• Please review our updated Terms and Rules here

TRS80 - Model 4 disk error

patscc said:
The settings are probably different, yes. The pots are there to adjust for component tolerances, in essence.
The pots, by the way, are at least 15-turn pots, so the relative position of the slot means nothing.
patscc
Click to expand...

To clarify, the pots are adjusted to compensate for differences on the logic boards themselves, but should make no difference in swapping the whole board to a different drive.


--T
 
Druid6900 said:
The drive speed is also important and check the strobe disk under a flourescent lamp which adjusting the speed control (usually a long blue object on the PCB with a little slot screw on the end)
Click to expand...

You get much sharper resolution using either a neon or LED night-light (the cheap LED ones don't have enough filtering to keep them from flickering at 60Hz).

The drive uses a "cam follower" type of head positioning mech, as described by someone else and the little metal plate they mentioned should have a small ball bearing under it that rolls in the groove on the round plastic part.
Click to expand...

No, I don't think so--these are taut-band units, not the follower style used on Shugart SA-450s. Take a look at the bottom-side photo.
 
I might have misread Dru's post, but these drives don't use the rotating cam trick to move the heads. I see the stepper motor and the metal drive band that moves the head assembly. Well, it doesn't move a large drive cam like the Shugart drives do, anyway.
 
Druid6900 said:
Ok, just to straighten out the terminology for you, the FDC controller is that board that the connector was off. The board on the floppy drive is called the drive logic board.

If worse comes to worse and you do have to send them, I have a couple of working, tested and aligned drives in case they are toast.

Wish I had some bootdisks to send you, but, until I get MY Model 4 worked up, I have no way of copying one.
Click to expand...

Thanks for the terminology lesson (I'm making notes as we go)- it's all new, as you can tell, to me.

Let's see if switching the logic board from B to A's FDD works (provided Terry Yager's reply is correct. At least if I have one drive working, I'll know if it's the boot disk or not.
 
Lorne said:
Let's see if switching the logic board from B to A's FDD works (provided Terry Yager's reply is correct. At least if I have one drive working, I'll know if it's the boot disk or not.
Click to expand...

OK I put A's board on the B FDD and tried it.
When the heads were toward the middle, I got a "cass?" message.
When the heads were toward the back, I got a "diskette?" message.
I inserted a disk, and nothing. I don't think the heads moved.

I put B's board on the A FDD and tried it.
When the heads were toward the middle, I got a "cass?" message.
When the heads were toward the back, I got a "diskette?" message.
I inserted a disk, and got a "disk error" message. However, the heads had moved slightly from the back to the middle, because the heads were no longer touching that switch.

I don't know what else to do now, other than get a package ready to ship to Druid6900.

Anyone else have any more comments/ideas?
 
I think we have beaten this one to death. Seems like we (you) are at the "let's get this thing outahere". I know I would be at that point also. Don't get me started on trying to get one of my Horizons working. I have been beating on that wall off and on for over 1 year now.
 
Now you're getting a 'diskette?' prompt? That's a very good sign. At least the computer is seeing the presence of a drive. At this point, my best guess would be, (along with others), a faulty boot disk. My recommendation, do nothing more until you have a known-good disk in hand.

--T
 
Lorne said:
OK I put A's board on the B FDD and tried it.
When the heads were toward the middle, I got a "cass?" message.
When the heads were toward the back, I got a "diskette?" message.
I inserted a disk, and nothing. I don't think the heads moved.

I put B's board on the A FDD and tried it.
When the heads were toward the middle, I got a "cass?" message.
When the heads were toward the back, I got a "diskette?" message.
I inserted a disk, and got a "disk error" message. However, the heads had moved slightly from the back to the middle, because the heads were no longer touching that switch.

I don't know what else to do now, other than get a package ready to ship to Druid6900.

Anyone else have any more comments/ideas?
Click to expand...

Hmm..I'm not sure of the significance of the above. I am suprised you get a "cass?" message when the heads are towards the middle though. I would have thought the disk controller would have returned to the back and asked for a disk!

Would the disk controller have issues?

One thought. Can you connect these drives on another machine just to check them? I'm not sure what they would be compatible with (an old PC?), or how you deal with drive selection considering there are no jumpers to select.

