SMPS Primary Side Short?

[OpenCircuit]

Am I supposed to have .38 ohms from the + terminal to the  - of the rectifier bridge? 

If I sever the jumper at the red X, the circuit (+ to - of rectifier bridge) goes OL.

Suspecting CM6800 ("Vertical Board").

My light bulb 100W (in series) is glowing bright. There is a definite short on primary side after the rectifier bridge.

The IN5406 was shorted. Q2 was shorted (lower MOSFET on the right). Fuse was also blown. Replaced all of these and still have dead short.

You will have to look past my errors in the schematic I made below. If your hunch is a misreport on my part, please excuse. This is of course a very simplified version of what I am  working on (Corsair SMPS Power Supply).

[peteb2]

...my only input would be go look at the .pdf for the CM6800 device and back engineer from there to see what the designer of your SMPS was thinking. I'm too confused on your schema sorry...

http://www.champion-micro.com/datasheet/Analog%20Device/CM6800.pdf

[james_s]

A short on the input almost always means the chopper transistor(s) are bad, occasionally the rectifier.

[Armadillo]

It's really really very very rare to see a shorted transformer. I've never seen one so far. I've seen transformers with milliohms of primary resistance, so I guess it's possible to get 0.38 Ohms without anything shorted.

not at the + and - terminals of the bridge rectifier.

[rob77]

It's really really very very rare to see a shorted transformer. I've never seen one so far. I've seen transformers with milliohms of primary resistance, so I guess it's possible to get 0.38 Ohms without anything shorted.

not at the + and - terminals of the bridge rectifier.

unless you have a shorted mosfet

[OpenCircuit]

A short on the input almost always means the chopper transistor(s) are bad, occasionally the rectifier.

Q2 was shorted (right side of my diagram).

It's really really very very rare to see a shorted transformer. I've never seen one so far. I've seen transformers with milliohms of primary resistance, so I guess it's possible to get 0.38 Ohms without anything shorted.

I completely removed all transformers on the entire PCB and short was still present. Very likely true in my case it seems.

unless you have a shorted mosfet

Had.

Replaced Q2 (MOSFET) and short is still present. There are only two ways out of the + terminal of the rectifier bridge:
1. Small trace that leads into the CM6800 controller IC.
2. Through the inductor coil where circuit splits
       A. Through  inductor coil then into the gate controller (Q2).
       B. The other way is through a low resistance ceramic resistor that leads into the negative side of the large cap (270uF/400V). If I break the circuit going into from the rectifier bridge +terminal the short is gone. This seems to eliminate the CM6800 being the case as this controller remains connected.


Waiting on desoldering wick...... 

[james_s]

Waiting on desoldering wick...... 

I piece of copper braid from a scrap of coax, dipped in some liquid flux makes a reasonably good desoldering wick.

Vacuum desoldering gun is the way to go if you do much of this though.

[dicky96]

Are you sure that diagram is correct because you seem to have a coil between the positive and negative of the bridge rectifier via the connection where it says .14

That can not be correct as this would produce a DC short or near as damn it.

Seeing as you read .38 ohms so there is a bit of resistance somewhere which means passing current should warm something up, Assuming you have a variable bench power supply, connect it across the + and - of the bridge, set it to maximum voltage and set the current limit to 0A

Now start increasing the current to say 1 amp and feel around for something getting warm.  If nothing warms up turn the current up to 2A 3A whatever your supply will go to, and hopefully something will warm up by now.  There is your short. 

Rich

[OpenCircuit]

Vacuum desoldering gun is the way to go if you do much of this though.

Been gawking at this for a few weeks now, but I know what "cheap" gets "you": http://www.ebay.com/itm/331086297520?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

The spring loaded ones are too big for smaller pin configurations.

[james_s]

Hard to say with stuff like that, it might be ok, it might be junk, I'm leaning toward the latter. I have a Hakko 808 which is a wonderful piece of gear that I've been very happy with but it was not cheap. I suspect there are some reasonable copies of Hakko or Weller gear that might work ok for you and be more affordable for occasional use.

[dicky96]

@Opencircuit
If you refer to the example application circuit for CM8400 you will see the is a PWM controller and also a PFC controller

Look at the Voltage mode Circuit - The two most likely places you will find your short and around Q3/Q4 MosFETS in the PFC section of the power supply or around Q3 in the Switch mode section.  Confusing the application circuit shows two Q3s!  The one in the switch mode section is connected to Q6/Q7 via R28

The 1N5406 will almost definitely be D6 in the application circuit.  The fact that this diode was short circuit suggests your problem is/was short circuit Q3 in the switch mode section.  However the fact that you replaced the 1N5406 and you still see a short across the rectifier says the short must be on the anode side of D6 which suggests you have short circuit  Q3/Q4 in the PFC section.  You don't need to look further than the 1N5406 for now.  Hope that helps

[OpenCircuit]

Are you sure that diagram is correct because you seem to have a coil between the positive and negative of the bridge rectifier via the connection where it says .14

That can not be correct as this would produce a DC short or near as damn it.

Rich

Thanks Rich, I totally screwed up.    Fixed and updated the first post (also below).

Squiggly line is the inductor coil.

Yellow wire is a sensor wire that solders to the copper on the protective tape around the inductor coil. Unwrapped and verified this is not the short, BUT resistance is .22 across  Q2's D and S.

2 green dots are on a very small transformer. Resistance is .36 across these two dots which seems expected when the wire is simply wound around a magnet. However, From either green dot to the two question marks on the same small transformer I have .5~.8ohms.

Pulled Q3 and Q4 and they both bench tested fine with 12v. Used a small .2 amp fan.

