Macintosh SE FDHD Not Booting From Any Drive

[jake18125]

Bit of an interesting problem this one.
I recently picked up a Macintosh SE FDHD which had suffered a battery leak, however, the logic board did clean up relatively well and it appears that no traces had been damaged.
Powering it up showed signs of life - it would bong, pass the memory check and would show the cursor. I could easily move the cursor around, so at least the system hadn't frozen, and at least ADB was working.
However, the blinking floppy, happy or sad mac icons just never appear. I've tested it with known working drives, and I have been able to prove that the ROMs and SWIM are still working by putting them in my regular SE. I'm guessing that either a via has became damaged or an IC has failed, but I'm not sure where I should start to check.
Any suggestions are welcome!

 

[cheesestraws]

Personally I would first check for oddities/brokennesses around the SCSI chip. It's entirely possible for something dodgy on the SCSI bus to wedge up the computer totally at that stage, because the initial process of looking for a boot device will just get stuck and it'll never get as far as displaying the blinking question mark.

 

[jake18125]

Ahhh ok, although I would of thought that the floppy drive would of had priority over the scsi bus?

 

[cheesestraws]

Ahhh ok, although I would of thought that the floppy drive would of had priority over the scsi bus?

Hmmmmm. I think it initialises SCSI before it attempts to boot from the floppy, even though floppy is earlier in the boot order. But I may be wrong. This is all rather rusty memory.

 

[jake18125]

Unfortunately the SCSI controller has been removed but... no dice. Exact same issue.

 

[rjkucia]

Do you mean the SCSI controller was removed before you started testing this, or you've just now removed it and saw no difference in behavior?

 

[jake18125]

The controller has just now been removed and there is no difference in behaviour.

 

[LaPorta]

The SE/30 definitely has this issue (no floppy icon with SCSI issue); to my recollection, the plain SE does NOT work this way. What you may be having an issue with is that a trace you cannot see may be having an issue. I had a problem that was similar on a battery-bombed SE myself: it would not work no matter how much I cleaned. I removed the SCC after theorizing where more goop could have gone. Sure enough, one of the through-hole vias was rotted out. Restoring it got the machine back running. If you have photos of where the battery leakage went and the extent, that will give you a better idea of where to look.

 

[fuegos]

@La Porta, would you have a schematic diagrams for FDHD please? I have just finished rebuilding badly damaged board and have a similar issue - no boot, no mac logo but moving cursor. Do you remember which trace was the causing the problem in your case?

 

[LaPorta]

My problem was not the same as this one, I had completely garbled information on the screen. I am just saying that these things can happen due to unrealized crud under chips/