View Full Version : 5.25 floppy issue at 10Mhz

August 5th, 2012, 06:27 AM
Hello. I just spent several hours getting my "new" XT up and running (XT clone, AUVA TXM10-II motherboard @ 10Mhz, D8087, 3c503 Etherlink, ISA monographics, WD MFM controller, and MCT-FDC-HD4 floppy controller). The drives includes a ST-225, 360K 5.25 and 1.44MB 3.5). The MCT floppy controller and its on board BIOS works great). The only issue I have is the 5.25 floppy does not read/write when I set the computer to turbo; otherwise it is fine. The 5.25 (B) is detected by the card's BIOS but any attempt to read/write at the DOS prompt is met with an error--the floppies are fine. I've had this problem before when the card was running on another XT. It is not a big issue since I generally run with the turbo off (4.77Mhz), but just thought I throw this out to see if others have had a similar problem.

I wish I would have purchased more of the MCT floppy controllers when Jameco still had them!

P.S. Here is a pic of the XT.


August 5th, 2012, 06:58 AM
I can think of two reasons that this would happen.
The bus is being run too quickly and it's messing up DMA transfers (least likely)
There's a CPU loop in the BIOS code that isn't running at the expected speed.

So, let's figure this one out. First stupid question:

Can you read and write 720K floppies on the 3" drive at 10MHz?

Second stupid question:

Before you put in the JDR controller (MCT is their brand), could you read and write 360K floppies using the old (legacy) controller at 10MHz?

August 5th, 2012, 07:35 AM
Thanks, Chuck. That's correct--I purchased it from JDR and not Jameco. I always get the two confused! Yes, I can read and write a 720K just fine at 10Mhz--just tested it. It has been a while since I tested it with the old controller; but now that I recall (it was many moons ago), I am fairly certain that I had a similiar problem with the old controller--the original setup was a 720K (A) and 360K (B). I'll have to swap out the boards to be certain--I am fairly confident though I experienced the same issue.

August 5th, 2012, 07:43 AM
What's the make and model of the 5" drive? From a controller's point of view, there should be no difference between a "360K" drive and a 3" drive operating in 720K mode.

August 5th, 2012, 07:45 AM

The 5 1/4" drive is a TEAC 55B.

August 5th, 2012, 08:01 AM
The FD55B is a good drive and fairly late in the firmament of 360K drives. So no issues with the type.

Two more questions.

What's the error message that you get?

Is the behavior the same if you swap the drives (after resetting the jumpers on the board)?

August 5th, 2012, 02:23 PM
Okay, now I'm embarrassed. I switched the XT into turbo mode in an attempt to replicate the issue to record the error message and I was now able to access the 5.25 drive--despite my numerous attempts before! The heads were cleaned beforehand but perhaps I have a simple case of a drive needing some attention and correcting the matter by selecting/unselecting the turbo was just a coincidence. R/W testing shows no errors but I’ll pick-up another drive to test.



August 5th, 2012, 02:52 PM
The heads were cleaned ......Hmmmmmmm... THAT, can make all the difference in the world!

Dwight Elvey
August 9th, 2012, 07:25 PM
You might want to put a phone book or two between the
monitor and the PC.

August 10th, 2012, 04:09 AM
Scheez... I have a swivel base for the monitor, which wasn't installed when the pic was taken. The desktop also rests on a rather high desk--really no different than the eye level of a 5150 monitor.

You might want to put a phone book or two between the
monitor and the PC.

August 10th, 2012, 08:50 PM
You might want to put a phone book or two between the
monitor and the PC.

That's often really REALLY good advice on a lot of clones. One machine that's notorious for that is the Tandy 1000 HX... I you put a CM-5 on top of it it's fine, but if you set the much better picture quality CM-11 on it, it won't access the primary drive properly. Elevating the display just two inches alleviates the problem.

Of course, with the plastic, plastic and more plastic and little in the way of an outer RF cage, a lot of the Tandy's are RF nightmares. (Mind you, I still love 'em)

I've also cleared up floppy and hard drive problems just by pulling all the cables, and routing them in a more 'clean' manner, trying to keep them away from the top of the case. Had a machine with a MDA years ago that ran great every time it was "on the bench" -- but when I put it "in the field" at a clients it wouldn't boot from the floppies. Problem was a different monitor and the floppy cable being flush against the top of the case. Doing a 'hard crimp' of the cable and forcing it to stay down towards the bottom of the case by stuffing it under the power cables got rid of the problem.

Which is funny since you'd expect if there were going to be RF issues, they'd come from the power cables inside it...

Could be worse though, had a client in the 90's who kept chewing through hard drives, they'd come back every week or two with another drive chock full... I'd ask them endless questions about how they were treating them because their failure rate was insane. "Sure you're not dropping it? Anything nearby like a giant TV or some sort of motor?".. Finally I they called saying it was acting up again after like the sixth drive replacement, and rather than them bringing it to me, I drove to them.

Only to find the secretary had covered the side of the case in refrigerator magnets. Though, this was the same ... robust woman who managed to shove a Centronics D onto a printer upside-down.

August 15th, 2012, 12:24 PM
wow refrigerator magnets.
although the teac 55 fd ? is and should be ok. there were some old cards and parts made for or intended for first generation pc's that did have problems running at faster speeds, That does not seem to be the case here.
Because testing real testing that part or situation is often nearly impossible,
the only thing you can do is change parts and software and do things differently.
that if you do it step by step, the problem will eb isolated. Otherwise the problem may re-appear.
the " move the cables" is a good first step.
I had a dtk xt high drensity controller that I returned.
it would format 720k properly OR 1.44 properly but not both. I think it was the board design or the bios on the card. another brand worked properly.
will the floppy disks format properly in another situation?
I must comment on JUMPER SETTINGS on the drives. ALL IBM and compatible drives ( not tandy)
are jumpered as B: the twist on the cable near the stripe, is for A: so the position of the drives on the cable determines which is a and which is b/
where only one hard driev was normally installed in a pc the 34 pin cable was straight thru.
later when two hard drives were often used,
there was a trict in the cable AWAY from the striped edge. so both hard drives could be jumpered the same. I THINK C
some thought of this as drive 0 and drive 1
others said drive 1 and drive 2.

Is it possible you are trying to use a hard drive cable? since 5.25" floppies and the original controller use card edge ( gold fingers) at both ends
and newer and HD and 3.5" floppy drives use pin connectors.
this can cause problems. Un
likely to cause damage.