The components at U5 and U6 are both EEPROMs. In current models, you would expect that one or both chips would need to be transferred from patient to donor. Judging by the date codes, your board dates from around July 2003 (which matches the label), so I don't know whether this applies in your case. I'm not a DR guy, so you would need confirmation from others.
In any case, here are the datasheets for the two chips.
L76R, Microwire BUS 8Kbit (512 x 16bit) EEPROM, SOP-8P:
BR93L76RF, Rohm
http://www.rohm.com/products/databook/e ... r93l-e.pdfAT45DB011B, Atmel, 1-Megabit 2.7V only, Serial DataFlash:
http://www.datasheetcatalog.org/datashe ... 3916_1.pdfhttp://www.atmel-grenoble.com/dyn/resou ... oc1984.pdfAs for your concerns regarding a shorted preamp, I believe that the anode (non-striped end) of diode D2 (near the top LH corner) is the negative supply for the preamp. Therefore, I would test the resistance between anode and ground, eg the mounting screw.
I would also test transistors Q1 and Q3 (to the right of the central mounting screw) on the diode range of your DMM.
If you need it, here is the datasheet for Q1 (2SA1242):
http://www.i-t.com/graphics/2sa1242.pdfCheck resistor R5 near the power connector, and also check the zero-ohm resistors, eg R4, R25, R29 (at about 10 o'clock from the central screw).