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Trs 80 disk error

J

jonathancox

Member
Joined
Dec 6, 2009
Messages
18
Location
Southborough MA
About a month ago, I found a TRS 80 model IV in our school's basement. There were three boot disks that were with it, so I hauled it out and tried it.

When I insert a system disk into drive A it says "DISK ERROR." When no disk or a non-system disk, it just hums for a while and then shuts off. It doesn't even say Diskette? unless I insert the disk upside-down(???)

I looted a 3.5" drive from the same basement to try to install. A tech guy helped me press a DIP connector to the cable. I couldn't find any jumpers on the drive itself (I guess it's a newer style drive hardwired as B) so I modified the cable as shown here: http://www.mainbyte.com/ti99/hardware/cables/35drive.html. I then wrote a 3.5" bootdisk with David Keil's emulator, which, while working fine in the emulator, is not even recognised by the TRS 80.

I have decided to try the 5" Tandon drive again. I have ordered some bootdisks from Ira at trs-80.com. He did mention the heads may be dirty or the stepper kaput. So, I dabbed the heads with Isopropyl alchohol and cleaned the rails with it too. The heads don't seem to even move. I don't want to try Ira's disks until I am sure the drive won't kill them.
Any ideas?
Thanks.
Jonathan.
 
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The wiring you found is for a TI 99-4a...


NOT THE SAME on the model 4.

Will attempt to put in the one I built for my 4p... should be the same!

Cable Diagram FDD.jpg

Rewire it this way for 3.5 drives...

This also assumes the drive is still PC compatible....
As far as the 5.25 steppers not moving, if the 3.5 is still connected that way it likely wont move or anything else...
If it (5.25) is connected by itself, move the head before powering up and see if it moves 'home' to read trk 0...
 
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I have removed the 3.5" connector from the cable. Now remaining are the two 5.25" drives. I moved the head to the middle, but they don't move back when I turn the machine on. Hmmm... I opened the back and gave the MB a clean, and all the contacts. The header from the FC to the MB may be at fault, seeing how flimsy it is.
Here's what happens now:
I turn it on without a diskette in. Sometimes it goes to Cass?. Most of the time it keeps a blank screen and after a couple minutes (long wait) I get lots of random text (mostly @ signs) scrolling on the screen. Then it will reset itself and hum again, and display "Diskette?" on the screen.

Hopefully I haven't fouled something up through cleaning or removing the connector.
Thanks for your response.
Jon.

EDIT: I cleaned both the heads and rails with alcohol. Perhaps this removed the lubrication?
 
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First, it doesn't sound like it's the drives (or it's the drives and something else).

Without a diskette in the 0 drive, it should come up with "cass?" and, if you hit ENTER, "Mem Size?"

If you hit ENTER again, it should go to ROM BASIC.

Since it doesn't do this consistently, I'd start by reseating all the socketed chips on the main board (you'll have to take the board shield plate off) and see what you get from there. You don't have to put the casetop back on every time, it'll work fine laying on its side next to the base. Might as well check all the power and interconnect plugs/ribbons while you have it open.

If you can get it working consistently with no diskette, we'll see if there is anything wrong with the drives.
 
Thanks Druid...
I pulled it apart and undid all the connections. The tech dept doesn't have a socket-extractor-thing so I can't attempt that just yet. I did notice that when I took the ribbon cable out of the Floppy controller, some of the metal strips bent back. I put them back in carefully and I think they make a connection. But just in case, I swapped the RS232 cable, which is perfect. I've got to go to a class now, but I'll come back in a bit and see what it did...

EDIT: OK so I plugged it all back together, and the first time, it said Cass? (and got to BASIC just fine) and after being reset went blank as if it was booting. After a minute or so the drive shut off and lots of "@~@~@~@~@~@~@~@~@~" appeared across the screen. I don't know what that means...
 
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jonathancox said:
Thanks Druid...
I pulled it apart and undid all the connections. The tech dept doesn't have a socket-extractor-thing so I can't attempt that just yet. I did notice that when I took the ribbon cable out of the Floppy controller, some of the metal strips bent back. I put them back in carefully and I think they make a connection. But just in case, I swapped the RS232 cable, which is perfect. I've got to go to a class now, but I'll come back in a bit and see what it did...

EDIT: OK so I plugged it all back together, and the first time, it said Cass? (and got to BASIC just fine) and after being reset went blank as if it was booting. After a minute or so the drive shut off and lots of "@~@~@~@~@~@~@~@~@~" appeared across the screen. I don't know what that means...
Click to expand...

You don't have to extract the socketed chips, just press them tighter into the sockets. Slipping something solid between the main board and the back of the shield will keep the board from stressing too much. Just slide it across until it's behind the chip you are pressing on and be careful not to snap any mod wires on the back of the main board, if there are any.

The @ sign is USUALLY a sign that there is a ROM decoding problem.
 
By thermal problem, i suppose you mean some of the solder has cracked and when it heats up, it expands, causing the connection to come undone?

