flatlinenj
New Member
Problem: Marantz 4240, Back panel fuse blows when powered on.
Troubleshooting:
Test 1: Transformer:
Test 2: Power Transistors:
For the bridge rectifier 5B2 Diode test the pins are referred to as:
Conclusion:
Replace bridge rectifier.
Notes:
The International Rectifier bridge rectifier 5B2 is not readily available so an electrically equivalent bridge rectifier was used to replace it. Replaced with KBPC804.
Observation after bridge rectifier replaced:
After replacing the bridge rectifier the unit will power up without blowing the fuse. But there still is a problem with the left channel being weak and distorted. Further troubleshooting needed. A separate post will be created.
Troubleshooting:
Test 1: Transformer:
- Disconnect input power leads on bridge rectifier 5B2.
- Power up unit.
- Measure voltage at transformer output: 42.0 Volts AC, Front panel lit.
Test 2: Power Transistors:
- Reconnect bridge rectifier 5B2 to provide power to amplifier circuits.
- When unit is powered up, the fuse blows.
- Visual inspection of bridge rectifier shows no damage.
- Cancel test of power transistors and test bridge rectifier instead.
- Disconnect all leads on bridge rectifier 5B2.
- Remove bridge rectifier from unit for testing.
For the bridge rectifier 5B2 Diode test the pins are referred to as:
- Pin 1 – Positive (+) pin
- Pin 2 – AC input next to positive (+) pin
- Pin 3 – AC input next to negative (-) pin.
- Pin 4 – Negative (-) pin.
Conclusion:
Replace bridge rectifier.
Notes:
The International Rectifier bridge rectifier 5B2 is not readily available so an electrically equivalent bridge rectifier was used to replace it. Replaced with KBPC804.
Observation after bridge rectifier replaced:
After replacing the bridge rectifier the unit will power up without blowing the fuse. But there still is a problem with the left channel being weak and distorted. Further troubleshooting needed. A separate post will be created.