Uploaded November 2016 | Updated September 2026, 2 weeks ago
Unit had about -10 volts DC on one of the speaker channels. This affected almost all voltages in the power output stage. Almost all transistors had wrong voltages; channel still worked though, but not correctly. Was initially difficult to troubleshoot because many transistors are tied together; what affects one then can affect many others. I then resorted to measuring the resistances to ground of the power output stage components in the bad channel, using the good channel as a comparison. A high resistance was found on the very last resistor I checked. Problem turned out to be soldering joint problem that I would have found right away if I would have taken a closer look at the underside (solder side) of the circuit board. Bias adjust was then done. Also, some electrolytic capacitors seem to have deteriorated; with lower values now then what they were rated for. It leads me to suspect that probably most if not all of the electrolytic capacitors need to be changed. Probably the same problem with all CR-420s.
Unit had about -10 volts DC on one of the speaker channels. This affected almost all voltages in the power output stage. Almost all transistors had wrong voltages; channel still worked though, but not correctly. Was initially difficult to troubleshoot because many transistors are tied together; what affects one then can affect many others. I then resorted to measuring the resistances to ground of the power output stage components in the bad channel, using the good channel as a comparison. A high resistance was found on the very last resistor I checked. Problem turned out to be soldering joint problem that I would have found right away if I would have taken a closer look at the underside (solder side) of the circuit board. Bias adjust was then done. Also, some electrolytic capacitors seem to have deteriorated; with lower values now then what they were rated for. It leads me to suspect that probably most if not all of the electrolytic capacitors need to be changed. Probably the same problem with all CR-420s.
