Transformer-based PSU repair

Repairing someone else’s design mistakes is much more difficult than starting from scratch. So whenever we come across someone who’s good at this type of trouble-shooting we pay attention. [Jim] had a Sangean HDR-1 in his home. It’s a tabletop HD radio that stopped powering up for some reason. He cracked it open and got to the bottom of the problem.

The first order of business is disassembly, which isn’t too hard with this model. With multimeter in hand he started probing the transformer and found that the contacts for the primary are an open circuit; signaling a problem. There’s no inline fuse for protection, and further study of the secondary winding let him to discover the use of 1N5817 diodes. These are underrated parts for this particular transformer. He replaced them with 1N4003 diodes to bring the device in spec. But there was still the issue of fuse protections. A bit of circuit free-forming allowed him add a fuse and varistor  by soldering the directly to the transformer’s contacts.

Why stop there? While [Jim] had the case open he also swapped out the low-end op-amp and a few electrolytic capacitors to improve the sound quality of the radio. Op-amp replacement seems to be a popular way to improve the sound from HD radios.

Comments

  1. MobileWill says:

    Nice! I got a 32in TV for free that I need to open up the PSU and see what is going on. I am fairly positive a fixed PSU will make it work again.

  2. asheets says:

    Did [Jim] get these units from the same friend at the e-waste company?

  3. jim says:

    op amps certainly affect sound quality, but they’re not the holy grail that CMoy users think they are

  4. Sanjay says:

    The 1N5817 is a schottky diode. Its a (relatively) specialized and expensive part. Replacing it with an ordinary silicon diode 1N4003 is stupid.

    • tony says:

      Schottky or not, they are being used as full wave bridge rectifiers. If this was a switching power supply, I would agree with you. Besides, in the writeup, he says they used 1n4003 in latter revisions of the board.

    • Wm_Atl says:

      These diodes probably ended up in the power supply as a mistake on the production documents. At 60Hz there is no need for a Schottky diode. And a conservative rating for the diode should have been at least 50volts (in my opinion). So the 1N4003 will work just fine. Seen them used in hundreds of analog power supplies. If this had been a switching power supply I would have gone to the Ultra Fast diodes since the Schottky diodes, generally, are not fast enough.

  5. mixmastersmike says:

    Kuddos for finding the flaw, Current is everything, especially when you try to save 4 cents on the yen

    Just ask the cover up CEOS at De_ll, or even fruit baskets on money saving decisions as such, leaky things holding some kind of “charge” should not be leaky !

  6. apothus says:

    Interesting work, I have a UPS from work that was going via the skip because of problems. I opened it up to start probing but did not get too far with it. A 240v is not something i want to experience and i dont need a ups that badly..

  7. tinkermonkey says:

    why do you ” hack a day” make reading you web site difficult with unexplained alphabet soup! you use anagrams like (PSU) with out explaining the meaning. A practice that is not only non grammatical, but just plain rude!!!! There is a convention in using the English language that requires that you define an anagram at it’s first usage. If I use IDE do you really know if I am referring to communing with a hard-drive or software for programing? Please stop acting like arrogant fools and treat your readers with respect.

    • mahoney says:

      I think you are refering to TLAs or three letter acronyms. I would consider it an insult to my intelligence if every article defined each acronym. I think you’ll find the vast majority of the people who frequent this site are savy with the tech acronyms and jargon. But a quick search of the internet will define any new ones you come across.

      Nice writeup BTW. Service logs on the net can be very useful.

      • Tony says:

        It’s called journalism, which of course ‘Hack A Day’ (HAD) is not.

        You write the term in full once at the start, put the abbreviation immediately afterwards, and then use it for the rest of the article.

        For example: “I fixed the power supply unit (PSU) and then…”

        I think I learned that when I was about 10. Not doing it is sloppy, but that’s par for the course on the internet.

    • Eirinn says:

      idk i think tbh that this is fine.

      If you were able to understand that – You owe the site an apology unless of course you’re angry on other people’s behalf which is just stupid :)

    • pfargtl says:

      i dont see the problem here, picture says everything (obvious Power Supply Unit). if somebody posted about advancements in IDE tech and had a picture of visual studio i think i could figure out which way they’re going there. i dont know, maybe i’m the one missing the point here.

    • Wm_Atl says:

      Unless you are using a babel fish to translate this page, PSU makes perfect sense in the context provided. IDE depending on the subject material will make perfect sense unless you are translating between languages using a babel fish. I could understand confusion if PSU was mistaken for Play Station U. But I am pretty sure that has not come out yet. And again context of the rest of the article is around a HD Radio. JMTC BB4N

  8. tinkermonkey says:

    My point is that many of TLAs, NES, PS3, PSU Play Station Universe, are not tech, they are advertising nonsense. The in-distinction is a waste of my time. The TLAs impede gaining a quick understanding of an articles content with having to read it.

    Hackaday could write all of their articles entirely in Pig-Latin. Wouldn’t that be just soo coool!

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