Biostar BT-250 got heated as soon as plugged in

[KoPhyoe]

Hi guys!

I'm new to this forum and I would like to get any technical advice from my seniors here. And I'm trying to repair Desktop Motherboards and GPUs. Here is one of my problem I'm having here. Biostar TB250-BTC motherboard has no power even power switch don't have 3.3V. As soon as I plugged in 24ATX pin , this regulator got heated. Remove/Replace isn't working there. Any Advice would be appreciate! Sorry for my bad English. Thank you in advanced.

[sam_sam_sam]

Re: Biostar BT-250 got heated as soon as plugged in

Have you checked to see if you have a short on this power supply rail that this ic chip is on its output pin

This is what I would do first

[Beton]

Re: Biostar BT-250 got heated as soon as plugged in

I've encountered this exact problem with exactly this ic (1117) on a few different boards, this LDO converts 5VSB to 3VSB on all of them. I attached the schematic for this board.

[SMDFlea]

Re: Biostar BT-250 got heated as soon as plugged in

Zetex (diodes Inc.) AZ1117CH-ADJTRG1

Datasheet https://cdn.badcaps-static.com/pdfs/...dc07ca3060.pdf

[DynaxSC]

Re: Biostar BT-250 got heated as soon as plugged in

Hi, most probably you have a short on the chipset. You will find on the chipset top side some small supply voltage filtering caps, measure resistance on them, if you find a very low resistance around 0-1 ohm, then the chipset is dead. Normal resistances are dependent on the chipset power supply line between several 10's of ohms to kohms. Check also the 5V stand-by voltage in stand-by mode, if lower than 5V (+/- 5% tolerance), then most probably the chipset is dead. The volatge regulator gets hot, because it's operating then at maximum amperes/temperature limits, but usually it does not get broken due to the short. The caps have their positive leg usually towards the silicon, the other meter lead just connect to ground. However I have seem also chipsets with shorted caps, this can also happen, and it looks like the silicon is dead. And, the chipset has usually two power voltages, 3,3V and 1V, the 3,3V is on such older boards usually generated from the 5V VSB stand-by by a linear regulator, the one like you desoldered.