One of my recent projects was restoring a RT 707.
In the process I noticed that the Plastic direction buttons were deformed from heat and in the case of one, didn't work because of this deformation. I assumed this was caused from the heat of the incandescent light bulbs. To solve the problem, I decided to use LED's as a replacement since they don't generate heat.
I acquired some 3mm white LED's, (green could also be used for a darker color). 5mm LED's are too big for the opening. The direction indicators in the buttons are green, so they appear green when lit. The issue with LED's is they operate at a max of approx. 20milliamps so current limiting resistors are needed. The voltage supplied to the lights is approx 26v dc. Some calculations indicated a resistor of 1,200 ohms would bring the milliamps down to approx 20ma. For a margin of safety, I decided to use two 1200 ohm resistors which brought the ma down to 11. I placed one on each side of the LED. Because of the heat dissipation, I used 0.5 watt resistors instead of the 0.25 watt versions.
The resistors could be incorporated in the wiring which would make the project very easy and fast, but I decided to mount the resistors on the RWX 152 Connector Assembly. Attached are some pictures of the board and the lights. There now is no heat at the plastic direction buttons, and very little heat at the resistors.
To use the board some of the pins had to be relocated. Here were the steps:
1) Relocate the pin at 27 to 26
2) Connect a 1200 ohm resistor across 25 and 29
3) Relocate the pin at 24 to 37
4) Connect a 1200 ohm resistor across 24 and 38
5) Relocate the pin at 34 to 45
6) Connect a 1200 ohm resistor across 36 and 46
You could accomplish the same result by doing just steps 1 & 2 by using a 2400 ohm resistor in step 2, although more heat would be generated at the one resistor. The value of the resistors controls the amount of current going to the LED, which is crucial. If there's more than 20ma the LED is toast.
After the above, all that's left is connecting the LEDs. The polarity is important, pins 28 and 30 are positive. I used some shrink tube that fit over the LED. That provided a snug fit in the opening so the LEDs stayed in place.
Now there's no issue with heat at the buttons.
I also had to replace the record and pause indicator LEDs. This was a straight forward replacement with 5mm LEDs.
In the process I noticed that the Plastic direction buttons were deformed from heat and in the case of one, didn't work because of this deformation. I assumed this was caused from the heat of the incandescent light bulbs. To solve the problem, I decided to use LED's as a replacement since they don't generate heat.
I acquired some 3mm white LED's, (green could also be used for a darker color). 5mm LED's are too big for the opening. The direction indicators in the buttons are green, so they appear green when lit. The issue with LED's is they operate at a max of approx. 20milliamps so current limiting resistors are needed. The voltage supplied to the lights is approx 26v dc. Some calculations indicated a resistor of 1,200 ohms would bring the milliamps down to approx 20ma. For a margin of safety, I decided to use two 1200 ohm resistors which brought the ma down to 11. I placed one on each side of the LED. Because of the heat dissipation, I used 0.5 watt resistors instead of the 0.25 watt versions.
The resistors could be incorporated in the wiring which would make the project very easy and fast, but I decided to mount the resistors on the RWX 152 Connector Assembly. Attached are some pictures of the board and the lights. There now is no heat at the plastic direction buttons, and very little heat at the resistors.
To use the board some of the pins had to be relocated. Here were the steps:
1) Relocate the pin at 27 to 26
2) Connect a 1200 ohm resistor across 25 and 29
3) Relocate the pin at 24 to 37
4) Connect a 1200 ohm resistor across 24 and 38
5) Relocate the pin at 34 to 45
6) Connect a 1200 ohm resistor across 36 and 46
You could accomplish the same result by doing just steps 1 & 2 by using a 2400 ohm resistor in step 2, although more heat would be generated at the one resistor. The value of the resistors controls the amount of current going to the LED, which is crucial. If there's more than 20ma the LED is toast.
After the above, all that's left is connecting the LEDs. The polarity is important, pins 28 and 30 are positive. I used some shrink tube that fit over the LED. That provided a snug fit in the opening so the LEDs stayed in place.
Now there's no issue with heat at the buttons.
I also had to replace the record and pause indicator LEDs. This was a straight forward replacement with 5mm LEDs.
