: Gen-8bit
author_rank: Newbie
timestamp: November 30, 2024, 07:35:21 pm
content: Ohh-to-the-m-of-the-flipping-gee, I feel so stupid now. How did that not stand out to me?? It seems I need to buy me a new set of eyeballs lol! Well in that case it makes things much easier. I have some that should be a close match. Adult ADD sucks! But I'm curious now, what's the extra lead for and what are the the allocations/pinouts of all three? These must be from the tube age!

author: bdunham7
author_rank: Super Contributor
timestamp: November 30, 2024, 07:42:50 pm
content: I can't load your eBay link. Can you post a photo of these 3-legged capacitors? I'm curious.As for fixing your PSU, as others have stated you need something that will physically fit and has specs greater than 780µF and 7.5V. The original capacitor may have had specific ESR or ripple specs, so you probably don't want to use just anything, but if you find something with say 1000µF and 10-25V ratings that is low-ESR and about as large as the original you'll likely be OK.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: November 30, 2024, 07:52:50 pm
content: Perhaps these are Russian caps, where the third lead is something to hold on to whilst you drunkenly solder the other two.

author: Gen-8bit
author_rank: Newbie
timestamp: November 30, 2024, 08:30:01 pm
content: Lol that could very well be the case

author: Dave Wise
author_rank: Regular Contributor
timestamp: November 30, 2024, 08:37:19 pm
content: In the electron tube era, multi-section electrolytic caps were common. In solid-state equipment, it's almost unheard of, and the third pin is for mechanical support. Tall thin parts need this - or gluing to the board - to pass shake/vibration testing.

author: Gen-8bit
author_rank: Newbie
timestamp: November 30, 2024, 08:42:45 pm
content: Yes, I indeed accidentally bought the correct value caps when searching for the wrong Voltage, what a derp coincidence lol!Here they are:https://www.ebay.com/itm/193860551121?_skw=mallory+capacitor+electrolytic+780%CE%BCf+75Vdc&itmmeta=01JDZCFGF8MHPCQZMPP5A86E8C&hash=item2d22fd41d1:g:YEQAAOSwv1hgC3Lj&itmprp=enc%3AAQAJAAABAHoV3kP08IDx%2BKZ9MfhVJKnNrXrEAKvJpn4yVogtP6vutUb0lctWBuSrEHa5o88kBkQOk0VBJULtb1TOeXE3KaDbmyYIuywZ9VOpeTwgn1oUy9kG5iWveR3F6%2FNoU3OUIF9s82mLKa6jIsuJgXpZZ06FZM5QzEwxtNALnP3TnVnstnutwZF4CTaH5xmEeggOIqo%2FO8E0jtOYjyTxScmpoe64ZxgMTbNbqtoesm5PvgFANdnQTj5d2AZ5ckJ4fPa7SioDco4HN%2BmdPPcCXThfXOklWfvCChC%2B9cgW%2FnU%2BhPm%2BzLq8wQqbeti0W1Hi96Zk50geA%2BRirlR%2BBMeKIi3AxvU%3D%7Ctkp%3ABk9SR9iHvuzvZA

author: factory
author_rank: Super Contributor
timestamp: November 30, 2024, 09:30:34 pm
content: Quote from: bdunham7 on November 30, 2024, 07:42:50 pmTry this link instead, there is no need for the rest of the crap after the ebay item number,https://www.ebay.com/itm/193860551121David

author: factory
author_rank: Super Contributor
timestamp: November 30, 2024, 09:47:17 pm
content: For the Mallory capacitor with an extra lead, it's for mounting only, the two leads at the bottom are the capacitor connections, the side of the can indicates the positive lead.Mallory part is VPR, the attached pdf if from this catalog;https://www.technicalaudio.com/pdf/Electronics_Catalog_Extracts/Mallory_general_catalog_1985.pdfSprague also make this type of capacitor as 672D.https://www.vishay.com/docs/42054/672d.pdfThis is one way these three lead caps were intended to be used, the extra lead is just for mounting purposes only, picture from a HP 5328A. The Mallory part is vertical use only, as the third lead is sleeved to the can.David

author: bdunham7
author_rank: Super Contributor
timestamp: November 30, 2024, 11:16:41 pm
content: Quote from: Gen-8bit on November 30, 2024, 08:42:45 pmYes, it appears that you have managed to track down the precise replacements you need after you trim off that third lead. As expected, they're a special low-ESR variety. However, they're pretty old at this point.