Rigol DP832 Random Reboots

[bd139]

Slightly glad I didn’t buy one now. Historically speaking I had an issue with some Farnell supplies at university years ago. They were weak so if there was a power glitch the output cap would discharge across the pass transistor and blow it up. On powerup full unregulated DC would hit the DUT. To work around this we used a fat 5W Zener across and a fuse in series with the power supply.

Shouldn’t have to worry about this in 2018 

[TurboTom]

I've got some issues with a DP811 (20V/10A or 40V/5A single output unit) also rebooting all by itself once in a while. It's working stand-alone, no LAN or USB connection so the behaviour shouldn't be induced externally. I recently updated it to the 01.16 beta firmware but it didn't make any difference regarding the reboot issue. Yet, it affected the 10s digit of the preset current display as not being able to properly display "0" -- the leftmost two vertical segments are clipped (btw, stupid idea to imitate a seven segment display on a graphic screen anyway...). So I'll probably return back to F/W 01.14 on that instrument. I'm curious if anyone will be able to find out what's actually causing the reboots on the DP800 series. A machine that's doing this all the time should be a good condidate for a fix. My one so far is only rebooting once every odd day or so...

[Smokey]

Since I bought the supply from the rigol clearance, it only had a 90 day warranty.  I would still be under the 3 year mfg warranty though.  They want $250usd eval to fix it.  I pushed back a bit since this reboot thing appears to be some sort of design problem. 

[Commodore8888]

Bit of a necro here, but I had the 832 out for some "upgrades" (namely changing to an 832A via the SCPI command), and saw this thread while digging around.

Figured I should add the data point that I too had an 832 from circa mid 2016 (post regulator "fix") that encountered random reboots. It had been sitting idle for about 5mo on a shelf. I was lucky to get even 20s out of it, sometimes it would just sit in a boot loop.

FWIW, it did seem to be somewhat temperature dependent. I sent the unit in for warranty repair
in late 2017 and it came back fine (knock on wood). All the service sheet said was "replaced control board".

[Smokey]

Ya, I should have followed up.  They ended up giving me a little break on the repair cost.

Before I sent my unit in it was pretty much in a constant reboot loop on my bench.  They claimed that they could not reproduce the problem, which is very odd considering it was 100% nonfunctional when I sent it.  Only thing I could figure was shipping knocked something back into place maybe?
Anyway I asked if they new exactly what the problem was with these "reboot" failures and he didn't tell me anything other than when they get one they just replace the whole control board, like Commodore8888 said.  All of my options were reset, so that does make sense.

It's been running fine since then.

[T2]

Hi there,

I know this thread is quite old.

Myself, I'm looking at a dp832 that has "developed" this reboot issue over time.
My Rigol has the v2.10 (2013-03-26) top board (with the large heat sink).

- the digital load seems quite "dynamic", the current comsumption is not stable but "jumps around"
- using an external 5V power source for the digital supply just intensivies the problem (Minutes instead of hours/days)
  -> longer cables, higher impedance

- Measuring the voltage with an oscilloscope (AC coupled) shows sporadic, rather high spikes/bursts
- >1.2Vpp (measured with the built-in 5V supply) !!

This leads me to believe that instabilities/noise on the 5V rail may be culpable for the spontaneous reset/reboots fo the DP832.
My next palnned steps are to dismantle the logic board (front board) and look there closer.
- Caps going bad?
- Insufficient decoupling close to the MCU or reset logic?


/Thomas

[T2]

Dug further down. Some of my previsouly observed 5V spikes may have been coupled in by my measurement setup.

The digital front board seems to be really a finicky thingie. I came across an 1117 linear regulator (5V in, 3.8V out, labeled "Battery") that basically 1:1 passed the input ripple from the 5V line to the output. With a maximum drop-out voltage of (according to datasheet) 1.1 to 1.3V, this seems a bit on the close side (5V supply has around 5.2V, so deltaV is 1.4V). There are 3 ceramic output caps present (see schematic fragment) but I don't trust them.

The other supply voltages (3.3V, 1.8V, etc) look more or less OK but have quite some digital noise on them.

