108AE – Replacement Hot-Air Repair

We have recently become aware of a higher than normal defect rate in the production batch of CSI8786D units, and we wish to inform our customers, both for future sales, and those who have purchased this item in the past. Along with informing you, we’d also like to provide a step by step guide to diagnose and/or repair your unit. In all the cases up to now since August, the common failed component is the HDS-501524H DC 24V 0.15A Fan, situated inside the Hot Air handle. If for any reason this tutorial is too difficult for you to complete we are more than happy to ship it back at our cost and ship it back to you fixed.

The symptoms in each case are very similar with a glowing red hot handle when the unit is powered on, due to no air being able to control the heat. Subsequently, the heater wire can burn itself out by breaking apart along the wire. (Fixable by just twisting them back together)

The issue that I’ve found to be the issue in each scenario is the voltage regulator for the fan allows the voltage to go over 24V to 28V, which fries a transistor built into the fan, causing the entire fan to fail. (See picture below) The transistor itself is irreplaceable without breaking the fan, so our solution is to replace the fan and place a 30 ohm resistor in series with the fan. To derive this value, we use Ohm’s law for;

V=IR or volts=current*resistance.

Since we know the current is .15A, then 4.5=.15*30. Next, we need to calculate for power dissipation with;
P=RI^2 or power=resistance*current(squared).
Which gives us 30*.15^2=0.675 Watts.

To begin the procedure, first unscrew the handle plastic nut, and the two screws at the back of the handle.

CSI8786D Handle Disassembly

Next, desoldering the old fan, and remove the rubber air redirection part, and place onto new fan in the same orientation. Solder the new fan’s black wire to the circuit board Fan-, and the new resistor in series with the red wire as show below.

Once this step is completed, reassemble and the unit is fixed. Thank you for helping us overcome this issue.

2 thoughts on “108AE – Replacement Hot-Air Repair

  • December 2, 2018 at 8:46 am

    The fix on the CSI8786D works fine the 30 ohm resistor is the way to go.


  • September 8, 2020 at 1:24 pm

    Thank you for this article, makes incredibly sense!! Question for you, where can I get one of those fans, can’t be found nowhere!! Please help!

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