This part is a kind of semiconductor called STK403-120.

Function of this product has 2-Channel AF Power Amplifier.

Manufacturers : Sanyo

Image and pinout :

Some of the text within the PDF file :

SPECIFICATION No. STK403-120 1. Case Outline 15Pins (See attached Package Outline Diagram) 2. Function 3. Application 2 channels AF power amplifier 80W audio use 2002.12.28 TENTATIVE 4. Maximum Ratings / Ta=25°C Item Maximum Power Supply Voltage 0 Maximum Power Supply Voltage Minimum Operation Supply Voltage #12 Maximum Operating Current *7 Thermal Resistance Junction Temperature Operating Substrate Temperature Storage Temperature Available Time for Load Short-circuit *4 5. Operating Characteristics Tc=25°C ,RL=6ohm(Non-inductive Load),Rg=600ohm,VG=30dB Item Output Power THD Symbol *1 Po 1 Po 2 THD 1 *1 THD 2 fL,fH ri VNO ICCO VN IST ON IST OFF V (V) +-40 +-40 +-40 +-40 +-40 +-40 +-48 +-48 +-48 +-40 +-40 V#13=5V #13PIN Resistance R1=13kohm 1k Conditions *2 f Po THD (Hz) (W) (%) 20 to [ ... ]

STK403-120 PDF Datasheet Download