Two SE logic boards, same issue

[LaPorta]

So I've got two original SE motherboards: one from the SE I took apart to build my test stand, the other from my own SE dual 800k. Both exhibit the same issue: incredibly slow sees and access time via floppy drives. Even startup is incredibly slow. The head moves back and forth maybe once every 30 seconds or longer. What is usually a thirty second startup from a floppy could take 5+ minutes. The drives work perfectly fine: the drives from each machine work perfectly inside another machine, and other machine's drives do not affect the problem with the affected logic boards. It's almost as if they are stuck in slow motion, as if there is interference of some kind. On my SE, I thought that possibly there was interference from bad filters, so I replaced them...to no avail. I have no idea how to proceed to tease out what is going on. Has anyone else had this sort of issue before? If so, any successful fix?

 

[LaPorta]

Is this one really so bizarre and off the beaten path that no one else has experienced, yet I have two that do this?

 

[AwkwardPotato]

To rule out the obvious: have you tried swapping the IWM with a known good chip, is the drive ribbon cable known to be good, and is the disk used known to be good?

Very bizarre problem for sure, I'll get my good SE 800k board and take some measurements to compare against your boards.

 

[LaPorta]

Have not tried swapping IWM chip out; I would figure it wouldn't work at all if that was bad but it's true I can't rule anything out right this second. ribbon cable and disk are good for sure, as they were used with another machine and worked perfectly without issue.

Let me know what you would want me to measure. All I can figure is ?some sort of interference along the line...if something was straight-up busted it wouldn't work at all.

 

[Franklinstein]

You could try moving logic boards between known good chassis (SE or SE/30 will work) and see if the problem moves. If the problem is the same in a known good chassis, it's a problem on the logic board; if not, you've got an issue on your analog board. For the logic board: make sure it has good caps and maybe check the ROM numbers; occasionally some of them have bugs. For the analog board: verify voltages and if they're out of spec, repair the board. 

 

[LaPorta]

Sorry this kind of died, I’ve been putting in full days at work. I’ll be testing soon.