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Old 08-01-2019, 06:02 AM   #10
dicky96
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Join Date: Mar 2017
City & State: Sunny Gran Canaria
My Country: Spain
Line Voltage: 220V 50Hz
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Posts: 514
Default Re: Philips 234e problem

Hmm the results were quite interesting

I connected a 5R6 resistor to the 5V line with the panel PCB disconnected but only got a few extra mA flowing when I expected about 900mA into that load. When I checked I only had about 0.35V on the 5V line. It didn't 'chirp' though

I then put other resistors in series with the 5r6 and tested again:

5R6 = 0.35V
10R3 = 2.29V
15R6 = 3.20V
35R6 = 4.2V
105R6 = 4.78V
275R6 = 4.99V

So the 5V line can not supply much current. I didn't bother look at the 3V3 line

Looking at the main board, 5V originates directly from what I assume is a FET marked GA4X29, pins 5,6,7,8 (Q492). This had some horrible looking corrosion around it so I cleaned that off but it makes no difference.

Assuming GA4X29 is a FET then It is not clear where the gate of the FET (pin 4) goes but pins 1,2,3 (source? Drain?) seems to be connected to pin 5 of the nearby APW7089 step down converter (U705). and the largish inductor marked .220.

That does not seem to make a lot of sense looking at the typical application circuit on page 2 of the datasheet https://pdf1.alldatasheet.com/datash...C/APW7089.html


It would also seem that the 5V line should be able to output more than a few mA but it is not obvious what is wrong with it.

Why did you say it could be dangerous to drive the 5V input on the panel edge PCB directly?

I can get a replacement working main board for this monitor for 30 euros. As I only paid a few euros for it and wanted to keep it for myself that wouldn't be a bad option, and it would still be a good purchase... but it would be nice to fix this one if reasonably possible.

Rich
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Last edited by dicky96; 08-01-2019 at 06:06 AM.. Reason: additional info
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