EEVblog #512 – Rigol DP832 Bad Design Investigation

Dave started out wanting to investigate the power-on spike on the Rigol DP832 Lab Power Supply, but ended up hunting down a reset bug that uncovered a bad thermal design mistake in the supply.
Watch Dave hunt it down step by step, and almost get duped by some marginal oscilloscope triggering.
How will Rigol respond to this?
UPDATE: Rigol have already fixed this issue HERE

Forum HERE

Initial user confirmations HERE

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  1. Even without the thermal management bug,

    is it “normal” to place the elkos very near to the heat sinks, or could this be an example of a lifetime limiting design?

  2. I guess, the design is part of the planned obsolescence. Nearly all electronic stuff is equipped with these lifetime reducing technics. So for me it’s no mistake, but done on purpose.

  3. I should imagine a lot of the tech guys will buy these cheap and do a hack or modification, probably creating a bigger heat shield to the exiting one, and maybe a separate fan, a lot of fiddling around , but some love that side of the hobby.

  4. Are rigol going to throw in a can of rust cure as well lol

  5. If they gave the 5V regulator its own tap, why the heck did they make it a 12V tap, forcing the regulator to dump more than half the power all that circuitry is drawing as heat?

    They could reduce the problem quite a lot by giving it a 7 or 8 volt tap.

  6. It’s good practice to connect caps and regulator with shortest trace possible, but also electrolytic caps shouldn’t be too close to hot parts, which regulators often are. The best solution is to not have hot parts in your design at all. In this case – lower the input voltage for regulator to Vout + Vdropout, add 10% for power line fluctuation and you are at minimal power loss posible for that regulator (notice, low dropout regulators produce less heat than standard regulators). I bet, with this fix, the heatsink would be barely hot. Maybe Rigol needed 12V and don’t want to add another transformer tap, but 110C is really horrible. I hate even 70C heatsinks or chips.

  7. Who uses LM317s these days? With all the low dropout regs it seems like a dumb idea to me.

  8. A little weird, RIGOL showed a very bad hand.
    This basic and rudimentary error?
    Now what all the DP832 to return?

  9. But does it really make sense to let some caps / off the shelf voltage regulator fail? Wouldn’t that be a quite easy fix?

  10. Even easy fixes aren’t done in many places. I’ve rescued a bench multimeter from the dumpster once, its only flaw was dirty zebra strips making the LCD fail sometimes.

    Many places don’t bother fixing. Something shows the slightest defect, and out it goes. Especially for ‘cheap’ items like this. (If the only staff on hand to repair stuff are well-paid engineers, a lot of even moderately expensive hardware starts to look cheap compared to those folks’ daily wages before taxes)

  11. We use a thermal infrared camera on all our designs. As a rule we try to keep max delta T below 20oC, but certainly no more than 40oC for active devices and 50oC for passives.
    Daves right. Rigol are amatures for letting this slip through. (Note I’ve owned 2 rigol instruments which both have had faults)

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