Professional Service Alignment



There is no provision for any home alignment of the FM-5, and under no circumstances should any adjustments be made without the following service equipment:

  1. Sound Technology 1000A FM alignment generator, or the equivalent, such as a Measurements Corporation Model 88 or 210A generator, plus a suitable multiplex generator with adjustable pilot level, and an accurate 67 KHz oscillator.
  2. Oscilloscope -- Hewlett-Packard 130C or equivalent with its Diode Probe and a 10:1 Probe.
  3. AC voltmeter with rms scale.
  4. DC voltmeterm with 0.5 volt or less full scale; 10 megohms input impedance.
  5. Intermodulation Analyzer.
Operate both the tuner and the instruments for at least 20 minutes prior to alignment.

IF Alignment

Locate a dial setting between stations. Switch the tuner to MONO, Dynatune OFF, and maximum volume. Tune the generator to the same frequency with 200 kHz deviation and 3000 µv output. Connect the diode probe to the scope vertical input, with a sensitivity of 10 mv/cm. Set the scope's horizontal external sensitivity for 1 v/cm, with the sweep ("external" or "horizontal") output of the generator connected to the horizontal input.

The diode probe connected to TP 1 of PC-25 will show tuning as a bandpass curve. Center the curve on the scope display with the tuning knob. The IF secondary, accessible through a hole in the front panel, is the only adjustment on the front end. Seek the best combnation of symmetry and amplitude.

Detector

Reduce the sweep to 75 kHz, but be careful not to touch the tuning of either the generator or the FM-5. Connect the DC voltmeter (on its most sensitive scale) to the tuner chassis and to eyelet #4 on PC-25. Adjust the secondary (top) of the detector transformer T 1 for zero. Disconnect the diode probe. Switch the generator to external modulation and connect IM analyzer to it. The IM signal should be in a 1:1 ratio to allow for de-emphasis. Adjust the IM analyzer level for 100% modulation as indicated on the modulation meter. Connect the tuner output to the IM analyzer. Adjust the primary (bottom) of the detector transformer for minimum IM. Remove IM analyzer.

Audio Level

Maintain 3000 µv signal level and switch to 400 Hz modulation. Adjust trimpot P 4 on PC-25 for 2 volts audio output from tuner with the volume control fully up.

Muting Threshold

Switch to MUTE, attenuate the generator output to 8 µv (assuming the use of a 2:1 balun), and adjust trimpot P 52 on PC-26 until the audio just mutes off. Adjust trimpot P 52 until audio just comes on (actually 4 µv).

Dynatune

Return the generator to 3000 µv. Connect the DC probe to eyelet #1 on PC-25. Retune for zero if necessary. Then switch the mute switch to DYNATUNE. If the zero indication changes at all, adjust trimpot P 3 on PC-25 for zero.

67 kHz Filtering

From an external oscillator connect an accurate 67 kHz source to the external modulation input of the FM generator. Connect the 10:1 probe to the negative side (the top end) of C 51. While observing the 67 kHz on the scope, adjust filter FL 52 for minimum amplitude.

Multiplex

Switch to STEREO. Connect the stereo generator to the external input of the FM generator. Connect the 10:1 probe to the vertical input of the scope, and set the internal sweep to approximately 2 milliseconds/cm. Connect the probe to eyelet #11 on PC-26. Peak both the 19 kHz coils L 52 and L 53 for maximum vertical deflection. Go back and forth.

Reduce the pilot level on the multiplex generator to 5%. Adjust trimpot P 51 until the STEREO light goes out. Then adjust trimpot P 51 until the STEREO light just comes on. The STEREO light should come on at 5% of the total modulation. Return pilot level at generator to 10%. Move the probe to eyelet #12 on PC-26 and adjust the 38 kHz coil L 54 for maximum vertical deflection. Remove probe.

With 1 kHz modulation on the left channel only, observe the right channel output and adjust first the 38 kHz coil L 54 and then the 19 kHz coil L 53 for mimimum indication (maximum separation). Compare left and right separation. Switch to 10 kHz modulation on the left channel and adjust filter FL 51 for mimimum indication (maximum separation).

Meter Adjustment

Switch to MONO and decrease FM generator output to 10 µv. Set trimpot P 1 on PC-25 for 25% meter deflection. Increase the FM output to 30,000 µv. Set trimpot P 2 for full scale meter deflection.



This page created and maintained by Greg Dunn.
Copyright © 2000-2001 Greg Dunn