Мои познания в ремонте данного вида техники: Занимаюсь ремонтом Наличие схемы: no Hi,
With the PSU disconnected from the outputs board, when I press the front panel power button the PSU is always switching on and off. The display also turns on and off. Main voltages reach close to 200V! I know the correct values are about 185V.
I would appreciate if anyone can give me any hints about this problem.
coper, Hi ! Most likely the problem is not PSU. Look under the spoiler
We can narrow down a fault condition between the power supply and BCA-side by disconnecting the high voltage power supply cable (red/blue/black cable) from the amplifier main board. If the amplifier still faults at power up with this cable unplugged, this generally points to a power supply failure. We will now break down the issues that can cause a power supply or BCA main board to fault in the following sub-sections. *Note: Before re-inserting the VCC power cable, verify that both the power supply and the BCA main boards have been completely discharged. Power Supply: The power supply assembly is composed of a SMPS main board, two gate drive boards and a control board - (The EMI module is mounted over the SMPS assembly). The most common cause of power supply faults is due to shorted or blown diodes and fets. Due to the inaccessibility to troubleshoot these boards; it’s highly recommended to perform board replacement only of any SMPS (Switch Mode Power Supply) issues, if you do find shorted components. BCA Main PWA: The single most common cause of faults in the I-tech HD series amplifier is due to shorted or blown output fets & diodes - Most of these failures occur in the VN quadrant. You can measure for channel shorts prior to powering up the amplifier by setting the DVM to read resistance and measure from +/- VCC at the cable connector to the output of both channels. For example: To measure channel 1, place one DVM lead on connector J1012 pin 6 (-VCC) and the other lead on the channel 1 output terminal (red banana plug) – This should measure approximately 15K ohms. Next, measure from connector J1012 pin 4 (+VCC) to the channel 1 output terminal; this again should measure 15K ohms. If there is an issue with the channel, you should see a short with one of the measurements and the other measurement should resemble a capacitor charging. Once a channel short has been confirmed, remove the coil assembly and gate drive board for the suspect channel; you can find the individual shorted component by measuring across the outside leads of all four fets – A good measurement will read an open and the bad fet will measure a direct short. *Note: It is imperative to replace all four fets in the shorted quadrant due to potential damage prior to the protection circuit shutting down the amplifier.
This amplifier has one output transistor in short-circuit but the test was done with the high voltage power supply cable disconnected. I did have the same problem with another amplifier and when I replaced the PSU the problem was gone.
I have no experience repairing these power supplies, only faulty outputs and some minor problems on the input board.
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