Electronics > Repair
HP E3615A power supply slow ramp up
<< < (7/7)
pqass:

--- Quote from: gaminn on September 27, 2024, 11:10:25 am ---Something is wrong with R62, R82 or the connections around R62, R82.

--- End quote ---

Check the traces (for micro fractures) and re-flow solder (or attach bodge-wire) from R62,R82 to the points where you connected to your external circuit.  Scratch the solder mask to get to the bare copper.  My E3611A has some sketchy looking traces; looks like corrosion where they meet the pads.   

What a bugger!
gaminn:
I further isolated the problem. I got rid off my external voltage control circuit, now the original voltage control circuit on the power supply's PCB is connected. When the midpoint between R62, R82 and R88 (I consider it midpoint even though there is also S2 switch between R88 and R62,R82) is on the pcb, then there is the ramp up. When I make the midpoint outside of the pcb, then there is no ramp up.

Now it is simple - connect the yellow alligator clip (it connects the midpoint to the PCB) - there is the ramp up. Disconnect the yellow alligator clip - there is no ramp up.

Now, what is the issue with the traces? The midpoint goes also via S2 and is connected to A12 (A3) and A13 (A4) terminals.

EDIT: I noticed I can further isolate the issue by switching S2 to the other position (switching it off). Now when the midpoint created by me outside of the PCB is connected to the side of the S2 switch that goes to R88, CR27, C37, then there is the ramp up. When the midpoint is connected to the other of S2 that goes to R82, R62, C29, there is no ramp up.

EDIT2: Now I have the solution to solve the ramp up issue of the power supply by making the midpoint outside of the pcb (I don't use switches and terminals on the back of the unit). But still I would like to know what causes the issue. However, now I don't know how to find the cause other than cutting physical pcb trace between R88 and S2 in half and isolating the issue further. Visually, the trace looks ok everywhere to me.
gaminn:
I noticed R88, CR27, C37 trace should go to A12 (A3) and A13 (A4) terminals on the back of the unit according to the service manual pdf, but on my pcb it goes to A10 (A2), A12 (A4) and A13 (A5) terminals. Hopefully that's the only difference, at least I don't see the trace goes anywhere else, potentially to the point that can cause all the trouble.
gaminn:
The power supply works now but I'm not very confident it won't break again. I know that the problem with the ramp up was the midpoint (R62, R82, R88, S2) - when it was connected to the PCB trace between S2 and Ax terminals there was the ramp up, when the midpoint wasn't connected to that place, there wasn't the ramp up. For this purpose I cut the midpoint trace (R62,R82 to S2 and S2 to R88) at many points to localize the part that causes the issue. Then I started to "repair" the cut trace and unfortunately I finished with fully repaired trace connected to the midpoint without any ramp up. No idea what happened...

When I put the power supply together I noticed CC works only when I moved front panel or touched the cables inside the power supply) and that there is poor load regulation in CV mode, ripple of almost 50 mV, etc. I touched all cable connections with soldering iron, desoldered and again soldered S2 switch. Don't know what happened but when I put the power supply together for the second time, it worked.

Next time I will throw the power supply away immediatelly and will buy another one...
pqass:
I'm glad it worked out in the end.
I hope it was at least a learning opportunity in power supply design, failure analysis and troubleshooting.
It's sad that the trend has been toward less durable, un-repairable, and disposable products.
I understand that time has value but rather than throwing things away, consider selling or giving them away when there's still significant value remaining.
Navigation
Message Index
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod