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Old 01-31-2021, 01:00 PM   #21
falcontech
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Default Re: Dual output power supply 5 and 12 volts (no output)

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Originally Posted by eccerr0r View Post
Fuse would have blew if the insulation wasn't there anyway?

Looks like there's a pull up to shut down if the resistor blew (incidentally it seems like I see two resistors in parallel there I think, this should be the 0.49Ω resistor? Which should be a fusable resistor? And it looks like a 100Ω resistor there in parallel with something else that I can't see underneath?)

Hmm...
the fuse in all this is not blown, see just for the resistors, because I did not find the 0.49 one and I put two 1 ohm in parallel
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Old 01-31-2021, 01:20 PM   #22
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Default Re: Dual output power supply 5 and 12 volts (no output)

Check the VCC voltage across the small electrolytic next to the ic. Post what this voltage is.
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Old 01-31-2021, 02:07 PM   #23
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Default Re: Dual output power supply 5 and 12 volts (no output)

does the psu even try to start?
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Old 01-31-2021, 02:59 PM   #24
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Default Re: Dual output power supply 5 and 12 volts (no output)

i've 8,2 volts, the capacitor is 47uf-35 volts
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Old 01-31-2021, 02:59 PM   #25
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Default Re: Dual output power supply 5 and 12 volts (no output)

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does the psu even try to start?
no no sign of life
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Old 01-31-2021, 03:00 PM   #26
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Default Re: Dual output power supply 5 and 12 volts (no output)

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Originally Posted by R_J View Post
Check the VCC voltage across the small electrolytic next to the ic. Post what this voltage is.
i've 8,2 volts, the capacitor is 47uf-35 volts
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Old 01-31-2021, 04:26 PM   #27
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Default Re: Dual output power supply 5 and 12 volts (no output)

If this is a td3843 the startup threshold is min 7.8v so the ic should be starting. It could be that it is not seeing the current sense pulse as I still don't know if that @#$% resistor is good or bad.
You also need to check the resistor between pin6 (output) of the ic and the GATE of the mosfet, it could also be open.
Quote:
however the resistors have all been replaced, except the smallest ones that look good to the eye

Last edited by R_J; 01-31-2021 at 04:40 PM..
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Old 01-31-2021, 04:40 PM   #28
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Default Re: Dual output power supply 5 and 12 volts (no output)

which resistor are you talking about? in the previous message some strange symbols appeared however the ic is now a uc3843, the original was a Td3843
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Old 01-31-2021, 04:47 PM   #29
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Default Re: Dual output power supply 5 and 12 volts (no output)

if you are talking about the resistor you were talking about, which must be connected between the cs of the ic and the source of the mosfet, help me to understand what it could be, I am available, if you want I can make a diagram, on the part of the circuit where there is are the welds to try to understand better
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Old 01-31-2021, 04:48 PM   #30
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Default Re: Dual output power supply 5 and 12 volts (no output)

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Originally Posted by falcontech View Post
if you are talking about the resistor you were talking about, which must be connected between the cs of the ic and the source of the mosfet, help me to understand what it could be, I am available, if you want I can make a diagram, on the part of the circuit where there is are the welds to try to understand better
If you can't trace one resistor between the CS pin and the fet, I can't help you. Go back and see post #13. It is the one in the yellow square.

Last edited by R_J; 01-31-2021 at 05:05 PM..
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Old 01-31-2021, 04:53 PM   #31
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Default Re: Dual output power supply 5 and 12 volts (no output)

ok tomorrow I will try to bring the component diagram on the part of the welds graphically so let's see if you can understand better, in the meantime thanks
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Old 02-01-2021, 07:55 AM   #32
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Default Re: Dual output power supply 5 and 12 volts (no output)

I hope I have done a decent job
Attached Images
File Type: jpg foto.jpg (548.3 KB, 11 views)
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Old 02-01-2021, 08:45 AM   #33
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Default Re: Dual output power supply 5 and 12 volts (no output)

I tested the 1kohm and 22ohm resistors, the first seems dead, the second gives me a lower value about 16.9 ohm
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Old 02-01-2021, 09:24 AM   #34
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Default Re: Dual output power supply 5 and 12 volts (no output)

replace the resistances, still nothing
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Old 02-01-2021, 10:15 AM   #35
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Default Re: Dual output power supply 5 and 12 volts (no output)

tried to replace the big capacitor and the Optocoupler nothing happens
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Old 02-01-2021, 10:22 AM   #36
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Default Re: Dual output power supply 5 and 12 volts (no output)

is there any way to test with the tester if voltage arrives at the input of the SM transformer?
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Old 02-01-2021, 10:40 AM   #37
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Default Re: Dual output power supply 5 and 12 volts (no output)

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Originally Posted by falcontech View Post
is there any way to test with the tester if voltage arrives at the input of the SM transformer?
What are you using as a "tester"? If it is a dvm or multimeter, just check the voltage with the ground on the negative lead of the 68f/400v capacitor and then on the DRAIN of the mosfet.
Also check and post the voltage on each pin of the ic
Pin1=
pin2=
etc.

Last edited by R_J; 02-01-2021 at 10:51 AM..
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Old 02-01-2021, 10:51 AM   #38
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Default Re: Dual output power supply 5 and 12 volts (no output)

one of this?
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Old 02-01-2021, 10:54 AM   #39
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Default Re: Dual output power supply 5 and 12 volts (no output)

Use either one of the multimeters, the network cable tester has no use here
Post the ic voltages
pin1=
pin2=
etc.
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Old 02-01-2021, 10:56 AM   #40
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Default Re: Dual output power supply 5 and 12 volts (no output)

the lan cable tester also acts as a multimeter, however can I use the yellow one? what voltage should i detect between the two points?
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