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Фрагмент инструкции
Solder a new zener diode “piggyback”-style onto each old one. Procedure: Installing new zener diodes in an ISA 450 or ISA 500T amplifier 1. Disconnect the amplifier from AC and wait at least 10 minutes for internal voltages to bleed down. Remove the top cover. 2. Remove the four screws on the bottom of the amplifier that fasten the heat sink to the chassis. 3. Remove the three screws that attach the channel module assembly to the chassis standoffs. 4. Locate zener diodes D107 and D110 on the channel 1 module (the upper circuit board). Bend and trim the leads of two new zener diodes and solder them piggyback-style to D107 and D110, oriented in the same direction (Figure 4). 5. Turn the channel module assembly over and repeat step 4 with zener diodes D207 and D210. 6. Check your work. Don’t reattach the channel module assembly and heat sink to the chassis yet. Instead, continue with the bias and current-limit calibration. Procedure: Bias and current-limit calibration Note: During the current-limiting part of this procedure, the amplifier will draw high amounts of AC: approximately 22 amperes at 120V, or 11 amperes at 230V. Be thorough, but work quickly to avoid tripping the amplifier's circuit breaker. 1. Start with the variable transformer turned all the way down to zero, the amplifier turned off, and its top cover still removed. 2. On the amplifier's circuit boards, locate resistors R147 and R247, and trimpots R131, R231, R139, R239, R140, and R240. To reach R147 on the ISA 750 and ISA 800T or R247 on the ISA 450 and ISA 500T, rotate the chassis module assembly and rest it on the heat sink so the bottom circuit board is accessible. Note that the trimpots for the bottom channel module are located on a small circuit board next to Table 1. the top module. 3. Plug the amplifier into the variable transformer. 4. Turn the gain controls all the way down. 5. Turn the amplifier on and gradually turn up the variable transformer to the amplifier's normal operating voltage while you monitor its AC current draw (it should not grossly exceed the idle current figures in Table 1). Make sure the amplifier is functioning correctly. Bias adjustment (perform only with unit at ambient temperature) Note: This calibration must be done with the amplifier circuitry at ambient temperature. If the amp has begun to *Figuresshownarefor120Vamplifiers;multiplycur rrentby0.5for230Vorby1.2for100V. Calibrations Adjust ISA 450 & ISA 500T ISA 750 & ISA 800T Channel 1 bias: DC voltage across R147 R131 0.12 V 0.07 V Channel 2 bias: DC voltage across R247 R231 0.12 V 0.07 V Output current into shorted load Channel 1: R139 & R140 Channel 2: R239 & R240 4–5 A 8.5–9 A AC current when driving shorted load* Channel 1: R139 & R140 Channel 2: R239 & R240 4.5–5.5 A 5.5–6.5 A Clipping voltage into 2 ohms (RMS) Channel 1: Adjust R139 for symmetry Channel 2: Adjust R239 for symmetry 33.5–37.5 V 44–49 V Clipping voltage into 2 ohms (peak) Channel 1: Adjust R139 for symmetry Channel 2: Adjust R239 for symmetry 47.4–53 V 62.2–69.3 V Idle AC demand* (at ambient temperature; higher when hot) 0.4 A, ±10% 0.6 A...
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