Sunday, September 27, 2009

Li'l Mar: Where Something Gets Snipped

Li'l Mar is the Marantz 4220 Quadradial receiver that has become my life's work. When we last visited her we were making progress, of a sort. The distortion in the left channel was healed, but we had worn out sliders. The front was totally kaput and the fader and the rear were less than perfect, so the executive decision was made to remove them from the circuit.

Here is the before, courtesy of Jay's telephone. Evidently modern telephones even come with very respectable macro capability:

Jay's photo is a bit overexposed. Not much of a telephone, eh? The strip attached to the face plate at the bottom via the sliders (note the 3 visible squarish posts) is a very simple circuit board that needs to be disconnected from the dangling preamp board. The wires from the sliders to the preamp (eg. the brown one at the right) needed to be removed, and the wires coming in to the sliders needed to take their place. Above is before, below is after.

The wires above were formerly connected to the sliders and now were connected directly to the preamp: front left and right, rear left and right . Hmm, Jay, much better photo. This might actually be useful at some point in the future.

So we fired her up and it sounded... awful. Arrggh! Now what?? Well, the power switch was humming like that guy from Crash Test Dummies on about every third click.

Note the blue wire above. This power switch is essentially a two parter: the front with all the wires attached (at the right, lower corner) is a muting switch to make your ons and offs nice and quiet. The taller back portion with the two rivets is the actual power switch and it was worn out. We jumpered the connection with the blue wire so it is on all the time. If I had the stomach to be (even more of) a hero I could have Dremeled the rivets and taken apart the switch, but even I have my limits. Mike and Robert claim they actually do this. Really.

So we gave Li'l Mar another listen... and it is getting late. There is more, much more.

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