ORBAN 2200 Manual Section 5 电路图.pdf

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1、Section 5 Troubleshooting pagecontents 5-2Problems and Possible Causes 5-2RFI, Hum, Clicks, Or Buzzes 5-2Poor Peak Modulation Control 5-2Audible Distortion On-Air 5-3Audible Noise on Air 5-4Whistle on Air, Perhaps Only in Stereo Reception 5-4Shrill, Harsh Sound 5-4Dull Sound 5-4System Will Not Pass

2、Line-Up Tones at 100% Modulation 5-5System Will Not Pass Emergency Broadcast System (“EBS” USA Standard) Tones at the Legally-Required Modulation Level 5-5Interference from Stereo Into Subcarriers 5-619kHz Frequency Out-of-Tolerance 5-6LR (Stereo Difference Channel) Will Not Null With Monophonic Inp

3、ut 5-6General Dissatisfaction With Subjective Sound Quality 5-7Troubleshooting IC Opamps 5-7Technical Support 5-8Factory Service 5-8Shipping Instructions CAUTION The installation and servicing instructions in this manual are for use by qualified personnel only. To avoid electric shock do not perform

4、 any servicing other than that contained in the Operating Instructions unless you are qualified to do so. Refer all servicing to qualified service personnel. OPTIMOD-FM 2200TROUBLESHOOTING 5-1 RadioFans.CN 收音机爱 好者资料库 page Problems and Possible Causes Always verify that the problem is not the source

5、material being fed to the 2200, or in other parts of the system. RFI, Hum, Clicks, Or Buzzes A grounding problem is likely. Review the information on grounding on page 2-12. The 2200 has been designed with very substantial RFI suppression on its analog and digital input and output ports, and on the

6、AC line input. It will almost always operate adjacent to high-powered transmitters without difficulty. In the most unusual circumstances, it may be necessary to reposition the unit to reduce RF interference, and/or to reposition its input and output cables to reduce RF pickup on their shields. Parti

7、cularly if you are using a long run of coaxial cable between the 2200 and the exciter, a ground loop or other problem may inject noise into the exciters composite input particularly if the exciters input is unbalanced. This problem can almost always be cured by the Orban CIT25 Composite Isolation Tr

8、ansformer (see page 2-12). Poor Peak Modulation Control The 2200 ordinarily controls peak modulation to an accuracy of 3%. This accuracy will be destroyed if the signal path following the 2200 has poor transient response. Almost any link can cause problems. Even the FM exciter can have insufficient

9、flatness of response and phase linearity (particularly at low frequencies) to disturb peak levels. Section 1 of this manual contains a complete discussion of the various things that can go wrong. Even if the transmission system is operating properly, the FM modulation monitor or reference receiver c

10、an falsely indicate peak program modulation higher than that actually being transmitted if the monitor overshoots at high or low frequencies. Many commercial monitors have this problem, but most of these problem units can be modified to indicate peak levels accurately. Audible Distortion On-Air Make

11、 sure that the problem can be observed on more than one receiver and at several locations. Multipath distortion at the monitoring site can be mistaken for real distortion. Verify that the source material at the 2200s audio inputs is clean. Heavy processing can exaggerate even slightly distorted mate

12、rial, pushing it over the edge into unacceptability. Refer to Orbans publication Audio Quality in the FM Plant (included with your 2200) for hints on how to achieve the cleanest source quality. The subjective adjustments available to the user have enough range to cause audible distortion at their ex

13、treme settings. Advancing the CLIPPING and/or FINAL CLIP controls too far 5-2 TROUBLESHOOTING OPTIMOD-FM 2200 RadioFans.CN 收音机爱 好者资料库 will inevitably cause distortion. Setting the LESS-MORE control beyond “9” will cause audible distortion of some program material with all but the Protection Limiter

14、structure. If you are using the 2200 or the analog inputs of a 2200-D, the headroom of the units analog-to-digital (A/D) converter must be correctly matched to the peak audio levels expected in your system (using System Setup). If your peak program level exceeds the peak level you have specified on

15、setup, the 2200s A/D converter will clip and distort. (See page 2-20). If you are using an external processor ahead of the 2200, be sure that it is not causing problems. For example, if a “stereo enhancer” is used, be sure that it does not significantly increase the average level of the stereo diffe

16、rence channel (LR). This will almost certainly exaggerate multipath distortion. The Orban 222A Stereo Enhancer is fully compatible with the 2200 and will not cause this problem. Amplitude modulation of the carrier that is synchronous with the program (“synchronous AM”) can cause subtle distortion, a