I added an input (22u, yeah I rounded up) and an output cap (100u) to the 3.8V regulator as the datasheet sugegsts. The output voltage then became rather stable, not passing on any ripple from input. Check the pictures for my hack.

I also noted that the CPU gets rather hot (you wouldn't let your finger there for long time), so I put a small heatsink on.

Now starts the waiting part...






EDIT: Still rebooting. Need to look further.

[T2]

Hi there,

I think I finally fixed it. My DP832 is now running without reboot for more than 24h.

If you have a Rigol DP832 with a DigitalBoard V02.00 2012-12-07 (front-side board with MCU)
and your Rigol is not doing sporadic reboots you may just be lucky.

TopBoard: v2.10 (large heat-sink for 5V regulator)
DigitalBoard V02.00

My DP832 started to develop the sporadic reboots over time, from once a month to about once a
day to multiple times a day by now. Let's face it - unusable as a bench supply. And yes, my DP832
is running 24x7 - but that's something you'd expect from a bench-supply.
Some days ago I dismantled my Rigol and started poking around on the digital board.

To summarize, aside from the linear 5V regulator/toaster on the top board that we all know about,
I identified 2 issues while checking the voltage rails on the digital front board.


The "Battery" rail:
The AC noise from the 5V rail was passed straight through to the output of the regulator (1117 ADJ).
I added input and output caps (although there are some ceramic caps on the output side, but I
don't trust them). Also the deltaV (Vin-Vout) was very close to the dropout voltage. My guess is that
this is the main reason for the ripple being passed straight through (the regulator was not regulating
anymore).

Studying the iMX28 (Application processor / MCU) datasheet a bit, shows, that this beast
is designed to be powered from two power sources. A 5V source as well as a Li-ion battery
source (3.1 ... 4.2V). The MCU automatically switches between those sources.


The "VDD4P2" rail:
This is an intermediate power rail (4.2V) from the MCUs integrated switching supply. I did
measure a *sh%@tload* of switching ripple (>2Vpp) on this rail. According to the reference
schematic for the iMX28, there *must* be a handful of decoupling caps installed on this rail.
However, by just quickly probing around I could not find any serious caps (just one tiny 0402 cap)
on the Rigol board (I don't say there are no caps, just say that I did not find any - hard to tell
for sure  without schematic). Luckily this rail is accessible from the back side of the board, no
need to disassemble the front.
I added some caps (ceramic and electrolyte) to this rail and the switching noise got *way* better.

I'm still measuring up to 400mVpp switching noise, but stability has improved massively.
Before this modification, with the voltage reduced to 4.9V on the 5V rail, I got multiple reboots
per minute. After adding the caps it just kept running. No reboots observed. :-)

So my guess is: fix #2 is actually the one that cures the spontaneous reboots. Problem #1
probably has no direct impact on that (depends maybe when/if the MCU actually takes
the power feed from the "Battery" rail - if at all).


A lower voltage an the 5V rail causes the reboots to happen faster / more frequent.
My guess is: lower voltage -> higher currents (switching supply in the iMX28) -> more switching ripple on 4P2 rail
-> at some point the MCU resets (likely the built-in reset circuit or brown-out detection triggers)

This could even explain why it happens more frequent on devices with the small heat-sink (old top board).
If the LM317 starts to cut back due to thermal conditions -> lower voltage -> higher probability for reboot

Note: This VDD4P2 rail issue might me systematic! A cross check with a properly working (no reboots)
DP832 of a friend (same DigitalBoard rev) did show massive ripple of close to 2Vpp on this rail as well.



To summarize my modifications:
1) I modified the 1117 "Battery" voltage regulator circuit to deliver 3.5V
(instead of the 3.8V) to get some voltage margin (dropout voltage 1.25V!)
and avoid issues there. I also added input (10uF) and output (100uF) caps.
]

To adjust the voltage, I put a 4k7 resistor in parallel to the existing 680E
(going to ground). Yeah, ugly...


2) Add a handful of decoupling caps to the VDD4P2 rail
10nF // 100nF // 1uF // 47uF
The VDD4P2 is on the cathode side of the fat shottky diode on the back side of the board.

