Author Topic: EEVblog #512 - Rigol DP832 Bad Design Investigation  (Read 260361 times)

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Offline ddavidebor

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EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #100 on: August 30, 2013, 12:44:50 pm »
Hi,
I have just buy DP832A ,
will have the same problem?
 :palm:

Power it up and power all the channel.

Then go to drink a coffe, if you return and the channel had became all off, it has resetted.
Davide Bortolami,
Fermium LABS srl
 

Offline salviador

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #101 on: August 30, 2013, 12:51:52 pm »
ok, i test it.
how many minutes should I wait?
 

Offline RupertGo

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #102 on: August 30, 2013, 12:57:14 pm »
It's surprisingly common - or used to be, anyway - to find overstressed and under=cooled regulator or switching devices in production equipment. I sometimes wonder if some of those designers even understand what makes their soldering iron heat up, and how many production lines include proper snake-and-bake testing. (Oddly, some famous cheapie brand names take it really seriously - I guess that's because they understand about margins and post-sale costs, and have done the sums on the price of getting it right versus getting it wrong.)

The real shocker here is that this is a PSU Design Silly 101 error in a precision power supply from a relatively new brand that has spent serious money on getting things right in the past, and has perhaps done the most to shake off the Chinese rep for, as Dave says, howya doin'? Even top-notch equipment goes to market with bugs, and mostly you can sorta see how they got through design, production and test: the real world is impossible to simulate.

But this is much harder to explain. A last minute spec or component change that wasn't properly reviewed, followed by lack of production sample testing? A minor piece of design shucked off to a student engineer and not checked thereafter (seen that one)? Has Rigol outsourced this design, or given it to a new division that doesn't have the same oversight as its other test equipment? Something systematic is broken, and that has repercussions for future products. All good engineers know that if there's a failure, it's not enough to fix it - you want to know why it happened, and whether it could happen again.

At this point, I think it would be really good for Rigol to invite Dave on a factory visit and let him talk to the designers, engineers and management on camera. I know this would mean Dave taking a chunk of time out from his schedule, and what that means for a one-man band running a pretty tight ship. And I know that Chinese companies do not have the same approach to media interaction as Western outfits.  I don't pretend that this would be an easy thing for either him or Rigol to justify, even before dealing with the potential problems if Rigol's competitors wanted to do the same thing.

He could ask about the rust, too.
 

Oracle

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #103 on: August 30, 2013, 12:59:12 pm »
Just a clarification.
There was some mistaken communication that Rigol would be replacing units in Oz. That does not appear to be the case, or at least was an incorrect assumption at this stage. The local rep will simply come good with whatever Rigol come up with (board replacement or whatever). Nothing is confirmed yet, talks are still in progress with Rigol.

maybe a big discount?
 

Offline firewalker

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #104 on: August 30, 2013, 01:04:57 pm »
just got mail from the reseller i am buying the PS from.

they state that there were problems with the transformer and so also with the voltage regulator. the transformer has been changed in the second generation of the PS and the problems should be void.

thats for the 240V model they sell here in germany… we'll see.

Interesting - I wonder if maybe the issue was (partly) that the transformer wasn't supposed to put out 12V on that winding - if it had been designed to supply 8-9V after rectification, that may have been OK with that heatsink.

What the label on the transformer states?

Alexander.
Become a realist, stay a dreamer.

 

Offline firewalker

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #105 on: August 30, 2013, 01:08:24 pm »
Someone posted this image.



Alexander.
Become a realist, stay a dreamer.

 

Offline Rufus

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #106 on: August 30, 2013, 01:13:32 pm »
Interesting - I wonder if maybe the issue was (partly) that the transformer wasn't supposed to put out 12V on that winding - if it had been designed to supply 8-9V after rectification, that may have been OK with that heatsink.

Someone already mentioned and previously posted photographs of the transformer in their DP832 being a 500VA unit with a 9v winding while Dave's unit has a transformer marked 400VA with a 10v winding.

LM317s are not specified with less than 3v across them, so with ripple and say a target 20% line variation tolerance 8-9v isn't realistic. Lowering the transformer voltage enough for that heatsink would require an LDO regulator.
 

Offline AlfBaz

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #107 on: August 30, 2013, 01:21:22 pm »
Hi,
I have just buy DP832A ,
will have the same problem?
 :palm:
The pcb Dave showed had DP832A written on it. So the internals seem the same except the 832 is software crippled.

Unless rigol publish serial numbers of before and after the pcb re-spin, you'll only really know by looking inside.
It appears to reboot with now air flow over the regulator so short of jamming the fan with a screw driver the only way to know is to open it up, unless it can be proven that drawing 500mA out of the USB can cause a reset even with the fan running

 

Offline mcinque

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #108 on: August 30, 2013, 01:29:11 pm »
I think Rigol is seriously mishandling this design issue so far and they will be forced to update their board again after your review Dave. Seriously your videos are so well known by the community (including Rigol themselves posting your reviews on their website), that there's no way in the Universe that they will escape a proper thermal management of this part now... They will have to handle so many returns, so many complaints (with mysteriously broken warranty stickers), so many questions to support... It's a direct path to a shameful failure. It's true these supplies don't sell like Iphones volume-wise, but considering that Rigol wanted to set a new market standard with this supply, they won't escape this. So in a certain way, your video is going to cost them the money they avoided spending in the first place... There may be some justice in this world after all...

