Uniross battery charger problems

[Myrmidon]

I have one of those uniross battery chargers than can charge 2 or 4 AA or AAA's.

However, it seems to not charge them properly. It charges with a high pitched whining noise coming from the charger unit and the green led that shows battery is charged comes on but the battery isn't fully charged most of the time and the charge times reflect this. ie 30min charge times when it should be around 3.5hrs etc.

Does anyone have any ideas as to what is causing this? I'v opened it up for a nosy but i can't see any faulty components or anything.

It's really annoying.

 

[Hero999]

How old are the batteries? Have you ruled out them being bad?

 

[Myrmidon]

Yeah i'v ruled out the batteries being bad as it does it with older ones and brand new ones.

Oddly, if i press the plastic cover fully down on certain occasions the high pitched whine disappears and the batteries charge normal.

I think the answer is to do with this whining noise but i don't know what's causing it.

 

[Hero999]

It sounds like it's a loose connection.

You need to pop the cover and take a look inside, it's probably a dry joint on the board or something.

The high pitched whine is caused by the oscillator working at a lower frequency than it's supposed to causing the transformer coils to vibrate at an audiable frequency instead of an ultrasonic frequency.

 

[Myrmidon]

I'v popped it off and had a look but don't see anything yet but i'll have a more in depth look.