Can fuses go bad?


Yesterday I turned on my Halo JC-1s for a little listening. As I walked over to drop a CD in the drawer I smelled a slight burning odor. When I looked back the lights were out on one amp. A check of the line fuse verified it had blown.

Since the Owner's Guide did not specify anything about fuses I sent a message to Parasound to make certain I used the proper replacement (blown fuse was not marked fast or slow blow). In spite of it being late Friday afternoon before a holiday weekend I received an almost immediate reply. Regarding my question on why a fuse would blow a second or two after turn on they suggested it could have become weak. This was a 12 amp fuse, does that seem reasonable?
pryso
Yes, fuses do fail. They're creating some resistance to the current and expanding and contracting with the resultant heat. You shouldn't be worried unless the replacement also blows.
As I walked over to drop a CD in the drawer I smelled a slight burning odor.

When a fuse blows and the event is contained within the fuse body, there would be no burning odor.

I sent a message to Parasound to make certain I used the proper replacement (blown fuse was not marked fast or slow blow).

Did you mention the burning odor in your message?

Regarding my question on why a fuse would blow a second or two after turn on they suggested it could have become weak.
Possible... Especially if the amp is turned on and off daily. When the amp is first turned on the current will spike as well as the voltage.

When you pulled the old fuse how did the metal end caps look? Shinny? Corroded? Any burn marks?

Corroded or burn marks could indicate poor contact pressure between the fuse and the fuse holder.

Poor contact pressure can cause more heat beyond the normal thermal heat up of the fuse when the amp is first turned on due to the high inrush current.

Also if the fuse does have burn marks on one end or both that might be the burning odor you smelled.

You could try a new fuse. Make sure it is exactly the same value fuse. If that one blows,... send the amp in for repair.

http://www.parasound.com/halo/jc1.php
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Ceramic fuses have a powder in them, maybe thats what smelled.
I would also check those surge current limiters, esp if you have an older production JC1.

They are on the AC input board and look like large green capacitors. The older design has four of them clustered together. These can "current hog" and burn out with sparks and smoke. The newer design replaces four of them with two much higher rated ones.

On one of my JC1s I was seeing arcing in the vicinity of this board when turning on my amp. It was sometimes accompanied by a burning smell and smoke. When I took the board out and looked, one of the surge current limiters was literally blown out in the middle with chunks of encapsulant missing. I am lucky they did not catch fire.

These limit the surge current going the power supply capacitors and come under a lot of stress on start up. The parts in the older design were underrated for the large amount of capacitance in the JC1 power supply.

Tony in the CS/Tech Support group at Parasound will send you free replacements or you can send the amp to them for replacement. If you have the older ones, get these replaced ASAP.
Many thanks Dhl. I popped the tops on both amps yesterday. I had replaced the blown fuse with a 10A slo-blo and that amp worked but I didn't leave it on long.

Looking inside it was just as you described. Two of the nickel sized green disk caps had exploded and a third was cracked in the damaged amp. Interestingly, the other amp has only one larger black disk cap (about the size of a quarter), one cap positioned jumpered, and the other two positions blank in place of the four green caps.

My amps are more than five years old. One failed after a year and my dealer sent it in under warranty. I don't have any paperwork from that so I don't even know which amp was repaired. From your comments I suspect it was the one which now has the single large black disk cap.

With your advice I'll contact Parasound tomorrow.
Pryso:

Looks like one of your amps has the replacement. The new parts are larger and thicker (and black in color). The originals were arranged by two parallel pairs in series. They are all replaced by one single part (although I used two of the large parts in series in mine), so the traces for one pair are shorted.

If you have cracked or damaged ones, DO NOT POWER UP your amp and send it to Parasound immediately (or fix it yourself). Those damaged current limiters can catch fire and you do not want that.

I think Parasound should have recalled all the older amps. This is a dangerous safety issue that should not be left up to customers to discover on their own.
Pryso

Can you please tell me if the JC1 fuses are fast or slow blow?
Thank you.
@10ht: All the JC1 fuses are slow blow type.