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Old 08-06-2010, 07:25 AM   #1
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Default Samsung 245 BN44-00195A Supply

Anyone have a schematic of this PS? Unit has no 24v output. On board 82uf @ 450 Cap has only 160v. Board notes 380v.
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Old 08-06-2010, 09:05 AM   #2
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Default Re: Samsung 245 BN44-00195A Supply

160V is about right if your line voltage is 120V. (Of course, if you are in the 220/230/240V parts of the world, 160V isn't good.)
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Old 08-06-2010, 12:37 PM   #3
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Old 08-10-2010, 08:11 AM   #4
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Default Re: Samsung 245 BN44-00195A Supply

This monitor has a power factor correction circuitry on the front end and therefor you should see 380-390VDC on the 82uF, 450V cap. When you measured the voltage across
the 82uF cap and it was at 160V I am assuming you did this with a DVM. If the 82uF is
very low in capacitance the voltage might be swinging from zero to 380V and giving you
an RMS voltage of 160V on the DVM. If you have a scope you might want to see what
the "real" voltage waveform is on this cap. I suspect it might be swinging from zero to 380V at a very fast rate. If no scope is available you might then try substituting a know
good 82-220uF, 400V cap in the 82uF cap location and see if the 24V comes alive.
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Old 08-10-2010, 07:00 PM   #5
pedro
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Default Re: Samsung 245 BN44-00195A Supply

Quote:
Originally Posted by Aruba View Post
This monitor has a power factor correction circuitry on the front end and therefor you should see 380-390VDC on the 82uF, 450V cap. When you measured the voltage across
the 82uF cap and it was at 160V I am assuming you did this with a DVM. If the 82uF is
very low in capacitance the voltage might be swinging from zero to 380V and giving you
an RMS voltage of 160V on the DVM. If you have a scope you might want to see what
the "real" voltage waveform is on this cap. I suspect it might be swinging from zero to 380V at a very fast rate. If no scope is available you might then try substituting a know
good 82-220uF, 400V cap in the 82uF cap location and see if the 24V comes alive.
First the big "CAUTION!!!" - both sides of the main input rectifier cap are live! Most CROs have a grounded reference. An isolation mechanism is required - either an isolation transformer in the CRO or (preferably) monitor supply line, or the more dubious floating chassis arrangement on the CRO which I would NOT recommend.

The voltage on the cap WILL depend on the line voltage. As the O/P hasn't identified his/her location/country we cannot assume a line voltage.
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Old 08-11-2010, 04:49 PM   #6
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Default Re: Samsung 245 BN44-00195A Supply

Quote:
Originally Posted by pedro View Post
First the big "CAUTION!!!" - both sides of the main input rectifier cap are live! Most CROs have a grounded reference. An isolation mechanism is required - either an isolation transformer in the CRO or (preferably) monitor supply line, or the more dubious floating chassis arrangement on the CRO which I would NOT recommend.

The voltage on the cap WILL depend on the line voltage. As the O/P hasn't identified his/her location/country we cannot assume a line voltage.
Yes extreme caution should be taken whenever you are working on the
primary (HOT) side of the circuit. The beauty of the power factor correction circuitry is that the bulk cap on the typical 400VDC bus will always be around
400VDC when working correctly regardless of the input voltage which may be
at 100VAC (Japan), 120VAC (North America), 208VAC (North America) or
230-240VAC rest of the world. This is such that the current drawn of the
equipment is more sinusoidal in sync with the voltage waveform rather than
small current peaks only near the positive voltage peak and at the negative voltage peak. Power factor measured with the power factor correction circuitry installed measures very close to the ideal perfect power factor of 1
at around 0.95-0.99. On equipment without power factor correction and is using a switching power supply is typically around 0.5-0.65.

peak
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Old 09-07-2010, 04:24 PM   #7
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Default Re: Samsung 245 BN44-00195A Supply

My IP board uses a full wave rectifier bridge to charge up the inverter capacitor. Since my line voltage is 120 VAC for North America, and the peak voltage is about 1.5 times that, it is normal to find about 170 volts DC in this can. Because the bridge is full wave, the peak voltage across the cap should never be more than 170 volts DC.

In Europe with 220 Volts AC as the line voltage, 1.5 times that would be 330 VDC on the same can and an electrolytic with a 400 volt rating should be a comfortable fit.

I have seen some fancy transformerless power supplies in my life which can create 340 volts DC from the 120 AC line voltage using a clever configuration of diodes and caps (called a voltage doubler).
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