Dual 800k SE Floppy Issue

[mattsoft]

I've got this dual 800k SE with a peculiar floppy issue. Both 800k drives work great when plugged in by themselves to either the upper or lower connector on the mainboard. However, when I connect both up at the same time, the floppy drive connected to the upper connector is very, very, very slow. If I shutdown, disconnect the lower drive, the upper is now normal speed. It doesn't seem to matter which 800k drive is in that position either, it's just always the upper connector when both floppy drives are connected when this occurs. Has anyone seen something like this before?

[LaPorta]

Yes. I have this similar issue with my second dual 800k that I have in storage. I never quite figured it out, either. I cannot remember if just one or both drives are slow, but, as you report, the drives themselves are good, it's only when attached to this motherboard that it happens. If I recall, I tried replacing the filters, but that did not work. If my symptoms are like yours, you can start the machine, but it will take something like five minutes to fully load to the desktop, with the head moving once every ten seconds or so. That sound similar?

[mattsoft]

49 minutes ago, LaPorta said:

Yes. I have this similar issue with my second dual 800k that I have in storage. I never quite figured it out, either. I cannot remember if just one or both drives are slow, but, as you report, the drives themselves are good, it's only when attached to this motherboard that it happens. If I recall, I tried replacing the filters, but that did not work. If my symptoms are like yours, you can start the machine, but it will take something like five minutes to fully load to the desktop, with the head moving once every ten seconds or so. That sound similar?

 

Yes, painfully familiar! It will boot, but takes 5 minutes or so. Hrmmm, maybe the mainboard is a good candidate for a single floppy 800k SE then.

 

Another strange twist, if I plug my floppy emu into the external floppy port and try to use the upper connector with an 800k drive, it runs fine. It's just using both those darn internal connectors.

[karrots]

Voltages ok when under load?

[mattsoft]

1 hour ago, karrots said:

Voltages ok when under load?

 

hrmmm, I will have to check. that sounds like a reasonable place to start. I haven't tried this board/drives with a different power supply. Will check loads. Thanks for the tip!

Edited December 14, 2020 by mattsoft

[mattsoft]

Looks like my most from last night got nuked.

 

I checked the voltages and they do not fluctuate under load. The only weird thing is that pin 9 on both headers is +12vdc and not +5vdc as described here: http://www.hardwarebook.info/Apple_Macintosh_Internal_Floppy_disk_drive

 

Another twist, I was testing voltages and I might have "cross the streams" somewhere with the multimeter probe. The SE went dark. I flipped the power switch and both both floppy drives are dead. FloppyEmu still works on internal/external ports, but both 800k floppy drives are dead. Must have over-volted them or something. DOH!