I got a blown up varistor ( vr44) located bet the two big capacitors.I don't know what is the value of it or what voltage to replace it?.Pls.help. can I just put any varistor there like 100.v?
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Varistor for Bestec ATX0300 D5WC
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Re: Varistor for Bestec ATX0300 D5WC
Can we see the pictures? Are the caps connected in series or parallel? Voltage rating of the caps, 250V? 450V? The more information you provide the better we can help you.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Re: Varistor for Bestec ATX0300 D5WC
You are going to have to remove the board and take hi-res pictures of the whole top side and the bottom side of the board, and then good closed up pictures around the VRxx.
Or you will have to locate the same power supply to see what the print on the VR are.
Right now I cannot tell how those VRs are connected to the circuits.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Re: Varistor for Bestec ATX0300 D5WC
I think the varistors should be across each cap. I looked at pictures of two ATX-300 units I have (12E and 12Z), and they both have the varistors across the primary caps. Probably 180V or 200V-rated varistors. These Bestec PSUs don't have APFC, so the primary caps are rated for 200V. You should see half of the AC rectified voltage across each - i.e. about 162V.
If the PSU is not in a mission critical PC or you don't care whether it gets killed from a voltage surge, then remove those varistors and run the PSU without it.
By the way, this thread should be in the Power Supply Design and Troubleshooting forum.Last edited by momaka; 12-04-2015, 10:47 PM.
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Re: Varistor for Bestec ATX0300 D5WC
Here is an ATX PSU schematic:
http://www.pavouk.org/hw/en_atxps.html
Here is the manufacturer's original circuit diagram:
http://web.archive.org/web/200901051...power/2038.zip
Here are lots more DTK PSU schematics:
http://web.archive.org/web/200901051.../circuitp.html
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Re: Varistor for Bestec ATX0300 D5WC
Originally posted by docchan2000 View PostIs it OK if I just put a 300v varistor there?I
The two varistors in your PSU are installed across each 200V capacitor. The idea behind a varistor is to clamp any power surges that go beyond the 200V rating of the primary caps. If you put a 300V varistor, then it won't protect the capacitor. However, you can't use a 100V varistor either, because the voltage on each cap will be around 165V and may go up to 170 V when your line is 5% high. So that's why you need a varistor rated between 180-200V.
I would say just don't bother putting it in there. It won't destroy your PC. It's just that *IF* the line voltage to your house goes high due to lightning/thunderstorm or other technical issues (both of which are very rare events), then your PSU will likely fail and blow a fuse. Since this is a Bestec PSU, chances are nothing else will blow when the PSU blows up, because Bestec PSUs tend to be well-engineered. So again, I just wouldn't worry about that varistor.
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Re: Varistor for Bestec ATX0300 D5WC
Thanks for the immediate reply momaka. If the varistor serves nothing in powering up my unit when it exploded...why can't it power up my Desktop?does this mean that there is more than the varistor that got messsed up?
So I need to remove that red varistor that i just put and check on the other parts?Last edited by docchan2000; 12-06-2015, 01:45 AM.
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Re: Varistor for Bestec ATX0300 D5WC
The 300v varistor is still better than nothing.
And besides most caps have a voltage surge rating.
I.e. they may be ok with a short over voltage of 50% for a couple milliseconds.
Check the datasheets"The one who says it cannot be done should never interrupt the one who is doing it."
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Re: Varistor for Bestec ATX0300 D5WC
Originally posted by docchan2000 View PostIf the varistor serves nothing in powering up my unit when it exploded...why can't it power up my Desktop?does this mean that there is more than the varistor that got messsed up?
Originally posted by Per HanssonThe 300v varistor is still better than nothing.
And besides most caps have a voltage surge rating.
Originally posted by docchan2000 View PostSo I need to remove that red varistor that i just put and check on the other parts?
Since the original varistor exploded, as you noted, then that means other parts could have been damaged as well.
The first things to check would be the fuse, bridge rectifier (black rectangular box with part number "GBU..."), and thermistor (that green, disk-shaped thing next to the bridge rectifier).
You will need a multimeter to troubleshoot these (and the rest of the PSU). May we ask how familiar you are with using one? Reason I want to know is so that we can give you troubleshooting instructions accordingly.
Originally posted by fzabkarWhat would happen if one of the capacitors were slow to charge up? If the two capacitors are not perfectly balanced, wouldn't one of them have a higher voltage than the other, and could this be a possible failure scenario for the varistor?Last edited by momaka; 12-06-2015, 03:31 PM.
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Re: Varistor for Bestec ATX0300 D5WC
I just do some you-tubing and readings in the net.I know not much about this things but I like doing things on my own because of the self fullfilment aside from saving a lot of money. I got to have that multimeter and test those parts you mentioned momaka. Many thanks and more POWER💪
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Re: Varistor for Bestec ATX0300 D5WC
Originally posted by docchan2000 View PostI got to have that multimeter and test those parts you mentioned momaka.
- The fuse should ideally read 0-1 Ohms across it (depending on how good your multimeter is).
- ^ Same goes for the the thermistor, except anything between 0-10 Ohms is generally acceptable. Make sure there are also no physical cracks or missing pieces in its body, as that might indicate a pending failure.
- Bridge rectifier is basically 4 diodes connected in a special way.
Between the two AC (~) legs, you should get infinite resistance (i.e. open-circuit, or OL on your meter), regardless of how you connect your multimeter probes.
With red (+) multimeter probe on positive leg (+) of bridge rectifier and black (-) multimeter probe on negative leg (-) of bridge rectifier, you should get infinite resistance again. Reversing the probes should give you approximately two diode voltage drops (800 - 1600 mV) on diode test mode on your multimeter.Last edited by momaka; 12-07-2015, 06:08 PM.
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