HP E3632A unreg operation

[gossamer]

I have a strange problem with the PSU. On both ranges 15v and 30v, if I set the voltage to above 7.2V and whatever load, CV and CC are working fine. (I left the PSU for an hour with 4A load on 10V.)
As soon as I set voltage bellow 7.2ish V (current limit has no influence, it can be open circuit), both current and voltage drops to 0 and PSU goes into Unreg mode. I dont see OVP or OVC being tripped.
If I change voltage to 8 or 9 Volts after it drops to 0 it start regulating again.

OVP and OVC are working fine, at least on the higher than 8v range.. So in a way it is perfectly fine PSU as long as I need more then 7.5V   

Any idea where to start poking ?

Thanks

[Chris56000]

Hi!

Service Manual:–

https://www.google.com/url?sa=t&source=web&rct=j&url=https://doc.xdevs.com/doc/HP_Agilent_Keysight/E3632A/pdf/E3632_service_sch.pdf&ved=2ahUKEwiz4eS538_oAhUEilwKHfn6A20QFjAAegQIBBAB&usg=AOvVaw3bFGOvaj-n59JEEear8GEj

Are you getting the permanent first stage low voltage d.c. from rectifier CR11 fed off taps P9 and P10 of the mains transformer?

This power supply uses an automatic tap–changing arrangement whereby the appropriate unregulated d.c. is selected by the microcontroller on the main board by comparing the regulated d.c. with preset reference voltages, then when the regulated d.c. reaches certain thresholds, the next transformer tap is automatically switched into circuit by pairs of switched thyristors!

Your symptoms sound like the unregulated d.c. input from CR11 is low or missing, so begin with a check on CR11 and the connections to P9 & P10 of the mains transformer!

To check, simply disconnect transformer leads P7 and P8 from the main PCB and see if the PSU produces any output – you'll only get o/p up to the first stage tap changeover point but it'll prove easily and quickly if CR11 is providing power or not!

Chris Williams

[gossamer]

Thanks Chris.

Disconnecting P7 and P8, I measured -0.5V across pin1 and pin4 of CR11, AC across P7-P8 is 11V.

[Chris56000]

Hi!

Remove and test CR11, if you're not sure then a DMM will do, as follows:–

a) Connect the BLACK lead of your DMM to the (+) terminal on the rectifier CR11, then switch the DMM to "diode–test" mode (marked with an arrow symbol), then touch the RED lead on the other legs, you should get a short "beep" and a reading of 0.5 to 0.6 on TWO other rectifier leads, they will be marked "AC" or a squiggle;

b) Now transfer your RED DMM lead to the (–) terminal of the rectifier, and touch the BLACK lead of the DMM on the other three leads, again expect a short beep and a reading of 0.5 to 0.6 with TWO of the other leads only!

No beep at all or a continuous beep and a zero reading when you connect the DMM leads as explained above means the rectifier unit is u/s,  bin it and get a new one, the type no. Is on the circuit diagram!

If the rectifier passes tests a) and b) above test ACROSS P8 and P9 from the transformer, this time you should get a continuous beep and a very low reading, less than 0.1, on your DMM.

No reading between P8 and P9 indicates faulty wiring or the transformer secondary feeding P8/P9 and CR11 is defective!

Since you said the power supply works and gives an output above a certain setting and the display is ok, I think I can rule out a dead short across CR11's output for the moment, as a short across CR11 would almost certainly have blown a fuse!

Chris Williams
 

[gossamer]

Right, so CR11 seems to be OK as both tests passed. Reading between + and - DC gives 0.8. Reading between AC pins is OL.

Can I just say that lifting that CR11 was absolute torture   
Not that C36 in front of it was a breeze..

Secondary winding seems to be OK as well as resistance is 0.1ish   between any of the Px-Py wires. (7-10).