Performance Tests and Electronic Alignment

Performance testing should be made at regularly scheduled intervals (every 150 hours or every month) to ensure that the recorder is performing within specifications. These tests should also be performed whenever the recorder appears to be malfunctioning and following repairs to the equipment that may affect performance.

If the performance test is not successful, proceed to the applicable electronic alignment procedure.

It is important to clean and demagnetize the head and tape guiding components before performing the following steps.

4-1 GENERAL NOTICE↑ TOP

It is important to clean and demagnetize the head and tape guiding components before performing the test and alignment procedures.

The voltages indicated in this section are for the MX-5050B-2H (D) model and are at a 1KHz frequency at reference recording level of 250 nWb/m (The RECORD LEVEL switch on the back panel is in the 'M' position). In the case of IEC equalization, the reference record level is 320nWb/m (RECORD LEVEL switch is in the 'H' position) that is 1.2 dB above 250nWb/m (RECORD LEVEL switch is in the 'M' position). Refer to Fig. 4-10.

⤢ zoomFig. 4-10 Input v.s Output and Distortion: output level plotted against input level with the distortion curve beside it, and the record level switch positions marked on the scale

The test and alignment procedures for the MX-5050B-F and the MX-5050B-4 models may be carried out in essentially the same manner. However, the sensitivity of the reproduce heads, the biasing current and the signal current of the record heads differ from the values in MX-5050B-2H(D). Refer to the block diagrams for 4-track and full-track type to obtain each value for the MX-5050B-F and MX-5050B-4. A double designated symbol number is for the left channel/right channel.

The test equipment listed in Table 1-1 are required for completion of the performance and alignment procedures.

4-2 TEST TAPES↑ TOP

Test tapes are precisely recorded under controlled conditions and must be correctly handled and stored to retain accuracy.

Handle the test tapes as follows:

1. Clean and demagnetize the head and tape guiding components before installing the test tape.
2. Never store test tapes in areas where there are temperature or humid extremes.
3. Never run the test tapes on speeds other than a normal play run (never use the rewind or fast forward mode). This is further explained below. During the alignment procedure, the rewind and fast forward modes should not be used.

After alignment, wind the tape completely on the takeup reel, interchange reels, thread the tape, and place the equipment in the play mode to wind the tape back on its original reel.

After extensive use, high frequency tones may be drop as much a 2 dB.

In addition, flutter indication may rise even though actual flutter remains unchanged.

Flutter increase is caused by demagnetization of the recorded signal from repeated plays, tape deformation due to tape tension, changes in temperature and humidity, and increased dropout resulting from tape wear.

4-3 TEST CONDITIONS↑ TOP

The test conditions specified in the following steps are to be met prior to performing the tests. After these test conditions are met, continue with the following procedures for checking overall signal-to-noise, overall distortion, crosstalk, and flutter.

1. Clean and demagnetize the heads.
2. Use high quality low-noise tape such as Ampex 406, 407, 456, or Scotch 206, 207, 250, or an equivalent, and bulk erase the blank tape.
3. Turn the power on and allow the unit to warm up for 20 minutes.
4. Be sure the head cover is installed for all tests. 4-2,

PERFORMANCE TESTS

Before performance testing, a SRL check, reproduce frequency response check, record level check, source level check, an overall frequency response check, and a SEL.REP level check are necessary. Refer to section 4-7, ELECTRONIC ALIGNMENT, in this manual for checking procedures. For performance testing, at first proceed as follows.

Demagnetize and clean the heads and all guiding components.

1. Set the REEL switch to the appropriate position, and set the EDIT switch to the "out" non-edit position.
2. Set the LINE OUT switch to 'H', set each RECORD switch to the appropriate position, set each SEL.REP switch to the "out" position, and set each MONITOR switch to the "out"SOURCE position.
3. Thread a reel of bulk-erased tape onto the transport, set the SRL switch to the SRL position, and push the PITCH CONTROL knob to its fixed position.

4-4-(1) OVERALL SIGNAL-TO-NOISE↑ TOP

The overall signal-to-noise test requires an ASA "A" weighted filter for weighted measurement and a noise filter for unweighted measurement to attenuate noise outside of the audible frequency band. The filter may be built into a small aluminum box as is shown in Fig. 4-1.

