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Lg Lst 4100P Power Problem

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#1 Steve_C


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Posted 08 March 2012 - 11:08 AM

Hi all,

I am trying to fix a 4100 for a friend. I am a tech, but have no experience with this unit. It has no power, rectified high voltage (344V) from mains is fine, but I don't seem to be getting the power on signal from the on/off button to the base of TR2 in the p/s.

Does anyone have any experience with this unit? I have the p/s circuit diagram, but no other circuit details.



#2 I am not a duck

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Posted 09 March 2012 - 09:25 PM

I've fixed maybe 3 of these, in all cases by using an ESR meter to find the dodgy caps and changing them out.

Is the power supply generating standby voltages?

#3 Steve_C


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Posted 25 March 2012 - 09:13 PM

Thanks. I'm not sure waht standby voltages are required as they are not clearly marked on the schematic. Both switching chips have supply voltage, (12V and 6V) but that seem to be it. It's as though the switching aren't oscillating correctly, although I can hear SPS2 one going, but not SPS1. Unfortunately I do not have a CRO to check, although i might be able to borrow one from work.

I might just go the re-cap route to see.