Author Topic: DSO-X 3024A Power Supply defect  (Read 7806 times)

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Offline georges80

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Re: DSO-X 3024A Power Supply defect
« Reply #50 on: February 16, 2021, 07:07:59 pm »
It's mostly self evident once you have the scope opened up and remove the dead PS. There's a few wires/connections.

Mains input, Front panel low voltage on/off control,  +12/0V main DC power and sense wires. If you are competent enough to use the scope then you can handle the re-wiring :)

Most of the work is getting the new supply to fit nicely (with the re-wiring) into the rather cramped space. Take your time.

cheers,
george.
 

Offline gman76

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Re: DSO-X 3024A Power Supply defect
« Reply #51 on: February 22, 2021, 11:37:34 pm »
Hi georges80, I'm buying the RPSG-160-12.  I took the original supply out and looked at the CCH125 pinouts. Everything looks obvious except the pin called REMOTE on the 1x6 header.  There are 3 wires coming from the main board into the CCH125, -S +S and REMOTE.

On the RPSG-160, I see two possibilities: PG and PS/ON.  I think its the PS/ON that I need to connect the REMOTE wire to, correct?  The pin called PG looks like an output.  If this is the case, then I'll need to remove the 3 wires from the orig connector and place the two sense wires in a new housing and the REMOTE wire into another housing since the RPSG has these split into two connectors.

 
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Offline 2N3055

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Re: DSO-X 3024A Power Supply defect
« Reply #52 on: February 22, 2021, 11:54:09 pm »
Hi georges80, I'm buying the RPSG-160-12.  I took the original supply out and looked at the CCH125 pinouts. Everything looks obvious except the pin called REMOTE on the 1x6 header.  There are 3 wires coming from the main board into the CCH125, -S +S and REMOTE.

On the RPSG-160, I see two possibilities: PG and PS/ON.  I think its the PS/ON that I need to connect the REMOTE wire to, correct?  The pin called PG looks like an output.  If this is the case, then I'll need to remove the 3 wires from the orig connector and place the two sense wires in a new housing and the REMOTE wire into another housing since the RPSG has these split into two connectors.

PG is power good output. Remote is ON/OFF..
 

Offline rolkinas

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Re: DSO-X 3024A Power Supply defect
« Reply #53 on: February 25, 2021, 03:08:01 pm »
Regarding original PSU.
I experimented with higher value resistors in place of cooking 4pcs 22K. AC voltage controlled by variac. Resistor values and coresponding psu start stop voltages below:

220k - start 80Vac , stop 75Vac
310k - start 98Vac , stop 75Vac
440k - start 135Vac , stop 75Vac
660k - start 190Vac , stop 75Vac
750k - start 217Vac , stop 75Vac

When psu starts, voltage drop on resistors becomes near 380V because PFC starts as well.
turn off voltage is determined by PFC

Even with 220k resistor stayed at about 70 degree C what is much more usable {hint to 110Vac grid fellas :) }
 
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Offline gman76

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Re: DSO-X 3024A Power Supply defect
« Reply #54 on: March 01, 2021, 08:19:44 pm »
Received the Meanwell RSPG160 supply, expanded holes to get the screw holes lined up, re-arranged wiring on connector.  Plugged it into 120VAC, not sure if it would go bang, but quietly powered up.  Scope is now back up and running.

Worked fine at 12.0V., but adjusted Vout up to 12.6V. 

The only issue now is that the front power button doesn't work.  I probed the REMOTE signal (PS/ON) and it's always low.  Pushing the power switch doesn't change the DMM reading, just slightly.  Maybe need a GND return?  Or is this the wrong signal?

EDIT:  It was indeed the ground connection of the 1x4 header (CN901).  I made a wire with a crimp on each end.  Front power button works great.
« Last Edit: March 08, 2021, 11:02:04 pm by gman76 »
 
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Offline tapelu

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Re: DSO-X 3024A Power Supply defect
« Reply #55 on: March 15, 2021, 10:09:13 am »
I'm liking the fact that the Murata unit is higher efficiency and most importantly does not have a perpendicular daughter board, like the meanwells. This should make the murata unit easier to repair, but then again, none of these units should need any attention for a long time.

The Murata PQC250-12 works just fine with three DSOX3014As that I've repaired - the oldest repair has had close to 1 year of constant use with no issues so far.

Like with other units, the wiring harness needs to be modified to make it work but it does offer remote sense as well as remote on/off (possibly with inverted logic, but the button will still work.)

I must also admit that I'm biased - I work at the Murata power supply design center where the PQC250-12 was designed and qualified.

Hi, how do I have to modify the wiring harness so that the power supply starts with the power switch? If I connect pin 1 to pin 8, the oscilloscope starts directly, but I want the power switch to be able to be used?

:-DD
 

Offline Madmanguruman

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Re: DSO-X 3024A Power Supply defect
« Reply #56 on: March 16, 2021, 12:50:44 am »
I'll share my reverse-engineering below.

The pinout of the Molex header (on the DSO-X side) is as follows:



1: +12V
2: +12V
3: +12V
4: +12V return
5: +12V return
6: +12V return
7: Return sense
8: +12V sense
9: Remote on/off

For the PQC250-12:

- Run 3 wires from the DSO-X Molex header pins 1-2-3 to +12V (any of J2 pins 1-6)
- Run 2 wires from the DSO-X Molex header pins 4-5 to +12V return (any of J2 pins 7-12)
- Run 1 wire from the DSO-X Molex header pin 6 to J3 pin 8 - this is the return for the remote on/off signal
- Run 1 wire from the DSO-X Molex header pin 7 to J3 pin 6 - this is the low-side remote sense
- Run 1 wire from the DSO-X Molex header pin 8 to J3 pin 5 - this is the high-side remote sense
- Run 1 wire from the DSO-X Molex header pin 9 to J3 pin 4 - this is the remote on/off signal
- The AC cable assembly will plug in directly without modifications.



Because the PQC250-12 is open-frame I usually put a thin insulating sheet behind the wiring harnesses / in front of the power supply.



Three DSOs with PQC250-12 are deployed in my lab, and all have passed their annual traceable calibration tests (done by an external accredited laboratory).

(Depending on the remote enable logic, you may find that the pushbutton is reversed: in=off, out=on - this can be changed via a few resistor pops/no-pops but why bother?)
 
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Offline tapelu

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Re: DSO-X 3024A Power Supply defect
« Reply #57 on: March 16, 2021, 06:02:32 am »
 :-+
Perfect ! Many, many thanks for your effort !
 

Offline ketch

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Re: DSO-X 3024A Power Supply defect
« Reply #58 on: April 21, 2021, 08:26:21 am »
Hello. I need to know the value of the resistor from the photo.
 


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