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About dengstro

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  1. Robert, Usually this symptom is the result of the +/-15V supplies energising or discharging nonsymetrically. To confirm this use the following procedure: 1. Monitor the +/-15V supplies with probes form your oscilloscope. 2. Slow the time base of the oscilloscope down in order to see the supplies energise. 100msec-500msec. 3. With no load and no signal turn the amplifier on. Observe the two DC voltages and try to determine if one is energising faster than the other. 4. If one is coming up faster check the following: a. Change U104 and U204. Retest. If problem still exists proceed to next step. b. Change the regulators: U1 and U2. Retest. If problem still exists proceed to next step. c. In the semiconductor test position check continuity of D1, D2, D4 and D5. Retest. If problem still exists proceed to next step. d. Connect in parallel capacitors with like values with C1, C2, C3 and C4. Usually by point d most problems have been resolved. If not ty the following: * Take note of which supply is energising faster. We are going to attempt to slow the rate of change to equal the energising time of the slower supply. Place in parallel with this polarity supply a small value electrolitic capacitor (2.2uf). If this does not solve the problem slowly increase the capacitance value. Dave Engstrom Crown Technical Support Department
  2. SAJ, Has this amplifier been tested on a test bench with a signal generator and an oscilloscope? Was the signal undistorted up to (roughly) 60Vrms? David Engstrom Crown Technical Support Department
  3. Platycerus, It is not Crowns policy to maintain semiconductor cross reference lists. As far as your request we do not know if this part (BURR-BROWN/TI 0PA627AP) can be used as a substitute for the LF357. David Engstrom Crown Technical Support Department
  4. Karlos, The C 7423-4 is a selected C 7064-6. In the case of the DC-300A-2 the C 7064-6 could be used in place of the C 7423-4. I've searched numerous sources and cannot find information on C 8210-4. However, C 5869-0 was used as the driver transistor for the DC-300A-2 for almost two decades. David Engstrom
  5. It appears you know your way around this older DC-300A. That's quite a list of parts to go though. DC-300A's usually are easier to repair. Hope it works well for you. Dave Engstrom
  6. Sr. Melaza, ¿Cuál de los tres transformadores? T900, T901 o T902 Si tiene alguna preguntas, por favor llame o escribe. David Engstrom Crown Departamento de Servicio Técnico (574)294-8224
  7. Crown does not maintain cross refference lists for field replacements. The desired part can be obtained from the Crown parts department under part number 101103-2: David Engstrom
  8. Sr. Delgado, << sigue sonando tan fuerte en 100w como en 3000w. >> Es el limitador de picos conjunto a la baja? << A que voltaje tendria que llevar para no exceder la potencia permitida de la 725? >> V² ÷ R = Vatios (100V X 100V) ÷ 4ohms = 2401vatios << podria usar la formula de raiz de(wXohm) para hallar el voltaje maximo de salida? >> Véase la respuesta anterior. Si tiene alguna preguntas, por favor llame o escribe. David Engstrom Crown Departamento de Servicio Técnico (574)294-8224
  9. Bobbysdad, It needs to be understood that Crown grades and matches our output transistors. This is especially important where transistors are paralleled with others. Theoretically they should turn on at the same base drive. In reality this does not happen. If matching is not used one transistor can carry more current that the remainder resulting in fatigue (failure). For this reason we suggest that the transistors found in the unit be replaced with the same Crown part number and the same Vbe grading number. The C 8188-2 is replaced by 139739-1. The D 6729-4 is replaced by 102659-1. David Engstrom Crown Technical Support Department
  10. High dc voltages are usually the cause of a failed semiconductor. This would include output transistors or anyother type of device in the signal chain. If you have dc voltage in both channels you may have something that is common to both channels: one of the regulators for example. If you have any further questions, please write. David Engstrom Crown Technical Service Department (800)342-6939 (574)294-8224
  11. Jake, * Understand that when we change from one output device to another the circuitry has to be compensated for that new device. The 2SD555 (Crown part number C 5869-0) replaced the 4718. When this change was incorporated in 1981 we had to modify the circuitry for operational stability. While the MJ15024 and MJ21194 are good devices the PSA-2 was not designed and compensated for their use. * All Crown amplifiers that use multiple bipolar devices in parallel are tested and graded in order to turn on and off at the same base current levels. Off the shelf 2SD555 devices will have variations which can lead to uneven current sharring. This, of course, can result in excess stress and possible failure. Sometimes people get away with using field replacements and sometimes they do not. These are the two main reasons we suggest that any parts used for repair should come from Crown because they are tested and graded. The 2SD555 (C 5869-0) is a very healthy and rugged device and I would confidently suggest its use. These parts can be order from our Australian distributor: Jands Pty Ltd 40 Kent Road (Locked Bag 15) Mascot, NSW, 2020 Australia PH: 61-2-9582-0909 David Engstrom Crown Technical Support Department
  12. If the amplifier was wired for 120V but plugged into 240V the +/-15V regulators (IC7 and IC8) may have been damaged. Without having the amplifier on hand to test it is difficult to diagnose via a forum. Unless you have the training and experience on amplifier repair I would suggest taking the amplifier to our distributor in the UK: Harman Pro UK Cranborne House Cranborne Road Potters Bar Hertfordshire EN6 3JN United Kingdom Tel: +44 (0)1707 668222 David Engtrom Crown Audio
  13. Since the PSA2 is a quazi-complimentary design I need to know which module you are working on. Does it have a + or a - on it? Dave Engstrom Crown Techncial Support
  14. Sr. Orellana, El cable estándar de la categoría 5 se utiliza para la interconexión. Enviar por favor tu dirección del E-mail así que puedo remitir la información solicitada. Si usted tiene más preguntas, escriba por favor. David Engstrom Soporte Técnico de Crown (574) 294-8224
  15. Bruce, Have you tried driveing the amplifier with an audio signal? If so, what were the results? The +/-Vcc supplies being equal is a good sign that the low side of bridge is functioning correctly. Dave Engstrom