Need help fixing Disk IIc 5.25

[spec@vax2.concordia.ca (Mitchell Spector)]

   I have a Disk IIc external 5.25 drive which is non-functional that
I'd like to repair. My guess is the mechanism is fine, but one or more
of the TTL chips (soldered-in) on it's analog board are blown. Could
someone out there help me pinpoint which chips would be affected?

   When connected to the Diskport of the IIc, it appears normal. 
The LED in front lights up and the head resets itself with the usual 
chatting sound and spins. If I insert a disk however, it just sits 
there, not knowing what to do next. Eventually the IIc just gives up 
and tells me "Check Drive". Interesting though, if I connect it to the 
Diskport on the IIc Plus, the LED flashs very briefly and it won't reset 
or spin the head at all (but does on the regular IIc or IIe with card).

I found the following TTL chips:

TD62003P
HD74LS125AP
HA1127P
MC3470AP

Assuming the above problem is some of the logic on the analog board,
which chip would be the best to try replacing? (remember, they're
soldering in).

Mitchell Spector
spec@vax2.concordia.ca