The big electrolytic was within 20% tolerance (5600 uF vs. 4700 uF nominal). However it's only rated for 63v. Is this normal to be rated that close to the actual voltage? Or would they choose that as a cheaper alternative to, say, a 100v cap?
Working on testing the other caps now.
Edit: The smaller polyester cap in parallel is also well within the 20% tolerance (218 nF vs. 220 nF nominal). These guys are rated at 250v.
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It'd be a good idea. Better yet, if you don't have a known good replacement cap, just swap them between the high ripple side and the good side, and see if it follows. WATCH YOUR POLARITIES!! A 63 volt-rated cap on a 62-volt supply is neither standard practice nor recommended, but theoretically, it should work. Is one side of the supply drawing significantly more current than the other? (Measure with a DC Ammeter in series, between the supply and the load)
So I'm back at it. Picked up an analog scope (not ideal but gets the job done) and got settled into a new apartment, so now I'm getting back into the swing of things.
That 4V ripple on the +62v supply is not showing up. It must have been a measurement error. However, I do still see the ripple on the -24v supply. So I checked the caps and replaced one of the ceramic caps that was rated for 0.1uF and measuring at about 75nF. The hum is still there.
But as I was replacing it, I noticed the 1000uF electrolytic in parallel (which measured fine) is bulging a bit at the top.
Is this cause enough to replace it or is it just a warning that it COULD be bad?
Edit: There's also a voltage regulator in this section of the power supply. How would I test this component, if the issue is not a capacitor?
That 4V ripple on the +62v supply is not showing up. It must have been a measurement error. However, I do still see the ripple on the -24v supply. So I checked the caps and replaced one of the ceramic caps that was rated for 0.1uF and measuring at about 75nF. The hum is still there.
But as I was replacing it, I noticed the 1000uF electrolytic in parallel (which measured fine) is bulging a bit at the top.
Is this cause enough to replace it or is it just a warning that it COULD be bad?
Edit: There's also a voltage regulator in this section of the power supply. How would I test this component, if the issue is not a capacitor?
A GOOD cap is only $0.93: Nichicon UFW1V102MHD. Change it!
Put your scope on the regulator output--should be a CLEAN +24 volts.
So I finally got around to opening this project up again. Did some more testing and noticed the noise is present at all inputs (at least the 1/4", I didn't look at any of the XLR ins). Why would this be? Also the noise (I posted pictures earlier in the thread) doesn't look like the power supply ripple. It has the same period (about 8 ms), but it actually oscillates for a cycle or so and settles down in between.
I got an order in from Mouser with various replacement caps. When I have the time I'm gonna replace stuff. I'm still not entirely convinced the problem is the power supply though. I'm also going to keep poking around with the scope to see if I find something more conclusive.
A schematic would be great right now...
I got an order in from Mouser with various replacement caps. When I have the time I'm gonna replace stuff. I'm still not entirely convinced the problem is the power supply though. I'm also going to keep poking around with the scope to see if I find something more conclusive.
A schematic would be great right now...
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