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Author Topic: Rigol DP832 - channel failure, "UR" = unregulated  (Read 3587 times)

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Offline mcvsama

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Rigol DP832 - channel failure, "UR" = unregulated
« on: January 19, 2015, 03:35:28 AM »
Hi everyone. :-)

Once upon a time I was trying to test a 24V fan, so I set up channel 1 on my DP832 to 24V, and connected the wires. Since the fan came with its own, very tiny connector, I tried to connect cables to that connector and… bam! While doing that I shorted Rigol's output for a brief second. Should be OK, right? Rigol has all those fancy protections, etc? No. At that moment it started showing about half of the set voltage (11…12V) and the output mode was "UR" (no CV, no CC, but UR, which is "unregulated" aka "broken"). Then channel is unusable since then.

So I opened it. My top board version is V02.10. I replaced broken fuse F3 (5A) and broken main MOSFET (CEP18N15). I checked some of the other components - diode bridges, main capacitors and triacs - they all seem good. But after reconnecting everything again, channel 1 still shows "UR" and measured voltage is far lower than the set one. The ammeter shows 0.0.

I tried contacting Rigol twice, it seems that my first attempt was lost completely. The second time I got a confirmation e-mail that they registered my problem. It was about three weeks ago, but no one from Rigol contacted me yet.

Can anyone give me advice what I should check next? I'm out of ideas and besides that - I'm a noob. :p
 

Offline TMM

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Re: Rigol DP832 - channel failure, "UR" = unregulated
« Reply #1 on: January 19, 2015, 04:08:05 AM »
I'm not familiar with the DP832, but it is likely that whatever is connected to the gate of the blown MOSFET has been taken out as well. Back-trace the circuit from the gate and you will probably find a blown driver transistor or opamp (or both).

As for why it blew in the first place - bench power supplies should be robust enough to survive being accidentally shorted out however most aren't designed to sink current - i.e. if a voltage is present at the powersupply's terminals which is higher than the powersupply's set voltage, damage can occur.
It is possible that inductive kickback from the fan killed your supply. When working with inductive loads or batteries, it's advisable to use a series diode to protect the powersupply. 
« Last Edit: January 19, 2015, 04:15:12 AM by TMM »
 

Offline saturation

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Re: Rigol DP832 - channel failure, "UR" = unregulated
« Reply #2 on: January 19, 2015, 05:39:39 AM »
Sorry to hear, shorting the outputs of a PSU should not cause any issues, in fact its the simplest way to to set the CC level or the current cutoff in other designs.

A blocking diode is always a good and cautious idea but it reads like you didn't even get inductive kickback to damage the output driver. 

That DP832 sure has a host of issues as discussed on the forum.   A good PSU should be built like a tank to take a lot of output abuse. 


Best Wishes,

 Saturation
 

Offline Skimask

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I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline mcinque

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Re: Rigol DP832 - channel failure, "UR" = unregulated
« Reply #4 on: January 19, 2015, 06:39:54 AM »
That DP832 sure has a host of issues as discussed on the forum.

Software issues for sure, but for the hardware (except for the heatsink issue, that has been fixed) I never heard someone questioning about a channel smoked without having done a particular mistake.

I can't believe the 832 will smoke only by doing a short...

I've done some shorts to the outputs of my 832 but it goes in CC.
Just to ask: you say you set 24V, but at which value you've set the current?
I'm basically still a rookie and because of this, even though the best of intentions, I often say bullshit, so never mind.
 

Offline mcvsama

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Re: Rigol DP832 - channel failure, "UR" = unregulated
« Reply #5 on: January 19, 2015, 07:26:59 AM »
I've seen that thread with broken current-sensing resistor. Mine seems OK (0.02?), I also don't see anything blown up on the board. No smell, looks OK, but doesn't work. All fuses are now OK, the only one that was blown is now replaced.

I've never though that a fan could introduce back some current, but anyway, I made the fan work, it was just that I was trying to hold both cables with one hand while the fan was spinning and there's when I shorted the output. There was just a small spark, like you would expect from discharching maybe 1000µF capacitor, and that's it.

I don't remember what was exact current setting, but by default I use 1 A unless I need other setting, so it was most probably set to 1 A. I was short-circuiting it at 3 A and 5 Volts just to test it when I first got it, but this time it was 24 V. I'll look for the gate driver, it seems that there's BD136 transistor connected to MOSFET's gate.
« Last Edit: January 19, 2015, 07:35:55 AM by mcvsama »
 

Offline wiss

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Re: Rigol DP832 - channel failure, "UR" = unregulated
« Reply #6 on: January 19, 2015, 07:34:41 AM »
If you set it to 20 V, what will it output? Will it output the ~10 V  the dvm-part shows or the correct 20 V?
 

Offline mcvsama

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Re: Rigol DP832 - channel failure, "UR" = unregulated
« Reply #7 on: January 19, 2015, 07:46:02 AM »
If you set it to 20 V, what will it output? Will it output the ~10 V  the dvm-part shows or the correct 20 V?

