PRR told you what the correct fuse actually was, installing a 3A or 16A fuse in that location could result in all sorts of excitement like a ruined power transformer, exploding or burning components or a slow thermal failure due a failed capacitor or other part and excessive current.
Unless you suspect them to be bad I am not sure why you would replace the voltage regulators. There are better ones out there today, but whether you could tell the difference is another question.
I would do the caps sooner than later, no need to wait for something to fail to prove the wisdom of doing so, particularly if waiting results in the destruction of a hard to replace or irreplaceable component.
Unless you suspect them to be bad I am not sure why you would replace the voltage regulators. There are better ones out there today, but whether you could tell the difference is another question.
I would do the caps sooner than later, no need to wait for something to fail to prove the wisdom of doing so, particularly if waiting results in the destruction of a hard to replace or irreplaceable component.
Yes and I'm glad he did. However I wouldn't have installed a fuse until I'd found the proper value anyway, hence the original post. I've never seen a fuse value expressed as a fraction, and in fact I never saw a fuse before that had less than a 1A rating. I didn't assume there wasn't, I've just never seen one.
When I redo power supplies its just a matter of course to replace the regulators. They're about 50 cents each, and since I typically have to do some disassembly to get to the filter and bypass caps to begin with, I wouldn't want to do that all over again just for a buck's worth of parts. Its cheap insurance and a labor savings in the long run.
I agree, as I said above. Cap replacement is on the schedule for this preamp. However, I want to get it working prior to doing that.
The very first time I ran into something like this, I had just gotten a batch of caps to rebuild an amp. It had failed so I figured I'd just get everything at once. My friend made an excellent point: what if I replaced all those caps and the amp still didn't work? Was the original problem fixed but now something else was wrong? Or maybe that problem still existed and I'd just compounded the problem by possibly adding a bad new part or a labor screwup? He talked me out of doing the upgrades and got me testing the thing to track down the problem. It ended up being a diode that cost 6 cents. With the amp repaired and working I was able to move forward with the upgrades, knowing definitively that if the thing stopped working it would be because of something I added or did wrong.
Besides, once I get started on up-capping this preamp, that means getting a huge magnifying lens and some bright light, and spending a few days cataloging every cap under the hood. Then spending probably a week trying to find the right caps, because I can run the same search with the same values twice on any of the major services and get different results each time. Right now I'm trying to find some caps for a power supply from another amp, and after about 9 hours of shopping over this past week I think I'm starting to get somewhere. At the moment I'd just like it to work. After that I'll start shopping for upgrades.
If I'm looking at the right equipment then I found an image of the rear panel that seems to say 580 watts total loading for the three outlets.
A very poor res diagram of the PSU seems to show that none of these outlets are fused internally.
So that leaves the fuse in the unit as really only supplying the preamp transformer... and so if that failed while being suitably rated then there has to be a problem with the unit itself.
My advice would be to isolate the secondary winding and power up just the transformer to make sure it is wired correctly. The power supply is simple and so we can 'guess' that the DC voltage across the reservoir caps will be around 25 volts. The 35 volt cap rating puts an upper limit on things in any case. That would suggest each winding should be giving around 17 or 18 volts AC give or take.
Under these conditions the transformer should be drawing minimal current, just a few percent at most of that needed to maintain the magnetic field/iron losses etc within the core.
A very poor res diagram of the PSU seems to show that none of these outlets are fused internally.
So that leaves the fuse in the unit as really only supplying the preamp transformer... and so if that failed while being suitably rated then there has to be a problem with the unit itself.
My advice would be to isolate the secondary winding and power up just the transformer to make sure it is wired correctly. The power supply is simple and so we can 'guess' that the DC voltage across the reservoir caps will be around 25 volts. The 35 volt cap rating puts an upper limit on things in any case. That would suggest each winding should be giving around 17 or 18 volts AC give or take.
Under these conditions the transformer should be drawing minimal current, just a few percent at most of that needed to maintain the magnetic field/iron losses etc within the core.
Attachments
I think I should try to clarify this.
The fuse that was in the unit I'm working on now was properly rated, but it was for UK current. It was 1/10 amp.
The fuse that was donated from my other IRIS preamp was properly rated, but for USA current, at 3/16 amp.
The UK fuse was fine in the USA unit for over an hour and then it blew. Since the fuse was one-half of the rated amperage that should have been in there, I would look at that as a weak spot that would be subject to failure, even during normal use. (As a further bit of info: the fuse pop happened when I was hooking the tuner up. There were three connections to make: power, signal, and remote cable. I believe I did them in that order and it was either when I plugged the patch cords in or the remote cable that the preamp went dead. And since I was adding the tuner while the preamp was hot, I'd think its safe to say that one of those connections could have caused a slight surge in current.)
The USA fuse was taken from a dead IRIS preamp, and it was most likely blown when I put it in, since that preamp went dead while I was doing chip swaps to try to fix lightning damage. I should have checked the fuse with a DMM prior to the install but I just did a visual check. Anytime I've seen a blown fuse, it blows somewhere near the center. This fuse is the first one I've seen that has no obvious open.
I'll put the new fuse in and see what happens. If it still pops then I'll start doing some diagnosis work.
OK 🙂 That is a valid approach under the circumstances, and thanks for the details as well...
(not all open fuses are obvious and very occasionally they can pass a full visual inspection and still be open. Typically in that case the wire has just parted company with the end cap. That failure can sometimes result in an 'intermittent fuse, something I have encountered just once)
It works until it doesn't. Then you pull the fuse to check, and by handling it the wire falls back into place and the continuity returns, so you get a proper reading on the DMM. You think "ok its not the fuse", then you put it back in and everything works. Until it doesn't. And the whole time, you'd be thinking its an intermittent fault in the equipment itself.
I'd probably lose my sanity if I ever encountered a fuse like that. If anyone ever asks you what causes us to anthropomorphize non-living things, I bet you could point them to a story with one of those fuses.
"I swear it was just working! That thing has it in for me!"
And that was how Clark Griswold lost his mind.
We won't live long enough to back-engineer that blurry schematic. But the actual audio could well be under 30V 20mA. There's LEDs, not all on at once, but some in a devious gain-control scheme. Say another 30V 30mA. And that 30V is regulated from about 50V. So 2.5 Watts of DC. Which tends to be like 5VA of AC.
5VA/120V = 0.04166 Amps
_I_ would not take this at face value. I have seen a 4VA transformer which would not hold on a 0.25A fuse. Teeny transformers can have large losses, even in excess of their rated output. However if neo-Hafler says 3/16A 0.188A then I'll go with their number.
I remember many many years that Sanyo had a Betamax recorder that had something like 160ma (and I have a recollection it was also fast) mains fuse fitted and these suffered nuisance blowing.
They were a regular source of service calls and yet what to do because it was a safety item. Again from memory I recall an official service bulletin suggesting the value be increased to something like 630ma slow blow. An absolutely massive change from the original design spec. They never blew again 🙂
They were a regular source of service calls and yet what to do because it was a safety item. Again from memory I recall an official service bulletin suggesting the value be increased to something like 630ma slow blow. An absolutely massive change from the original design spec. They never blew again 🙂
That schematic has been a long time aggravation for myself and every other Hafler collector out there, and I'm sure the techs as well. I'm betting they at least had something better to work from but I doubt they'd part with copies of the real docs. I was going to call Landis, since he once was listed as a Hafler tech, but it seems he's gone out of business.