17、nd can exaggerate existing multipath distortion. Syn- chronous AM should be better than 35dB below 100% modulation as measured on a synchronous AM detector with standard FM de-emphasis (50s or 75s). The “incidental AM” position on most modulation or stereo monitors is insufficiently wideband to prov

18、ide an accurate reading of synchronous AM such metering was designed to indicate non-synchronous AM like hum and noise. Audible Noise on Air (See also RFI, Hums, Clicks, or Buzzes on page 5-2.) Excessive compression will always exaggerate noise in the source material. The 2200 reduces this problem w

19、ith its compressor gate, which freezes the gain of the AGC and compressor systems whenever the input noise drops below a level set by the GATE THRESH (Gate Threshold) control, preventing noise below this level from being further increased. If you are using the 2200s analog input, the overall noise p

20、erformance of the system is usually limited by the overload-to-noise ratio of the analog-to-digital converter used by the 2200 to digitize the input. (This ratio is slightly better than 90dB.) It is important to correctly specify the AI CLIP level in the System Setup Analog I/O screen to optimize th

21、e noise performance available from the analog-to-digital converter. You should specify the level as the highest peak level that will be presented to the 2200 under normal operation. If, in an attempt to build in a “safety factor” or increase headroom, you specify a higher level than this, every 1dB

22、of extra headroom that you gain will be accompanied by a 1dB increase in the 2200s noise floor. The 2200s optional AES/EBU input is capable of receiving words of up to 20 bits. A 20 bit word has a dynamic range of approximately 120dB. The 2200s digital input will thus rarely limit the units noise pe

23、rformance even with very high amounts of compression. If a studio-to-transmitter link (STL) is used to pass unprocessed audio to the 2200, the STLs noise level can severely limit the overall noise performance of the system because compres- OPTIMOD-FM 2200TROUBLESHOOTING 5-3 RadioFans.CN 收音机爱 好者资料库 s

24、ion in the 2200 can exaggerate the STL noise. For example, the overload-to-noise ratio of a typical analog microwave STL may only be 7075dB. In this case, it is wise to use the Orban 8200ST Studio Chassis to perform the AGC function prior to the STL transmitter and to control the STLs peak modulatio

25、n. This will optimize the signal-to-noise ratio of the entire transmission system. Section 1 of this manual has a more detailed discussion. Composite STL systems with marginal paths or co-channel interference can cause noise (hiss) which will be most apparent when listening in stereo. Whistle on Air

26、, Perhaps Only in Stereo Reception This could be caused by a number of problems, any of which could present a spurious tone (perhaps supersonic) to the input of the stereo encoder. In any such case, the first thing to do is to examine the left and right analog outputs with a spectrum analyzer to see

27、 if any spurious tones are visible. If the whistle is 6kHz, there could be a beat between the 2200s 32kHz sampling frequency and the 38kHz stereo subcarrier. In this case, the most probable cause is a failure of the 2200s digital-to-analog converter system, including a failure of the reconstruction

28、filter following the converter. A whistle at another frequency might be associated with power supply oscillation, oscilla- tion of any opamp in the digital-to-analog converter system, or composite STL problems. Shrill, Harsh Sound This problem can be caused by excessively high settings of the HF ENH

29、ANCE control. If you are driving an external stereo encoder with built-in pre-emphasis, you must set the 2200s AO PRE-E to flat to prevent double pre-emphasis, which will cause very shrill sound. You will always achieve better peak control by defeating the pre-emphasis and input filters of an extern

30、al stereo encoder, permitting the 2200 to perform these functions without overshoot. Section 1 of this manual contains a detailed explanation of these, and other, system design considerations. Dull Sound If driving an external stereo generator, dull-sounding source material can sound dull on the air

31、. If the 2200s output is set to flat there will be no pre-emphasis unless it is supplied elsewhere in the system. This will cause very dull sound. System Will Not Pass Line-Up Tones at 100% Modulation This is normal. Sine waves have a very low peak-to-average ratio by comparison to program material.

