Basic info on unjamming your National Cash Register


Some of the most common Email I get asks for advice on unjamming a cash register where the keys are stuck or the crank won't move. So I am going to convey some of the very basic info I can give in this form.

I will focus on 2 registers: the 300 class total adders like the candy store 313 or the wider 332 Dolphin style machines and also the 400 class crank machines.


First, the 300 class machines (see page 4 on clarification on what principle machine you have)

Ok, very frequently 2 keys are pressed down at the same time or one key is stuck partway down. Here are the steps to take with this type of machine.

First try the obvious:

1. If one key is partway down grab hold of that key between the thumb and forefinger and shake and press it hard. See if you can make it move. Remember this is nearly 90 years old and may just be sticky. Do not press super hard just try and work it along. Remember it must go all the way down and then come back up. It may get stuck on the down stroke or on the way back up.

2. If you machine has a printer on the right side open up the cover and look to see if any parts are out of place or preventing movement. Sometimes the printer gets parts out of place and causes a jam. I no specifics her but see what you can find. You maybe able to remove a couple of pieces and see if it will let go. Don't do too much here before you try steps 3 and 4.

Now for the more advanced help:

3. Ok, if 2 keys are pressed or one key just won't move, you will need to open the machine up. Lift up the lid and remove the dust cover (the lid over the counters) by taking out the 2 screws and lifting it out. Take a look inside if your machine is in really bad shape and full of rust or other stuff there may be no hope but try this. Over to the right inside the machine is a catch lever that is engaged to a gear's teeth. This catch should be held on by one screw and have a small spring on it. This is the anti-reversing catch that does not allow the gears to rotate backwards. Try lifting it up so it no longer is engaging the gear. This may allow the register to rotate backwards and allows the keys to come back up. This often unjams a register.

4. This is very advanced but may be the last hope: Frequently the counter mechanism in total adder machines is the culprit for cash register jams. This is why it is often removed or missing from registers. You must remove your adder now. The adder is the self contained unit in the center of the register which shows dollars and cents. It is held into the machine by 2 slicing pins on either side down deep in the machine. These slider pins move in sideways to hold in the adder. These pins have a screw coming in from the top keeping them in place. Loosen this screw on each and the pins should slide sideways. This will allow the adder to lift out of the machine. Try steps one and two to see if you are successful.

Well folks this is the best advice I can give on the most common jams on total adders. If this did not work your machine probably has serious problems or major rust and dirt down in the gears. So seek professional help or take the case completely off and see what you can find down inside. Good luck.

Now, the 400 class crank machines (see page 4 on clarification on what principle machine you have) 

First you must know that in order to crank a 400 class machine you have to press an amount key and one of the letter keys, or you can use the rare No sale key. Also make note of the reset lever which if found on the left bottom front of the register. This will pop out the amount keys if the register has not started cranking. Also sometimes the springs that make each push keys pop back up sometimes fail, so see if you can lift the keys up.

If you have a crank machine that is stuck in mid crank you are in trouble. These machines are not easy to unjam and I only have a couple of tips to offer. It usually takes a complete disassembly and a professional tinkerer to unjam one of these, but here are a couple of things to try.

1. First like the 300 class above, grab the crank and move it back and fourth but absolutely do not force it. If you crank real hard you will break the register.

2. Take the printer cover off the side. Jams often occur in here. Move the crank back and forth and see if you can see anything impeding the movement.

Ok now for the hard stuff.

3. You must now remove the back panel from the register. Remove the top cap with the 2 larger screws on top and then remove the smaller screws holding on the back. Now you will see the greasy mess on the inside of the register about the middle of the machine you will see a gear with fine teeth on it (much finer that the other gears.) You should be able to see an anti reverse catch on it. Take a small screwdriver and wedge it between the cog and the gear. The mechanism will now crank backwards. See if you can get the crank to move back and forth.

4. Now for the last straw: remove the front of the register around the push keys. You pretty much have to remove all the case to do this. Once inside look toward the bottom of each row of keys and you should find a tab, which engages a bar that goes across the front of the machine and attaches to the reset lever. The reset lever is prevented from moving when the register is partway through a crank cycle but you can move the lever at the bottom of each row of keys and try to pop out the amount keys individually. This only works on the $ and cents keys. And it has worked to unjam things for me before, but it is rare. I am sorry to say that jams in 400 class machines are often quite complex and it may require professional help. Now that you have the case off you should give it a good cleaning and relubricate. Good luck.


I hope to have more photos on this subject in the distant future but I hope these tips help for now.

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