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DIY to Replace the Flip Mechanism Belt on the RX Series

I have two RX-202's and a RX-505 and the flip mechanism on the RX-505 was getting a little slow so I figured it was time to replace its belt. First I checked what belt I needed by going to my Nak FAQ web page and found that I should use the SCX5.1 belt from PRB. I picked up three since I'm also going to replace the flip mechanism belt in all three decks. Price was $1.50 each, but, I'm told that the price will be going up soon. I've never done the Flip Mechanism belt before and was a little unsure of how to start. After a false start I think I got it figured out.

Tools Required
Belt, SCX-5.1
#2 philips screw driver
belt installing tool (picture in step 6 below)

Step 1 - Remove the 4 screws holding the motor plate down and then 1 screw holding the bracket to the back of the transport. Note, this screw is shorter than the rest.

Step 2 - Remove the back cover. To do this there are 10 screws. 5 on the bottom, 2 on the top and 3 on the back.

Step 3 - Cut the cable tie holding the transformer leads to the chassis in the back left corner. Pull CN-5 located in the back right corner.

Step 4 - Pull the back of the deck off and rest it on the top of the deck.

Step 5 - Remove the old belt, but, before you do, take a look at where the belt is located and how it goes around the pulleys. Lift the motor plate to loosen tension on the belt then with tweezers or forceps pull out the old belt. Try not to move any of the gears too much. Their alignment will be checked and adjusted later, but, you don't want it too far off.

Step 6 - Install the new belt. With the motor plate slightly raised loop the belt around the large pulley like in the picture above. After the belt is on lower the motor plate and put a couple screws in to hold it in place. Now loop the belt around the motor pulley. In order to get the belt over the motor pulley a belt installing tool is really handy to have (see picture below). Make sure the belt is not twisted.

Step 7 - Replace the back cover of the deck. There are 10 screws total, 5 on the bottom, 2 on the top and 3 on the back.

Step 8 - Reinstall CN5. Replace the cable tie that was cut in Step 3.

Step 9 - Check mechanism alignment. By hand move the flip mechanism so that it is exactly half way between side A and side B with the transport out and half way spun around. You might need to rotate the gears a little by hand to allow the flip mechanism to move freely.

Step 10 - Looking through the two slots in the motor plate make sure that the arrows on the two sets of gears are aligned. The lower one (closer to the capstan motor) should be aligned still since its alignment is not affected when removing the motor plate. The upper one (next to the position feedback pot) is the one that gets screwed up when taking the motor plate off. It can't be seen in the picture, but, make sure the arrows on the two gears point toward each other. If they are off, lift the motor plate, rotate the gear attached to the pot and reposition the motor plate. Repeat until the arrows point toward each other. Install the 5 screws. The screw holding the bracket to the back of the tape transport uses the short screw.

Step 11 - Put it all back together.


You may need to perform the Slide Base Position Adjustment. (This is from the RX-202 manual except that the manual has an error where the pots VR502 and VR503 are reversed. I'm not sure if it's the same on the RX-303 and RX-505)

Step 1 - Pull out connector CN-7 on the Logic Board.

Step 2 - Ground test pin CAM B with a jumper wire to set the cassette to side A.

Step 3 - Adjust VR503 to obtain a gap of 2 to 4 mm as shown in Fig 2.4.

Step 4 - Ground test pins CAM B and CAM A with jumper wires to set the cassette to side B.

Step 5 - Adjust VR502 to obtain a gap of 2 to 4 mm as shown in Fig 2.4.

Step 6 - Ground only test pin CAM A with a jumper wire to set the cassette to its eject position.

Step 7 - Adjust VR501 to the position where the cassette is about to start rotation.

Step 8 - Repeat steps 2 to 7 two or three times.

Step 9 - Plug CN-7 back in.