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IBM PC/XT floppy drive LED stays on

D

Denniske1976

Experienced Member
Joined
Jan 17, 2011
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The Netherlands
Hi guys,

I have a bit of a weird situation here: the drive LEDs on my IBM PC/XT stay on all the time. I've been looking around for info and mostly it's because of the cable that's on backwards, but not this time. Weird thing is: the drives just work as if all was normal!! I can boot DOS 2.10 from them, get a DIR etc etc. It's just that the drive LEDs are on ALL THE TIME, from powerup and won't go out.

Any idea? I was thinking the LED is on backwards maybe, but it's all original so with the cable running all the way to the back of the drive (it's the big Tandon 360K ones BTW) and going into the plug that's in the back. It's both drives BTW, not just one.

Dennis
 
Was it like this when you got it? Or did it just start doing this?

The first thing that comes to mind is check drive select/motor jumpers. I don't recall if tandons can do that, but with some drives you can jumper them so the motors stay running all the time. Normally the drive lights would not stay on but somebody may have jumpered or wired something weird.

Do both drives actually work? Usually when this happens, it is because something shorted with the drive select. But that will usually prevent one of the drives from working.
 
Well, I got it this way... but I've figured it out!!

I had changed everything: FDC, cable, drives and it kept acting weird. The one that would work with the drive light on, wouldn't work anymore with the other drive installed next to it (went to BASIC). Even with the FDC etc not connected but just power, I have the LEDs on all the time so it wasn't comping from the computer anyway.

So I took like 3 other drives I have (known good) and compared them to the ones that were installed. First thing I noticed was that both had a TERM chip installed so that explained a lot. Removed one and the drive that worked before started working again... but still LEDs remained on.

Now check this: with all my other drives, there's another chip socket in front of the TERM socket but more to the edge of the PCB. All of my drives have a little metal arch in it that connects pin 3 with the opposing pin in the socket. So I checked the other two (weirdo acting) drives and there's an IC in them!?!?!?! WTF?!?!?! I don't know what it does, the chip in the socket is a 74F365N (week 01 year 1986). So I removed those chips, cut off the legs of an old CAP I still had, bent them en also connected pin 3 with the opposing pin.

Result: both drives work, LEDs behave accordingly and all is well :)

What those 74F365N chips do, I have no idea, nor do I know why they would be in the sockets of both drives if they quit working... but problem solved!
 
Denniske1976 said:
Now check this: with all my other drives, there's another chip socket in front of the TERM socket but more to the edge of the PCB. All of my drives have a little metal arch in it that connects pin 3 with the opposing pin in the socket. So I checked the other two (weirdo acting) drives and there's an IC in them!?!?!?! WTF?!?!?! I don't know what it does, the chip in the socket is a 74F365N (week 01 year 1986). So I removed those chips, cut off the legs of an old CAP I still had, bent them en also connected pin 3 with the opposing pin.

Result: both drives work, LEDs behave accordingly and all is well

What those 74F365N chips do, I have no idea, nor do I know why they would be in the sockets of both drives if they quit working... but problem solved!
Click to expand...

That will be the socket shown in the top-left corner of the photo at [here].
Used for configuring certain options.
The wire jumper between pin 3 and 14 is configuring the drive for the second drive-select option.

I have no idea as to why someone would put a 74F365N in the socket.
 
I've heard of a guy who, since his eyes got weak, exchanged resistors regardless of color codes .. and mostly it works, he said :)
 
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