I have a Mosconi amplifier from the AS line. The amplifier seems to function as it should except there is no output. I have -/+ 13v, 50v and 45v rails present and I have traced the input signal through the vertical daughter cards (has the xover and gain pots) and those are ruled out as I am getting signal all the way to the each amplifier/channel section of the pcb.
I believe the mute circuit is the issue, I'll take some close up pics and show exactly where the input signal is present on the amplifier sections.
I am feeding it a 60hz sine wave that is 2v and I have made sure the LP and HP crossovers are bypassed or set to allow the sine wave to go through....which I have verified both daughter boards work because I notice the input signal that was in the amplifier section of each channel change as I fiddle with the xover pots and switches. So the signal is reaching each channel amplifier section that is why I believe the mute transistors perhaps have failed or not properly switching.
Any help is greatly appreciated.
I believe the mute circuit is the issue, I'll take some close up pics and show exactly where the input signal is present on the amplifier sections.
I am feeding it a 60hz sine wave that is 2v and I have made sure the LP and HP crossovers are bypassed or set to allow the sine wave to go through....which I have verified both daughter boards work because I notice the input signal that was in the amplifier section of each channel change as I fiddle with the xover pots and switches. So the signal is reaching each channel amplifier section that is why I believe the mute transistors perhaps have failed or not properly switching.
Any help is greatly appreciated.
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Here's a pic of the amplifier section of one channel. The yellow traces is where the signal is present it comes to the amplifier section from what I believe is the via hole from there it goes through two 10k resistors then to the pin 1 of the op amp.
Mosconi AS300.2
Tough amps to repair...sometimes.
Zed Audio does all the Mosconi repairs for the USA and Canada.
Make sure you have about +/- 5-7v on the opamp's power pins (8 and 4)
The small SMD electrolytic is the input blocking cap for the power amplifier.
Make sure you have good signal on this cap
Steve
Tough amps to repair...sometimes.
Zed Audio does all the Mosconi repairs for the USA and Canada.
Make sure you have about +/- 5-7v on the opamp's power pins (8 and 4)
The small SMD electrolytic is the input blocking cap for the power amplifier.
Make sure you have good signal on this cap
Steve
The op amp on vertical board (that has the RCA's) has the -/+13v on pin 4 and 8, as well as the -/+45v and 50v rails.
Cap 33 had the 60hz sine wave signal present on both sides so that's good.
Cap 33 had the 60hz sine wave signal present on both sides so that's good.
Looks pretty similar, some components and resistors are a bit different but overall looks like the same layout/design. Do you have the rest of the schematics? Perhaps the mute circuit or is it Q66?
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Did you get my email Perry? I sent it on the 27th, perhaps it went to spam or got deleted by the system.
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