Electronics > Repair

Killed my Riden RD6018. Need help with measurements or identifying components.

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MBY:
I was working with using the fan header pin as a control for enabling a case fan, and did a stupid thing that destroyed the fan and a small DCDC on board. After some fault finding, I found that a step down converter for the main electronics works, but another DCDC after that is blown. First i thought it was an LDO, but the circuitry shows it's a DCDC. Its a SOT-23-6 with the marking "B6280n" that I can't identify. I noticed resistors for the feedback, but I don't know about the reference voltage, and I have a suspicion that it may be an inverting DCDC.

Attached is a picture of the main board and arrows to the suspected area. If someone knows that the component U3 is, or can measure the input and output voltage of it, it would be very helpful!

The input voltage (output of the first DCDC) is also needed to confirm. I measured the feedback resistors of the first DCDC (an XL7015) but in circuit and I'm not sure that my calculations is correct. I calculated that it would provide about 4.7 volts.

To clarify, the topology is something like this:
70 VDC in->stepdown XL7015->Vin->SOT-23-6 DCDC that may be a stepdown, a stepup or a rail inverter->Vout

Vin should probably be 5 volts (the power relay seems to need 5 volts) and I have no clue about Vout. It seems excessive to use a DCDC to get say 3.3V, as a LDO should suffice. And, it seems that there are a LDO (U6) there anyway.

I've drawn lines to points where Vin and Vout should be present (don't worry about the missing SS110 diode, I've removed it temporarily).

So, can anyone measure these voltages and/or know what the U3 is for component? Possibly this part of the circuit could be same on the more common RD6006 or RD6012 models.

Swainster:
My guess: Shouding SDB628 boost regulator. You can get it from LCSC.com.

MBY:
Thanks! That makes sense! Stupid me who already put an order on LCSC.com yesterday of all kinds of components I did identify, now I have to pay postage again! :D

With a 0.6V of FB voltage and 130/10k (measured by removal, not in circuit as the case with the XL7015) that gives 8.4V (0.6*(1+R1/R2)). I hope someone could confirm that!

MBY:
Okay, now I can confirm myself that the calculation was right. The boost converter takes the 5ish volts to 8.4V. Hopefully this info can be useful for someone else.

MBY:
So I got these components from LCSC that I could identify. Changed the power FETs (that had shorted), the SDB628 regulator and some diodes. But it didn't work. The display comes on, but goes off after a fraction of a second. The 5V rails measures 2.7V and seems to be shorted at "U1", a SOT-23-5 with the code "7517". It gets hot. But I can't identify it. Based of the location, it doesn't seem to belong to the power generation, but is among some OPamps, small signal and SOT power-transistors and some unidentified 10-pin circuit (that's not a SO-10, but something with finer (0.625?) pitch.

Anyone have a guess what a "7517" in a SOT-23-5 is?

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