The problem could be the disk, the (two!?) drives or the drive controller. We really need to figure out exactly what is faulty. If your very unlucky it could be more than one problem.

There is no-one nearby with a working Model 4 you could visit?

Another option is to try to make a boot disk from one of the emulators detailed at www.trs-80.com. If you have an old MS-DOS PC and a 5.25 360k drive it's possible (apparently).

Tez
 
You did say something earlier about getting more boot disks in soon? Waiting until they arrive and trying that last combo where the heads move would be a good next move (cheap anyway). I got out a good flashlight and would sit there with my face about 3 feet above the drive, carefully watching what the head did. Does sound like it is seeking some anyway.
 
I just had a "yikes" thought. As we all know, you should NOT get a Cass? prompt when the head is in the middle. It should turn on the drive, move the head backward in single steps until the track 0 microswitch gets tripped, then read the diskette directory and go get the file.

I already noticed that if the "track 0 active" signal is missing, the computer doesn't think there is a diskette drive present. This is very strange behavior!! As in " Floppy Controller is messed up ". And I do mean the floppy controller board, not the drive logic board.
 
chuckcmagee said:
You did say something earlier about getting more boot disks in soon? Waiting until they arrive and trying that last combo where the heads move would be a good next move (cheap anyway). I got out a good flashlight and would sit there with my face about 3 feet above the drive, carefully watching what the head did. Does sound like it is seeking some anyway.
Click to expand...

I've ordered some but haven't heard anything back yet. Not sure when they'll arrive. I requested them from: http://www.trs-80.com/ and I don;t know how long he takes to make/ship them.

The thing that's bugging me, is that the disk heads don't seem to move much. The one that did move off the switch, moved maybe 1/8th of an inch. I think it could be the disk drives.

@Tezza
That seems to be the problem. The heads don't seem to move (or be able to move to the back and ask for a disk. There's just a lot of clicking from what I think is the stepping motor. I don't know anyone else with a TRS-80 and I don't have the hardware hooked up to make a boot disk from an image.
 
Time for that flashlight trick.

If the head moves ONE tiny step and dies, what is likely happening is the floppy controller card issues a seek, the microswitch goes off because the head moved slightly in, and then the controller gets totally confused because the beloved "track 0 active" signal goes away.

If the head moves MULTIPLE times before dying, then so much for that theory.
 
chuckcmagee said:
I just had a "yikes" thought. As we all know, you should NOT get a Cass? prompt when the head is in the middle. It should turn on the drive, move the head backward in single steps until the track 0 microswitch gets tripped, then read the diskette directory and go get the file.

I already noticed that if the "track 0 active" signal is missing, the computer doesn't think there is a diskette drive present. This is very strange behavior!! As in " Floppy Controller is messed up ". And I do mean the floppy controller board, not the drive logic board.
Click to expand...

This is what I'm wondering too. In all the drives I've played around with, the disk head returns to the beginning to read whatever is on the disk as soon as the drive is activated. Given that BOTH drives exhibit the Cass? behaviour and do not reposition the head, points to a floppy drive controller problem, yes?

Tez
 
@ chuckcmagee & tezza

I switched the boards on the drives and the same thing happened with both.
They couldn't both be bad, could they. Well, maybe they could, but wouldn't that be unlikely?
That's why I'm thinking maybe the heads aren't moving as they should be. Maybe the stepper motor, maybe gunked up movements (although they look real clean).
 
hehe, repeat after me, floppy controller card, floppy controller card. Remember that card mounted inside that had the 4 wire connector that was unplugged? Yes, yes, THAT floppy controller card.
 
Of course, I don't have a clear plan of action at this point. Well, I do. Let's replace the floppy controller card. Of course, that is usually pretty tough to do.
 
Yes, we are not talking about the circuit boards on the individual drives. The floppy controller is not on the drives. It's in the machine itself. It's the thing at the other end of the drive cable.

Tez
 
...or the cable/connections. There are 2 movement signals "DIR" and "STEP". DIR specifies the direction; STEP says to do it. It could also be the 7438 drivers, but that would exhibit the same as a bad cable.

In my experience, FDCs don't fail a whole heckuva lot. If that were otherwise the case, I'd be in a world of hurt trying to find another WD1781 for a couple of my systems.
 
You must log in or register to reply here.
Back
Top