⤢ zoomFig. 4-1 Filter Schematics: two filter circuits: the ASA "A" curve filter for weighted measurement, and the noise filter for unweighted measurement

The signal-to-noise ratio depends on the SRL calibration, reproduce equalization, bias calibration, and record equalization. Proceed as follows:

1. Connect the filter to CH-1 LINE OUT and connect an ac voltmeter to the output of the filter.
2. Set the reproduce head selector switch on the head assembly to the appropriate position.
3. Set the SRL switch to the "SRL" position and set the RECORD LEVEL switch to the "L" (185nWb/m) position.
4. Hold the TEST OSC pushbutton depressed and adjust the CH-1 INPUT LINE control for a 0 VU indication on the VU meter. Note the ac voltmeter indication; the ac voltmeter will not read +4 dBm due to the insertion loss of the filter.
5. Depress the CH-1 MONITOR switch to the "in" TAPE position, and set the CH-1 INPUT LINE and CH-1 INPUT MIC controls to their full counterclockwise positions. Reset the TAPE TIMER to "0000".
6. Start the record mode and record for one minute. Rewind the tape to the "0000" indication on the timer.
7. Reproduce the recorded portion and read the noise level on the ac voltmeter.
8. The signal-to-noise ratio is determined by calculating the difference in readings obtained in step 2 and step 5 plus 9 dB (A-B)+9 dB (peak recording level-520 nWb/m-is 9 dB above SRL-185 nWb/m)
9. Repeat steps 1 through 6 for the other channels as required, and change the tape speed to check all signal-to-noise ratios. Table 4-1. Signal-to-Noise Specifications

Tape Speed	1/2 Track		1/4 Track		Full Track
	Weighted	Unweighted	Weighted	Unweighted	Weighted	Unweighted
15 ips	65/63 dB	62/60 dB	62/60 dB	59/57 dB	68/66 dB	65/63 dB
7 1/2 ips	65/63 dB	62/60 dB	62/60 dB	59/57 dB	68/66 dB	65/63 dB
3 3/4 ips	63/63 dB	60/60 dB	60/60 dB	57/57 dB	66/66 dB	63/63 dB
Note: 65dB/63dB indicates NAB/IEC equalization

If signal-to-noise specifications are not met, check and adjust the following items.

1. SRL calibration.
2. RECORD BIAS adjustment.
3. Reproduce equalization.
4. Record equalization.
5. Record and/or reproduce electronics.
6. Head magnetization.
7. Magnetic flux of a motor, a soldering iron or a transformer near the recorder.

4-4-(2) OVERALL DISTORTION TEST↑ TOP

For accurately checking distortion it is necessary to use an audio oscillator with less than O.1% distortion and a wave analyzer with an adjustable bandwidth capability. A wave analyzer with too narrow a bandwidth may make it difficult to measure harmonics due to flutter components within the transport. Instruments that measure total harmonic distortion will be affected by tape and modulation noise in addition to harmonic distortion. To measure overall harmonic distortion proceed as follows:

1. Connect a wave analyzer to CH-1 LINE OUTPUT and connect an audio oscillator to CH-1 LINE INPUT.

2. Set the MONITOR switches to their "in" TAPE positions, set the audio oscillator frequency to 1000 Hz, set the SRL switch to the "SRL" position, and set the RECORD LEVEL switch to the "M" (250 nWb/m) position.

3. Set the wave analyzer frequency to 1000 Hz, the bandwidth to 100 Hz, and the mode selector switch to AFC.

4. Start the record mode and adjust the CH-1 INPUT LINE control for a 0 VU reading on the VU meter.

5. Adjust the fine tuning control on the wave analyzer and adjust the analyzer input level control for a full scale reading of 100%.

6. Change the wave analyzer tuning control to 2000 Hz and measure the second harmonic content. The second harmonic content should not exceed 0.1%.

7. Change the wave analyzer tuning control to 3000 Hz and measure the third harmonic content. Third harmonic distortion is dependent upon the type of tape used, and the accuracy of the RECORD BIAS setting. A typical reading for low noise high output tape is 0.4%.

If distortion specifications are not met, check and adjust the following items.

1. SRL calibration.
2. RECORD BIAS adjustment
3. Head magnetization.
4. Record and/or reproduce electronics.

4-4-(3) CROSSTALK TEST↑ TOP

It is important that blank bulk-erased tape be used for the crosstalk test. To measure crosstalk between channels proceed as follows:

1. Follow the procedure in the Overall Distortion Test, steps 1 through 5.

2. Connect a wave analyzer from the output of CH-1 to CH-2 LINE OUTPUT.

3. Measure the crosstalk in dB. Crosstalk should not exceed that shown in Table 4-2. If crosstalk specifications are not met, record and reproduce head alignment (height and tape contact) is incorrect or the record or reproduce head is defective.