When I turn the channel on, it shows CV for a half a second, then CC, and then UR. When I set 1 V it shows 1 V. If I set something like 10 V or more it shows slowly rising voltage, but not getting past a couple of volts (and of course still "UR"). This is with a new MOSFET, the first one was completely shorted. I don't want to wait longer with channel turned on and overstress it, even though I ordered 10 identical transistors from China in case I blow more. ;-) I'll buy and replace the BD-136 (if I can find it in a local shop) and see what happens.

Right now I'm going to sleep. Need to go to work tomorrow. ;-)

Edit: oh, you asked about the actual output, not measured internally by the PSU? I haven't checked, actually. I'll need to do it.
 

Offline wiss

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Re: Rigol DP832 - channel failure, "UR" = unregulated
« Reply #8 on: January 19, 2015, 08:00:12 AM »
I'm thinking that maybe the dvm is blown...
and you could measure the current drawn by the psupl by measuring ripple on the main cap.
 

Offline Skimask

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Re: Rigol DP832 - channel failure, "UR" = unregulated
« Reply #9 on: January 19, 2015, 08:58:25 AM »
I've seen that thread with broken current-sensing resistor. Mine seems OK (0.02?), I also don't see anything blown up on the board. No smell, looks OK, but doesn't work. All fuses are now OK, the only one that was blown is now replaced.
Pull that one fuse F3 next to J12 and check it out of circuit.  Mine checked good in circuit for some reason.  Didn't bother working back thru the PCB to figure out why.
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline mcinque

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Re: Rigol DP832 - channel failure, "UR" = unregulated
« Reply #10 on: January 20, 2015, 09:35:31 AM »
It would not help you fixing the PSU but just for test I've tried many times to do some shorts on my dp832 with 24V 1A as your setup and it goes - as expected! - in CC when shorted and returns in CV when opened.

I think that even if you didn't realize it, there was some inductive kickback from the fan to the PSU as TMM said.

Rigol are definitely not top quality products and their support is quite crappy, but their PSUs can of course accept a short...
I'm basically still a rookie and because of this, even though the best of intentions, I often say bullshit, so never mind.
 

Offline saturation

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Re: Rigol DP832 - channel failure, "UR" = unregulated
« Reply #11 on: January 20, 2015, 11:57:11 PM »
Here are issues I found doing a quick search:

http://www.eevblog.com/forum/testgear/dp832-problem/msg484593/#msg484593


http://www.eevblog.com/forum/testgear/dp832a-problem-ch1/msg424491/#msg424491

http://www.eevblog.com/forum/beginners/nonsense-behaviour-of-rigol-dp832/msg575509/#msg575509

They describe either assembly or premature part failure.

So my suspicion is the fault of the OP was related to either and not necessarily happen to everyone with the same unit.  Such issues should be caught by better QC checking.  It would help for owners to do their own such as opening and inspect its construction thoroughly, burn test it for a 24 hours, while checking for overheating of any critical components and insure it lives up to its published specs after burn testing.
« Last Edit: January 21, 2015, 12:23:31 AM by saturation »
Best Wishes,

 Saturation
 

Offline mcvsama

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[fixed] Rigol DP832 - channel failure, "UR" = unregulated
« Reply #12 on: January 21, 2015, 04:39:37 AM »
Problem solved! But you'd not guess how. ;-)

Apparently I'm stupid. I removed the BD136 that was connected to MOSFET's gate and checked it with a diode tester. It looked OK (about 0.6 volts on both "diodes"). So I put it back again and rechecked output voltage with an external multimeter to see perhaps if it was a problem with internal DVM. Now guess what - when I was testing it the previous time, I set output current limit to 1 mA. And when I connected the multimeter I though about its internal impedance… and then I had enlightment. Obviously, with 1 mA limit the voltage will start rising slowly because of the output capacitor that needs to be charged.! So I changed the current limit to 100 mA… and bang! It works! CV, no more CC or UR. Channel 2 exhibits exactly the same behaviour, when I set current limit to 1 mA.

Turns out that I actually fixed it on the first shot, when I replaced the F3 fuse and main MOSFET. I just didn't test it correctly.
Nevertheless, I think I'll do some testing with a high power resistor, since my electronic load is still in the making. ;-)

Thanks everyone for help, I think I'd be stuck until now without you. ;-)

As for quality - I don't expect Rigol to be top quality, this PSU is quite cheap, so I don't blame them that bad things sometimes happen, albeit they could at least respond to my issues posted via their website. Anyway, I'm happy that it works now, I think I can go back to experiments with my first PLL… :-)

So to sum up:

1. I shorted CH1 for a brief moment, voltage readings went berserk.
2a. I opened it and replaced open F3 (with a regular glass 5A fuse).
2b. I replaced main MOSFET (CEP18N15, ordered from alibaba.com), which was totally shorted.
3. It worked… but I didn't realized it, since my current limit was set to 1 mA (for safety…).

That's all folks. Thanks again. :-)
 


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