Tecnoware FAL501FS12 does not turn on

[falcontech]

Hi everyone I would like to repair my power supply that does not turn on, it is a FAL501FS12 tecnoware, I have already done some testing, on the primary the mosfets are good, same thing on the secondary, there are 5 standby volts, I have replaced a capacitor swollen on the secondary, I noticed that the large capacitors on the primary do not give me the same voltage, both with the power supply in standby and with the power supply turned on, the capacitors are from 560uf 200v, measuring them one from 210v (both in standby and on) a 99V one (both on standby and on) if you need the photos I can attach them, I wait for someone to help me thanks

[momaka]

Re: Tecnoware FAL501FS12 does not turn on

Hi everyone I would like to repair my power supply that does not turn on, it is a FAL501FS12 tecnoware, I have already done some testing, on the primary the mosfets are good, same thing on the secondary, there are 5 standby volts, I have replaced a capacitor swollen on the secondary, I noticed that the large capacitors on the primary do not give me the same voltage, both with the power supply in standby and with the power supply turned on, the capacitors are from 560uf 200v, measuring them one from 210v (both in standby and on) a 99V one (both on standby and on) if you need the photos I can attach them, I wait for someone to help me thanks

Pictures are always helpful, as it helps people to see what we are dealing with. So please post them.

As I mentioned in the other Tecnoware FAL501FS12 thread (copy-pasta'd from there)...

Since you are in Italy and you have 230V AC line voltage, the total *DC* voltage across the two big capacitors should be about 230 x 1.41421 = 325V DC. Thus, each cap should have about 160-170V DC across it, with or without the PSU turned On.

You appear to have unbalanced voltage across the primary caps. Please check again to verify. If that is the case, those primary caps may be bad.

[falcontech]

Re: Tecnoware FAL501FS12 does not turn on

OK thanks
Tomorrow I will let you have the photos and recheck the voltage, however I have already replaced the large capacitors but the result does not change

[falcontech]

Re: Tecnoware FAL501FS12 does not turn on

I checked, I have about 322 volts between the two capacitors, but individually tested one gives me about 210 and the other starts from 118 and goes down to 99 and stops

[Per Hansson]

Re: Tecnoware FAL501FS12 does not turn on

There is a resistor to discharge each capacitor.
Make sure they have not drifted, they need to have the same value...

[momaka]

Re: Tecnoware FAL501FS12 does not turn on

I checked, I have about 322 volts between the two capacitors, but individually tested one gives me about 210 and the other starts from 118 and goes down to 99 and stops

Are you measuring that voltage directly across each capacitor between the two terminals or are you using something else as ground reference?

If you are measuring directly across them, then like Per mentioned, you may have open/drifted balancer resistors (usually small 1/4W to 1/2W, several 100 KOhms each, same value.)

[falcontech]

Re: Tecnoware FAL501FS12 does not turn on

ok guys tomorrow place the photos so explain to me what these resistances are, however I did the test directly on the capacitors, I tried them both individually, and together and as I said when I try them individually they are unbalanced, together instead they give about 320 volts

[Behemot]

Re: Tecnoware FAL501FS12 does not turn on

If that's the case, only explanation is one of them went high(er) ESR, hence, by ohms law, the different voltage. But, that situation likely happened over time and I think is not the most accute problem - the PSU should still start as the primary switching works with the combined voltage of both, 325 V. Must be something else (but replace both if we manage to repair the other problem).

Consider that learning excercise only though, that unit is utter crap, totaly not worth repairing otherwise.

[falcontech]

Re: Tecnoware FAL501FS12 does not turn on

it is not so much the value of the power supply, but in this period that we are forced to stay at home, I decided to try to repair some things that I had to scrape, also to do some practice for similar situations in the future since I have a computer shop and I like electronics, a few days ago I repaired thanks to this forum 4 power supplies for the power mac g4 which are more complex, now I am stubborn that I want to repair this too

[falcontech]

Re: Tecnoware FAL501FS12 does not turn on

what is ESR?

[CapLeaker]

Re: Tecnoware FAL501FS12 does not turn on

ESR = equivalent series resistance. By measuring the ESR of a capacitor with an ESR meter, we can determine if a capacitor is good, so so or bad. Capacitors can look physically like new, but yet be bad!

ESR changes with heat. When the caps are warm they have lower ESR as when they are cold. When The ESR is too high, on specific capacitor(s) it will prevent the PSU from turning on.

I am not really sure why you want to fix this old thing, unless you have an old computer that needs it? I guess we need some straight shot high quality pictures to start. Try to heat up the power supply with the wife’s hair dryer to like 50C and then try to turn it on. See what happens...

[Behemot]

Re: Tecnoware FAL501FS12 does not turn on

Can send ya decent ESR meter, caps too, post should still work

[falcontech]

Re: Tecnoware FAL501FS12 does not turn on

Happy Easter guys to everyone, as I already told you, the big capacitors have already been replaced and among other things the ones that I removed I tried them on a working power supply and they work well

[CapLeaker]

Re: Tecnoware FAL501FS12 does not turn on

Happy Easter!
Yes, you did... but there are other capacitors in that PSU as well. The problem is not always on the big capacitors. Big or small, the caps close to a heat sink are always suspect.

[Per Hansson]

Re: Tecnoware FAL501FS12 does not turn on

Take a look at this schematic: http://www.pavouk.org/hw/en_atxps.html
R2 and R3 discharge C5 & C6.
There is not anything else in the circuit that can cause imbalance.
Except a bad diode in the bridge rectifier or such because after this stage it is a shared DC bus of 325VDC.

[falcontech]

Re: Tecnoware FAL501FS12 does not turn on

They are the pictures let me understand what are the resistances to check, so I also replace the rectifier bridge thanks

[CapLeaker]

Re: Tecnoware FAL501FS12 does not turn on

the big 200V capacitor next to the bridge rectifier looks bloated to me.

[falcontech]

Re: Tecnoware FAL501FS12 does not turn on

it's one of the old ones, but it's working I tried it on another power supply, however even with the new ones it does the same problem, now I try to change the bridge

[falcontech]

Re: Tecnoware FAL501FS12 does not turn on

I replaced the rectifier bridge but nothing to do, same problem, I also put the new capacitors to scruple, we hope to understand what's going on

[CapLeaker]

Re: Tecnoware FAL501FS12 does not turn on

so the main filter caps are still not balanced? Hmm... can you measure how much current the power supply draws from the power mains? something like a watt meter?
check Vcc on pin 12 on the TL494 IC. In the schematic there is a C21 that supplies pin 12 on that TL494. Change C21.