Variable power supply in 12v, 5v and 3.3v  Considering  a cheap chinese one that you unplug when you leave the room.

When I plug PS into my 100w light bulb safety device the bulb glows like I have stuck a nail across the outlet terminals.

[dicky96]

So Q2 is short circuit D-S then, this will be a FET in the PFC section of the power supply.  Pull Q2 and check it for shorts

[tautech]

Vacuum desoldering gun is the way to go if you do much of this though.

Been gawking at this for a few weeks now, but I know what "cheap" gets "you": http://www.ebay.com/itm/331086297520?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

The spring loaded ones are too big for smaller pin configurations.

You would be surprised...........especially if you've never owned one.
Never had a component I couldn't remove with just a spring loaded sucker and a little bag of tricks when it isn't straight forward. Use mine on SMD too, just got to watch those littles ones. 

[dicky96]

Vacuum desoldering gun is the way to go if you do much of this though.

Been gawking at this for a few weeks now, but I know what "cheap" gets "you": http://www.ebay.com/itm/331086297520?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

The spring loaded ones are too big for smaller pin configurations.

I wouldn't be too sure of the usefulness of that desoldering pump as it is only 30W and that seems a bit low especially for PCBs with a heavy ground plane. 

There is this model that seems to be all over ebay http://www.ebay.co.uk/itm/100W-220V-S-993A-Electric-Vacuum-Desoldering-Pump-Solder-Sucker-Gun-350-c-450/111365837937?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D43782%26meid%3De54490e192124202bb0a3609f177155a%26pid%3D100005%26rk%3D3%26rkt%3D6%26sd%3D251640793299  which is 90W but I've never actually used one so couldn't say if it is actually useful or not.  When I used to work for ICL back in the 80s we had Pace desoldering stations which you activated with a foot pedal and they were great, even for 5 or more layer through hole boards we were working on at the time  I can't remember what model they were but think the base stations were blue in colour.

[OpenCircuit]

So Q2 is short circuit D-S then, this will be a FET in the PFC section of the power supply.  Pull Q2 and check it for shorts

Thanks for pointing me there. Another lesson for me....Short resolved.

[OpenCircuit]

You would be surprised...........especially if you've never owned one.
Never had a component I couldn't remove with just a spring loaded sucker and a little bag of tricks when it isn't straight forward. Use mine on SMD too, just got to watch those littles ones. 

I have  a few of them, but would sure like to get something better.

[tautech]

You would be surprised...........especially if you've never owned one.
Never had a component I couldn't remove with just a spring loaded sucker and a little bag of tricks when it isn't straight forward. Use mine on SMD too, just got to watch those littles ones. 

I have  a few of them, but would sure like to get something better.

I might be lucky that the cheap one I got yeeeeeears ago is better that many available these days so I've never felt the need to upgrade it or go to a desoldering iron.
I was advised waaaaay back to steer clear of them but that was in the day when the only units available were Pace and the like whose cost for consumables was excessive but things are different now.
There's threads that come up from time to time of what's available now and some look quite decent but remember that when you NEED something like this you want plenty of wattage for multi layer PCB's. A good 50W station will solder most things but for short dwell time in a desolder iron I'd be looking for much more than 50W.
As you are now past the hill on this repair you are in the position to watch and wait for good advice from those that know more than you and I about recent additions to the marketplace.

[OpenCircuit]

I got some life out of it...although I don't think it is charging the main cap. as it should. It sits around 160 until unplugged from the wall. Ordered some CM6800 and PS229 controller ICs a week ago per another user's suggestion.

[dicky96]

@opencircuit
Are you saying you now have 160V across the main electrolytic? Could you post a photo of the component side of the board  or mark where the 160V across the electrolytic on the track side of the board?

Also what do you measure across the +ve and -ve of the bridge rectifier?

What is the mains voltage in your location  110/220V?

Is your limiter light bulb now off, or dim?

Rich

[OpenCircuit]

@opencircuit
Are you saying you now have 160V across the main electrolytic? Could you post a photo of the component side of the board  or mark where the 160V across the electrolytic on the track side of the board?

Also what do you measure across the +ve and -ve of the bridge rectifier?

What is the mains voltage in your location  110/220V?

Is your limiter light bulb now off, or dim?

Rich

Yes; 160v at main electrolytic.

+ve and -ve: 160v

Mains: 120vAC

Limiter: Does not come on at all. With a normal good working power supply the bulb will start bright for a fraction of a second then go out quickly.

Image:



Q3: Drain connects directly to main cap + terminal. Gate is erratic  (image below). Source is .12

[james_s]

160V on the main electrolytic sounds perfectly normal.

[dicky96]

Yes 160V sounds correct if you are on 110V mains

What happens to the 160V when you disconnect the power?  Does it discharge quickly or slowly?

How were you taking those readings on Q3 gate? I'm not familiar with that type of chart, what does the vertical scale represent? Volts?

Do you have an oscilloscope and if so what type?

Cheers
Rich

[OpenCircuit]

Yes 160V sounds correct if you are on 110V mains

What happens to the 160V when you disconnect the power?  Does it discharge quickly or slowly?

How were you taking those readings on Q3 gate? I'm not familiar with that type of chart, what does the vertical scale represent? Volts?

Do you have an oscilloscope and if so what type?

Cheers
Rich

Right at 77ms AC was removed and discharge began (100ms interval):


Software that came with DMM: Y-axis is volts X-axis is milliseconds.

Do have a DSO138 (toy scope), but volts are limited to 50Vpk-max. DMM has Hz on it.

Thanks for the help everyone.

[OpenCircuit]

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