Fender Passport PD-250, Руководство по обслуживанию

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PASSPORT
POWERED PORTABLE
SOUND SYSTEM
7
THEORY OF OPERATION
Switch Mode Power Supply Unit (SMPSU)
This unit is not recommended to be serviced in the field except by replacing the complete module as a total
assembly.
The following information is provided to assist in the trouble shooting of the unit. Please note that the
mains fuse must be replaced with exactly the same grade of fuse for safety regulations and to avoid risk of
damage and potential fire hazard.
The mains input to the SMPSU allows for operation from 90-130V in 115V setting and 190-250V in the 230V set-
ting. The output of the SMPSU is ±15V DC to power the operation amplifiers and K51V dc for the main power sup-
ply rails of the power amplifier. The unit also has connectors for the LED status indicators, main power switch,
amplifier protect circuit and auxiliaries ±36V dc Input for an optional DC-DC converter for 12Vdc operation.
SER-
VICE TIP: You can connect to the auxiliaries Input to test the output voltage to the rails before you open the set for
service to get an indication of a possible power supply fault as it is connected to the rail output. Do not short these
terminals.
The SMPSU incorporates several protection circuits other than the fuses, including over current protection in which
the unit will shut down and the protect LED will light and must be reset with the main power switch. Secondly, the
unit will protect itself if the voltage on the rails sags to below ±33V dc after which it will go into protect mode. The
reason for this is that during normal operation with 8 ohm loading, the rails will remain at about ±48V dc and with 4
ohm loading are allowed by design to sag to around 36V at full output. If loads lower than this are applied, either
the rails will sag lower or the current will be exceeded and the unit will go into the protection mode. The protection
PCB connected to the amplifier board serves this purpose.
Service Notes on Changes and Updates
Mixer Board VIP circuit values for Z1 and R11 have been changed from 4.7V to 10V and 2.2M to 1M respectively
after the first 100 sets production. This allows more even channel ducking and shorter ducking recovery time.
Please update early sets if returned for servce.
Stereo Power Amplifier circuit values for Z201, and R206 have been changed from 4.7V to 6.8V and 10K to 1K
respectively after the first 100 sets production. These changes improve turn off transient pop noise. Please update
early sets if returned for service.
Digital Reverb circuit value for VR401 is a fixed resistor with a value of 18K. This resistor controls the reverberation
regeneration feedback and its value may vary from model to model depending on the local requirements.