Sharp Aquos LC20E1-S LCD TV Strange AC adapter

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So there maybe one or more floating voltages, you'll need perhaps 3 separate supplies and moulding up/exchanging for, your own connector

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Well for testing I just soldered all of the positive contacts togeather to one wire and the same for the neg and then soldered those to a barrel connector jack.

It didn't let out any magic smoke when doing this so I guess it is okay still, although I'm unsure if it was working beforehand because I have no power supply.

Mike

There are several reasons why Sharp chose to use three separate supplies. One was to minimize the cost of a building a single "rilllly big" supply. The other is that it wanted to minimize the amount of bypassing and decoupling needed on the boards.

The obvious answer to the question of why the set didn't work is that it doesn't "like" being driven from a single supply. (The original supply was likely missing because the was tossed out as defective (for whatever unknown reason)).

I would not have plugged a single supply into it, simply on the (admittedly remote) possibility that it might be damaged.

Cha Ching! You 'don't' know if it was working prior to your purchase. My guess is it was not and that reason could be why the supply wasn't provided to you.

Well if I were back home where I have a workbench and loads of wire and power supplies laying around I would have wired it up as it was intended. But unfortunately where I'm at now I don't many tools or parts to work with. Upon first looking at I thought they made seperate supplies just to save money on the design of the PSU and or for RFI protection.

I rescued a similar set. The three supplies are, in fact, separate (common return). I didn't bother to sort out "why" as the set I have came with the brick. But, the schematic shows them as separate.

Some possible reasons:

- keep the backlight supply isolated from the signal processing supply (keeps audio/video cleaner)

- make sure the "processor" power supply comes up before other supplies

- allow the processor to run even if the other supply(ies) die (so it can blink an error indicator)

- etc.

I'm not sure I would have arbitrarily tied all of the supplies together. There might be some power sequencing issues that your "patch" could make problematic. Of course, its too late *now*... :>

That's the *first* thing I would have tried (realizing that you

*could* possibly toast their brick in the process -- so hope it is an understanding friend! :> )

Well I was wrong about my friends tv. It was a newer version which included the smps inside the case...

Anyhow. I managed to find 3 different supplies around here and wired them all to the TV. It responded the same as before. A little noise from the audio amp and the power light briefly flashed once.

I started probing around with the meter and can't see where this thing is using the voltages to combine to make a floating voltage. What I can see is they did use it to completely isolate the inverters from everything else. The ground for the inverter is seperate as well. On the main PCB they have

2 circuits that have their grounds tied togeather. I think one is feeding the tuner and one is feeding the audio amp.

Anyway.. I guess its on to trouleshooting the main pcb.

Mike