Table 4-2. Crosstalk specifications

Track	Crosstalk
1/2 track	55 dB
1/4 track	55 dB

4-4-(4) ERASURE TEST↑ TOP

It is important that blank bulk-erased tape be used in the erasure test. To measure depth of erase, proceed as follows:

1. Follow the procedure in the Overall Distortion Test, steps 1 through 5. A 1000 Hz signal is being recorded at SRL.

2. Set the SRL switch to the off position and adjust the OUTPUT control for a -10 VU reading on the VU meter.

3. Adjust the INPUT LINE control for a 0 VU reading on the VU meter, a 1000 Hz signal is being recorded at 10 dB above SRL. Continue recording for a few minutes.

4. Disconnect the audio oscillator.

5. Rewind and reproduce the recorded section. The VU meter reading should be 0 VU. Check the wave analyzer and readjust it as necessary for a full scale reading of 100%.

6. Press the RECORD pushbutton to place the recorder in the record mode. As the tape is being erased, adjust the percent scale on the wave analyzer to read the residual 1000 Hz tone.

7. Repeat the same procedure for the other channels.

8. The depth of erase should be more than 70 dB. If erasure specifications are not met, check and adjust the following items.

9. Erase and/or record head alignment, (height, tape contact).

10. Erase head wear.

11. Erase head surface cleanliness.

12. Bias oscillator adjustment.

4-4-(5) TAPE SPEED MEASUREMENT↑ TOP

A flutter test tape is used for measuring tape speed.

Since tape tension affects tape speed, it is important for accurate measurement that the flutter test tape used is attached to the end of a full reel of blank tape as shown in Fig. 4-2, and is used with the REEL pushbutton set to the appropriate reel size.

Proceed as follows:

1. Place the PITCH CONTROL in the fixed position and set all RECORD switches to their off "out" positions.

2. Connect a flutter meter to LINE OUT and set the MONITOR switch to the TAPE position.

3. Set the SPEED switch to "HIGH" and use the test tape at its appropriate speed.

4. Attach the test tape to a 10 1/2 inch NAB reel as shown in Fig. 4-2, place the test tape on the supply reel table, thread the tape, and set the REEL switch to the LARGE position.

5. Place the recorder in the play mode and note the reading on the frequency counter. The reading should be between 2994 and 3006 Hz (3000Hz ± 0.2%).

6. Repeat the procedure at a point towards the end of the reel, for a 7 inch EIA reel, and for low tape speeds.

7. If adjustment is necessary, refer to section 3-5. If speed accuracy is not within ±0.2%, check and adjust the following items.

8. Pinch roller tire wear and pressure.

9. Brakeshoe for brake drum contact.

10. Tape tension.

11. Power correctness.

12. Pinch roller and capstan cleanliness. ⤢ zoomFig 4-2 Test Tape Loading: a reel of tape seen face on, the test tape wound inside and blank tape outside

In addition, check the following items for the dc servo capstan motor.

6. Servo control circuit.

7. Capstan motor. Or for the hysteresis synchronous capstan motor:

8. Capstan belt, pulley, and fly-wheel cleanliness.

9. Capstan belt tension. NOTE

To avoid error affected by the line frequency, it is recommended that the time-base of a frequency counter be set as follows: A. On the dc servo capstan motor, set the time-base to the crystal oscillator B. On the hysteresis synchronous capstan motor, set the time-base to the line frequency.

4-4-(6) FLUTTER AND WOW TEST↑ TOP

It is recommended that these checks be made with standard flutter test tapes (See Table 1-2) which are recorded on precise equipment to produce less than 0.03% rms flutter. After recording a section of tape, rewind to the beginning and start the tape in the reproduce mode. Flutter meters are sensitive to amplitude modulation that results from poor head-to-tape contact or from signal dropout. Therefore, clean the heads before making a flutter test.

The following method is used with a test tape:

It is important that the flutter test tape used is attached to the end of a full reel of blank tape as shown in Fig. 4-2, and is used with the REEL pushbutton set to the appropriate reel size.

1. Place the PITCH CONTROL to the fixed position and set all RECORD switches to the off "out" position.

2. Connect a flutter meter to the LINE OUT of an inner track channel's MONITOR switch in the TAPE position.

3. Set the selector switch of the flutter meter to the NAB weighted position, set the SPEED switch to H1, and use the test tape at an appropriate speed.

