 Posted: Fri Mar 23, 2012 7:28 am Post subject: 2405FPW D19 zener |
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| The IFR5305S drain should be at 5VDC. I measured this from a properly working monitor. This means a 3V Zener is incorrect. Use at least a 6.8V Zener which should be quite safe for downstream parts. I managed to supply 5V to the drain (after removing the burnt FET) from an external 5V SMPS and all works well. I am not sure I want to replace the FET, for fear that the gate controller logic may be fried. I also recapped the SMPS board, and it is sending 19V and 7V to the other boards as is normal. | |
| Posted: Thu Mar 08, 2012 10:23 pm Post subject: |
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| The zener, if connected between source and gate, is there to reduce damage caused by MOSFET failure, because often MOSFET failure results in a short-circuit between drain and gate, putting drain voltage on the gate, and thus back to the gate drive circuitry, causing much damage.
A zener of the right value will protect the drive circuitry. If a similar MOSFET is using a 3V zener, then that may well do for D19 too, if they are operating with similar gate voltages. You will not damage anything by using the wrong zener as it's there for protection if the MOSFET fails. In fact, you could run the monitor without D19. Try it. Measure the voltage on the MOSFET gate using a 3V zener and if the MOSFET connected to D19 uses approximately the same voltage, then put a 3V one there. Let us know how things go, because lots of people from my googling seem to have come across this same fault and don't know what D19 should be. |
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| Posted: Thu Mar 08, 2012 6:47 pm Post subject: 2405FPW D19 zener |
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| Same problem here badcaps.net/forum/showthread.php?p=222789. D18 looks like a 3V zener, but no particular reason why D18 and D19 should be identical. Unfortunately, powering this up with a wrong zener may kill parts downstream. Any progress on figuring out what D19 is? | |
| Posted: Fri Jan 01, 2010 7:42 pm Post subject: |
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| Same problem here on a Dell 2405FPW, FET IFR5305S shorted, along with D19 Zener.
I've found the International Rectifier FET on eBay and locally. Haven't tried to remove or identify zener D19 yet. Perhaps D19 is identical to D18 (in a similar SWPS circuit right next door). Did you succeed with your repair? Any more info would be appreciated. Happy New Year.  |
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| Posted: Tue Oct 27, 2009 10:12 am Post subject: |
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| just incase anyone does have the scvhematics, the zenar is D19 |
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| Posted: Tue Oct 27, 2009 8:47 am Post subject: Dell 2405fpw LCD - need "common" equivalent part |
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| Hunting down an issue with a dell 24" lcd monitor. Looks to be that the mosfet - 5305S has died and also took down one of the zener diodes near by.
I'm trying hard to find a common replacement for the mosfet but the specs indicate its a "Hexfet". Never seen a hex fet before. Looking for help as to what might be a suitable replacement (http://www.irf.com/product-info/datasheets/data/irf5305spbf.pdf). Other issue is that the zener diode is burnt beyond recognition. It joins the Gate to ground in reverse direction ) Gate -----|<|----- Ground. Is this diode just for protection, anyone recomend a replacement for this too (or better yet has access to teh dell schematics? Was hoping the datasheet for the IRF5305s would have a sample with the diode in place but no luck 
Any help greatly appreciated, would love to get this guy back up and working, even has composite inputs etc |
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