I scraped away some solder-mask on a ground-plane and botched in a handful of caps.



Fragment of the reference schematics:


I'm quite sure that modification 2 alone will fix this issue, but I didn't bother to undo my other modification.

I hope this will help some Rigol DP832 owners to get their device working properly again!

/Thomas

Update: Running for one week now, without issues.

[_Wim_]

Hi there,

I think I finally fixed it. My DP832 is now running without reboot for more than 24h.

Great work! I do not experience the reboots (yet?) of both of my DP832s, but it is good to know there is a solution when it happens. How old is your DP832? I wonder if this problem is related to a certain batch of instruments...

[Smokey]

Great job! 

Who is going to be the brave soul that tries to simulate the conditions on a perfectly functional supply to see if it starts rebooting?

[T2]

Hi there,

I think I finally fixed it. My DP832 is now running without reboot for more than 24h.

Great work! I do not experience the reboots (yet?) of both of my DP832s, but it is good to know there is a solution when it happens. How old is your DP832? I wonder if this problem is related to a certain batch of instruments...

I bought my DP832 in Sept 2014. It already had the Rev 2.1 TobBoard with the large heatsink. FrontBoard is V2.0 (with a 2012-12 revision date).

By the way, still running without issue (48h now).

[T2]

Just a heads up: My DP832 is not running for 2 months with this fix and has not experienced any issue (= reboot) since.
This modification definitively fixes the reboot issue.

/Thomas

[cgz2001]

All,

I came into possession of one of these units this week which has the constant reboot symptom described above.  The unit never manages to stay up longer than a few seconds, if that.  I intend on performing a modification to 4p2 V rail on the unit as T2 has described.  For reference this unit has the silver heatsink.  Screenshots below are documenting the performance on the LM317T regulator input and output as well as 4.2 V rail.

Once I perform the modification I'll advise on the performance, hopefully with screenshots.

[frank.van.dinteren@home.n]

This fixed the reboot (resetting the output to off, not a whole machine reboot)  issue for me as wel. Have mine DP832A  since mid-2014. Started having random reboots a few years ago (once every few days). It would never stay up for a whole weekend and now it's already is running for 2 weeks.

Thanks.
 

[cgz2001]

All,

Adding ceramic class 1 and class 2 capacitors as alluded to above seems to have solved the problem on my unit.  I will advise if it eventually fails.

[chrisrossx]

My DP320 (Board Rev 02.20) started randomly rebooting a few months ago, once every 10 minutes or so... Today, it was rebooting every 5 seconds or so.

I took the cover off, to poke around, and I couldn't replicate the problem.  I buttoned everything back up, and it's been on for over an hour.  The only thing I can think of is that I did stress the wires on the top board trying to take it apart.  However, I did not try and reseat any of the connectors...

Not a solution, but it did stop my issue...

[blurpy]

Jerry Walker has a series of videos where he troubleshoots and fixes his rebooting DP832:



I found it very interesting, even though I don't have that device myself.

[T2]

Part 3 of this video series points out exacly what my conclision was, just *much* better explained than I could.

[TurboTom]

I just installed a 220µF/25V Rubycon ZL low impedance electrolytic across the troublesome 4.2V rail (because I had those handy) and verified that the noise on that rail dropped by at least a factor of five (from close to 2Vpp to  ~400mVpp). I used existing pads for this and tacked the caps with a drop of glue to the PCB. No reboot problems after that anymore...

[baldengineer]

I did both the LM1117 voltage mod and added additional decoupling caps. In my case, I used a combination of polymers and MLCCs. After 48 hours, my DP830 has stopped the reboots.

Thanks for taking the time to diagnose and document your fix.

Not my favorite soldering job, but it works.

[hcoverlambda]

I only added the 47µF cap and that fixed it for me. Was restarting a few times p/m. Thx to everyone who dug into this!

[BTBlueSkies]

Ha! you guys should rule the world, I would vote for you.

Thanks so much for this thread and the info, it worked for me. Here is a post showing my old man solution of hot gluing the caps in a stack and then, after gluing em down so they don't move, I could solder them into place quite easily since they didn't dance around any more.

Thanks again.