4. Attach the test tape to a 10 1/2 inch NAB reel as shown in Fig. 4-2, place the test tape on the supply reel table, thread the tape, and set the REEL switch to the L position.

5. Place the recorder in the play mode and note the reading on the flutter meter. The reading should be as shown in Table 4-3.

6. Repeat the procedure at a point towards the end of the reel, a 7 inch EIA reel, and at low tape speeds.

The following method is used when a test tape is not available:

1. Connect the oscillator signal output of the flutter meter to an inner channel (not an edge channel) LINE INPUT of the recorder.

2. Connect the same channel's LINE OUTPUT of the recorder to the signal input of the flutter meter.

3. Set the SPEED switch to "HIGH", set the SRL switch to the SRL position, set the MONITOR switch to the TAPE position, start the record mode, and adjust the appropriate INPUT LINE control.

4. Rewind and reproduce the recorded portion, and note the flutter and wow on the flutter meter.

5. Check the flutter and wow at a low tape speed, and check it at a point towards the end of the reel.

Table 4-3 Flutter and wow specifications

Tape speed	Flutter and wow
15 ips	0.06%
7.5 ips	0.08%
3 3/4 ips	0.12%
Flutter and wow can be caused by any element in the tape path. Excessive flutter and wow may be traced by observing the flutter component on an oscilloscope screen connected to the demodulator output of the flutter meter. If the fluctuation rate observed on the oscilloscope coincides with the rotational elements, such as the supply or takeup reel, capstan or pinch roller, the problem source may be easily traced. Other sources of excessive flutter and wow are:

1. Defective capstan servo control.

2. Damaged capstan motor.

3. Capstan needs lubrication (dry bearing).

4. Incorrect tape tension.

5. Brakeshoe is contacting brake drum.

6. Defective tape reels or tape.

7. Pinch roller tire is worn or has insufficient pressure, or the pinch roller solenoid is not bottomed.

8. Dirty pinch roller and capstan. ACCESS TO ELECTRONICS ASSEMBLY

The record/reproduce electronics assembly can easily be opened for adjustment. To gain access to the electronics assembly, proceed as follows:

1. Place the equipment in a horizontal position.
2. Remove the bottom cover by removing the four screws on the cover as shown in Fig 4-3, remove the two screws on the electronics front panel, and remove two screws on the electronics chassis, as shown in Fig 4-3.
3. Pull the electronics assembly up, rotate it to a horizontal position, and push it to fix it horizontally. ⤢ zoomFig. 4-3 Electronics Access: the recorder with its bottom cover removed and the electronics assembly rotated up and forward into its service position

ELECTRONIC ALIGNMENT

If the previous performance tests were not successful, perform the following applicable reproduce, record, and bias amplifier alignment procedures.

4-6-(1) REPRODUCE SYSTEM↑ TOP

Reproduce system alignments consist of reproduce head azimuth adjustment, frequency response adjustment, SRL adjustment and SEL.REP. level adjustment.

VR101/201: SEL. REP. LEVEL VR102/202: REP. EQ. 15 and 7 1/2 ips VR103/203: REP. EQ. 3 3/4 ips VR104/204: SRL VR105/205: OUTPUT LEVEL (TAPE) VR107/207: PEAK INDICATOR TRIGGER LEVEL SW101/201: MONITOR;TAPE SW302/402: SEL.REP.;OFF SW503 : RECORD LEVEL;M SW504 : SRL;OFF SW506 : OUTPUT LEVEL;HIGH

⤢ zoomFig. 4-4 Reproduce System Simplified Diagram: a simplified diagram of the reproduce chain, from the head through the amplifiers to the peak indicator circuit

The levels in the peak indicator circuit is at peak indicator trigger level.

4-6-(2) REPRODUCE HEAD AZIMUTH ADJUSTMENT↑ TOP

The head azimuth adjustment should be adjusted with a "LOW" tape speed for a critical alignment. Use the test tapes listed in Table 1-3.

