Denon PMA 250 Amplifier Repair



Published
Fault
Right channel output transistors running hot at idle current and no input or speakers connected.

This particular Amplifier had been serviced before.

The Amplifier was tested with the Dim Bulb tester in circuit, the bulb was seen to glow dimly and at time become brighter for a few seconds.

Heat could be felt from the heat sink T208 2SC53853 / TR210 2SA1489 output transistors were also running hot.

The bias voltage on the base of the transistors was checked and found to be low and drifting.

IC202 UPC 1225H Driver IC was replaced fixing the issue.

Bias resistors R219 / R220 were fixed at 39 ohms.

Amplifier fully tested working correctly.
Category
Audio
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