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FDD Controller Problem

E

eight088

Experienced Member
Joined
Oct 31, 2018
Messages
158
Location
Perth, WA Australia
Hi guys,

I have a PC where the 5 1/4" drive is not working. I've taken the drive apart and cleaned it up and re lubed it and tested it in another machine which was successful. I put the drive back into its original computer and it didn't work again. So this leads me to believe the controller has failed in one way or another. Just wondering if anyone has any pointers on what I can look for to try and fix this? Swapping controllers isn't an option because the PC uses a proprietary controller built into the motherboard and has no ISA slots.

Cheers

Matt
 
Yep the cable is a known working one from a standard controller. The only thing is though I'm not sure if the pinouts on the proprietary controller are the same as a standard controller and I can't seem to find any info on what the pinouts might be so not sure if the original cable may have some of the connections in different spots?
 
Chuck(G) said:
The other question is "exactly does what 'not working' mean?" It's uncommon for an FDC to fail.
Click to expand...

By not working I mean it seems to do nothing. Light comes on but don't hear any noises coming from it so it seems like it's not even trying to read from the disk. The computer doesn't have a working hdd either (it's an ISA hardcard which funnily enough works in another machine) so can't boot the machine up at all.

I thought it may have been a power problem but the 12v and 5v seem to read okay.

Cheers
 
Exactly what kind/model of PC is this? If you can't describe it, post some pictures including some of the inside.
 
Chuck(G) said:
Well, does the disk spin when the LED comes on? (You should be able to hear it).
Click to expand...

From what I can tell, no.

SomeGuy said:
Exactly what kind/model of PC is this? If you can't describe it, post some pictures including some of the inside.
Click to expand...

It's a Sharp PC7100.

From what I can tell by looking at the mainboard where the fdd plugs into, the socket is called FD Drive. Then there is one row labeled as A1-A17, and the other B1-B17. Is it possible that one row drives drive A and the other drive B, instead of relying on the twist in the cable to designate drive A? The other thing I've noticed is that on the underneath of the spade connector on the disk drive appears to have all the pins connected as a common plane. So I am now theorising that one pin on the row A1-A17 is ground and then the disk drive takes that ground and "delivers" it to the the other points needed?

Just as a little background about this PC range, the Sharp PC7000 has two disk drives and no hdd while the 7100 has one disk drive and one hdd plugged into an ISA slot. I've read somewhere that this slot might not be a standard ISA slot so might be configured to only work with the hdd card that it was designed for... I'm not sure, I'm only guessing.

Cheers :)
 
eight088 said:
So I am now theorising that one pin on the row A1-A17 is ground and then the disk drive takes that ground and "delivers" it to the the other points needed?
Click to expand...

Well I think I just proved myself wrong here... Every second pin is ground and from what I can tell that is normal.
 
From a quick Google search, that appears to be a small all-in-one portable with a built in floppy drive(s). Is the cable and drive you are using one that came with it? That is an early enough clone I would speculate it might require a flat cable (first drive jumpers set to DS0 second DS1) instead of IBM's twisted style (all drives jumpers set to DS1).
 
Somewhere on the web there's a service manual for the PC7000(I've found it before), which should be identical in most respects regarding the FDD setup. And yes, I'd suspect the flat/DS0 situation might well be the case here.
 
SomeGuy said:
From a quick Google search, that appears to be a small all-in-one portable with a built in floppy drive(s). Is the cable and drive you are using one that came with it? That is an early enough clone I would speculate it might require a flat cable (first drive jumpers set to DS0 second DS1) instead of IBM's twisted style (all drives jumpers set to DS1).
Click to expand...

The cable I'm using is a standard cable from a desktop computer but the drive is the standard OE item. When I pulled the Sharp PC apart to inspect it I was bemused by the fact that the original cable had been removed and discarded. By flat cable do you mean straight through with no twist? I've tried this and still no luck.


Chuck(G) said:
Somewhere on the web there's a service manual for the PC7000(I've found it before), which should be identical in most respects regarding the FDD setup. And yes, I'd suspect the flat/DS0 situation might well be the case here.
Click to expand...

Yep I found a copy which is now on minuszerodegrees but couldn't find any useful info. I might have skimmed over it too quick though so will take my time tomorrow and have a good read. Most of the diagnostics looks like you need to use a diagnostic disk which seems rather pointless.

Thanks for your help so far everyone
 
I've got the download (probably from NoDevice.com) of the PC7200 manual and it does include schematics, if that's any help. Looking at the schematic there, the pinout at CN6 is a bit bizarre.

It looks to be a "flat" pinout, but with DS2 on pin 12 and DS1 on pin 14 and a single motor enable on pin 16. So almost PC "twisted", but not quite. A "flat" cable with the drive set to DS2 (third select) might do the trick. Anyway, there you go--it explains why the drive isn't spinning.
 
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Yes, but as I said "not the second, as is usual with PCs", so I don't get your point.

Did you read my post #14? The PC7000 seems to be an odd bird.
 
Chuck(G) said:
I've got the download (probably from NoDevice.com) of the PC7200 manual and it does include schematics, if that's any help. Looking at the schematic there, the pinout at CN6 is a bit bizarre.

It looks to be a "flat" pinout, but with DS2 on pin 12 and DS1 on pin 14 and a single motor enable on pin 16. So almost PC "twisted", but not quite. A "flat" cable with the drive set to DS2 (third select) might do the trick. Anyway, there you go--it explains why the drive isn't spinning.
Click to expand...

Thats some great help :) Are you able to link/upload the schematic? I'll have a play around with it tonight.

Thanks heaps! I'll keep you updated
 
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