Odd issue with Rigol DL3021 CC mode - something broken, or is it me?

[stryc9]

Hello everyone,

I bought a DL3021 about two months back, but I haven't really had time to play with it until now...

When I first got the instrument I didn't notice anything obviously wrong with it (although I did not test it beyond turning it on and off a few times).
I finally got around running a few simple tests today and I noticed that the constant current mode is behaving odd.

- When entering the CC mode, the load is supposedly disabled (the On/Off button and Short buttons are not illuminated). I assume there should be no (or very little) conduction between the inputs in this state.
- The display shows 0A current as expected, but the inputs are actually shorted and will draw (excessive) current when a power source is connected - the UI will stubbornly read 0A though.

- Pressing the On/Off button to enable the load has no effect, the button illuminates, and the UI reflects the change, but the inputs remain shorted.

- The short can be removed by quickly toggling the Short button (from initially Off, to On, back to Off). Only a quick toggle (pretty much as fast as I can double tap the button) will work. Slowly toggling has no effect.
- Successfully toggling the Short button will cause the load to start sinking it's set current, regardless of the state of the On/Off button. Even when the button is in the Off state, the load will still start drawing the set current after toggling Short, the only difference being that the UI remains stuck at 0A again...
- Pressing the On/Off button at this point brings back the short

CV mode appears to function correctly. Battery capacity measurement suffers from the same issues as CC mode (not that surprisingly, since they're probably closely related).

I figured this could be a firmware issue, it's Rigol after all but the instrument was already running the latest version out of the box. In desperation I tried installing the latest firmware again - to no effect.

I'm running out of ideas here, except for just turning it in under warranty... Has anyone experienced similar problems with this instrument before? Maybe it's some silly menu option that I missed, or is this thing just broken?

[TurboTom]

I observed a similar, but by far not as severe, problem three years ago when I tested such a load for a week and then decided to return it to the distrubutor since it wasn't fit for the job.

I also found that the load wouldn't actually disconnect after toggling on/off with no current flowing. Up to a few milliamperes were recognized as "zero" and would flow uninterrupted through the load. The measured current would show zero as well. Only if the (apparent) offset of the current measurement was exceeded and the display started to show some off-zero values, the load disconnected.

Could it be possible that this offset is much higher in your particular load? It would be a real shame if Rigol didn't correct this problem in firmware meanwhile. Whatsoever, either if it's a calibration issue or a plain and simple defect, your load shouldn't act like that. If it's still under warranty, have Rigol take care of the problem!

[stryc9]

I returned the unit to my distributor and they had Rigol repair the load under warranty.

It turns out the main board was defective. Unfortunately I didn't get any more details than that.
The main board has been replaced by Rigol and I just received the unit back after sending it in about 5 weeks ago. Took a little longer than I would have hoped, according to the distributor this was mostly due to the lead time of the replacement board.

Anyway, the unit is now functioning correctly again, so I'm satisfied.