• Please review our updated Terms and Rules here
  • Exhibitor application for VCF West 2022 is now open! If you are interested in exhibiting, please fill out the form here.
  • Here are the results of the VCF East 2022 Post Event Survey: Survey Results

Model 4 upper drive problem

miniman82

Member
Joined
Dec 23, 2021
Messages
16
Your photo shows a late model Texas Peripherals drive. There are no drive select jumpers like on the Tandon drives. Drive select is done with pins removed from the flat ribbon cable.
You mentioned the drive cable has good continuity in your original post. If you have a straight through cable using all wires, that's your problem.
Also, a terminating resistor pack is not used on internal drives. It is only used on the last EXTERNAL drive on the system.
Good info, thanks!

it's not straight through, the manual says for Drive 0 pins 12, 14 and 32 should be missing- they are. For drive 1 pins 10, 14 and 32 should be missing- they are. Not that I assumed a problem with the cable as it looks original to the machine, but for the sake of covering all my bases I checked and it looks good to me.
 

ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
According to what the Radio Shack Manual shows there are Drive Selects 1, 2, 3, and 4 marked on the PCB.
Those should really be DS{0..1} with 2 & 3 being cut, assuming the Data Cable has all the Card Edge Connector
Pins installed. Drive 0 needs the DS1 PCB trace cut. Drive 1 needs the DS0 PCB trace cut.

Larry
 

Attachments

  • DriveSelect.png
    DriveSelect.png
    54.6 KB · Views: 2

ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
miniman82,
Looks like I skipped another step in test #3.

Your cable has Pins removed so it automatically selects what Drive should be 0 or 1.
And test #2 showed Pins 18 & 20 as being +5.0 VDC (Pin 18 was suspect from previous tests.)

TEST #3
With the Data cable connected to just Drive 1 (Top Floppy Drive and removed from Lower Floppy Drive)
Test Voltage on Edge Card of Floppy for Pins 18 & 20. (should be +5 VDC) Use TP4 (COMMON - LOGICAL
COMMON for the Logic PCB).

Now check the Voltage on Pin 8 of U9 (Pin 18's HIGH Voltage is on Pin 9) and Pin 8 of U9 should be 0 VDC
and is TP10 on Logic PCB.
Do the same test for Pin 10 of U9 (Pin 20's HIGH Voltage is on Pin 11) and Pin 10 of U9 should be 0 VDC
and is TP6 on Logic PCB.

What do you get?

Larry
 

ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
OK, If I didn't overlook something those signals should be correct. The next step I'd try
is the TRS-80 Diagnostic Floppy. You can boot from it in Drive 0 and select the various
menu's to see what is available. Then when you are comfortable with the menu's
choices, Select Drive 1 to test. Test the RPM, the Stepping, and other options for the
suspect drive. I wouldn't be adjusting anything on the Floppy Disk Controller (FDC)
until you know 100% what you are doing and know what it needs to be set for.

Larry
 

ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
Well, I was lucky to have created a *.DMK file when I backed up the Floppy. I have installed
the SDLTRS software and have the image booting on my Debian 11 - 64 Bit Laptop. Now,
all I have to do is install it on my Debian Desktop and connect a 5.25" Floppy and write the Floppy.

Here are a few of the Menu's in the Software.

Larry
 

Attachments

  • M4-menu0.png
    M4-menu0.png
    13.4 KB · Views: 11
  • M4-menu1.png
    M4-menu1.png
    11.4 KB · Views: 10
  • M4-menu2.png
    M4-menu2.png
    11.9 KB · Views: 8
  • M4-menu3.png
    M4-menu3.png
    11.9 KB · Views: 8
  • M4-menu4.png
    M4-menu4.png
    13.1 KB · Views: 10
  • M4-menu5.png
    M4-menu5.png
    13.6 KB · Views: 7
  • M4-menu6.png
    M4-menu6.png
    10.8 KB · Views: 9

miniman82

Member
Joined
Dec 23, 2021
Messages
16
Thank you for the offer, I’ll see about dropping a few disks in the mail. Just send one good one back with the program, you can have the other for your stock.
 

miniman82

Member
Joined
Dec 23, 2021
Messages
16
I have a set of disks going out this coming week, one you can keep. Send the other back with whatever programs you think may help.
 

ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
OK, I'm waiting on them to arrive. Did you have a chance to look at the Hinge Part and see if yours
looks like the Photo I attached? Also, is your Hinge Rod a Full Length Brass Rod, or two short White
Nylon Pins?

And how much do you have to move the Loading Arm to get the top Floppy to read a Floppy?

Larry
 

miniman82

Member
Joined
Dec 23, 2021
Messages
16
Edit-

I have a long brass rod on mine, but I don’t see anything that looks like the piece in the rendering. Is this possibly a case of not spinning the media because it’s not clamped solidly? Because it definitely feels like it’s grabbing the disk enough, the the head is going all the way down.
 
Last edited:

ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
I received your two 3M Floppy's yesterday 01-20-2022. Will try to get them done this weekend
and mail Monday, if everything works properly.

Larry
 

ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
Nick,
The two 3M Floppy's are the same Diag Software, the other New floppy I added is another version I located
in my stash. I've marked the two floppy's that I booted to the Diags so you know 100% they worked
for me on a Model 4.

I'll put the box in the Sun City, AZ PO this morning with tracking. You should have it Saturday or
Monday.

Here is how I created the Floppy's. https://forums.debian.net/viewtopic.php?f=16&t=151313

Larry
 
Last edited:

zombienerd

Veteran Member
Joined
Mar 31, 2017
Messages
553
Location
New Hampshire
Greetings,

I got a model 4 from a neighbor and got it running (blown power supply caps replaced, brother was able to make me a TRSDOS 6 disk on his XT), but there’s one last issue I can’t seem to figure out.

The upper drive (1) refuses to read disks.

Now here’s the strange thing- if I swap drives, the upper drive works flawlessly in the drive 0 position.

The drive cable has good continuity, as does the ribbon cable connecting the floppy controller to the motherboard. Is it possible something failed in the controller?
My model 4 was the exact same way. I assumed something was wrong with the floppy controller. The :1 position would not work with any drive I installed (and I tried several compatible drives)

I installed a HxC modded Gotek in the lower :0 position and haven't thought about it since.
 

Patrick.B (TTR)

Experienced Member
Joined
May 11, 2011
Messages
344
Location
Houston, Texas, USA
does your floppy drive cable look like this ( look into the slots for missing pins)

O0oIi1J.jpeg
 

miniman82

Member
Joined
Dec 23, 2021
Messages
16
I think we just dodged a bullet, I came home and by pure chance the box of disks were sitting directly on top of another box from eBay containing a subwoofer with an unusually large and powerful magnet. But all the disks seem to have survived, I assume you’ll want me to run the disk checking program first?
 

ldkraemer

Veteran Member
Joined
Mar 14, 2013
Messages
2,096
Location
Chaffee, MO
Well, both floppy's have Diags for the Model 4, and I'm not exactly which is the best. That will be your
area ox expertise. I just wanted to make sure that you had both copies. I've booted both but that is
about the extent of my testing.

Glad you got them so quickly.

Larry
 
Top