Schonstedt TraceMaster II repair

[SRecker]

So I come across one of these underground pipe and cable locators on Craigslist for almost nothing. I checked on E-Bay and these things have sold recently for quite a bit of money, so I figure it's worth repairing. It was listed as base unit not powering on, I hoped that it was just a bad connection from the batteries or other simple mechanical fix. No such luck.

I snapped a couple of pics of the unit here, including the main board which I think has the problem.
http://imgur.com/a/luHvH

So this thing runs on 12V DC and has a battery compartment with 8 D-cell batteries in it. When I try to power it on I get nothing on the display and key presses seem to do nothing. So I pulled the thing apart and removed the main board from the rest of it. With just powering the main board it was pulling 350mA @12V, which seems like a lot of power for a board doing nothing.

I don't have a schematic and I don't have a lot of experience troubleshooting to the component level.

So, I start measuring voltages and was getting nowhere, but I noticed the power MOSFETS getting hot. I figure something has shorted out. So I power off the board and start checking different test points to ground, etc. Eventually, I find something odd and I'm not sure how I stumbled across this, but checked a few resistors and all measure open  , EXCEPT the 47 ohm resistors, they are all good. This seems very strange to me that all of the resistors would be open. I checked and checked again, thinking I was doing something wrong, but if I am, I haven't figured out what I'm doing differently. I mean, I don't seem to have a problem measuring the 47 ohm resistors, and I'm measuring the others the same way, so I guess I'm doing it right. I suspect these resistors are not the problem, but a symptom of something else, but what do I know. Could they of had a bad batch of resistors? This thing is fairly old, my guess it was made in the '90s as someone wrote in marker that it was updated in '03 and repaired in '08

This is turning into a bigger job than I thought.

I thought I found a resistor that was shorted, so I removed it and I poorly soldered in a temporary through hole one in it's place, but no apparent change in power use or function. I did try the board without it and when it was missing there was no current draw at all from the PS.

The 2 power mosfets get hot pretty quick as well.

I guess I'm looking for pointers as how to proceed, or even schematics, but I won't hold my breath.

[PedroDaGr8]

I have seen MOSFET's blow and take the attached resistors with them. Pull all MOSFETs and suspect resistors and test them out of circuit.