Author Topic: Rigol DS4000 power supply details?  (Read 901 times)

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Offline H.O

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Rigol DS4000 power supply details?
« on: August 29, 2017, 05:35:08 PM »
Yesterday my DS4000 died on me :-(
Cycling the hard power switch brings it back up in standby mode but as soon as I press the power button on the front it makes a clicking sound and just dies completely. (The clicking sounds like it does during a normal startup).

When in standby mode I measure 19V between the orange (GND) and the black (+19V) wires of the power supply but I haven't yet figured out what the other two thinner wires are for, if it's supposed to output anything here (it doesn't) or if it's feedback/control signals.

I've literally just spent 20 minutes opening it up and checking the obvious things so I'll continue digging but if some reverse engineering has already been done I'd appreciate the information.

Thanks!

 

Offline H.O

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Re: Rigol DS4000 power supply details?
« Reply #1 on: September 08, 2017, 05:19:50 AM »
Pulling this back up to the surface as I could really use some help from a fellow DS/MSO4000 owner.

I spoke to Rigol who said that my symptoms usually is the result of bad powersupply so I ordered a replacement from them which arrived today. I exchanged the old one and powered up the scope. This time it didn't say "click" it said "pop" - I could both see and smell the magic smoke and I could see roughly where it came from.  :-\

After inspection of the area I could not find any visible damage so I removed the main PCB in order to inspect the other side and the damage was pretty obvious. A dead short across one of the 47uF/35V tantalum capacitors for the "upper most" switch mode supply.



Since the power supply didn't shut down on overcurrent (at least not untill I pulled the plug (I was prepared)) it also took out the MOSFET (FDS4435A) that sits between the power input connector and the rest of the system so that's now shorted as well but I don't think it matter much for further trouble shooting, it will be replaced in the end though. I removed the damaged capacitor (actually all four), cleaned the PCB (it was pretty badly scorched under the shorted cap, I hope there wasn't any internal traces at that spot) and measured from V+ to GND, no more short so that's good.

The good thing with getting the new powersupply is that it had text silkscreened around the output connector so now I know that the there is only one output voltage (around 20V). So I tried powering the board up using a lab power supply set to 20V with a 3A current limit but the board just makes the characteristic hissing noise and lab supply goes into CC. I'm not sure I want to try raising the current limit further at this point.

So, finally, here's what I'd really appreciate some help with:
Is anyone willing to open up their DS4000 and do some basic measurements? There's no need to remove the main PCB just take the scope apart and remove the back metal shield case.



What I'd like to know is the resistance between GND and points (A), (B), (C) and (D) and - if possible - also the voltages at these respective points when the scope's running would be awsome.

EDIT: I've traced out a couple of the feedback networks and as far as I can see output (A) should be 5V and output (B) should be 3.3V.





 
« Last Edit: September 08, 2017, 06:39:06 AM by H.O »
 
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Online jjoonathan

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Re: Rigol DS4000 power supply details?
« Reply #2 on: September 08, 2017, 10:43:47 AM »
The 20V supply provides 5A once everything is powered up.

A=5V, B=3.3V, C=1.85V, D=1.05V

Good luck!

EDIT: by 5A I mean a few hundred mA under that. 5A would make a decent current limit.
« Last Edit: September 08, 2017, 11:00:05 AM by jjoonathan »
 
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Offline H.O

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Re: Rigol DS4000 power supply details?
« Reply #3 on: September 08, 2017, 07:09:48 PM »
Thank you!
That verifies my traced out part and knowing the normal current drawn from the PSU helps alot, I think I can comfortably increase the I-limit then.

I measure a quite solid 5.5ohm across the 3.3V rail, I wonder if that's correct.... Not that it's particularly low but it doesn't act as the usual "a lot of capacitance across the rail" measurement.

Found another strange thing: On the 5V regulator output, the "lower side" of two smaller ceramic caps (values are 10n and 100n) right next to current sense resistor seems to floating. While on the other three rails all three ceramic caps seems to be parallel across the rail.

 

Online jjoonathan

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Re: Rigol DS4000 power supply details?
« Reply #4 on: September 09, 2017, 08:01:02 AM »
I'm not near my scope at the moment, but I'll be returning on Sunday. Let me know if there's another measurement you'd like me to take.
 

Offline H.O

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Re: Rigol DS4000 power supply details?
« Reply #5 on: September 10, 2017, 01:32:10 AM »
I temporarily replaced both tantalums with electrolytics, set the lab supply to 5A I-limit and the scope now appears to start up. This is still with the main PCB on the bench, no front panel or display so not entierly sure but it does do the its normal clicking and beeping.

The shorted P-channel MOSFET on the input got really hot (like smoking hot) so it's apparently not "shorted enough" but I had enough time to check the voltages at the four main rails and they're all fine.

I'll order the proper capacitor and MOSFET hoping this will fix it.
 

Offline H.O

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Re: Rigol DS4000 power supply details?
« Reply #6 on: September 14, 2017, 04:29:46 AM »
IT'S ALIVE  :-+

I replaced the two tantalum capacitors with some KEMET KO-CAP series 47uF/35V polymer caps and fitted a new FDS4435 P-channel MOSFET and powered it up using the lab supply without any noticable issues. While I was in there I mounted some small heatsinks on the ADCs and replaced the multifunction encoder with a detented one. Put Everything back together only discover the washers and nuts for the BNC-jacks still lying on the bench  :palm:

While waiting for the parts I've "enjoyed" myself figuring out part of the power supply section in this scope, the standby voltage, power switch and a few other details that might be useful for me, or one of you, in the future. Please note that I make no promises as to the correctness of it all.
« Last Edit: September 14, 2017, 05:37:30 AM by H.O »
 
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Offline glarsson

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Re: Rigol DS4000 power supply details?
« Reply #7 on: September 14, 2017, 05:17:34 AM »
The PDF file is 0 bytes long.
 

Offline H.O

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Re: Rigol DS4000 power supply details?
« Reply #8 on: September 14, 2017, 05:40:53 AM »
Weird, re-uploaded and now it seems fine. Thanks for bringing it up!
 

Offline glarsson

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Re: Rigol DS4000 power supply details?
« Reply #9 on: September 14, 2017, 05:49:35 AM »
Thank you. Filed away for, hopefully NOT, future use.
 

Online jjoonathan

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Re: Rigol DS4000 power supply details?
« Reply #10 on: September 14, 2017, 08:16:04 AM »
Congrats! Special thanks for that writeup, too.

> Put Everything back together only discover the washers and nuts for the BNC-jacks still lying on the bench

You and me both.
 


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