A Tandy 1000EX is harder to disassemble than a typical 1980s PC clone. And for as popular as this machine is, I couldn’t find any thorough explanation of how to do it. Even the 1980s service manuals for the machine gloss over or omit disassembly. So here’s how to disassemble a Tandy 1000EX, such as to give the case a thorough cleaning.
Why no disassembly instructions?
Lack of disassembly instructions anywhere else online may be because all the major chips are socketed. That means you can do many repairs without removing the board. But if you need to recap the board, replace some other non-socketed discrete component, or fix a damaged case, you’ll need to remove the board. And you’ll find that takes more doing than it first appears.
Unplug the system before disassembling it. The power supply is completely open inside the case, so there are high voltages present. Avoid touching the power supply components if at all possible, as the capacitors can still hold some charge even after unplugging.
The Tandy 1000 EX is completely held together by screws. There are no tabs. So if you are used to removing screws and then having to force tabs, you will damage the machine. The Tandy 1000 EX comes apart easily once you have removed all the screws, it’s just that some of them are hidden.
On the underside, you will find nine Phillips head screws of two different lengths. The screws at the back of the machine are much longer than the screws at the front of the machine.
But wait, there’s more! Additionally, there are two more screws inside the case holding the top and bottom halves together. The two screws are under the expansion slots. Remove the slot cover, assuming you still have one. Don’t force that either. The trick with the top cover is to push it down and back, and then it slides right off. It’s much easier than it looks.
Once you have the slot cover off, you can access the expansion slots. There are two more screws in that bay, next to the power supply. You may need to remove the expansion cards to be able to see them. The expansion cards screw into the back of the case. Two screws hold each expansion card, and then the expansion cards plug into the slots. The connector uses pin headers, even though it is electrically the same as an 8-bit ISA expansion slot.
Once you remove those last two screws, the top half of the case lifts right off.
The internal floppy drive is screwed to a metal bracket that is in turn screwed to the case. One of the lower case screws helps hold that cage in place, but there are three additional screws inside that secure the bracket. Two of those screws are toward the back of the case, and it’s a tight squeeze to reach them. Once you loosen the screws, you may need a pair of needle nose pliers to retrieve them.
These screws are a different length from the other screws. Do not confuse them with the other case screws, or you will damage your case.
Once you remove the screws from the bracket, it lifts out. Disconnect the power and data cable from the drive if you need to remove it completely.
If you need to service the drive, it is secured to the bracket with regular machine screws. My example only had three, and given how tight one of them was, it probably came from the factory that way, but it can certainly take four screws.
Replacing the floppy drive
Note that if you intend to replace the drive, it can be a bit tricky. The cables are exactly long enough to reach the positions on a Teac 5.25-inch drive. If the position is a bit different on another brand, it may not fit. Also, a 1.2 MB floppy drive is not compatible. You will also have to jumper the drive to DS0 rather than DS1, which is the jumper setting most PCs use.
You can use a 3.5-inch drive, even a high-density drive, and the BIOS will use either type as a 720K floppy. But you will have to find a way to set the drive to DS0. Depending on how old your floppy drive is, it may not have jumpers to select DS0. And the twist in a standard PC floppy cable isn’t compatible with the Tandy 1000. If you cannot select DS0, you will need to swap two wires on the floppy cable to make a 3.5-inch drive work.
The motherboard is wrapped in metalized plasticized cardboard shielding to reduce interference since the outer case is plastic. The RF shielding isn’t necessary for the operation of the PC, so you can leave it out. Originalists like to keep it, but since the shielding acts as a heat trap, many hobbyists remove it. The motherboard can short out against the metal plate if you remove the shielding entirely, so I cut the top part and left the portion that sits under the board.
If you need to get out the motherboard, say to swap the CPU for an NEC V20, you will need to remove the shield at least temporarily.
Removing the motherboard
Removing the motherboard is very different from a standard PC. Flip the system over and remove the volume knob by pulling it straight up. Then flip the case back over. Remove three screws on the right side of the board. Then remove the four small nuts that hold the RF shield in place. Flip the shield up, then remove three more screws and the large brass ground lug at the back right. Finally, turn the system around and remove the two hex standoffs from the RGB connector. A small 5mm nutdriver is very helpful for this.
Unplug the power supply and fan cables from the board. Remove the two screws on each side of the keyboard. Flip the keyboard up and unplug the speaker. Unplug the keyboard if you wish. There are three connectors. Lift up on the ribbon connectors before attempting to pull the ribbon cables out.
The motherboard tilts out once you remove all the screws.
With the motherboard out, you can repair the case with plastic epoxy if needed. I did.
Replacing the motherboard
Replace the RF shield if you’re going to use it. It’s much easier to do so outside the case, to get the holes in the shield lined up with the holes in the board. Secure them with a bit of tape to help hold everything in place.
Next, tilt the board into the case.
To avoid damaging the threads in the posts, place the screw in the post, then turn the screw left until you hear a click. That’s the sound of the screw dropping into the threads. Then turn the driver to the right to secure the screws. This minimizes damage to the posts.
Replace the three screws on the right, then flip up the shield and replace the screws on the left and the brass ground lug. Flip the shield back down and replace the four nuts.
Replace the two hex standoffs on the RGB connector. Reconnect the speaker, fan, and power cables. Then reconnect the three keyboard cables and screw the keyboard down. Finally, replace the volume knob on the underside. It only goes in one way, so don’t force it. Just rotate it until it fits correctly.
Replacing the floppy drive
The trickiest thing about reassembly is the floppy drive.Double check the screws to ensure you’re using the three medium-length screws, and not confusing them with case screws.
You probably will not be able to reach to hold the screws in place while you drive them in. It helps to secure the screw temporarily to the screwdriver with a bit of masking tape or tacky wax to make it easier to drive those two screws in.
Reconnect the data and power cables to the drive. The floppy drive connector isn’t keyed but the stripe goes toward the keyboard.
Closing up the case
Place the top half of the case over the rest of the assembly. Replace the two screws on the inside next to the expansion slots.
On the underside, the threads were slightly different on the long screw that went next to the floppy drive, so I used that same screw next to the floppy drive. The other three long screws go to the back of the case.
You don’t need all six screws at the front to hold the case together, but I put all of mine back in. They’ve been together with the machine this long, so there’s no reason to separate them now.