Electronics

This is a work in progress.  We'll see how it goes (August 2019)

Things I've worked on and what I've found to have been wrong with the device.

Carver M400 #1
Symptoms: no audio output
Cause: issue with the Triac and Optocoupler, not sure which was root cause, but replaced both.
Other: replaced all electrolytic capacitors
Noteworthy: the power supply for this device uses a triac to rapidly switch power to the transformer primary winding on and off rapidly; this creates high/rapid magnetic flux which excites the secondary winding.  Because the transformer doesn't stay "ON" all the time, the amp can get away with a relatively small transformer (hence small size).  However the switching on/off of transformer often causes it to make "ticking" sounds at idle.  As you place more demand on the amp, the triac switches faster, and the ticking seems to go away (or get masked by music..)

Carver M400 #2
Symptoms: no audio output
Cause: blown fuse on back panel
Noteworthy: someone else had already replaced a number of electrolytic caps in this amplifier.

Bose 901 Series 1 Equalizer
Symptoms: no audio output
Cause: "Monitor" sliding switch on front panel had oxidized contacts.  Fixed with DeOxIt spray
Noteworthy: Katie on Craigslist was very pleased to get this fixed so that she could use her dad's 901s

Denon DRA 635
Symptoms: noisy audio output
Cause: not sure yet, but noise originates in input selector or muting circuits
Noteworthy: this machine uses integrated circuits to switch inputs rather than mechanical pieces of conductors coming into contact with each other.  Specifically Toshiba TC9163N and TC9164N chips.