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Download HP 8901B Service vol..
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Service Model 8901B TROUBLESHOOTING General Procedures for checking the Audio Section of the instrument are given below. The blocks or points to check are marked on the block diagram by a hexagon with a check mark and a number inside, for example, (J3) . Before performing any check, perform all the checks on Service Sheet BD1. Tighten SMC connectors to 0.6 N . m (5 in. lb). Hand tightening of connectors is insufficient. Hand-tightened connectors can work loose and came reduced performance or malfunctions. Equipment Audio Synthesizer. ................................................................ Oscilloscope ...................................................................... Signal Generator. ................................................................. HP 3336C H P 1740A HP 8640B Audio Filters and Gain Check 1. Set the audio synthesizer to 1 kHz at -17 a m . (The synthesizer output impedance should be 500.) Connect its output to A2J1 (AM IN). If the Modulation Analyzer is to be turned off, disconnect the audio synthesizer first to prevent damage to the CMOS switches. 2. Connect a high-impedance, ac coupled oscilloscope (with 1O:l divider probe) to A2TP4 (AMPL 3 OUT). 3. Set the signal generator to approximately 20 MHz CW a t 0 a m .Connect its RF output to the Modulation Analyzer’s INPUT. 4. Press the blue key, then press INSTR PRESET (the AUTOMATIC OPERATION key) to preset the instrument. Press AM. Key in 2.1 SPCL to set the audio gain to maximum. The oscilloscope should show the 1 kHz sinusoidal waveform with an ac amplitude of 2.4 to 2.8 Vpp. If faulty, see Service Sheet 12 and check the audio path beginning at the 260 kHz Low-Pass Filter at the AM output. 5. Increase the synthesizer frequency to 260 kHz without altering the amplitude. The waveform should have an ac amplitude of 1.2 to 1.6 Vpp. If faulty, see Service Sheet 12 and check the 260 kHz Low-Pass Filter a t the AM output as well as checking to see if the 15 kHz or >20 kHz are in the circuit. (They should be out.) 8D-40 Service Sheet BD4
