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TRS-80 Model 1 Level II

vwestlife said:
There should be two power supply "bricks" hiding inside the expansion unit: one for the expansion unit itself, and one for the system unit (keyboard).

The expansion unit connects to the keyboard with a ribbon cable on the left, as shown. The cable is short and stiff enough that it can really only fit correctly one way, especially if you want to reinstall the trim pieces that cover up the connectors.
trs80mod1system.jpg


I can't help you with hooking up the disk drives because my own Model I system didn't have any.
Click to expand...

Regarding the short ribbon cable between the system unit and the expansion interface, the cable has a stripe on one edge, should the stripe be to the left or right when the cable connects to the expansion interface? I can't make out in the picture above if there is a stripe on that cable.

The expansion interface I got apparently has a parallel and serial port. I think I have determined that the front right connector is for the serial port and the rear is for the parallel port. The connector on the left side of the expansion interface is for the floppies.

In regards to the trim pieces, how do you reinstall them after you put the cable on? The ones I have actually attach to the edge connector which obviously can't be done if a cable is attached.
 
All cables on a Model I exit the cable connector downwards.

The drive cables, at the drives themselves, have the stripe at the top, even if you have to twist the cable into a loop (the loop thing depends on which side of the E/I you have the drives on)
 
Also, look at the part number on the two disk drives you got. One should be a 26-1160, and the other should be a 26-1161. They are exactly the same except the 26-1160 has a termination resistor and needs to be the last drive on the cable. So, it goes like this... You got a ribbon cable with 5 connectors on it, right? Four connectors are relatively close together, and the 5th connector goes to the Expansion Interface (connector on the back, left side of the expansion interface). Attach the ribbon cable to the expansion interface. Attach the 26-1161 drive on the connector that is closest to the expansion interface. This will be the boot or :0 drive. Attach the 26-1160 drive to the next connector down the line. This will be the :1 drive. The drive number :)0 or :1) is determined by the position on the cable. :0 is the closest connector to the EI, and :3 is the last connector on the cable.

If the drives you have are something else (like a 26-1164 which is an external drive meant for a Model III or something non-Radio Shack), you may have to open up the drive case to see which drives have term resistors. The 26-1164 has a term resistor. Also, I've used TRS-80 color computer drives, but they all have term resistors as well.

If you are unsure which drive has the term resistor, for now don't worry about it. With only two drives, it doesn't matter that much, but you'll want to get it figured out for sure later.


After hooking it all up, if you have problems booting from a disk, make sure the expansion interface is connected correctly. Do the eraser thing on the edge card connectors (all of them) and re-seat the cables. Disconnect the disk drives from the EI and power up while holding the BREAK key to bypass the disk system and enter Cassette BASIC. Press ENTER a few times to get to a BASIC prompt and type ?MEM. If your EI has memory (do you know how much memory it has?), it should list something greater than 16K. If the EI isn't connected correctly, then ?MEM will print just shy of 16K or the computer won't boot period. Clean the contacts again, re-seat the cable between the keyboard and Ei and try again. Once you have this working, then re-connect the floppy disk drives and try booting from a floppy disk.
 
I finally cabled everything and powered it up! First I tried holding the BREAK key while turning the power on, then I hit ENTER a couple of times which brought me into cassette BASIC. I entered ?MEM and got 48340 so it looks like I have a full 48K.

If I power up without pressing the BREAK key then all I get is a really ugly checkerboard looking screen with a bunch of characters scattered around on it. The disk drive cable is marked "This side up" so I plugged it in that way. Plugged in that way the only drive 0's drive light comes on and stays on with the motor running, nothing from drive 1. I tried flipping the cable over but when I do that nothing happens. Is the checkerboard screen normal and, if so, how long should it take until the system looks for a disk to be in the drive?

The drives came already cabled in cases so my next step is to open the cases and check to see if the cables are on correctly, clean contacts with an eraser and check terminators. Wish me luck!

The text on the display is rotated to the right slightly, I guess 2-3 degrees. Is that normal? Is there a user adjustment for it or does it require opening up the monitor to adjust it? I'm not sure if it's a gun alignment or the CRT has shifted internally.
 
If drive comes on IMMEDIATELY with the power, the cable is upside down. As in, comes on and stays on forever.

Can't help with the checkboard.
 
Yes, the checkerboard (random character) screen is normal. If there is a valid disk in the drive, the checkerboard screen will disappear immediately and you'll hear disk seeks as it boots. If the disk isn't valid (i.e. no valid boot sector found) or there is no disk, the drive light will come on for a couple seconds and then go out and the random character screen will remain. You may or may not hear head seeking, probably not as the head will already be seeked to the boot sector. If the light goes on and remains on, that may be a cabling issue (wrong connection, or dirty cable).

Also, I forget the order, but if you have two drives connected, but power up only one drive, you will get the LED on solid, and the powered up drive will spin continuously. So, either completely remove the second drive for these tests, or make sure they are both powered on, and not spinning once all drives are powered up.

To make sure your cables are correct... When looking at the Expansion interface from the rear, pin 1 is on the right side of the floppy disk connector (closest to the corner of the EI), and the cable should exit down from the edge card connector (if it's an original TRS-80 cable and not one someone made incorrectly). The pin 1 wire should connect to the bottom of the floppy edge card connector on all the drives. Note, if your cable has a striped wire (which normally means pin 1), it may not match pin 1 on the expansion interface. Druid's comments above said that the stripe is up, not down, but that would mean the stripe means pin 34, not pin 1. Don't trust the stripe. It may not be correct (I think I've seen cables with the stripe up and down). The original TRS-80 cable has keys that prevent the cable from being attached upside down to a floppy drive. If your cable doesn't have these keys, it's probably one someone made on their own. Remember these are old machines and who knows what people have done over the last 30 years.

If still no success, then clean all the contacts again, or check the cable to make sure it doesn't have a broken wire. As you said, you may have to clean the contacts inside the drives as well. But, make sure everything external is correct first.

The text on the display is rotated to the right slightly, I guess 2-3 degrees. Is that normal? Is there a user adjustment for it or does it require opening up the monitor to adjust it? I'm not sure if it's a gun alignment or the CRT has shifted internally.
Click to expand...

It's probably the CMOS inverter(s) in your video sync circuit. I have had to fix this on two of the three Model I's I have, and at least half the Model I computers I've seen for sale have this issue (vertical or horizontal sync issues). People think it's just an adjustment issue. Nope. It's a blown or partially blown CMOS inverter IC.
 
Both of the disk drives are hooked up and working now! I am able to boot to a DOS READY prompt and I can do DIR or DIR :1 to find the contents of disks. Like I mentioned in an earlier post many of the disks are labeled with different DOSs like TRSDOS, LDOS or NEWDOS. It seems that a disk formatted with one DOS isn't readable by another, is that true? Anyway, I am now wading thru the 100's of disks I have to try and figure out if I have any "useful" software.
 
Good to hear it's going.

The DOSes MAY read other's disks. Many people with newer DOSes configured them so they read the old TRSDOS standard disk configuration anyway.

Tez
 
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