The Beocord 5000 (Type 4923) is performing very well in recording and playback testing. This stage of restoration always highlights the quality of the component. While it lacks auto-reverse and a monitoring tape head, the Beocord 5000 is a high-quality cassette deck with features some users prefer.
The previous post detailed the electrical adjustments outlined in the service manual. These procedures, while not overly complex, necessitate specialized calibration tapes and testing equipment.
A few adjustments raised questions during the process.
One such adjustment involved the Advance functionality. This procedure entails applying a test signal to the Beocord 5000’s record inputs and fine-tuning the record potentiometers until the PPM’s first LED illuminates. Subsequently, the test signal is attenuated by 30 dB and set to a frequency of 2.5 kHz. The adjustment requires making test recordings with these settings and modifying the 1R182 “Advance” trimmer. The goal is to achieve an alternating 12-volt and 0-volt reading on a DC-coupled oscilloscope connected to point 1TP12.
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This test aims to fine-tune the Advance tape function on the Beocord 5000 Type 4923 cassette deck.
Bang & Olufsen’s Advance function is a noteworthy feature that enables users to advance a cassette containing recorded audio by one to eight tracks, depending on the number of times the Advance button is pressed.
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Pressing the Advance button triggers the Beocord to fast-forward the cassette while simultaneously scanning for silent gaps between audio tracks.
This function endeavors to tally the silent spaces between tracks and align it with the number of Advance button presses.
The Advance function’s compatibility with cassettes recorded on different decks was a pleasant surprise.
Therefore, the Advance adjustment likely aims to calibrate the sensitivity of track detection. However, adjusting the 1R182 trimmer didn’t result in a noticeable change in the Beocord’s track detection ability.
The service manual lacks specifics regarding the minimum and maximum ranges for pulse detection. It solely instructs adjusting 1R182 until the reading at 1TP12 alternates between 0 and 12 volts.
This ambiguity raises the question of whether the trimmer should target the minimum detection point between tracks. While plausible, pinpointing a clear condition for this adjustment using the 1R182 trimmer proved challenging. Consequently, the 1R182 trimmer was left near the center position.
A typical oscilloscope reading at 1TP12 when playing a cassette is shown below. The oscilloscope illustrates the detection of the gap between audio tracks.
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Although the pulse width measures 70 milliseconds, its accuracy as the target measurement for the test remains uncertain.
Another perplexing adjustment involved the Dolby Skewing test.
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The images below depict the test setup using a blank chrome tape and measurement probes connected to 2TP5 (R-CH) and 2TP6 (L-CH).
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A tape recording source signal of 19.9 kHz at 300 millivolts is used.
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Adjusting the recording potentiometers to achieve a 300-millivolt reading at test points 2TP5 and 2TP6 is essential. The Dolby C switch should be engaged.
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The procedure recommends adjusting the Dolby Skewing inductors (2L102 & 2L202) to minimize deflection at test points 2TP5 and 2TP6.
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Having already calibrated the potentiometers for a 300-millivolt reading at 2TP5 and 2TP6, the impact of adjusting the variable inductors on an already accurate measurement was unclear.
It seemed more logical to aim for minimal deflection between the two test points, 2TP5 (R-CH) and 2TP6 (L-CH).
To verify this, a two-channel oscilloscope measured 2TP5 and 2TP6, while also utilizing the oscilloscope’s math function to display the difference between the two (2TP5 minus 2TP6).
Photos of this measurement are included below.
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This setup allowed for the simultaneous measurement of the left and right channels while adjusting their respective Skewing inductors. The goal was to achieve the flattest possible result on the Math function (Right channel minus Left channel) and to ensure both channels were perfectly in phase.
Following the final electrical adjustment, attention shifted to a mechanical adjustment from the service manual: the Take-up Moment adjustment. This adjustment, utilizing a Sony TW-2231 Torque Meter cassette, had been a point of interest.
This test employs a specially designed cassette tape to gauge the moment of the Beocord’s take-up reel.
The Sony TW-2231 Torque Meter cassette provides measurements in gram-centimeters (g-cm). The photo below shows the Take-up Reel during testing.
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The Take-up Reel measured precisely 60 g-cm. The Beocord 5000 Type 4923 service manual specifies a Take-up Reel moment between 30 and 80 p-cm, which is believed to be equivalent to the Sony meter’s g-cm unit, based on comparisons with other units. Further investigation into this adjustment procedure is necessary.
The Beocord 5000 22061 Clutch Assembly houses a tension spring that can be adjusted to modify this take-up moment value. However, accessing this spring requires partially disassembling the tape transport mechanism.
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Adjusting the clutch spring tension involves manipulating the brass tabs shown in the photograph. Lifting and moving the tabs left or right increases or decreases the force applied.
With the completion of the service manual adjustment retesting, the focus returned to assessing the Beocord’s recording and playback capabilities using audio cassettes.
The Beocord 5000 exhibited outstanding performance and is nearly ready to be returned to its owner.
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