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7704A Fuse
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Picked up an auction win 7704A today and immediately powered it up only to find it was completely dead. The line fuse was blown, which should have been a 4 A fast blow, but was 3 A slo blow. Do the plastic fuse holders shrink with age? I think I will need a jackhammer to remove the bad fuse. Break the bad fuse and hope the new fuse, with it's slightly rounded ends, will insert easier?
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Getting the fuses out is probably a bit more difficult that inserting them. The inner edges of the end caps are much sharper than the very ends. There's not much room to break the fuse as the plastic covers virtually the entire glass cylinder. Perhaps a bit of heat (soaking in hot water or a gentle application of a heat gun) might help.
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Good luck with it. Thanks, Barry - N4BUQ ----- Original Message -----
From: "John Kolb" <jlkolb@...> Picked up an auction win 7704A today and immediately powered it up only to find |
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I haven't tried this, but you might consider drilling a hole in one end, say 1/16 inch, and then taking a wood screw or drywall screw and threading it in.? If nothing else, it will turn the fuse and perhaps loosen the contact.? You might be able to pull out the fuse at that point.
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Harvey On 4/8/2022 9:30 AM, n4buq wrote:
Getting the fuses out is probably a bit more difficult that inserting them. The inner edges of the end caps are much sharper than the very ends. There's not much room to break the fuse as the plastic covers virtually the entire glass cylinder. Perhaps a bit of heat (soaking in hot water or a gentle application of a heat gun) might help. |
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The fuse holders in the 7704A are a bit like some that are used in older HP gear where the fuses are held plastic cylinders that that are attached to an outer housing. Removing the housing exposes the fuses and the ends can be readily pushed (or pulled) as needed; however, the IDs of those plastic cylinders are very close to the OD of the glass. Once a fuse is pushed in place, it can be pretty difficult to remove it from those small plastic cylinders. I think the plastic cylinders have shrunk just a bit over time which exacerbates the removal process.
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Thanks, Barry - N4BUQ ----- Original Message -----
From: "Harvey White" <madyn@...> I haven't tried this, but you might consider drilling a hole in one end, |
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Got it out finally. Not much quality control on fuse dimensions. Sample size of 4 varied from 0.251 to 0.2535. Size made a large difference in insertion/removal force required.
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Replacement fuse blew instantly with a loud band, which is good news. Indicates probably a dead short very close to power input. Much easier to troubleshoot than an overload somewhere causing ticking. John KK6IL On 4/8/2022 7:44 AM, n4buq wrote:
The fuse holders in the 7704A are a bit like some that are used in older HP gear where the fuses are held plastic cylinders that that are attached to an outer housing. Removing the housing exposes the fuses and the ends can be readily pushed (or pulled) as needed; however, the IDs of those plastic cylinders are very close to the OD of the glass. Once a fuse is pushed in place, it can be pretty difficult to remove it from those small plastic cylinders. I think the plastic cylinders have shrunk just a bit over time which exacerbates the removal process. |
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