Power but no startup sequence

I recently dug out my old gameboy, but despite supplying power, I do not get the logo block or sound when turned on. the led is red, though that just proves the led works.

I've tried with and without a cartridge, and with an 6V AC Adaptor, as well as four AA batteries that are fully charged.

I've checked for leaked capacitors, or acid damage from leaking batteries, but it looks like i've been lucky and there is no visible damage.

I've measured the voltage on the contrast, and I get a range of about 0.05 to 10V on the pot.

I couldn't find a voltage differential on the audio pot however. should there be one there yet if a startup hasn't occurred?