32、 The processing thus automatically reduces their peak level to bring their average level close to that of program material, promoting a more consistent and well-balanced sound quality. 5-4 TROUBLESHOOTING OPTIMOD-FM 2200 The 2200 can generate its own test tones, and these can be triggered from the 2

33、200s optically-isolated remote control terminals, or by recalling a tone preset from the front panel, Page 1-10 provides a further explanation. Recall bypass Test Tone to pass line-up tones transparently. System Will Not Pass Emergency Alert System (“EAS” USA Standard) Tones at the Legally-Required

34、Modulation Level See System Will Not Pass Line-Up Tones at 100% Modulation (directly above) for an explanation. These tones should be injected into the exciter after the 2200. Interference from Stereo Into Subcarriers A properly-operating 2200 generates an immaculately clean baseband, with program-c

35、orre- lated noise below 85dB above 57kHz. If the 2200 and the rest of the transmission system is operating correctly, subcarriers should experience no interference. Interference from the stereo into a subcarrier is best diagnosed with a spectrum analyzer. First examine the spectrum of the 2200s comp

36、osite output. If the 2200 is operating properly, program-correlated noise should be below 85dB above 57kHz. Even the slightest amount of composite clipping will degrade this protection dramatically. Such composite clipping may be intentional (in a composite clipper), or unintentional (you could be o

37、ver-driving a composite link between the 2200s composite output and the exciters input). If the exciter is non-linear, this can cause crosstalk. In general, a properly-operating exciter should have less than 0.1% THD at high frequencies to achieve correct operation with subcarriers. To prevent trunc

38、ation of the higher-order Bessel sidebands of the FM modulation, the RF system following the exciter must be wideband (better than 500kHz) and must have symmetrical group delay around the carrier frequency. An incorrectly-tuned transmitter can exhibit an asymmetrical passband which will greatly incr

39、ease crosstalk into subcarriers. Amplitude modulation of the carrier that is synchronous with the program (“synchronous AM”) can cause program-related crosstalk into subcarriers. Synchronous AM should be better than 35dB below 100% modulation as measured on a synchronous AM detector with standard FM

40、 de-emphasis (50s or 75s). The subcarrier receiver itself must receive a multipath-free signal, and must have a wide and symmetrical IF passband and a linear, low-distortion FM demodulator to prevent program- related crosstalk into subcarriers. OPTIMOD-FM 2200TROUBLESHOOTING 5-5 19kHz Frequency Out-

41、of-Tolerance First, verify that a problem really exists by using a second frequency-measuring device and/or verifying the problem with your monitoring service. If the problem is real, you must replace crystal Y602; there is no frequency trim available. LR (Stereo Difference Channel) Will Not Null Wi

42、th Monophonic Input This is often caused by relative phase shifts between the left and right channels prior to the 2200s input. This will cause innocuous linear crosstalk between the stereo main and subchannels (and vice versa). Refer to step 5-K on page 4-13. General Dissatisfaction With Subjective

43、 Sound Quality The 2200 is a complex processor which can be adjusted for many different tastes. For most users, the gamut offered by the LESS-MORE control is sufficient to find a satisfactory “sound.” However, some users will not be satisfied until they have accessed other Modify Processing controls

44、 and have adjusted the subjective setup controls in detail to their satisfaction. Such users must fully understand the material in Section 3 of this manual to achieve the best results from this exercise. By comparison to competitive processors, the 2200 offers a uniquely favorable set of trade-offs

45、between loudness, brightness, distortion, and buildup of program density. If your radio station does not seem to be competitive with others in your market, the cause is usually problems with the source material, overshoot in the transmission link (including the FM exciter) following the 2200, or an

46、inaccurate modulation monitor that is causing you to under-modulate the carrier. A station may suffer from any combination of these problems, and they can have a remarkable effect upon the overall competitiveness of a stations sound. If you are competing with a station that has Orbans high-end 8200

47、Audio Processor, you will not be able to get the source-to-source consistency and low voice distortion offered by the 8200s Five-Band structure. However, you will still have a loud big-sounding signal. Stations that need the ultimate in state-of-the-art processing should upgrade to the Orban 8200. S

48、ection 1 of this manual provides a thorough discussion of system engineering considera- tions, particularly with regard to minimizing overshoot and noise. Orbans publication Audio Quality in the FM Plant (included with the 2200) provides many suggestions for maximizing source quality. 5-6 TROUBLESHO

49、OTING OPTIMOD-FM 2200 Troubleshooting IC Opamps IC opamps are operated such that the characteristics of their associated circuits are essen- tially independent of IC characteristics and dependent only on external feedback compo- nents. The feedback forces the voltage at the () input terminal to be extremely close to the voltage at the (+) input terminal. Therefore, if you measure more than a few millivolts difference between these two terminals, the IC is probably bad. Exceptions are opamps used without feedback (as comparators) and opamps with outputs that have been saturated due