Merwyn
New Member
I had given my Sansui AUX-711 for servicing to a techie in Brisbane. Unfortunately after months of repairs which included re soldering, replacement of transistors and resistors, the amp has gone into protection mode. I don't blame the tech guy because he kept me informed every stage and charged me a very small fee. Is there anything I need to look, considering this amp is not very common in Australia?
The summary of the repairs as given by the techie:
The summary of the repairs as given by the techie:
- Re-soldered all circuit boards and replaced electrolytic capacitors on all boards. All circuit boards had many dry solder joints and very fluxy. Many caps were beyond 20% tolerance
- Passive test of key semiconductors with digital multimeter - transistors etc
- Passive test of components on driver boards, power supply, protection circuit etc
- Main filter capacitors tested OK, well within 20% tolerance
- Installed new thermal washers and paste on main output transistors and test gain on outputs - good
- Driver Boards: Noted Zener diode and adjacent wire wound resistor had been running hot causing PCB to burn and go black. Burning caused damage to PCB tracks was remediated and cleaned in so far as possible and checked circuit continuity. Checked resistance across burned patch - no impedance reading to indicate conductivity across PCB. Replaced Zener diode. Don't remember replacing the the WW resistor
- Replaced some TO92 transistors on driver boards, 2SC1845 and possibly 2SA992’s
- Replaced some resistors that measured out of tolerance from memory
- Replaced ZD01 Zener diodes on driver boards. 6.2V
- Replaced 2SC2458 transistors on protection board as gain was below spec on a couple
- Gave a general clean and re-lubed switches, potentiometers
- Turned bias/trim pots down to avoid possible overcurrent
- Attempted to start amp with and without driver boards in circuit, but still will not come out of protection