 :-+
I'm basically still a rookie and because of this, even with the best intentions, I often say bullshits
 

Offline EEVblog

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #109 on: August 30, 2013, 01:47:45 pm »
What the label on the transformer states?

Mine states 10V and measures 10.5V (RMS)
 

Offline M0BSW

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #110 on: August 30, 2013, 01:49:30 pm »
Now will be a goodtime to see how much their rivals will discount their prices !!!
no one would or will tell me how to delete this account
 

Offline riconette

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #111 on: August 30, 2013, 01:52:17 pm »
Someone posted this image.

Alexander.

mine hasn't been delivered jet. i'll post pictures.
free bradley manning!
 

Offline Kjelt

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #112 on: August 30, 2013, 02:21:44 pm »
Anyway this thermal issue has shifted all attention from the previous bad problem: the voltage glitch at startup.
Adding it all up, i'll pass on this product, i'll stick with my three full analogue Delta power supplies. Some of them are now 20 yrs old, last year i have recapped the elco's and they still work like a charm. And best, no firmware onboard that over time will fail  ;) .
 

alm

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #113 on: August 30, 2013, 02:28:15 pm »
There's nothing wrong with analog power supplies if you don't need presets, computer control or programmability. Performance hasn't improved much: it's not like the ripple, transient response or regulation of the Rigol supplies is better than that of the old analog supplies. Plus those analog meters have much more bandwidth than that wanky fake analog dial of the DP832.
 

Offline free_electron

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #114 on: August 30, 2013, 02:31:13 pm »
Meanwhile, i am wondering about something toally different....

Why put in an lm317 where a 7805 would have done ....
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alm

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #115 on: August 30, 2013, 02:34:11 pm »
I was wondering the same. My guess was that they use an LM317 somewhere else on the board, so it reduces BOM size. Haven't looked at the teardown pics to check, though.
 

Offline G7PSK

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #116 on: August 30, 2013, 02:40:53 pm »
It's rather sad that they didn't take the opportunity to increase the gap between the heat sink and those two electrolytic caps a bit further, it's not as though there's no room :(

Technically they are arse backwards. The airflow will come from the side vents, over the heatsink, and then out the back over the caps. The heatsink should have been toward the rear (left in image).

Interesting that you should say that as I was thinking the same thing but for a different reason today about my scope the fan sucks air from the front and expels it out the back therefore sucking in any fume from soldering, this is a problem that manufacturers of welding equipment are aware of and the fans blow air from the back to the front thus lessening the amount of dust and fumes drawn over the insides, not such a problem with solder fumes I know but they still leave sticky residues on surfaces, equipment that is designed for industrial use should be made with industrial situations in mind, I don't do that much soldering but the scope I have could easily be used in an industrial situation it as it is not one aimed at the hobbyist. To my mind all fans on equipment should exhaust to the front and not the rear.
 

Offline sync

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #117 on: August 30, 2013, 02:41:53 pm »
Meanwhile, i am wondering about something toally different....

Why put in an lm317 where a 7805 would have done ....

Perhaps a 7805 was going into thermal shutdown. >:D
 

alm

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #118 on: August 30, 2013, 02:45:30 pm »
In general it's more efficient for the fan to be blowing out than blowing in. It also gives a more diffuse airflow across the components. So that would involve mounting fans on the front panels, something that's not feasible for most equipment where front panel real estate is extremely limited. It's also less comfortable for the operator.
 

Offline c4757p

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #119 on: August 30, 2013, 02:57:56 pm »
Perhaps a 7805 was going into thermal shutdown. >:D

The sad bit is that you are probably correct.
No longer active here - try the IRC channel if you just can't be without me :)
 

Offline salviador

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #120 on: August 30, 2013, 03:03:03 pm »
If hack with switching regulator ?
 

alm

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #121 on: August 30, 2013, 03:03:23 pm »
The problem is probably that they were supposed to use counterfeit LM317s without a working thermal shutdown. But some idiot at the assembly house bought genuine LM317s.
 

Offline free_electron

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #122 on: August 30, 2013, 03:13:31 pm »
Why put in an lm317 where a 7805 would have done ....

Probably because the 7805 drifts much more with temperature than an LM317 and low temp co. resistors.
Irellevant. This the logic supply. A 7805 will do perfectly fine.
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Online AndyC_772

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #123 on: August 30, 2013, 03:41:12 pm »
I still find it odd that the CPU was resetting even though we never actually see the 5V supply drop out - just a fairly minor increase in the (frankly awful) ripple voltage on the 5V supply.

Is the amount of ripple already marginal in terms of what the CPU can tolerate? Could it be approaching the brown-out trip point even under normal operation? If so, the thermal problem really isn't the only problem.

How much voltage margin is there between the output of the LM317 toaster and the minimum the CPU requires in order not to reset? How does this vary from unit to unit and over time and temperature?

Offline LoyalServant

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Re: EEVblog #512 - Rigol DP832 Bad Design Investigation
« Reply #124 on: August 30, 2013, 04:10:19 pm »
Perhaps a 7805 was going into thermal shutdown. >:D

The sad bit is that you are probably correct.

And if THAT tidbit got past them then it's a worse fail than it is now.
I am sure that detail would never make the light of day because that would confirm they knew something was up...

I am still trying to get my head around the that xformer having a 12 volt tap for a 5 volt supply.
Must have had a shitload of those xformers laying around :D

 


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