I'll go try it out again now to confirm that this is what happens... but shouldn't I get a Diskette? message when I turn on the computer (not a Cass?) I can *always* get Cass? by holding <break> as I push reset... and OUT commands will spin the drives. Arghh... I just have no idea.
 
OK I've just gotten back from break, so I went and turned the TRS 80 on. It goes straight to the Cass? prompt every time now. The floppy drive light turns on and spins when turned on as well.
Someone in another forum said to try PRINT MEM and it returned the proper amount of 48082. I've pulled it to bits again to give everything a check over and pressings chips in again.
Since it looks like the floppy controller is fine (I assume as the light turns on) what else could be wrong?
 
Is this a 2 drive unit? If so, disconnect the floppy drive cable from the drives and attach the connector on the end of the cable to the upper drive and see if it boots from that one.

If it does, then the original drive 0 has a problem. If it doesn't, the problem could be with the floppy controller.
 
I tried that just now- the light came on and it spun but the head isn't skipping and it went straight to Cass?
What I may do this afternoon is get a multimeter and see if the cables are a fault.
 
I checked the continuity of the cables and the connections from the floppy controller. They were all fine. I think that the controller is working becase OUT 244,1 causes the 0 drive to spin and light up and OUT 244,2 causes drive 1 to do likewise.
I could not hear the head stepping, though I did notice that when power was going to the drive, the head could be moved by hand in 'steps.'

What should the computer do if there is a floppy controller present, but not a drive? Is there a test to determine if the disk system is actually active?
I apologise if the wording is off; I'm a newbie.
Thanks...
Jon.
 
It might pay to get a small screwdriver and just prise all socketed chips up a little, then press down on them. Maybe in this case just pressing down isn't enough to knock off some possible oxidation?

Just a thought.

However, I've revived enough computers now to know that components can and often do just fail. So all the connections could be fine...it's just that a small logic IC, a capacitor, a controller chip etc. has gone west. These faulty parts can be very hard to diagnose.

It sounds like the floppy controller might be the offending part. Any chance of borrowing one off someone locally so you can swap it with yours and see if you get the same symptom. At least this will isolate the problem.

Tez
 
Thanks Tez, I'll give that a try.
The first few weeks I had it I was able to get a DISK ERROR message as opposed to just the Cass? It's just after I came back to school, it won't do anything other than ROM BASIC. It would, before, try to boot and give lots of @ signs.

I'm in Boston; I suppose I could ask around. I could start with the ICT department but I don't know where to look. In the place I got this machine, there is also a DEC VT180 which has a similar CPU but could I somehow get that floppy controller into the TRS-80? That is probably a really daft question, but thought it may be worth asking...
 
Being able to select drive 0 or 1 does not mean that the controller is working properly. The select/motor-on latch is independent of the actual controller logic in this case...

If I am right, this system has a separate FDD board? (I have a 4p... different beast... see above, tho the LOGIC is the same/similar!)

IF THE HEAD is already at track 0 it will MOST LIKELY NOT step... again, try forcing the carraige away from track 0 THEN power-up and see if it moved back.
IF IT MOVES there may be a problem with the drive(s)...
IF NOT, there is an issue w/ the FDD board.

IF I recall, you had a disk IN THE DRIVE the 1st time when you were getting the DISK ERROR.... ?

And no... systems of this 'age' were EXTREMELY proprietary... asking it to fit would require a GAGGLE (?) of druids... :)
 
Yeah the FDD board lives under the main board, connected by a dinky ribbon cable.
So the controller must be faulty. I tried moving the head and it returned the same Cass? message. Arghhh... :(
I have had it out for a while. I could, before, get the drives to step back to 0 and ask for a Diskette?, and just needed some lubrication, but now for some reason it's just quit
I don't understand what else, other than connections, I could have damaged by opening the machine.
So at this point is my only option to find a parts machine, do you think?
Thanks by the way :cool:
 
jonathancox said:
Yeah the FDD board lives under the main board, connected by a dinky ribbon cable.
So the controller must be faulty. I tried moving the head and it returned the same Cass? message. Arghhh... :(
I have had it out for a while. I could, before, get the drives to step back to 0 and ask for a Diskette?, and just needed some lubrication, but now for some reason it's just quit
I don't understand what else, other than connections, I could have damaged by opening the machine.
So at this point is my only option to find a parts machine, do you think?
Thanks by the way :cool:
Click to expand...

Yes, it's frustrating when things that were working, stop working.

Sometimes things can be diagnosed by slowly tracing out where signals should go with the aid of a scope, multimeter, logic probe, technical manual and (in my case) a lot of generous help from people who know. The TRS-80 floppy drive controller is a specialised piece of equipment though and a lot of people won't be familar with it. You'd need to be prepared to spend a lot of time with no guarantee of success.

As you are in the US a parts machine might not be that hard to find. Another opion would be to try the comp.sys.tandy group over in google groups. Some people there know these machines backwards.
 
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