Philips High Fidelity Laboratories 673 Tuner Repair and Alignment

From the Rain City Audio Repair Blog:

This Philips 673 tuner just came through the shop for an overhaul and adjustment. It was working for the most part but the alignment had shifted and there was room for improvement on the sound quality. Philips designed this tuner sparing no expense. It’s an extremely well designed setup, with all of the components on removable PCBs for even easier service.

The power supply received all new capacitors.

All of the buttons in this tuner are capacitative touch sensors, with a relay controller to actuate the various settings.

There are several more capacitors hidden under the shield.

The large blocks with the Philips logo are a set of 8-pole tuned filters. These were pre-tuned from the factory, and Philips provided no alignment instructions. Without specifications they’re impossible to align, but fortunately none required adjustment as the tuner met its specifications after an alignment.

The AM board has a large shielded area, and two 4-pole and an 8-pole filter.

Next up was the AM alignment, which required just a test signal, level meter, and some alignment tools. The center and signal indicators built into the tuner provided the rest of the indication.

AM alignment raised the received signal 2 full units on the signal indicator.

Next up was an FM RF alignment. This involved watching the FM Multipath Vertical output with an oscilloscope.

There were quite a few adjustments.

Calibrating the multipath indicator.

Some alignment tests required shorting out this junction to ground.

Time to align the discriminator and measure distortion. Starting in, the tuner was receiving 0.178% THD – better than even some other contemporary high end tuners, but it could do better.

Not bad. Next was adjusting the outputs to 1V each.

Time for the MPX alignment.

The instructions involve adjusting the VCO on the chip for a 19 kHz pilot signal.

Initially, the oscillator was running at 18.54 kHz; the spec is 19 kHz +/- 50 Hz, which would be from 18.95 to 19.05 kHz. This misalignment would have caused the stereo separation to be off; it settled on 19.02 kHz after adjustment.

Ultimately, 78 capacitors were replaced in this unit along with the alignment.

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This entry was posted in Audio, Electronics, Radio, Vintage and tagged , , , . Bookmark the permalink.

2 Responses to Philips High Fidelity Laboratories 673 Tuner Repair and Alignment

  1. David DeRosier says:

    Nice job.It Must have taken you many hours to do the repair. Most people would simply buy a new Receiver.

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