Repairing Agilent E3632A Power Supply - UNREG Mode

[amexlive]

Hello, everyone,
and I have a similar problem with Agilent E3632A.

The problem is the following - The power supply has two levers up to 15V/7A or 30V/4A
and I noticed the power supply work not properly.
At 15V/7A I have connected LED Stripe and up to 7 volts there is no change, at 8V it going to the UNREG mode and more than 9V can not give.

At 30V/4A I connected an electric motor (the motor work at 24V) and as you can see in the video I have been upload here since I can turn the digital potentiometer there is no change and suddenly the 16V and more of 25V can not lift.

https://youtu.be/jGSGJWt8Si4


https://youtu.be/m1bI8MULyNY

Now I see when I connect a multimeter at the output of the power supply that up to 7 volts there is no voltage, at 8 volts and 9 volts there is, at 10 volts the meter shows 9 Volts but it can be seen how the LED pulsates.

https://youtu.be/RcACKvTSEXI

Any ideas?

Sorry in advance for my not good English and thanks for understandning.

[Armadillo]

The symptom looks like you are in a constant current mode.

Edit: Press "Display Limit button" and Check what voltage limit you have set.

[floobydust]

I would look at the power section to see if it is damaged, leaving a weak power supply.

Check if the pass-transistors are damaged. This is MOSFET Q4, Q3 IRFP044 on the heatsink. With a steady DC load, voltage drop across R11, R17 should be equal if they are correctly sharing current.

The DC bus voltage (at R34, big C65/C46/C36) I would also check if it is not collapsing under load. The PSU uses SCR's to autorange and select hi/lo transformer winding, I think.
The E3634A had a bridge-rectifier fail: https://www.eevblog.com/forum/repair/agilent-e3634a-power-supply-teardown-repair/

[amexlive]

I check the Display Limit button
When I press it on the display showing:

00.000V   7.000A and I can edit it with Ajustment to the 15.000V and 0.000A

but when I wait and  the blinking limit symbol disappear on the display stay:

-0,356V   0.057A with UNREG symbol

[Armadillo]

Can you adjust display limits to 15.000V and 7.000A ?
I trust you know how to do it. 

[amexlive]

Hi floobydust

I check the MOSFET Q3, Q4 R11 and R17 and the voltage are the same and look like ok - what I mean: the power supply accept only 8V and 9V by mode 15V 7A

The power supply when I receive it (second hand) was working ok but it was so dirty. I open it to clean it and when I assebly it the problem come. I change only the filter capacitors C91, C92, C93 with new one original of RIFA.
This faulty is interesting and mistake for me.

[amexlive]

Hi Armadillo
Yes I can adjust display limits to 15.000V and 7.000A but the output voltage is only 9V and when I ajust it the 7V the output voltage down slow to 0V (capacitivy)

[Armadillo]

Can you hook up a resistance of above 1K and try again.
What load was you using by the way.

[amexlive]

Hi Armadillo
I try with 910 Ohm resistor and the result is the same. As load I use LED Stripe and DC Motor

[amexlive]

[THE PROBLEM IS FIXED]

THANK YOU GUYS FOR THE HELP!

I make some measurement and see that P9 and P10 between the transformer and bridge-rectifier have not connectivity. I check it and the problem was that the cable terminal was broken. I change the cable terminal with new one and now all is perfect!

Thank you again for the help!