Hi Guys,
This is my first real mixer on the workbench. I went to the usual sites,
hifimanuals, hifiengine, electrotanya, eserviceinfo, one-electron... it didn't turn up.
Does anyone know of a website dedicated to providing free service manuals for mixers/pro audio equipment? Tanks.
Also, I'll list the symptoms in case we can head the issue off with experience instead of the manual. When the phantom power had been turned on, the first thing I checked was the voltage. 39-40 volts, stable, depending on whether a condenser was attached and turned on. I checked for AC as well. No fluctuations. The two analog level meters jump up to midway, as if calibrating to a new starting point, even if all of the volume and gain faders are at minimum swing. Then, after 5 seconds, a pulsing condition takes over the visual meters, and a pulsing can be heard through the monitors - the rhythm is about 90Hz. When speaking into the condenser mic while the console is doing this, the volume of the voice rides up and down in amplitude just like a tremolo unit.
Is this an oscillation caused by a faulty capacitor? Shouldn't a professional series mixer be using 48V for phantom power? Is the analog meter offset the best indicator that the phantom power circuit is no longer fully isolated properly in some way?
This is my first real mixer on the workbench. I went to the usual sites,
hifimanuals, hifiengine, electrotanya, eserviceinfo, one-electron... it didn't turn up.
Does anyone know of a website dedicated to providing free service manuals for mixers/pro audio equipment? Tanks.
Also, I'll list the symptoms in case we can head the issue off with experience instead of the manual. When the phantom power had been turned on, the first thing I checked was the voltage. 39-40 volts, stable, depending on whether a condenser was attached and turned on. I checked for AC as well. No fluctuations. The two analog level meters jump up to midway, as if calibrating to a new starting point, even if all of the volume and gain faders are at minimum swing. Then, after 5 seconds, a pulsing condition takes over the visual meters, and a pulsing can be heard through the monitors - the rhythm is about 90Hz. When speaking into the condenser mic while the console is doing this, the volume of the voice rides up and down in amplitude just like a tremolo unit.
Is this an oscillation caused by a faulty capacitor? Shouldn't a professional series mixer be using 48V for phantom power? Is the analog meter offset the best indicator that the phantom power circuit is no longer fully isolated properly in some way?
Maybe. Close enough. No.
Phantom is blocked from the rest of the mixer by caps.
I would not call 90Hz a tremolo, to me it is a hum, since the mains is already 60Hz. But I guess that is nit picking.
Find your power supply. It looks like this runs on 25v rails. SO my first reaction to pegging meters is a missing power supply voltage. See that you have both +25v and -25v that are free of ripple.
A quick google for "Yamaha M512 schematic" found the entire manual:
Download YAMAHA M512 Service Manual
JonSnell, that was an OMEGA (3) high score! I loved jumping back into the project with this increased level of excitement, knowing someone else who has been here before myself. I replaced the 10u/100V cap. Prior to this posting, I had replaced the 4 electrolytics in the screen printed box labeled "DC", paying close attention to the layout surrounding any caps rated for 50V or more. The 10u was just outside the box. DC on Q1 was "close enough" and no AC.
Enzo, thanks for your help. I will respond in reverse to your post. I have been using duckduckgo (makes me laugh). I downloaded the manual from your link then went to google and found the search successful. That's a game changer.
The signal I was describing at 90Hz is actually a tremolo because it modulates the amplitude of my voice as I speak into the condenser mic. It reminds me of a elevated heart beat, with more fluidity. Ah! There it is - I accidentally called it 90 CPS instead of waves/beats/pulses per minute. That helps in understanding.
Enzo, thanks for your help. I will respond in reverse to your post. I have been using duckduckgo (makes me laugh). I downloaded the manual from your link then went to google and found the search successful. That's a game changer.
The signal I was describing at 90Hz is actually a tremolo because it modulates the amplitude of my voice as I speak into the condenser mic. It reminds me of a elevated heart beat, with more fluidity. Ah! There it is - I accidentally called it 90 CPS instead of waves/beats/pulses per minute. That helps in understanding.
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