After finishing my previous work on the Beocord 5000 cassette deck, I planned to make some recordings, but realized I needed to perform a full electrical adjustment procedure outlined in the service manual. This process is more time-consuming for two-head decks like this one, as it involves recording, rewinding, and playback for each adjustment.
Let’s dive into the adjustments made:
Reference +5 VDC: With the Beocord stopped, I monitored the +5 VDC power supply at a test point and adjusted trimmer 3R24 on the power supply board until it measured +5 VDC.
Azimuth: After cleaning and demagnetizing the tape head, I played a 12.5 KHz calibration tape and adjusted screw “A” on the tape head until the left and right audio signals (monitored at test points 1TP3 and 1TP4) were in phase.
Tape Speed: Using a 3.15 KHz calibration tape and a WOW and Flutter meter, I adjusted the Beocord’s capstan motor speed to minimize drift. I confirmed that the WOW & Flutter measurement was within acceptable limits (±0.13%) and the speed deviation (drift) was less than ±1.5%.
Playback Level: I performed two checks using different calibration tapes. First, using a 315 Hz, 250nWb/m tape, I adjusted trimmers 1R217 and 1R417 to achieve 660 millivolts at test points 2TP5 and 2TP6 respectively. Next, using a Dolby Level 400 Hz, 200 nWb/m tape, I ensured the same test points measured 580 millivolts.
The following adjustments require the Beocord to recognize the type of cassette tape being used. To ensure this, I used a Type I (Fe), Type II (Cr), and Type IV (MP) cassette.
Record Boost: With a Type II (Cr) tape loaded, I applied a 333 Hz, 30 millivolt sine wave from a signal generator and adjusted the record potentiometers until test points 1TP7 and 1TP8 measured 100 millivolts. I noted the measurements at test points 1TP3 and 1TP4. After switching the test signal to 19 KHz (keeping the amplitude at 30 millivolts), I adjusted the record potentiometers to match the readings at 1TP3 and 1TP4 to those previously noted. Finally, I adjusted variable inductors 1L201 and 1L401 until test points 1TP7 and 1TP8 measured 1.4 volts.
PPM Adjustment: I applied a 333 Hz, 300 millivolt sine wave and put the Beocord into Record (paused) mode. Adjusting the record potentiometers to achieve 660 millivolts at test points 2TP5 and 2TP6, I then fine-tuned trimmer 1R133 until the first red LED on the PPM display just began to glow.
Dolby Filter: Using the same test points (2TP5 and 2TP6), I temporarily connected 10 MΩ resistors between test points 1TP1 and 1TP2 to their respective tape head connections. With the Beocord in Record (paused) mode and the record potentiometers centered, I adjusted variable inductors 2L101 and 2L201 to minimize voltage readings at their corresponding test points.
Skewing: With the Dolby switch set to Dolby C, I applied a 19.9 KHz (±200 Hz) sine wave at 300 millivolts. Setting the Beocord to Record (paused) mode, I adjusted the record potentiometers until test points 2TP5 and 2TP6 measured 300 millivolts. Finally, I minimized deflection at the same test points using the Dolby Skewing adjustment variable inductors.
Bias and Recording Current: With the Dolby switch off, I set the Cr bias trimmers 3/4 turn to the right of center and the Recording Current trimmers to their center positions.
Bias Amplifier and Filter: I adjusted variable inductors 1L202, 1L402, 1L203 and 1L403 to minimize the DC voltage readings at test points 1TP9 and 1TP10 (measured with respect to -15 VDC).
Recording Current: Using a Type II (Cr) cassette, I applied a 333 Hz, 300 millivolt sine wave. With the Beocord in Record (paused) mode, I adjusted the record potentiometers until test points 2TP5 and 2TP6 measured 200 millivolts. After recording and playing back the signal, I adjusted trimmers 1R270 and 1R470 until the playback level also measured 200 millivolts.
Cr (Type II) Bias: With the same test setup, I recorded a 333 Hz signal at 20 millivolts (measured at 2TP5 and 2TP6). I then recorded a 15 KHz signal at the same level. Using the Cr Bias trimmers, I made adjustments until the playback levels of both the 333 Hz and 15 KHz signals matched at 20 millivolts.
Fe (Type I) Bias: Following a similar process to the Cr bias adjustment, I used a Type I (Fe) cassette and adjusted trimmer 1R159 until the playback levels of a 333 Hz and 15 KHz signal matched the previously established 20 millivolts.
MP (Type IV) Bias: Repeating the process again with a Type IV (MP) cassette, I adjusted trimmer 1R162 until the playback levels of the 333 Hz and 15 KHz signals matched. Notably, the playback levels for the MP tape were lower than those observed with the other tape types, but consistency between the 333 Hz and 15 KHz signals was the goal.
Advance: While I believe it is functioning correctly, the Advance adjustment using trimmer 1R182 yielded unexpected results. I need to investigate further to fully understand this adjustment.
With the electrical adjustments completed (except for the Advance), I can now move on to testing the Beocord 5000 with the Beomaster 5000 by recording and playing back music.