Want to share:
Have downloaded the schematics from this forum to help repair the amplifier of a friend.
Turned out that Sony decided to route the earth through the chassis, even the earth between the various supplies.
When one takes the main board out of the chassis and switches the amp on, there are up to 20 volts difference between the eart (and hence reference) of the pre-amps and the main amps.
Luckily the amp goes into protection but from a design point of view it is not nice to rely on screws and aluminum face plates to conduct up to 0.2 amps of current from one supply to another.
What I did is solder wires to every eart point and connected them on the main board to make it stand alone and not rely on conducting current through the chassis anymore.
Bad design, simple repair but took some digging in the schematics to find out what exactly was going on!
Hi all,
I need a little help to repair my Akai PM-750 amplifier (part of system mx-750).
The voltage selector has broken and I don't know wich wires shoud I put together to get it work under 240V.
Service manual is no help, they just give spares parts...
Huge thanks to who could help me :-)
Hello, I am in the process of repairing the Mackie ProFX12 V2 mixer for a client, and am running into the unavailability of schematics. Does anyone have a copy they could share? I have already reached out to Mackie directly but am still waiting for a reply.
Additionally, I am having trouble identifying the failure mode for the two channels that have failed: one produces loud static (indicating bad op-amp or feedback resistor perhaps?) and the other has the right channel producing a 60hz hum, the other is functional. (see board photos, with the two failed channels being marked with "F". The browned area is residual flux from having replaced two opamps, and having reflowed other components around them)
Any help on either of these fronts would be invaluable. I have mainly worked in laptop and computer repair, and am just getting started with my first scope and first set of board level repairs.
Hi,
My column Marshal Acton 2 , is dead . Power suplyy is it ok ... 18 V , but not light and not power on.
I need some help, and i try to find schematic !
Do tou can help-me ?
Best regards