whbuddin
New Member
OK, here’s my problem: I have six Marantz MA 500u monoblocks. I won these on eBay a few weeks ago, and were attested by a reputable seller to all be perfectly functional. In any case, they showed up in less-than-functional shape, likely due to poor packaging (he packed all six into a single, old Thule car rack box, with various bits of cardboard, bubble wrap, and packing paper between them; it’s actually a small miracle that they showed up in otherwise perfect cosmetic shape). Anyhow, after testing, I found that two work brilliantly, one does not output sound at all (but does turn on), and three of them work, but with a low/diminished output (as compared to the two that seem to output “full” power). From what I can tell, this is likely due to the old electrolytic capacitors, and is a problem common amongst amplifiers of its age (about 20 years old). I whipped out my Fluke, and, as predicted, each cap I tested was well below its printed value. So, I bought new caps from Digikey, all matched for capacitance per the service manual, with a slight voltage bump on one of them (from 50 to 100V). For reference, the caps I am focused on are: C701, C705, C710, CN01, CN02, CN03, and CN05.
On my first attempt at re-capping one of the three low-output amps, I took a more “shotgun“ approach by replacing all of the capacitors in the power and protection circuits. Result: no dice — the front power light turned on as it should, but there was no “clicking” sound (of the relay, should click on after about three seconds) and the amp did not output sound. I did the second one this way, with the same result. For my third amp re-capping, I decided to replace and test one capacitor at a time. I replaced the first capacitor (C701), reassembled, and … same result: no relay “click” and no output.
I am officially at a loss. This seems pretty simple as far as repair work goes: swapping out capacitors. I’ve read posts at other sites where people with a stated lack of electronics repair ability perform this service successfully, with no issues similar to mine. I don’t understand how replacing a single capacitor (polarity and capacitance correctly matched) would cause a fault of some kind in the power or protection circuitry. Does this have anything to do with the primary/filter caps? I just don’t know. Any ideas?
On my first attempt at re-capping one of the three low-output amps, I took a more “shotgun“ approach by replacing all of the capacitors in the power and protection circuits. Result: no dice — the front power light turned on as it should, but there was no “clicking” sound (of the relay, should click on after about three seconds) and the amp did not output sound. I did the second one this way, with the same result. For my third amp re-capping, I decided to replace and test one capacitor at a time. I replaced the first capacitor (C701), reassembled, and … same result: no relay “click” and no output.
I am officially at a loss. This seems pretty simple as far as repair work goes: swapping out capacitors. I’ve read posts at other sites where people with a stated lack of electronics repair ability perform this service successfully, with no issues similar to mine. I don’t understand how replacing a single capacitor (polarity and capacitance correctly matched) would cause a fault of some kind in the power or protection circuitry. Does this have anything to do with the primary/filter caps? I just don’t know. Any ideas?
