Electronics > Repair

Repairing Agilent E3631A Power Supply


Picked up Agilent E3631A Tripple O/P Power Supply fairly cheaply with display showing "Unreg" on 6V output ONLY.

1.Power supply passes initial power on test with NO errors recorded.
2. Actual output voltage and current range is within specs on ALL outputs.
2. On 6v output initial voltage calibration was out by about 20mv and current by about 35ma, easily re-calibrated.
3. ON +25V and -25V outputs all functions appear to be operating correctly.
4.Checked internal Bias supplies for 6v output and they are OK, very close to +15V and -15V.
5. +1.2V and -1.2V reference voltages are about 1.23V and about -1.23V  measured with HP 34401A multimeter that is fairly accurate. I am not sure if this ref. voltage should be closer to 1.2V??
6. Checked regulation on 6V output with Electronic load. Voltage regulation appears to be OK but there is no CV (constant voltage) displayed on the screen. Current limiting cuts out at constant 110% of limited preset across the whole 5A range. When current limiting cuts in display changes from "Unreg" to CC which is correct.

The only real problem appears to be current limiting on 6v output that is 10% over the preset limit.

Voltage regulation appears to be OK but no CV (constant voltage) displayed only "Unreg" (Unregulated)?

I would appreciate any advice from anyone that is familiar with operation and/or servicing/repairing of this type of power supply.


unreg fault : check the lm339 on the main board ( between heatsink and the gpib interface )

Thanks Guys,

Service manual that mianchen posted the link did not have the schematics, thanks anyway mainchen.

I did find service manual with full schematics at http://www.ko4bb.com/manuals/index.php?dir=HP_Agilent

U13 LM339 comparator checked out OK but the following U3 optocoupler (2211) has LED blown open circuit. U3 is the optocoupler in the CV line between U13 comparator and J3 pin 4 connector leading to micro controller input pin 5 (+6v CV sensing).

A very well designed power supply with full isolation.

In the end fairly easy repair and good value $275 for a fairly late model Agilent E3631A power supply.

Once again BIG THANKS to FREE ELECTRON (Agilent/Hp Guru).

Best Regards.

unreg problems are always situated around that comparator circuit. in your case the opto. only two conditions around these comparators are valid. any other logic combination give 'unreg' as the cpu can't make heads or tails of what is going on. if the supply behaves correctly but still shows unreg then the circuit is at fault. on the other hand if the regulator goes wonky then unreg is normal.

275 is a steal for this beast. they are tanks , have excellent regulation and are very reliable lab supplies. i got a 3632a on the operating table that has a defect in the regulator. haven't found it yet ... gonna start swapping chips blindly soon ... ( semi blindly .. i have an idea what it is but i ordered the 4 chips , i suspect one of em is bad but for 5$ i'm not going to spend 3 hours finding which one , just swap em all...


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