Hi. I recently acquired an iFi iPhono (version 1) preamp on eBay for $28. It was known bad, with the seller indicating distortion was coming from both channels.
I confirmed that there is a loud (for line level) sort of rapid clicking distortion coming from both channels.
The distortion takes maybe thirty seconds to start. After being plugged in, the unit's power LED illuminates, then the class A LED, then a few seconds later you hear the output turn on (a soft click and no distortion at this point) at the same time the ready LED illuminates. Then it sites for fifteen seconds more or so and then the distortion starts.
I disassembled the unit and powered it up with the board on my bench and got the same startup results followed by the same distortion. I unplugged the power and with the back of my hand felt around and felt a lot of heat on one of the corners.
It seems the heat is being generated the component in the picture, at which my bamboo skewer is pointing.
Right next to this surface mount component is an LED marked "class A."
Any guesses as to the type of component that may be? It sort of looks like a TVS diode that I sometimes lift/remove from hard drives that won't otherwise spin-up.
Any idea what that component may be or general troubleshooting ideas?
Thanks in advance.
I confirmed that there is a loud (for line level) sort of rapid clicking distortion coming from both channels.
The distortion takes maybe thirty seconds to start. After being plugged in, the unit's power LED illuminates, then the class A LED, then a few seconds later you hear the output turn on (a soft click and no distortion at this point) at the same time the ready LED illuminates. Then it sites for fifteen seconds more or so and then the distortion starts.
I disassembled the unit and powered it up with the board on my bench and got the same startup results followed by the same distortion. I unplugged the power and with the back of my hand felt around and felt a lot of heat on one of the corners.
It seems the heat is being generated the component in the picture, at which my bamboo skewer is pointing.
Right next to this surface mount component is an LED marked "class A."
Any guesses as to the type of component that may be? It sort of looks like a TVS diode that I sometimes lift/remove from hard drives that won't otherwise spin-up.
Any idea what that component may be or general troubleshooting ideas?
Thanks in advance.
Attachments
Looks like a diode to me, I would measure the voltage across it.
Measure all of the supply voltages, there is a switcher right next to that area "power inverter" which probably makes the negative rail and might have gone away due a shorted component across it or some other problem.
Measure all of the supply voltages, there is a switcher right next to that area "power inverter" which probably makes the negative rail and might have gone away due a shorted component across it or some other problem.
Thank you for the help.
So I measured across that D5 and D6 (not pictures) and they both measured 9vdc which is what the input voltage is. And I guess they aren't that warm.
But the board has a few different groups of capacitors that are electrolytics with the surface mounting, and there are test points on the back of the board. So I started measuring the voltage on those and when I hit one row of them, the noise stopped. I removed my probes and the noise started.
I tried it a few more times, same result.
So I pulled the power and used a small magnifier to look around those two caps and it looked sort of like solder residue, like tiny balls. But it is hard to tell if it was some sort of rosin because the magnifier isn't great. But I used a cotton swap to wipe that area and it looked better w/ the magnifier and the noise seems gone.
I'm gonna leave it till tomorrow and give it another shot.
But maybe I'm getting somewhere (thanks to you!).
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Some flux residues are conductive if contaminated with moisture, so it could well be that.. I had a similar problem in one of my crossovers - self inflicted, solder paste between two pads of an op-amp, just an annoying crackling noise. Gone since I cleaned the area - this took 2 years to show up after I built them.
The original owner, in his listing, said he had used the unit for about four years before the problem occurred. And when I first disassembled the unit, the bottom of the double-sided board looked kinda fluxy/messy. So I used some iso alcohol and a toothbrush and cleaned it up, and blew everything off with my air compressor.
But the top of the board didn't look terrible. I did notice, with the magnifier, that there was some residue.
Maybe I should iso alcohol + brush the top side and blast it off, as well. But I could make it worse, too, I suppose.
But the top of the board didn't look terrible. I did notice, with the magnifier, that there was some residue.
Maybe I should iso alcohol + brush the top side and blast it off, as well. But I could make it worse, too, I suppose.
I was wrong, still making the noise. I had disconnected my speakers from the RCA/3.5mm splitter when I took it to the basement to clean it, and apparently forgot to connect it when I returned.
It sounds like a choppy sort of machine gun noise. Fairly loud through a small pair of cheap unamplified speakers attached to the output.
I attached a phono cartridge to the input and can hear it when I run my finger over the stylus, just the noise is substantially louder.
The AC to DC adapter is 9v 1.5a, and it is measuring correctly.
I measured voltage at some of the test points on the back of the unit that correspond to capacitor locations and there are a couple where measuring between them stops the noise, but also seems to shut-off all amplification. Within ten seconds or so, the preamp starts "working" again and I get the noise.
I measure the voltage across the output and I think I'm getting about 4.5v at each (left and right), which is interestingly half of the power supply voltage.
Anyway, I relisted the thing on eBay with an explanation of what I found and I'll let someone else tackle it. Maybe someone will just want it for the wall wart.
Thank you for your help.
It sounds like a choppy sort of machine gun noise. Fairly loud through a small pair of cheap unamplified speakers attached to the output.
I attached a phono cartridge to the input and can hear it when I run my finger over the stylus, just the noise is substantially louder.
The AC to DC adapter is 9v 1.5a, and it is measuring correctly.
I measured voltage at some of the test points on the back of the unit that correspond to capacitor locations and there are a couple where measuring between them stops the noise, but also seems to shut-off all amplification. Within ten seconds or so, the preamp starts "working" again and I get the noise.
I measure the voltage across the output and I think I'm getting about 4.5v at each (left and right), which is interestingly half of the power supply voltage.
Anyway, I relisted the thing on eBay with an explanation of what I found and I'll let someone else tackle it. Maybe someone will just want it for the wall wart.
Thank you for your help.
maybe this thread helps:
https://www.diyaudio.com/community/...phono2-creating-schematic-help-needed.325728/
https://www.diyaudio.com/community/...phono2-creating-schematic-help-needed.325728/