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TD-001517-01
K.2 Series Service Manual

8.6 LF and HF amplifier LEDs

Each amplifier section has an LED that is driven at LF_LO and HF_LO output of the gate driver (pin11). If the amplifier is on
and switching, the LED will constantly illuminate green, which is a good indication that the amplifier circuit is working. The LF
amplifier section uses LD1 and the HF amplifier section uses LD2. These two LEDs can give us a good information about
the behavior of the amplifier circuit.

LED behavior notes:

• During normal operation, LD1 and LD2 should always be on

together. If just one LED is turned on, then the LED that is
turned off most likely has a problem in the correlating amplifier
section.

• During standby operation, LD1 and LD2 should always be off.

In standby the DSP shuts down the amplifiers.

• If both LEDs are turned off

and

the amplifier is in normal opera-

tion, look at the +12VLOW rail and the secondary power rails
(VDD and VSS).

• If

both

LEDs are randomly turning off and on at the same time,

an issue with the +12VLOW rail could cause this behavior.
Check the components in the AUX OUTS section in the power
supply. Also, this issue may be related to service bulletin K2-
002.

• Recycle AC power to start the amplifier in normal operation, or, input a low amplitude signal to keep the amplifier run-

ning in normal mode.

8.7 +12VLOW voltage rail failures

The class D amplifiers require a steady voltage from the +12VLOW rail to correctly function. If this rail fluctuates, the class D
amplifiers could pulse off and on. If the rail is too low, the class D amplifiers will latch into a shutdown mode and not allow
audio output. +12VLOW is generated on the secondary side of the transformer T2 in the AUX OUTS circuit.

Symptoms:

• All 3 signal LEDs (Ch.A, Ch.B, and Ch.C) turned on

without signal input

• Chirping or buzzing sound heard in speaker, especially

when coming out of standby mode.

• No audio, especially when coming out of standby

mode.

+12VLOW notes:

• If the chirping/buzzing sound is heard, or there is no

audio when coming out of standby, please refer to the
latest Service Bulletin. The AMP/PSU board may need
to be replaced with a new one.

• If the amplifiers LEDs are not turned on

during nor-

mal operation

, the +12VLOW rail could have failed.

Immediately check the -15V rail on the input/DSP
board at J11 pin3.
• The +12VLOW and -15V voltage rails are generated after fuse F1. If +12VLOW has a shorted component, it will proba-

bly cause F1 to blow. The -15V rail will also measure 0▲Vdc if F1 is open.

• SMD MOSFET Q16 could be the culprit. Q16 is located on the bottom side of the AMP/PSU board. Also check the

Schottky diodes in the circuit as highlighted in Figure 8.7.1.

Figure 8.6.1 - The amplifiers are active if the LEDs are on

DNI

2X IRS2092 = 11MA * 2 = 22MA

NOMINAL -15V RAIL IS AT -13.5V

THETAJA = 180C/W

JUNCTION AT 25C=33

2X LO LEDS = 500UA * 2 = 1MA

HF DEADTIME = 948UA

TOTAL = 91MA