Looking to cross-reference replacement power supply diodes - Page 1
Forum section: electronics / repair

author: WildcatMatt92
author_rank: Newbie
timestamp: December 03, 2022, 03:20:44 am
content: I have a few old Mitsubishi VCRs that I'd like to get working. They are notorious for power supply issues -- half of them have caps that have leaked over the diodes which appear to be pretty cooked also.The service manual identifies these types (now with links to datasheets I could find):RM 1BEM 1ZEM01ZHZ30-21SS252The first three at least appear to be Sanken part numbers which appear to be hard to track down. Ithinkthe first one is 800ma/800v (which seems difficult to match) and the next two are both 1a/200v (which seems pretty common).I've added the diagram from the service manual and two views of the supply itself as attachments (I've already removed the caps on the one).Can anyone help identify substitutions for currently available part numbers I could plug into DigiKey, Mouser, or eBay for replacements?

author: james_s
author_rank: Super Contributor
timestamp: December 03, 2022, 03:38:46 am
content: Well you don't need to match the current or voltage, you just need diodes that are rated at least as high for both. What matters more is speed, assuming this is a SMPS most of the diodes are likely to be much faster than jellybean stuff like the 1N4007. If you can find datasheets for them that would make it a lot easier to suggest replacements. Otherwise it would be helpful to know how they are used in the circuit.

author: fzabkar
author_rank: Super Contributor
timestamp: December 03, 2022, 03:42:44 am
content: It would help to see the service manual ...

author: amyk
author_rank: Super Contributor
timestamp: December 03, 2022, 06:30:26 am
content: The first 3 appear to be general-purpose mains rectifier diodes. I'd try 1N4007 for all 3.HZ30-2 is a 30V 0.5W 3% zener. BZX55B30 seems suitable.1SS252 is a 90V 130mA fast diode and someone previously suggested a 1N4148 for replacement:https://www.eevblog.com/forum/repair/repair-denon-amp-stuck-for-diodes/

author: WildcatMatt92
author_rank: Newbie
timestamp: December 03, 2022, 01:57:01 pm
content: Quote from: james_s on December 03, 2022, 03:38:46 amThat's helpful to know, thanks!Quote from: james_s on December 03, 2022, 03:38:46 amI've updated the post to include links I could find, and to the relevant section of the service manual.

author: wasedadoc
author_rank: Super Contributor
timestamp: December 03, 2022, 03:37:36 pm
content: Quote from: WildcatMatt92 on December 03, 2022, 01:57:01 pmYou have not shown what is feeding the primary of the transformer but I don't recall ever encountering a switched mode power supply with full-wave bridge rectifiers on the secondary so I assume this is a linear supply with the transformer at 50 or 60Hz. In which case nothing special speedwise about the rectifiers or the zener.

author: WildcatMatt92
author_rank: Newbie
timestamp: December 03, 2022, 03:49:59 pm
content: Quote from: wasedadoc on December 03, 2022, 03:37:36 pmYeah, unfortunately the left side of the diagram is cut off in my copy so that's the best that I have.

author: fzabkar
author_rank: Super Contributor
timestamp: December 03, 2022, 05:52:05 pm
content: Quote from: wasedadoc on December 03, 2022, 03:37:36 pmThere is a 120V, 0.047uF capacitor across the primary winding. At SMPS frequencies this cap would not exist, and in any case it would be a short. Moreover the low voltage rating of the cap makes me wonder. :-?

author: WildcatMatt92
author_rank: Newbie
timestamp: December 03, 2022, 10:36:23 pm
content: Quote from: fzabkar on December 03, 2022, 05:52:05 pmThat one is a mystery to me also. It seems like both sides are connected to the ground plane, I've attached a photo.I also have a later revision of this supply for another model which omits that cap.

author: amyk
author_rank: Super Contributor
timestamp: December 03, 2022, 11:50:32 pm
content: I didn't find the full service manual (except sites which are begging you to pay...) but I did find one for another model, HS-B82, which uses a regular linear PSU. I also found one for HS640/641 and that one uses SMPS but I assume it's a much newer model. No signs of any 1SS252 in the PSU though.

author: james_s
author_rank: Super Contributor
timestamp: December 04, 2022, 12:06:36 am
content: Now that I see the picture, yeah that is clearly a linear power supply. For most of the diodes I would expect a 1N4007 to work just fine, obviously a zener will have to be replaced with a zener.