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Help with LED sign (Silent Radio) power supply please

Discussion in 'Troubleshooting and Repair' started by slywuf, Jan 31, 2019.

  1. slywuf

    slywuf

    7
    0
    Jan 31, 2019
    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?

    Maybe someone out there actually has one of these power supplies and can tell me about it?
    Many thanks in advance!
     
  2. Tha fios agaibh

    Tha fios agaibh

    1,882
    596
    Aug 11, 2014
    I think you need to also draw out what plugs into P2 to better understand the ckt.

    The voltage is probably between 9 and 15v but don't guess.
    Perhaps D1 is a zener diode that may be marked with a Voltage?
     
  3. slywuf

    slywuf

    7
    0
    Jan 31, 2019
    Yes, I would love to see the rest of the schematic for what plugs into P2. However, that is a PC board about 2.5 feet long and life is too short to try and draw all that out. I looked closely at D1 - yes, you are right it is a zener. 1N5232, which is 5.6 volts. Does that help at all to determine what the voltage coming from P1 pin 5 should be?
     
  4. Tha fios agaibh

    Tha fios agaibh

    1,882
    596
    Aug 11, 2014
    It not a bad idea to understand what the load is instead of guessing at the values and smoking the thing. But that's your call.

    The 5.6 zener won't tell you what the supply side is but it is a clue and can explain how the op amp circuits work. If you were willing to look at what pin 4 goes to that would also be a big clue.

    It you want to guess, a regulated variable power supply would be ideal. Id start at 6v dc with +6 on pin 4, 0v (gnd) on pin 1,3 and -6 on pin 2 and using discretion slowly increase voltage. If you don't have a vps you could step from 6v to 9v to 12v.

    As far as pin 5, I haven't a clue at this point.
     
  5. slywuf

    slywuf

    7
    0
    Jan 31, 2019
    I certainly agree - knowing what the load is would be a real benefit. I'll spend some time looking at the circuitry connecting to P2 pin 1 and 4. Since the op amp seems to operate typically at +/ - 15 volts, I would think that the voltage needed on P1 pins 2 & 4 would need to be at least +/- 12v. I have a variable power supply that I can use for the 15 volt part. I'll let you know what I find.
     
  6. 73's de Edd

    73's de Edd

    2,609
    1,063
    Aug 21, 2015
    Sir slywuf . . . . .

    Very important . . .do you have the ~ $250 keyboard . . . (used) . . . that the unit uses for its programming ?

    Everything that you assigned to your P1 power connector seems correct. I just see the pin 5 as supplying the display LED's MAIN POWER for the display.
    And as it is drawn out, it would be using the TIP121 and its companion TL072A as a shunt regulator for that LED power supply.
    TL072 Beeeeeee is taking a sampling of P1 #4 supply voltage and it also relates to P2 pins 4&3 . . . so we would have to know what they connect to on the BIG board. But I sort of expect it to be voltage feedback info from them.

    Give the voltage rating on C2 electrolytic and also the 3300 ufd fiter associated with P1 pin 5, to establish the expected absolute MAX voltage of those 2 supplies..

    Can you also take a complete LED count to guesstimate the times . . . ~ 20 ma current for each Hi Intensity LED . . . . . and what they will total up to.
    It must be a bit . . . by virtue of that .01 ohm value of current shunt resistor R1.

    That's all that I presently see . . . . .

    73's de Edd . . . . .
    . . . . . . . . . . . .


    Why are hemorrhoids called hemmorhoids ? . . . . . it certainly seems like " assteroids " would be much more appropriate .
     
    Tha fios agaibh likes this.
  7. slywuf

    slywuf

    7
    0
    Jan 31, 2019
    Thanks 73's de Edd - I appreciate your comments.

    Keyboard? Well, I did happen to get lucky there. Shortly after I found this LED sign I found a Cybernetic Data Products keyboard on ePay and didn't even have to mortgage the house to buy it. Even had the proper 8 pin RJ45 connector on the end. Some of the earlier signs used a long straight connector for the keyboard. So, hopefully I will be able to put that keyboard to work.

    C2 electrolytic = 3300 uf 16 volt

    The LED display consists of (29) LTP2157AE modules that are a 5 x 7 dot matrix. Typical current draw for each LED is 20 ma so each module with 35 LED's would draw .7 amp. Total LED would be 35 x 29 modules = 1015 LEDs, which if all lit at the same time would draw 20.3 amps.

