Denon UD-M31 Amp

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Repair of Denon UD-M31 CD/FM tuner/Amplifier.



Symptoms.

The amplifier showed no signs of life at all, no standby condition and would not switch on.

Investigation.

revealed that the internals had suffered from water damage which had corroded one of the pins on the Power PCB. This carried the standby +5v to the rest of the unit.


Damage can be seen around the end of the edge connector for this PCB with some copper sulphate (green) present.






After rework, the PCB is now much cleaner. But it was then found that the connector pin itself was isolated from the PCB track under the PCB due to corrosion. Lifting the PCB out was very difficult and would have resulted in a major disassembly exercise.

As a result a wire link was fitted bypassing the connector and supplying the +5v standby to the rest of the set.

Image at the back is a reflection of the PCB in a screening can fitted just behind the PCB.


It is not clearly visible here but there is a link wire running from close to the front of the picture around various components to the back of the board where it bypassed the corroded pin on the connector.





After fitting the wire link the unit worked properly again.

In term of safety this was not a “professional” repair where really the connector itself should have been replaced, but for home use and the fact that this was only +5v and protected by a PCB fuse it was felt an adequate repair and the unit was returned as operational to the owner.

Peter Dobson. Farnham Repair Café, 2016.