I have an IRIS preamp that got hit by lightning a decade ago. I replaced a bunch of the ICs on the board and the preamp came back to life, but ... The amp starts up in "MUTE" like a good IRIS, and then it sits there until I push the "NORM" button to take it out of mute, and when I do that the fuse overheats and burns out.
I'm using the proper fuse, btw - 3/16A, 250V.
I bought another IRIS preamp online. This one is doing the exact same thing. It sits in mute until I push norm, then the fuse glows like a christmas light and burns out.
I bought a third IRIS, and its working perfectly. I just finished recapping it and it sounds stellar. I'd like to get the other two preamps working as well, because when these things are in good order, they really bring out the best in my system.
Suggestions on what to look at would be appreciated.
I'm using the proper fuse, btw - 3/16A, 250V.
I bought another IRIS preamp online. This one is doing the exact same thing. It sits in mute until I push norm, then the fuse glows like a christmas light and burns out.
I bought a third IRIS, and its working perfectly. I just finished recapping it and it sounds stellar. I'd like to get the other two preamps working as well, because when these things are in good order, they really bring out the best in my system.
Suggestions on what to look at would be appreciated.
No.
The one you linked was from JB. I participated in that thread but it wasn't mine. My original thread was :
Help me diagnose my IRIS problem
That thread was about possible replacements and upgrades for the chips on the board following the lightning hit. I got as far as the mute button fiasco and gave up, and the preamp has been sitting there ever since.
I'm now working my way through a backlog of things needing repair, and I finally got into my Hafler pile yesterday. My original preamp is sitting there with some kind of defect that wasn't there prior to getting hit by lightning, so I want to figure this out.
Its probably some garbage 10 cent diode passing voltage when it shouldn't, and there's no way to find out without lifting every single component and testing it out of the chassis. If you've never worked on an IRIS, desoldering is one of the hardest things to do on it. The board has extremely high quality metal traces, but for some reason the guys at Hafler felt it was necessary to cover the traces between components with solder. So that means for every component I pull, I have to spend 10 minutes cleaning all the solder off both sides plus I have to "rod out" the lead holes with a hot piece of metal lead wire to get all the solder out of the hole.
The one you linked was from JB. I participated in that thread but it wasn't mine. My original thread was :
Help me diagnose my IRIS problem
That thread was about possible replacements and upgrades for the chips on the board following the lightning hit. I got as far as the mute button fiasco and gave up, and the preamp has been sitting there ever since.
I'm now working my way through a backlog of things needing repair, and I finally got into my Hafler pile yesterday. My original preamp is sitting there with some kind of defect that wasn't there prior to getting hit by lightning, so I want to figure this out.
Its probably some garbage 10 cent diode passing voltage when it shouldn't, and there's no way to find out without lifting every single component and testing it out of the chassis. If you've never worked on an IRIS, desoldering is one of the hardest things to do on it. The board has extremely high quality metal traces, but for some reason the guys at Hafler felt it was necessary to cover the traces between components with solder. So that means for every component I pull, I have to spend 10 minutes cleaning all the solder off both sides plus I have to "rod out" the lead holes with a hot piece of metal lead wire to get all the solder out of the hole.
When I have been hit by lightning, it is often a 1N1001 rectifier right after the power transformer.
> for every component I pull, I have to
I don't follow; but do you know "desolder needles"?
> for every component I pull, I have to
I don't follow; but do you know "desolder needles"?
No, I've never heard of "desolder needles" but by the sound of it, thats a fancy term for what I'm already doing: I rod out the hole with a hot wire.
Using a pair of needle nose pliers I grab a piece of radial lead that I trimmed off an installed capacitor, I dip the end of the needle in flux, stick it into the solder-covered hole, and then I heat the joint with the soldering iron. The flux boils, the solder jumps onto the wire, and I stick it through the hole and move it around while I take the iron away. If the lead does the job it moves freely. If it sticks to the hole I heat it again and apply desolder braid.
It takes about 5 minutes per location now that I have the technique down, but it was frustrating until I figured it out.
Using a pair of needle nose pliers I grab a piece of radial lead that I trimmed off an installed capacitor, I dip the end of the needle in flux, stick it into the solder-covered hole, and then I heat the joint with the soldering iron. The flux boils, the solder jumps onto the wire, and I stick it through the hole and move it around while I take the iron away. If the lead does the job it moves freely. If it sticks to the hole I heat it again and apply desolder braid.
It takes about 5 minutes per location now that I have the technique down, but it was frustrating until I figured it out.
One by one I started puling up the diodes to check them. The four in front of the big power caps checked out ok. I didn't have time to pull up the diode after the caps, but those will be next.
I found something very interesting, speaking of the large power caps. They were slightly loose on the board. I don't know if the solder joints under them were fatigued, or if there was something else going on, but since I had to get them out of the way to begin pulling diodes I took the caps out as well. I left the two small electrolytic smoothing caps in place for now.
The two large caps are 2200uF 35V. I noticed the bottoms were somewhat deformed on them and maybe even bulging slightly. I checked them out on my BK LCR meter. They both came in at about 2300uF give or take. But something told me to keep checking, so I put them on my Fluke DMM and checked resistance.
One cap gave out a resistance value of something enormous, like 14.5Mohms. Thats in line with ESR for a lot of capacitors, especially 30 year-old ones. The other one showed OL, which I would expect means the cap is open, or at least provides an infinite resistance or close to it. Bad cap, right?
If this cap is damaged, could this possibly be connected to why the fuses are blowing, or is it just a symptom of a larger problem?
I checked out the desolder needles. Thats a neat product, and thanks for posting it. That could save me some time especially when I'm dealing with the fat solder traces on these IRIS preamps.
Is that 14.5 meg ohms or 14.5 milli ohms ?
If its the latter the cap is toast.
If the former then sounds ok.
If its the latter the cap is toast.
If the former then sounds ok.
its 14.5 MegaOhms. Most of the caps I found started at 11.5MO ESR and worked upwards, so like I said this one is right in line with that.
I'm more concerned with the other cap, which shows OL on my meter. That can't be right.
I'm more concerned with the other cap, which shows OL on my meter. That can't be right.
Sounds like a scope job to look at the ripple.
If massive ripple compared to good one then its knackered.
If massive ripple compared to good one then its knackered.
Come on man, that means I'd have to learn how to use my scope. 😀
This cap is already out of the board. I have a couple caps of the same value from the last IRIS preamp I upgraded, so I'll just weld those in there and see what happens.
This cap is already out of the board. I have a couple caps of the same value from the last IRIS preamp I upgraded, so I'll just weld those in there and see what happens.