Emerson AA27020L Failures

[mwarchut]

Hello

I have 15 failed power supplies, all Emerson AA27020L units. At $400 a pop to replace they are starting to get a bit expensive. These all failed in the last 6 months so I am starting to think there is some common failure with them. Does anyone have any info on them and why they fail so I can take a shot at repairing them. I haven't seen much on the net about them but I suspect someone somewhere knows something about their secrets..


TIA

Mike

[stj]

Re: Emerson AA27020L Failures

post foto's & stuff - upload them here, no linking to other sites!

[mwarchut]

Re: Emerson AA27020L Failures

Sure thing.. I can take some thorough photos and upload them. I have good and bad psu's does it matter if I take a pic of a bad one or a good one? I opened a bad one and don't see any apparent issues visually.

[stj]

Re: Emerson AA27020L Failures

bad ones please

[mwarchut]

Re: Emerson AA27020L Failures

Pics below of 4 different units.... Let me know if I missed anything.. Or if you need a 4K picture of one view.

[cpt.charlie]

Re: Emerson AA27020L Failures

Do you have a proper voltage at the stand by rail (5Vsb)? what is the voltage at the main cap (the big cap at the primary)?

[PeteS in CA]

Re: Emerson AA27020L Failures

Adding a little to c.c's post above, it should be OK to power those on with no load. Look for the 12VSB pin and see if you have the standby voltage. That's a server PSU, of a type with a 12V standby voltage. I think the pin will be a single "finger", on the side opposite from the label. Also, look at the voltages on the other single pins, as you might see internal 5V or 3.3V housekeeping voltages. The chassis will be ground.

Then, as c.c said, check the voltage across the big 450V rated electrolytic capacitor. If the PFC is working, the voltage should be around 400V. If the PFC is not working and your input voltage is 120VAC, then the voltage across that capacitor will be around 165V. Make this measurement carefully, as that is on the primary side. You do not want to short anything to the chassis, and you want to be careful for the sake of your safety.

So, the first things all this checks are the Standby circuit and the PFC. If the PFC doesn't work, everything after it will be shut down. If the Standby circuit isn't operating, nothing will, as that provides the primary and secondary housekeeping voltages necessary to operate everything in the PSU.

BTW, do pictures of just one PSU. Doing four at once just makes everything smaller, resolution for each PSU is worse, and the lighting is not optimized for any one PSU.

[mwarchut]

Re: Emerson AA27020L Failures

Sorry for the long delay. Personal issues got in the way of this project. So I finally got to look at these. The voltage at the big cap was 65V on both leads. I opened up a good PSU and found 65V on one lead and almost 0V on the other lead. Not quite sure what that means.

When I plug in the good psu it makes a single click like a relay. The bad units do not. I will look at these a bit more closely today based on the additional data from PeteS as I had not seen the update until now. Thanks.

[mwarchut]

Re: Emerson AA27020L Failures

I found a bunch of marked pins that said 12v. They all came up almost 0. Anything else I should look for? Looking for any and all suggestions.

Thanks

[mwarchut]

Re: Emerson AA27020L Failures

So scratch everything previously posted. I found out that the old meter I bought like 15 years ago had finally given up the ghost. I went out and bought a new fluke. And now I have more accurate measurements.

Across the biggest cap the voltage is 160.1 On a good psu it's coming up as 392.6.

[PeteS in CA]

Re: Emerson AA27020L Failures

OK, your PFC is not working. Now try what I suggested above:

Look for the 12VSB pin and see if you have the standby voltage. That's a server PSU, of a type with a 12V standby voltage. I think the pin will be a single "finger", on the side opposite from the label. Also, look at the voltages on the other single pins, as you might see internal 5V or 3.3V housekeeping voltages. The chassis will be ground.

If you don't have 12VSB, your problem is probably in that regulator circuit (it also supplies internal housekeeping voltages, without which the PFC cannot work). If you have 12VSB but no internal housekeeping voltages, something is wrong on a control board, and that is keeping the PFC shut down. If you have 12VSB and the logic level housekeeping voltages, the problem is in the PFC circuit.