Re: Power Supply Voltage

Well i changed out ic902 and with 12v on vcc still no 400vdc. So in looking at the datasheets some more and the schematic it looked like it might need more then 12v to turn on. So I started turning up the external P/S and when it hit app. 12.5vdc the PFC came on and I had 400vdc and the 12 and 24 volt supplies. I think it actually should be around 15vdc on the vcc.
So back to T904 I rechecked voltage at D908 and had 5.85vdc. Lifting R976,R917,R991,R921 it dropped to 3.1vdc at D908. Both D908 and C969 test good and I do not have replacements.
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Re: Power Supply Voltage

Yes, this was how I found out that ic901 was bad. At first I only had @ 2vdc on this line when Q922 was on and after disconnecting most other components on this line it then came up to the 5v when ic901 was removed. After new ic was installed it held at the 5v when Q922 was turned on.
Last night I lifted 1 side of R976 and connected my external supply and set it at 12vdc and jumped Q922 and I had a good 12v on my vcc's at the ic's. But ic902 was still dead. I have another new ic but have not installed it yet.

I figured that once I see...

Re: Power Supply Voltage

I believe you mean C969.
I have tested on both sides of R976 (5v) And tested D908, replaced C969 and checked winding for open.

Hot gnd meaning any location with an open triangle, neg side of C907 or anywhere else that has an open triangle. All hot gnd..

Re: Power Supply Voltage

It is a Sharp LC-42SB45UT

Complete manual here:

DC is 5v on e and c of Q922 when switched on. 5vdc on e when off.

Yes I am using hot gnd when testing hot side and cold gnd when testing cold side.

Re: Power Supply Voltage

The complete manual was to large to upload so I pulled out the PS page and attached it.

This supply had some damage. ic903 was blown apart and a couple other components in that circuit. Q902 was also damaged so it and ic902 were also changed. ic901 was pulling down the vcc line so it was changed.

Now when plugged in I have app. 4.75v on 5v line. When jumped to standby it comes up to the stated 5v. Q922 is switched on and I have 5v at the vcc of ic902 and ic901. But neither ic seems to be running.

But I think I...

Re: Power Supply Voltage

Ok. So Q902 mosfet has to be running for the circuit to boost the DC to 400v. Correct?

I am working on this power supply and curious as to how the DC voltage of the rectifier output is increased to what the manual indicates it should be. The manual says the DC output of BD901 should be 320vdc when off and 400vdc when turned on. Now I know the output of the rectifier is only around 170vdc by itself and this is about what I have now, way less then what the manual says it should be and the supply is not working. How does this circuit increase the DC line to 400vdc? My thought was the switching of the mosfet,Q902 but I am not an engineer. Thanks....

Re: New Members - please post your introductions here

Hello everyone. Great forum. Have been reading here for years. Time to join.