    I got the magnifier out today and had a close look at the main board, which mounts on top of the long LED display board.
    Pin 1 from the P2 connector connects to the drain of seven power MOSFETs - type IRFZ34. I take it these MOSFETs (one for each segment?) power the LED modules.

    Pin 4 on that main board connector had a 10 uf electrolytic (35v) connected and then connected to numerous components on the main board. Pin 5 connected to a long trace on the LED display board - I'm assuming it is providing 5v power for the LED logic. Pin 3 on the main board connected to a small diode, at least one IC, and who knows what else... difficult to trace.

    Does this help to predict what the power supply needs to be?

    Here is a picture of that main board -

    mainboard1.JPG

    The white connector on the right is what plugs into P2 on the power supply interface board. Just to the left of that you can see the (7) power MOSFETs. In the middle of the board you see a NiCad pack - 3.6 volts - probably for memory retention. To the left of the batteries is the RJ45 connector where the keyboard plugs in. I have no idea what the dip switches control.
     
  8. 73's de Edd

    73's de Edd

    2,609
    1,063
    Aug 21, 2015
    Sir slywuf . . . . .

    I would just gradually creep up with the supply level to the LED's, until . . . one / they . . . can just be seen to illuminate and then evaluate to see if the system can be seen as operating.
    I just hope that blank 28 pin socket is surplus or for more memory info . . .and is not being the slot where the whole operating systems program was stored on a RAM / Eprom, and was pulled to test / use in another unit. But, with you having two units . . .or more . . . that may be confirmable.

    If you will " GOGGLE" your unit, you will find that others . . . as late as 2018 . . . have been traveling down your same path, you might try to get together online and pool your findings so far.

    73's de Edd . . . . .
    . . . . . . . . . . . .


    At my age . . . . . I'm still hot. . . . . it just happens to come in flashes.


     
  9. slywuf

    slywuf

    7
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    Jan 31, 2019
    Thanks 73's de Edd... Google?? Yea, been there, done that. I started last fall trying to contact people that showed up in a Google SilentRadio search. Most of those search results were so old, the links have long since disappeared. I even tried contacting the original owner of Cybernetic Data Products (Mike Levin) but no luck there at all. There was a very good history of the SilentRadio sign that was written by Julian Macassey, who personally knew Mike Levin, but Julian did not know the nuts and bolts of the sign design, nor have any contact info for Mike. There is a guy by the name of Bob Davis that has done a lot of work with this sign and other LED signs... put quite a bit of his info up on a blog site. He pretty much used just the LED portion of the sign and designed his own Arduino interface to drive the display. I tried writing to him about 3 times..... no response. Some of my posts requesting help have come up in the search results, but I have not seen any recent search results that have any helpful information in them.
    One of the problems I have run into is that the older SilentRadio signs had a built in power supply and the driver circuitry was a little different than the newer signs like I have.
    Seems odd, since there were probably thousands of these signs made, that I cant find anyone who has a newer one that can tell me something about the external power supply.

    I have not messed with LED arrays or dot matrix arrays in the past, but am learning a few things with this sign. Looks like you cant light up all the LEDs at once on a dot matrix display... just one column or on row at a time. By using multiplexing, the LEDs can be lit fast enough that they "appear" to all be on. Therefore, the maximum current drawn by a 5 x 7 LED matrix would be about 140 ma. This is good news because the size of the power supply for the whole sign then becomes 4 amps instead of 20 amps.

    Since that opamp is typically powered by +/- 15 volts, do you see anything wrong with putting -15 volts on pin 2 of P1 and +15 volts on pin 4 of P1. Placing +5 on pin 5 of P1 should then be the minimum voltage needed to light up the LED display?
     
  10. slywuf

    slywuf

    7
    0
    Jan 31, 2019
    Update on the LED sign project -

    Just got in a power supply that has a +/- 12v output, so hooked that up to the P! 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?
     
  11. slywuf

    slywuf

    7
    0
    Jan 31, 2019
    Additional update - Hooked up the 2nd LED sign that I have to the power supplies as in my last post. No action from the LEDs on this sign either. Hooked up the keyboard and tried both signs again. First sign made the keyboard LED come on, but not when hooked to the second sign. Probably the only hope in lighting up this sign will be to use Arduino. Not really sure how to do that.
     
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