Unusual diode package - Page 1
Forum section: electronics / repair

author: ebastler
author_rank: Super Contributor
timestamp: March 23, 2023, 11:48:11 am
content: I am repairing a 1980s linear power supply (FG Elektronik NMC 8006, used in a small-series German computer). One of the diodes in the 5V rectifier has become conductive.The diode comes in a package I have not seen before -- see the attached photo: The body is a flat disk, 10 mm diameter, 4.5 mm tall. The terminals are flat and circular too, a tad less than 6 mm diameter. There is no lettering on the package, just a red color code for the anode side, and "10 A diodes" silkscreened on the PCB.FG Elektronik have done a nice job mounting these diodes, with good heat transfer both to the PCB and to a mounting/connecting tab on the opposite side. Two diodes share one connecting tab -- one of these is also shown in the photo. Hence I would like to replace the diode with one in the same package.I have scrolled through many catalog pages of diodes at Mouser but can't find this type of package. Any hints how it might be called? Thank you!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 23, 2023, 01:18:06 pm
content: Possibly some of these?https://www.digikey.com/en/products/filter/diodes-rectifiers-single/press-fit/280?s=N4IgjCBcpgbFoDGUBmBDANgZwKYBoQA3AOygBcAnAV3xAHsoBtEAFlgGYWBOdkAXQIAHMlBABlSgEtiAcxABfRUAYou might have to search far and wide for an exact equivalent, or NOS originals. Also, depending on which side of Germany that was, consider ex/Soviet sources?If nothing else you could keep the block and stuff an SMT schottky underneath, almost no one's the wiser? (Schottky just for the poorer on-board heat dissipation, save a bit of temp rise.)Tim

author: mzacharias
author_rank: Frequent Contributor
timestamp: March 23, 2023, 01:37:19 pm
content: Looks more like a button cell battery to me.

author: wasedadoc
author_rank: Super Contributor
timestamp: March 23, 2023, 01:50:10 pm
content: Quote from: mzacharias on March 23, 2023, 01:37:19 pmThere is a saying "Looks can be deceiving". Applicable to you in this case.They are rectifiers. I have some of that package type.

author: simba15
author_rank: Regular Contributor
timestamp: March 23, 2023, 02:10:33 pm
content: I was able to find a few examples with the keyword "Press-pack Diode".Seems to be available from the typical rectifier manufactures IXYS, Infineon Little fuse etc. but it seems they are mostly larger than your example.Hope you can find a suitable one.

author: ebastler
author_rank: Super Contributor
timestamp: March 23, 2023, 02:25:34 pm
content: Thank you all for the replies and ideas!Turns out that the off-base reply from mzacharias (the "button cell" association, which had me rolling my eyes to be honest) was quite helpful: It prompted me to try and search for "button diodes", and that's indeed what those packages are called!Google image search results for "button diode"The 10 mm diameter seems to be common, so I should be able to find a suitable replacement type. I'll go looking for a local source now... Thanks again to all who chimed in.

author: floobydust
author_rank: Super Contributor
timestamp: March 23, 2023, 04:00:16 pm
content: "button diode" as they are called were used heavily in automotive for car alternators e.g. AR504, MR2402 but none are fast-recovery. The package did not really work as far as good connections, unless you spot-welded wires to them, so that style became unpopular.I would confirm if they are Schottky or not, and this PSU has a cooling fan? The heatsink is not great, no fins.Instead I would toss them out and use a TO-220 or TO-204 dual Schottky rectifier diode.

author: ebastler
author_rank: Super Contributor
timestamp: March 23, 2023, 05:50:34 pm
content: Quote from: floobydust on March 23, 2023, 04:00:16 pmForward voltage of the good diodes is 0.45 V without current, so they are not Schottky types. The 5V output of this PSU is specified at 6A, and the PSU has no fan of its own. But is an open-frame type and sees decent airflow from the computer's fan. Nevertheless the diodes did apparently run quite hot; the PCB is slightly discoloured where they sit.Given that, combined with the fact that the button diodes are very obolete indeed and expensive to buy, I am inclined to follow your recommendation. Just need to figure out a decent way to mount the TO2xx packages; the PCB only provides four fat 6 mm holes for those button diodes...

author: floobydust
author_rank: Super Contributor
timestamp: March 23, 2023, 06:19:14 pm
content: 4 holes? It's a full-wave bridge, two sets and heatsinks? Schottky lower Vf will run a bit cooler.I'd look at duals in TO-220, TO-204, D2PAK (with common anode/cathode - you need one of each...) and you'll need some wire. I think getting rid of the heat, that heatsink seems small to me, is the challenge. If you can fit a small heatsink (with fins)? Or add to the original with some stick-on heatsinks like used for small CPU's. Just trying to give ideas.