1. Thread a low speed test tape, depending on the model of the equipment, to the recorder.
2. Connect the ac voltmeter to the LINE OUT connector and set the EQUALIZER switch on the back panel to the appropriate position depending on the test tape to be used.
3. Reproduce the coarse azimuth adjustment signal (250 Hz at 3 3/4 ips or 500 Hz at 7 1/2 ips) of the test tape and adjust the OUTPUT control for a 0 dBm reading on the ac voltmeter.
4. Then, reproduce the fine azimuth adjustment signal (8kHz at 3 3/4 ips or 16kHz at 7 1/2 ips) and adjust the azimuth screw "A4" for a maximum reading on the ac voltmeter. CAUTION

DO NOT ADJUST ANY OTHER SCREW EXCEPT THE AZIMUTH ADJUSTMENT SCREW (LABELED "A4" IN Fig. 4-5).

5. If a maximum reading cannot be achieved within one full turn of the azimuth screw, or a maximum reading on the ac voltmeter is well below 0 dBm, a full head alignment may be required. Refer to section 4 of this manual.
6. Repeat step 3 and 4 for the auxiliary reproduce head. In this adjustment, the adjusting screw is "A2". ⤢ zoomFig. 4-5 Head Assembly: the head assembly seen from the front: erase, auxiliary reproduce, record and main reproduce heads, each with its azimuth, height and wrap adjustment screws

ERASE HEAD REPRODUCE HEAD (AUXILIARY) RECORD HEAD REPRODUCE HEAD (MAIN)

4-6-(3) FREQUENCY RESPONSE↑ TOP

Since the reproduce equalizer adjustment controls are commonly used for both 15 ips and 7 1/2 ips on the high speed version, an adjustment is made firstly, for 15 ips. Table 4-4 shows the time constant at each equalizer. On the low speed version, adjustment controls for each speed are provided.

1. Connect the ac voltmeter to the LINE OUTPUT terminals and set the EQUALIZATION switch on the back panel to the desired position.

2. Thread the test tape through the equipment. For 15 ips:

3. Reproduce a 500HZ signal on the test tape and adjust the OUTPUT controls for a OdBm reading on the ac voltmeter.

4. Reproduce the frequency response test signal (from 31.5 up to 20KHZ) and note the reading on the ac voltmeter.

5. Adjust the VR 102/202 adjustment controls with a frequency of 10 kHz for a 0 dBm reading on the ac voltmeter. The reading should be 31.5 Hz to 20 kHz ±2 dB. For 7 1/2 ips:

6. On the high speed version, repeat steps 3 and 4 to check the frequency response. The reading should be 31.5HZ to 16KHZ ±2 dB.

7. On the low speed version, repeat step 1 through 5 at 7 1/2 ips tape speed and adjust the VR102/202 as necessary. The reading should be 31.5HZ to 16KHZ ±2dB. For 3 3/4 ips:

8. Repeat step 1 through 4 with the test signal from 31.5 up to 10KHZ and adjust the VR 103/203 adjustment controls with a frequency of 8KHZ for a OdBm reading on the ac voltmeter. The frequency response should be 31.5 Hz to 10 kHz ±2 dB.

Table 4-4 Equalizer Time Constants

Equalizer	Time Constants
NAB 15 ips	3180 + 50 µsec
IEC 15 ips	∞ + 35 µsec
NAB 7.5 ips	3180 + 50 µsec
IEC 7.5 ips	∞ + 70 µsec
NAB & IEC 3.75 ips	3180 + 90 µsec
Table 4-5 Standard Reference Level of MX-5050B

RECORD LEVEL SW	SRL
	RECORDED FLUX	OUTPUT
		VU METER	CUTPUT LEVEL SW
			HIGH	LOW
L	185nWb/m
M	250nWb/m	0dB	+4dBm	-10dB
H	320nWb/m
RECORD SEL.REP RECORD RECORD EQUALIZER RECORD TEST MONITOR 1 2 1 2 BIAS 1 2 LEVEL OSC HIGH LOW HIGH LOW 1 2 SW301 SW401 SW302 SW402 VR306 VR406 VR304 VR305 VR404 VR405 VR303 VR403 SW501 SW101 SW201 VR407 VR307 RECORD BIAS OSCILLATOR VR204 LINE LINE INPUT INPUT AMP-1 AMP-2 REC. EQ. REC. EQ. LINE LINE AMP-1 AMP-2 OUTPUT OUTPUT AMP-1 AMP-2 TEST OSCILLATOR SEL. SEL. VR202 VR203 VR501 REP REP AMP-1 AMP-2 MIC MIC LINE LINE AMP-1 AMP INPUT INPUT TRANS. TRANS. -2 -1 -2 (OPT) (OPT) SW502 SW503 VR101 VR201 REP. EQ. AMP-2 REP. EQ. AMP-1 VR103 VR102 SW505 SW506 H M L NAB IEC HIGH LOW OFF -20dB 0dB MIC ATTENUATOR RECORD LEVEL EQUALIZER OUTPUT LEVEL

