[sdiy] Looking for advice about powered reference monitor problem

[Roman Sowa]

I also think it might be one of the small caps. One of very few examples 
of bad capacitor I experienced in servicing was indeed small 4u7 
capacitor in audio path that was causing about 10dB attenuation if not 
more. It showed massive increase in ESR and acted like voltage divider 
with following resistor. After replacing, both channels played equally. 
BTW it was audio pwer amp, so pretty much the same.
But your picture does not show any electrolytic caps in preamp & 
crossover section, so this is probably dead end anyway.

As others said, it also could be cold joint or corroded connector. Yes 
those things can sit there non disturbing and start acting after years 
of use. You moved the board while replacing caps, so it cured the 
problem for a while. Poke the board with a stick to check if small bend 
pressure changes something.

 From your picture I reckon there's probably no limiter, but that was 
also a reason once of "quiet speaker" problem. It was because of badly 
designed limiter circuit in KRK speaker, which at some point had to go 
wrong.

Roman

W dniu 2020-11-20 o 09:34, Gordonjcp pisze:
> On Thu, Nov 19, 2020 at 02:19:00PM -0500, Shawn Rakestraw wrote:
>>
>> I don't have a schematic, but I can tell you there is a giant toroidal
>> transformer that sends power to a single circuit board with 2 amplifiers,
>> one for an 8" speaker and the other for the tweeter. It seems like both
>> speakers suffer from the same volume attenuation problem. The capacitors I
>> replaced were 2 big 10000 uF where the power enters the board and 7 100uF
>> in the amplifier section. There is a bass and treble section, as well as a
>> gain pot.
> 
> It won't be one of those if it is a bad capacitor, it'll be a really small one below about 10μF connecting the inverting input of an opamp to ground through a resistor.
>