Recap.IT – Aldi Vivid 32″ LCD TV

One of these Aldi TV’s came in – a Vivid 32″ LCD TV with a problem where the screen display goes out from time to time. I had seen it happen a couple of times, and could see that it was the backlight that was the problem. However, the backlight circuitry appears to be working fine most of the time, so the fault could be due to the power supply.

The power supply is a Megmeet MP-116A – a search of google shows that a lot of people have had problems with this power supply. Also searching for Vivid 32″ shows some similar faults but no real fix.

SONY DSC

I checked most of the electrolytic capacitors, they all appear to be within tolerance as far as ESR is concerned. ESR or Equivalent Series Resistance is a measure of how well a capacitor is working, in addition to its capacitance. Power supplies tend to get quite hot, and when capacitors get hot, they can start to dry out – and noticeably it’s ESR tends to increase, until eventually it is unable to filter out any ripple currents effectively.

I also used an oscilloscope and looked at the 12V output of the power supply – it was showing some 200mV of ripple, not a lot but could be causing a problem if the ripple increases during higher loading.  The large main capacitor ESR was not high, at 0.66 ohms, but usually this is one that would go first.

In any case, it is usually best to “recap.it“, i.e. replace all of the electrolytic capacitors – so this is what I did. I got the parts yesterday and replaced them today. After removing the parts, I also checked the actual capacitance and found a couple that appeared to be slightly low, but most were within tolerance. I will test it further during the weekend and see if the backlight fails again – if it doesn’t, then it could be that replacing the capacitors in the power supply did the trick.

[NOTE]  The replacement 68uF 450V main capacitor as a comparison had an ESR of 0.2 ohms – this means that its power dissipation for ripple currents will be considerably less than the original capacitor, and hopefully run cooler.

Advertisements