I have attached a link to the circuit schematic for my McIntosh MA-5100. One of the capacitors in the power amp intermittently shorts (becoming a 2- 20 –ohm resistor) and causes the DC offset to go berserk. The original capacitor (C208 in the diagram) is a Sprague “Trans-lytic” cap, rated at 200uF and 3V.
I have an Elna cap rated at 220uF and 6.3V. Would this be a suitable replacement, or too far out of tolerance?
Click image for larger view…(approx. 512KB)
I have an Elna cap rated at 220uF and 6.3V. Would this be a suitable replacement, or too far out of tolerance?
Click image for larger view…(approx. 512KB)
An externally hosted image should be here but it was not working when we last tested it.
Thank you very much. I expected that it would work, but this McIntosh has re-written a lot of what I thought I new about amps.
Just curious: Judging by the circuit design, could the failure of this cap cause severe DC offset? That was the initial problem, and as I was comparing the “good” channel to the bad one, I noticed that the same cap in the good channel responded to a resistance test how it should: starting a low value, and quickly rising in impedance. The one in the bad channel first measured at 2-ohms. I removed it and tested it, and it was at 20-ohms. A third time I tested it, it did as it should.
This seemed to be consistent with the occasional and intermittent DC surges at the speaker terminals: some times as little as 0.1mV of DC offset, other times as high as +27VDC.
Whatever the case, the DC offset is consistently low after replacing the cap. I replaced the same one in the other channel, just to be safe, as it is of the same brand and age as the faulty one.
Just curious: Judging by the circuit design, could the failure of this cap cause severe DC offset? That was the initial problem, and as I was comparing the “good” channel to the bad one, I noticed that the same cap in the good channel responded to a resistance test how it should: starting a low value, and quickly rising in impedance. The one in the bad channel first measured at 2-ohms. I removed it and tested it, and it was at 20-ohms. A third time I tested it, it did as it should.
This seemed to be consistent with the occasional and intermittent DC surges at the speaker terminals: some times as little as 0.1mV of DC offset, other times as high as +27VDC.
Whatever the case, the DC offset is consistently low after replacing the cap. I replaced the same one in the other channel, just to be safe, as it is of the same brand and age as the faulty one.
Hi Mike,
Failure of that cap will increase the gain at DC from 1 to whatever the AC gain is. A small DC offset will become much larger. A bipolar cap might be nice, but only if it isn't too large. Otherwise, replace it with whatever was there. I find 16V caps to be the lowest reliable voltage rating.
-Chris
Failure of that cap will increase the gain at DC from 1 to whatever the AC gain is. A small DC offset will become much larger. A bipolar cap might be nice, but only if it isn't too large. Otherwise, replace it with whatever was there. I find 16V caps to be the lowest reliable voltage rating.
-Chris
mjarve said:
Don't worry about the tolerance...usually electrolytic capacitors are made with tolerances of 20% and sometimes more. And 220 are only 10% of 200.
But use in both channels the some type of capacitor...
PS: Your Mac don't have the output transformer?
Actually, you could use 330uF or 470uF and it really wouldn't make much of a difference in that circuit. Be at peace with your caps.
-Chris
-Chris
thanks for the info, I had the same question about a 100 @ 12 in the feedback loop of a ma-230
I replaced it with a high temp 105 c 100 @ 25 with a leloa name.
Not that the pair failed but 50 yr old electrolytic caps ... scary...
I'm in the process of replacing all the caps, that I skipped 3 yr.s ago.
I replaced it with a high temp 105 c 100 @ 25 with a leloa name.
Not that the pair failed but 50 yr old electrolytic caps ... scary...
I'm in the process of replacing all the caps, that I skipped 3 yr.s ago.
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