author: ebastler
author_rank: Super Contributor
timestamp: March 23, 2023, 07:07:29 pm
content: Quote from: floobydust on March 23, 2023, 06:19:14 pmThanks again! Yes, it's a proper full-wave bridge. Each of the two wires from the transformer secondary is attached to one sheet metal "flag" which is soldered to two diodes. Heat-sinking is meant to work via the "flag", as well as via large copper areas on the PCB which holds the other side of each diode.Mounting a standing heatsink to the PCB, then attaching the TO cans to the heatsink would be one way of putting this together. This would also allow the AC to come in from above (the transformer connections), and the rectified voltage go down to the bottom. Or maybe just mount a single, integrated bridge rectifier package to the heatsink? There is a bit of spare room next to the transformer -- I'll take a closer look at available packages and heatsinks.

author: floobydust
author_rank: Super Contributor
timestamp: March 23, 2023, 07:34:10 pm
content: Oh, if the transformer connection is to the heatsink... then I don't think dual-diodes can be found. The dual-series type, those with tab center-tap, so you can bolt it to the heatsink and use no insulator- don't exist for power parts that I can see.

author: GandalfDerGraue
author_rank: Contributor
timestamp: March 24, 2023, 05:00:50 pm
content: You can throw out all that (ancient?) diode types plus the metal sheets and try to securely mount some proper 10 Ampere full bridge rectifier, maybe you can mount some chassis-mount type to the power supply frame. That would be the most reliable and stable solution. These types of diodes were used in some more or less ancient power supplies from radios or so, they are usually not at all used in moderately modern hardware.The only case where I know pills somehow looking a little bit like these is if they are used for very high voltages and with enourmous currents in high voltage applications (probably Multi-Kilovolt range!) and these ones are not at all small like your pills seem to be!!!So, if it really is a linear power supply with output of about 6Amps at 5Volts then you will go best with some modern full bridge rectifier. Maybe you search at digikey for "diodes - bridge-rectifiers", you then select "chassis mount type" and as current you might choose something around 10A or so to gain some safety margin if your power supply really delivers round about 6A. Choose one of the rectangle ones you can see on the product photos meeting your specifications, they should have some center hole to screw it down to some chassis parts. The body of the rectifiers should be isolated but you better double-check before screwing them to some chassis parts using the chassis as cooling. Use some decent wire (as short as possible) to hook them up to the transformer and to the PCB , transformer cables going to the "~" marked ports, the "+" and "-" plug going to the PCB. BTW, all commonly used bridge rectifiers should be able to handle the voltage of a 5 Volts linear power supply, so just go for the right current and maybe size so you can mount it and you will be fine. You can use some shrinking tubes to isolate all the connection tabs and solderings at the rectifier bridge.Then you should be on the safe side as far as you can be.

author: factory
author_rank: Super Contributor
timestamp: March 24, 2023, 05:19:10 pm
content: I've seen these diodes in fairly recently in a cheap & nasty car battery charger, I did try & get it going againbutit wasn't having any of it and suffered badly from a Widlarizing incident.Some pictures of the innards here, the diodes were AR501 or RA501 ??, possible replacement was AMP1502;https://www.letonkinoisvarnish.co.uk/rac_chargerrepair_6.htmlDavid

author: ebastler
author_rank: Super Contributor
timestamp: March 24, 2023, 09:09:25 pm
content: Quote from: GandalfDerGraue on March 24, 2023, 05:00:50 pmYes, I already had one of these in my Reichelt shopping basket this morning. But could not find a good way to mount it on the power supply's main heat spreader frame, short of having it dangling on the outside. (The supply has a large "wrap-around" heat spreader, which forms a partial enclosure, but there is not much spare room on the inside.)I ended up ordering a few NOS MR2504 diodes, which should have the right form factor to directly replace the failed one. This won't be an upgrade in performance and reliability, but it will keep this vintage computer clean and close to the original state.(It's a "Gepard" 68000 machine, by the way. If you (a) were a serious computer hobbyist around 1984, with (b) an Apple II background, and (c) happen to be German, you might know it -- otherwise you almost certainly won't...Only around 300 Gepards were made to my knowledge. Nice build quality and a modular design from half-size Euro cards, so I'd like to restore it to working and close-to-original condition.)

author: Stray Electron
author_rank: Super Contributor
timestamp: March 24, 2023, 11:19:55 pm
content: Quote from: simba15 on March 23, 2023, 02:10:33 pmYes, I was going to say "Press in Diode". They're widely used in automobile alternators where space is a premium.