⤢ zoomFig. 4-6 Location of Record/Reproduce Electronics: the record and reproduce board layout, with the switch and trimmer positions labelled across it

4-6-(4) SRL ADJUSTMENT↑ TOP

Table 4-5 shows each SRL (Standard Reference Level) of the MX-5050B. For example, when a recorded flux of 185 nWb/m is reproduced with the RECORD LEVEL switch in the "L" position, the VU meter will indicate a 0 dB and a standard output level will be obtained at the LINE OUTPUT terminals. For a SRL adjustment, proceed as follows:

1. Set the SRL switch to the SRL position and thread the test tape through the equipment.

2. Place the RECORD LEVEL switch to the appropriate position depending on the reference recorded flux of the test tape to be used.

3. Reproduce the reference recorded flux on the test tape and adjust the VR104/204 adjustment controls for a 0 dB indication on the VU meters.

4-6-(5) SEL. REP LEVEL ADJUSTMENT↑ TOP

This adjustment follows the SRL adjustment.

1. Press both the CH1 and CH2 SEL. REP buttons for the SEL. REP mode.
2. Reproduce the reference recorded flux and adjust the VR101/201 adjustment controls for a 0 dB indication on the VU meters.

4-6-(6) RECORD SYSTEM↑ TOP

Before performing record system adjustments, a reproduce system adjustment must be made.

4-6-(7) RECORD HEAD AZIMUTH ADJUSTMENT↑ TOP

The head azimuth may be adjusted at a low tape speed for critical head alignment and at 20 dB below the standard recording level.

1. Connect the ac voltmeter to the LINE OUTPUT terminals and connect the audio oscillator to the LINE INPUT terminals.

2. Set the SRL switch to the SRL position, the OUTPUT LEVEL switch to the HIGH position, and the MONITOR switch to the TAPE position.

3. Thread a blank tape through the equipment.

4. Set the audio oscillator frequency to 1 kHz.

5. Place the equipment in the record/reproduce mode and adjust the LINE INPUT control for -20 dBm on the ac voltmeter.

6. Adjust the record head azimuth screw "A3" for a maximum reading on the ac voltmeter in the 7.5 kHz for 3 3/4 ips or 15 kHz for 7 1/2 ips record/reproduce mode. CAUTION

DO NOT ADJUST ANY OTHER SCREW EXCEPT THE AZIMUTH ADJUSTMENT SCREW (LABELED "A3" IN Fig. 4-5).

7. If a maximum reading can not be achieved within one full turn of the azimuth screw, or a maximum reading on the ac voltmeter is well below -20 dBm, a full head alignment may be required. Refer to Section 5 of this manual.

4-6-(8) RECORD BIAS ADJUSTMENT↑ TOP

Figure 4-7 shows the variation of the frequency response by the bias set and the RECORD EQ. adjustment control, and Figure 4-9 shows the characteristic of the bias current v.s output and distortion of Scotch #206 tape.

The record bias affects the distortion and the overall frequency response.

The record bias should be set between the peak bias and 1 dB over bias at 1 kHz for low distortion and high maximum output level (MOL). The overall frequency response may be adjusted with both the RECORD EQ. and the RECORD BIAS adjustment controls for a flat frequency response curve.

1. Set the tape speed to 7 1/2 ips, place the SRL switch in the SRL position, and set the MONITOR switch to the TAPE position. BIAS ADJUSTMENT AT 1 kHz

2. Record and reproduce the 1 kHz signal of the TEST OSC and adjust the LINE INPUT control for a 0 dB indication on the VU meter.

3. Adjust the RECORD BIAS adjustment controls (VR306/406) for a peak indication on the VU meter and then turn the RECORD BIAS adjustment controls clockwise until a decreased level of 0.2 dB is obtained. The standard biasing point of the MX-5050B is at 0.2 dB overbias at 1 kHz for 7 1/2 ips.

BIAS ADJUSTMENT AT 5 kHz

It is recommended that the bias adjustment is made at 5 kHz for ease.

