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Help identifying a fuse in a GEM Jumbo?

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  • Help identifying a fuse in a GEM Jumbo?

    I recently repaired the vibrato on an old GEM Jumbo that I bought last year by replacing three small capacitors in the vibrato circuit. It worked perfectly for a couple of days, then the whole thing stopped working and I discovered that the fuse on the power board had blown (see photo).

    I thought it was about time I tried some DIY re-capping after years of combo organ tinkering, so today I replaced all the big caps on the power board and the one on a separate board just below - you can see most of the new ones in the photo.

    I replaced the fuse too, but when I switched it back on the fuse blew again straight away. I checked all the cap connections were solid and tried yet another fuse - ZAP.

    I had to guess which fuses to buy - the original only had a barely discernable and cryptic “11/250B” printed on one end, and the schematic I have doesn't seem to show it at all. I went for “Cartridge Fuses 250 V 0.25A 5x20mm Fast Acting” from Mouser (576-0217.250MXP) and the slo-blo version of the same.

    Did I get the fuse rating completely wrong? Or is there something else wrong that's going to blow whatever fuse I put in there?
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  • #2
    Here's the schematic in case anyone can spot a clue...
    You may only view thumbnails in this gallery. This gallery has 1 photos.

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    • #3
      Looks like 0.5A to me, probably fast-blow. If the fuse isn't it, I'd look at:
      1. Make absolutely certain you didn't get the polarity wrong on the caps. A backwards cap can look like a short.
      2. I'd then check the diodes right after the transformer. When those short, they will blow the fuse instantly.

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      • #4
        Originally posted by NoTalent View Post
        Looks like 0.5A to me, probably fast-blow. If the fuse isn't it, I'd look at:
        1. Make absolutely certain you didn't get the polarity wrong on the caps. A backwards cap can look like a short.
        2. I'd then check the diodes right after the transformer. When those short, they will blow the fuse instantly.
        Thanks! I'll triple check the capacitors, try a 0.5A fuse and check the diodes. Watch this space...

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