From 2008 to 2010, I worked in a lab where my primary project was the upgrade of a helium dilution refrigerator so that RF measurements could be taken on a experimental package. This system, previously used for helium experimentation, was massive. Huge pumping speed with 6 or 8″ lines, double sealed mechanical pump, roots blower. This is no small dilution fridge!
I was probing around a bit more and I’ve found the obvious problem, and it’s not the transistor. The power connector to tI can envision what happened now: an unregulated supply – works fine for just charging the battery, the current is low and the TPS65250 has a wide input voltage range. But, upon power up current demands go up, voltage drops, and this tiny connector melts because it can’t handle the current. It surprised me this would happen before the input fuse blew – bad design I guess, should have used a connector rated for higher current since the connector is on the supply side of the fuse. It took longer to find since I never suspected this, but, was fairly easy to fix. Next time check the simple things first.
Tom gave me his PSP after frying it by using the wrong powersupply. The micro fuses were okay, so onto the SMPS! It’s self contained – up in the top left corner in the picture, but, on the other side of the board. I didn’t take a picture of that size for some reason. So, this supply is based on a Texas Instruments Power Management IC, TPS65250. Anyways, closest datasheet I could find online was for the TPS65050 series. I assume the rating are simply a bit different, or this is OEM’d. I’m thinking right now that the main switching transistor is shot…and since those SMD transistors are basically impossible to identify – since they never seem to have any text on ’em – I just pull random ones off of old broken computer motherboards and assume they’re close enough….they all have been so far.