1. In the same mode at 1 kHz bias adjustment, connect the audio oscillator to the LINE INPUT connectors, feed a 5 kHz signal with the record/reproduce mode, and adjust each relative LINE INPUT control to obtain a 0 dB indication on the VU meter.
2. Adjust RECORD BIAS adjustment controls (VR306/406) for a peak on the VU meter. Turn the VR306/406 clockwise until a decrease of 2.2 dB is obtained. 2.2 dB overbias at 5 kHz for 7 1/2 ips is a standard biasing point for the MX-5050B.

⤢ zoomFig. 4-7 Overall Frequency Response: two response curves, record bias against frequency and record EQ against frequency, with the direction each adjustment moves them

VR301/401: MIC INPUT LEVEL VR302/402: LINE INPUT LEVEL VR303/403: RECORD LEVEL VR304/404: RECORD EQ. HIGH VR305/405: RECORD EQ. LOW VR306/406: RECORD BIAS LEVEL

VR307/407: SOURCE MONITOR LEVEL VR501 : TEST OSC. LEVEL SW501 : TEST OSC.; OFF SW502 : MIC ATTENUATOR; 0 dB SW503 : RECORD LEVEL; M

⤢ zoomFig. 4-8 Record System Simplified Diagram: a simplified diagram of the record chain, from the line input through the amplifiers and bias oscillator to the head

STANDARD BIASING POINT FOR MX5050B

OUTPUT dB +2 +1 0 -1 -2 -3 -4

2.2dB

MX5050B-2 TAPE SPEED 7.5 ips TAPE: Scotch #206

5kHz 1kHz BIAS v.s OUTPUT

RECOMMENDED BIASING RANGE

1kHz DISTORTION RATE

PEAK BIAS

1dB OVERBIAS

BIAS CURRENT (mA)

Fig. 4-9 Bias Current v.s Output and Distortion

⤢ zoomFig. 4-9 Bais Current v.s Output and Distortion: output and distortion plotted against bias current, with the recommended biasing range hatched and the standard biasing point marked

OUTPUT LEVEL NAB IEC 3rd DISTORTION MX5050B-2HD

• 15 ips
• NAB EQ.
• Scotch #206
• 1 kHz 14 12 +10 *3 (520 nWb/m) 8 6 RECORD LEVEL

H(320 nWb/m) 4 3.8 dB M(250 nWb/m)*2 2.6 dB 2 L(185 nWb/m)*2 0 -2 -4 -6 INPUT LEVEL 2 4 6 8 10 12 14 16 18 3rd DISTORTION OUTPUT DISTORTION -30(3.2%) dB -40(1%)

NOTE 1 : 320 nWb/m: DIN REFERENCE LEVEL This is "open circuit flux" and corresponds to 290 nWb/m of "short circuit flux". 2 : 250 nWb/m, 185nWb/m. These are "short circuit flux" *3 : 520 nWb/m: reference level for signal to noise measurement and trigger level for peak indicator.

Fig. 4-10 Input v.s Output and Distortion

RECORD SEL.REP RECORD RECORD EQUALIZER RECORD TEST MONITOR BIAS 1 2 LEVEL OSC 1 2 1 2 1 2 HIGH LOW HIGH LOW 1 2 1 2 SW301 SW401 SW302 SW402 VR306 VR406 VR304 VR305 VR404 VR405 VR303 VR407 VR403 SW501 SW101 SW201 RECORD BIAS OSCILLATOR VR307 VR104 LINE LINE INPUT INPUT AMP-1 AMP-2 TEST OSCILLATOR VR501 SEL. SEL. REP. REP. AMP-1 AMP-2 VR202 VR203 LINE OUTPUT AMP-1 LINE OUTPUT AMP-2 REP. EQ. AMP-2 REP. EQ. AMP-1 VR103 SW506 VR102 SW505 LINE LINE INPUT INPUT TRANS TRANS -1 -2 (OPT) (OPT) SW502 SW503 VR101 VR201 H M L NAB IEC HIGH LOW OFF -20dB 0dB MIC ATTENUATOR RECORD LEVEL EQUALIZER OUTPUT LEVEL Fig. 4-11 Location of Record/Reproduce Electronics

⤢ zoomFig. 4-11 Location of Record/Reproduce Electronics: the record and reproduce board layout again, labelled for the alignment controls

4-6-(9) OVERALL FREQUENCY RESPONSE↑ TOP

At 15 ips, overall frequency response is measured at SRL, and at 7 1/2 ips and 3 3/4 ips, it should be measured at at least 20 dB below the SRL.

The overall frequency response is affected by the biasing.

