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Old 01-03-2020, 05:26 AM   #1
nbdy
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Default Corsair 750W SemiMOD

Got an corsair 750w semi mod, which will not turn on ...

Now I have 5VSB,The relay clicks when connectin it to 220V (with gren to black) ...

But have no 12V,5V,3.3V, -12V ...

All caps are ok,nothing seems to be burned (no smell, no brown place)

The supply is CS750M ...

Any advice,

thx
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Old 01-03-2020, 02:00 PM   #2
PeteS in CA
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Default Re: Corsair 750W SemiMOD

More info about the PSU might help us be more helpful.

Is the large electrolytic capacitor on the primary side rated for 400, 420, or 450 volts? If so, what is the voltage across it? If so and the voltage is around 390V, the PFC circuit is probably working, and the problem is probably with the PWM or inverter circuits.
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Old 01-04-2020, 07:40 AM   #3
nbdy
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Default Re: Corsair 750W SemiMOD

They are 400V and I have 340 on them DC ...

It's a CM750M from corsair
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Old 01-04-2020, 11:14 AM   #4
nbdy
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Default Re: Corsair 750W SemiMOD

Sorry CS750M from corsair ...

Faound that Q103 i Q104 PNP transistors BCW69,BCW70 (H2P,H1F - board marks) ...

Now :
base - colector - 0.646V
base - emiter - 0.660V

with + on base ...

base -colector - 1.047V
base - emiter - 0.646V

with - on base (that's for Q103)

Q104 is behaving opposite the Q103 (switched + and -)

D103,D104,D5,D6 both sides 0.004V ...

ZD201 one side 0.707, other 2.45V ...

ZD204 one side 0.725, other 1.197V ...

D101,D102 both sides 0.660V ...

Last edited by nbdy; 01-04-2020 at 12:32 PM..
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Old 01-12-2020, 10:01 PM   #5
momaka
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Default Re: Corsair 750W SemiMOD

Quote:
Originally Posted by nbdy View Post
They are 400V and I have 340 on them DC ...
That's normal for when the APFC is not running (i.e. PSU outputting only 5VSB).

It's LOW for when the APFC >IS< running (i.e. when you try to turn ON the PSU). Should be around 375-385V DC. If not, the APFC is not switching properly - and that can be due to the APFC being faulty, due to the 5VSB being faulty (on the primary side), or due to the secondary side being faulty and telling the PSU not run.

Pictures of your PSU would help us see what you are seeing. So if possible, please upload some.
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Old 01-14-2020, 03:09 PM   #6
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Default Re: Corsair 750W SemiMOD

I have had nothing but bad experiences with Corsair, and wont have anything to do with them after going through 4 of the things in 6 years. I find they have a habit of exploding so extra band for your buck. The end result were boards with large areas of copper tracking burnt of the substrate along with a number of un-identifiable burnt or exploded smd devices.

I have had about a dozen of the things come through the workshop for repair mostly the 1200 watt ones with similar faults, few were repairable due to the extensive damage to the PCB substrate the majority of them I had to advise the customers were scrap. At the time they were in excess of 200 with a service life that just made it to the end of the warranty, thankfully in my case there was no damage to the main boards (motherboards) although one did damage a KB.

Last edited by llonen; 01-14-2020 at 03:12 PM..
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