Tuesday, August 11, 2009

The Perils of Li'l Mar: Episode Two

When we last visited our intrepid hero trying to save Li'l Mar, little did we realize he was more at risk than the fair damsel! Li'l Mar is trouble, trouble! And our shouts of warning are not directed towards Li'l Mar in peril, but instead to warn our hero. Look out! Things are not what they seem!

Our first effort in restoring the Marantz 4220 replaced the caps on the regulator board and the phono board, pretty simple stuff. But the power amp board promised to be trickier to work with given the space limitations in the undersized chassis. Here's a gander from the left side of the chassis, heat sink backing the amp board. Buried down at the bottom is a metal sandwich around the 8 Toshiba 2SC790 output transistors.

The amp board put up a tussle but eventually was exposed enough to work on, although not easily. The still attached wires and the dangling outputs (don't break!) made for slow going. A total of 19 caps were replaced with Panasonic FCs:

The outputs had little black pads glued on them to seat them in the heat sink sandwich. Cute. And note the Toshiba TA7109P IC drivers, rare, but can be purchased from Acme if needed.

The driver board was re-sandwiched and replaced and we gave it a listen... and it was still weird. Weak in one channel, with odd behavior from the balance sliders. And the FM was barely there.

Ominous music swell from an unseen and properly functioning sound system (no, not Li' Mar) ... And here is nothin' but trouble:

Yes, time to mess with the preamp. Something is wrong with the tone control board. Lots of little caps in a very cramped space, with too many wires limiting your room to maneuver. Nothin' but trouble. But we will have to await the next episode of the Perils of Li'l Mar to see if our intrepid tech survives.

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