Friday, October 2, 2009

The Perils of Li'l Mar: Like Pulling Teeth

In our last episode things were looking up, as usual, in my efforts to restore the Marantz 4220 receiver. The sliders had been clipped and the power switch bypassed, the unfortunate result of years of actual use. Mar evidently lived in a dorm room, not a closet shelf. And unfortunately, despite all my efforts, my work was not done.

On testing she seemed to work, but moving and flexing the preamp card caused all sorts of symptoms: hum, drop outs and distortion. (Just shoot me now.) I resumed chasing bad solder on the card, and eventually made a discovery. At the corner opposite the slider-snipping were 5 posts: front/rear, left/right, and ground heading back to the amp section. Several of these posts were loose, with the ground post in the middle wobbling like a loose tooth. I realized touch ups were futile so I clipped the card free and reached for the pliers.

The ground post was pulled:

The preamp card is double sided, a major source of this receiver's problems. Each side has the ground trace running along the outside, away from the front of the unit. The ground post bridges the two sides of the ground, or would if it were actually soldered. The two ground wires wrapped around the post had obscured the less than ideal solder work made worse by the several removals from the unit. This work would have been much easier if I had just bitten the bullet and removed the card at the first sign of trouble.

Anyway, I fashioned a new post out of some solid core wire and bent one end at a right angle. I scraped the traces above and below to copper and replaced the post. The bottom right angle followed the trace and provided a good anchor for the solder. After the bottom cooled I bent the upper part a bit down the trace so the top would be stable and was generous with the solder. Here is how it looks from the top:

This is before trimming... (to be continued.)

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