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Cybernetic Data Products LED sign PS help please

Thread starter #1
I recently came across a couple of old LED signs made back around 1990 by Cybernetic Data Products. These went by the name "Silent Radio." Unfortunately, the ones I have did not come with the power supply module. I think earlier models had the complete power supply built in and you just plugged in a standard AC cord to power it up, but mine have a 5 pin DIN connector on the back instead. I took the circuit boards out of the case and found that 5 pin DIN connector mounted on a circuit board that appears to be the power interface for the rest of the sign.

I made a schematic drawing of this board in order to figure out what voltages are needed at the 5 pin DIN connector in order to bring the sign to life.
I'm pretty sure the drawing is accurate, but I'm not understanding all that I am seeing there.

PS interface.jpg

So - in the upper left of the drawing is P1, the 5 pin DIN where power comes in. On the right is a 5 pin connector that connects to the remainder of the LED sign. The TL072 op amp specs say that VCC is normally +/- 15 volts, so looks like pin 2 on P1 should be -15 volts and pin 4 of P1 should be +15 volts.
Pin 4 of P1 also connects to the input of a 5 volt voltage regulator, so that 5 volt output appears on pin 5 of P2. Pin 1 and 3 of P1 are ground, so that just leaves pin 5 to figure out. I don't really see what is going on with the two op amps and the TIP121 power transistor. Can someone help me figure this out so I can build an appropriate power supply to feed P1 please? Many thanks in advance!
Thread starter #3
All power for the LED sign enters through the 5 pin DIN connector. Looking closer at the main board that this regulator board plugs into -
Pin 1 from the P2 connector connects to the drain of seven power MOSFETs - type IRFZ34. These MOSFETs are probably the column drivers for the (29) 5x7 LED modules. Guessing they need 9 - 12 volts to operate, so pin 5 of the P1 (DIN connector) needs to have
that 9-12 volts applied. Looks like the TIP121 will act as a shunt regulator for that voltage. Soon, I will try firing this sign up by putting +12v on pin 4 of P1, -12v on pin 2 of P1 and I'll put a variable power supply on pin 5 of P1, start at around 6v and go up a few volts while observing any life coming from the LED display. See anything wrong with that approach?


Well-Known Member
The image is not clear - what is the value of R1?

Pin 1 - GND
Pin 2 - V- for the opamp
Pin 3 - GND
Pin 4 - V+ for everything
Pin 5 - ???

Because of the large value (not clear) of the capacitor and the connection to a power transistor collector, pin 5 probably is the main power for the LEDs. Are R10? and R13? both connected to GND near the TIP121 emitter?

You can use a variable power supply to test it, start with "5VDC/ 0.5ADC" and keep increasing the voltage until you reach 12 not more. Then try again from 5 to 12 but with "1ADC" and so on.

Maybe it will be better to use "8VDC" as the upper border and "1ADC", its up to you since you are risking. Do it at your own risk!
Thread starter #6
Yes - R10 and R13 are connected to ground, along with the TIP121 emitter. R1 is a power resistor .01 ohm, probably about 2-3 watt.
Agreed - pin 5 on the P1 connector will supply power to the (7) IRFZ34 power MOSFET transistors (on main board) to drive the LED columns.
Waiting for a power supply to show up that will provide the +/- 12v for pins 2&4 on the DIN, and I will be able to test this.
Thread starter #7
Update on the LED sign project -

Just got in a power supply that has a +/- 12v output, so hooked that up to the P1 connector pins 2 & 4. Put a variable voltage power supply on pin 5 of P1 and set it to 5V. Turned on the power and got no life from the LED display at all. Monitored the voltage output on P2 pin 1, which looks to be the voltage being applied to the 7 column drivers of the LED display. It was showing just a little less than 5 volts at that point. I slowly turned up the voltage going into P1 pin 5 and it continued to increase until it got to 5.6 volts and then would not increase further. Appears that the TIP121 regulator is holding it at that voltage. Voltage going into the TL072 op amp was good at +/- 12v. The LM2940 regulator was doing its job - good output at 5 volts. Maybe something else on the main board with all the logic is kaput... I dont know. I have one more of these signs that I will apply power to tomorrow. I suppose if all else fails, I can try driving the LED matrix displays with an Arduino, but I have no experience in that area. Thoughts?

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