bad board?

[pentium]

My week was made today when I got a dreamcast with pretty much every clipping for FREE!
The last owner had ued the system for a few years and then suddenly the system just refused to power on.
Pushing the power button made the fan spin and the power light go on but then suddenly the poly fuse engaged and you had to leave the system off for a bit before you got another respone from turning it on again where the fuse engages again. I opened the case and began searching.
Everything looked good and the battery had not leaked so it was not a corrosion problem. Frustrated, I powered the system on anyways without the cd drive and it's controller oard attached and the system powered on aand remained on. I couldn't use the system for the unit would just remain at "looking or cd" and with no cancel button you were just stuck there. Reinstalling the cd assembly (the board and drive are a single module) and powering up again made the fuse go out.
That means two things:

-the power supply for some reason can no longer supply enough power for the drive

or

-the controller for the drive is a dud and and needs to be replaced.

since replacement parts are becoming rare and expensive, I need to find a way to be certain that the power supply is not the problem. What should I do?

[pentium]

Re: bad board?

Wow, did I really stump everyone?

[kc8adu]

Re: bad board?

measure the psu with and without load.
measure at the polyfuse and see if psu is still running.
if it is the drive is bad.

[cods69]

Re: bad board?

Have you checked the DC voltages from the PSU when it's under load?
From memory its reg'd pretty tight and should sit pretty much right on the spec'd V.

I killed a PSU for my Dreamcast years ago and tried unsuccessfully to fix it for some time (still got it). Got a new PSU from LikSang and it has been fine since. Shame they are gone now.

EDIT: beaten by kc8adu

[pentium]

Re: bad board?

everything is within specs with the drive removed except 12v.
It clocks 13.5 volts.

With the drive on, 12v reaches 2.18 volts before cuttoff, 5v reaches 1.25 volts and slowly returns to zero and 3v reaches 1.25 volts and also slowly returns to zero. I noticed also that there is always .01 volts in the 3.3v line even with the drive removed and the power off. I also want to note that stamped onto the drive assembly is 3.3v but that might not mean voltage.