Refer to 4-7-(8) RECORD BIAS ADJUSTMENT to adjust the record biasing.

RECORD EQUALIZER adjustment controls HIGH(VR304/404) and LOW (VR305/ 405) relate to the HIGH and LOW of the SPEED switch.

1. Connect the audio oscillator to the LINE INPUT connectors and connect the ac voltmeter to the LINE OUTPUT.

2. Set the MONITOR switch to TAPE, place the SRL switch in the SRL position, and place the OUTPUT LEVEL switch in the HIGH position.

3. Place the equipment in the record mode. For 15 ips:

4. Feed a 1 kHz signal, and adjust the LINE INPUT control to obtain a 0 dB indication on the VU meter.

5. Shift the frequency to 10 kHz and adjust the RECORD EQ. HIGH adjustment controls (VR304/404) to obtain a 0 dB indication on the VU meter.

6. Vary the frequency from 20 Hz to 20 kHz and confirm that the frequency response is within the specifications.

The frequency response specification should be 30 Hz to 20 kHz ±2 dB.

For 7 1/2 ips:

7. Shift the frequency to 1 kHz and adjust the LINE INPUT control to obtain a -20 dBm reading on the ac voltmeter with the record mode.

8. Shift the frequency to 10 kHz and adjust the RECORD EQ. adjustment control [LOW (VR305/405) on the high speed version or HIGH (VR304/ 404) on the low speed version] so that a -20 dBm reading on the ac voltmeter is obtained.

9. Vary the frequency from 20 Hz to 20 kHz and confirm that the frequency response is within the specifications.

The frequency response specification should be 20 Hz to 18 kHz ±2 dB. For 3 3/4 ips:

10. Feed a 1 kHz signal when in the record mode and adjust the LINE INPUT control to obtain -20 dBm reading on the ac voltmeter.

11. Shift the frequency to 8 kHz and adjust the RECORD EQ. LOW (VR305/405) adjustment controls to obtain a -20 dBm reading on the ac voltmeter.

12. Vary the frequency from 20 Hz to 10 kHz and confirm that the frequency response is within the specifications. The frequency response specification should be 20 Hz to 10 kHz ±2 dB.

NOTE

If the specified frequency response characteristics were not obtained in the above procedures, adjust the record biasing within the recommended biasing range (between peak bias to 1 dB over bias at 1 kHz).

4-6-(10) MONITOR SOURCE LEVEL ADJUSTMENT↑ TOP

1. Connect the audio oscillator to the LINE INPUT connector and feed a 1 kHz for a -15 dBm signal.

2. Place the MONITOR switch in the SOURCE position and turn the LINE INPUT controls fully clockwise.

3. Adjust the VR307/407 to obtain a 0 dB indication on the VU meters.

4-6-(11) TEST OSC LEVEL ADJUSTMENT↑ TOP

Before making this adjustment, the monitor source level adjustment should be completed.

1. Shift the audio oscillator level to -5 dBm and adjust the LINE INPUT controls for a 0 dB indication on the VU meter.

2. Press the TEST OSC. switch to generate the test oscillator signal and adjust the VR501 to obtain a 0 dB indication on the VU meter.

4-6-(12) RECORD LEVEL ADJUSTMENT↑ TOP

A record level adjustment should be made whenever the tape used with the equipment is changed and the head is replaced.

1. Set the SPEED selector switch to HIGH and set the MONITOR switch to the SOURCE position.

2. Press TEST OSC and adjust the LINE INPUT controls to obtain a 0 dB indication on the VU meter.

3. Change the MONITOR switch to the TAPE position and place the equipment in the record mode.

4. Adjust the RECORD LEVEL adjustment controls (VR303/403) to obtain a 0 dB indication on the VU meter (record/reproduce output level).

4-6-(13) PEAK INDICATOR TRIGGER LEVEL ADJUSTMENT↑ TOP

Peak indicators are triggered at the recorded flux level of 520 nWb/m. This point is 9 dB above 185 nWb/m (RECORD LEVEL switch in "L" position), 6.4 dB above 250 nWb/m (RECORD LEVEL switch in "M" position), and 5.2 dB above 320 nWb/m (RECORD LEVEL switch in "H" position as shown in Fig. 4-10. For peak indicator trigger level adjustment, proceed as follows:

⤢ zoomFig. 4-12 VU Meter Amplifier P.C.B.: the VU meter amplifier board, with trimmers VR107 and VR207