Leadman LP-6100E problems

[pdavid]

A friend got this psu out from his parts chest. He would have used it to power some p4 desktop, except the psu won't do anything. All secondary and primary caps were bad. There is definately some heat damage, both fans are stuck. I started to replace the bad caps and test other parts when I noticed that the 5vsb circuit is completely dead. The Fet and it driver transistor and a resistor for sure, Q7; Q3; R4.
The main fet test good (irfpc60 maybe), not shorted at least. Secondary diodes and fuse are good. But I'm not sure about the 3842 pwm.

I bartered a 300W Fsp for this. Maybe I can learn something from this psu.

[everell]

Re: Leadman LP-6100E problems

What brand were the primary and secondary capacitors that were bad?

Please post some pictures showing the entire top side of the power supply.

[999999999]

Re: Leadman LP-6100E problems

I don't bother trying to repair PSU that had the fans seize then the whole thing baked... too much chance of more than just caps failed and that something else will still fail prematurely.

What they teach me is don't run PSU with low quality fans unless you can constantly monitor them and relube them on a schedule.

[pdavid]

Re: Leadman LP-6100E problems

What brand were the primary and secondary capacitors that were bad?

Please post some pictures showing the entire top side of the power supply.

Original caps were Jee and Kosin. The primary cap's capacitance were droped to near zero, maybe one even got arced to the heatsink...
One 100pf film cap has burned glue, measures good but I replaced that too.
Also replaced a filter choke in the emi stage since the original got too much crap burned into it and when I was trying to remove it the enamel got damaged.

You can see I sort of recapped this one. I guess wasting some Teapo caps is okay
If I can't fix it it's still good for some parts.

What they teach me is don't run PSU with low quality fans unless you can constantly monitor them and relube them on a schedule.

The second fan actually had a third sense wire but is stuck anyway.

[Pentium4]

Re: Leadman LP-6100E problems

Looks much better! Now it isn't a typical Leadman eye-sore. Those 4 diodes on the primary look pretty good sized but I'd still put a bridge rectifier there instead. I like how Jee tried to copy Rubycon's vent stamp.... Have you tested to see if it's working yet?

[999999999]

Re: Leadman LP-6100E problems

Are there any (consumer/PC grade) ATX PSU that can sense fan seizure? I've never owned any, though I had a LiteOn server PSU that could do it with only the two power leads. The fan didn't seize but if you stuck a straw in to stop it then the PSU shut off.

[pdavid]

Re: Leadman LP-6100E problems

I think some older Chieftec psus like Gps series or Channel Well's psh shuts of if the fan isn't running or if not connected... maybe Forton pnf too but I'm not soo sure.

I'm still looking for problems in this psu. Those Jee caps werent holding up good for sure. All the 2200uF ones measured like 300uF max.
Small transistors and diodes test ok. I'm replacing the fet and 3843 pwm chip.

[pdavid]

Re: Leadman LP-6100E problems

I replaced the 3843 pwm and main fet but somehow it keeps shorting the 5vsb fet There is about 340Vdc after the bridge rectifier and that's all. Resistors check up small caps too... I'm probably missing something here.

[momaka]

Re: Leadman LP-6100E problems

Check everything connected to the 5VSB circuit - both on the primary and secondary side.

On the primary side, the Auxiliary winding of the 5VSB transformer generates power for the 3843 PWM chip. IIRC, before this aux rail reaches the 3843 controller, it is first rectified by diode D2 and filtered by a 47uF 25V cap. This is actually the critical cap for the 5VSB so make sure to replace it with a known good one. Also make sure to check diode D2. After that, the aux rail goes through a transistor which is controlled by an optocoupler and then to the 3843 (this is the on-off function of the PSU. There may be a few other diodes in the circuit - make sure they're not shorted either. More particularly, check the snubber diode, D4.

On the secondary side, make sure the 431 shunt regulator is good. If you have a spare one, replace it anyways. They rarely go bad, but they can. Make sure the output diode and filter cap(s) are good as well.

If the transistor still keeps blowing, the 5VSB traffo may be toast.

I would suggest to use a 25W or 40W incadescent light bulb in series with the line input of the PSU - this will minimize (if not eliminate) the damage to the new components you put in the 5VSB. It will also stop your new fuses from blowing each time.

OR
If you want to check the power supply without the 5VSB circuit, first provide a 5V supply to the supervisory chip with an external power supply, and only then provide 18V to 25V to the input pin on the 3843 PWM IC. The external power supply for the 3843 PWM IC MUST BE isolated (i.e. not grounded), or you'll run into big big problems. The output ground wire on the external power supply for the 3843 PWM IC should be connected to hot ground (i.e. the (-) side of the bridge rectifier).

[pdavid]

Re: Leadman LP-6100E problems

Thanks momaka! Now that you mention it I haven't checked the trafo and opto. I'm going to be away for a few days, but when I get back I'll give it a try.

[hkqq2010]

Re: Leadman LP-6100E problems

I would suggest to use a 25W or 40W incadescent light bulb in series with the line input of the PSU - this will minimize (if not eliminate) the damage to the new components you put in the 5VSB. It will also stop your new fuses from blowing each time.

This really is a very good practice.
In the past, when I first to repair PSU, it burn me so many fuse. Besides of fuse, it is also full of scare caused it always accompanied with some flash and a little flame. With a light bulb, it is safer.

I would use a 40W light bulb rather than 25W, caused it provides sufficient current to drive the PSU 12V fan when testing.

[pdavid]

Re: Leadman LP-6100E problems

This really is a very good practice.
In the past, when I first to repair PSU, it burn me so many fuse. Besides of fuse, it is also full of scare caused it always accompanied with some flash and a little flame. With a light bulb, it is safer.

I would use a 40W light bulb rather than 25W, caused it provides sufficient current to drive the PSU 12V fan when testing.

Thankfuly I have a stock of 60W bulbs. Now I can "legaly" buy only 20W in the EU. No more incadescent bulbs, cuz it's not good for the enviroment and wastes power... too bad.

The psu is working now. Turns out one opto was open on the primary side no matter what. Voltage regulation isn't great. I'm only going to keep this unit for parts and reference.
Thanks for the help everyone!

[Th3_uN1Qu3]

Re: Leadman LP-6100E problems

The most common failure mode of an opto is open. You're lucky it didn't go open on the secondary - it would have caused complete loss of regulation and definitely some smoke.

[pdavid]

Re: Leadman LP-6100E problems

Somehow I always expect the least that an optocoupler or trafo going bad. Only seen some really lame psus fail catastrophically, with obvious signs.