Help Identify Custom Shift Register

I scored a 7-seg LED board from a school basketball court. The unit has four of these massive 13" 7-seg displays with each segment comprising of 15 LED's and is just begging to be turned into a massive clock!

I took out the driver boards and they seem to be very simple except their is a custom SOIC chip that I need help figuring out how to operate.

Ok so here is the design: (Ignoring Power and GND as they are quite obvious)
The input connection has 4 signals. They go through a HC541 octal line driver to a custom 24-SOIC chip. At first I thought the chip was 4 wire SPI controlled but then I discovered that the IN connector and OUT connector trace back to separate pins on the SOIC. Now I am convinced that this is just a custom (probably high current) serial shift register. As their are 15 LED's per segment assuming 10mA per led each output would need to handle 150mA. That is much higher than a standard 74HC shift register so maybe they got their own made as each chip drives two 7-segs and two decimal points. So 7+7+2=16 and a dedicated Data-Out sounds right to me!
Here is my deduced pinout and info:

17-bit serial shift register. 5V on Vcc
1) GND
2) In-1
3) In-2
4) In-3
5) Out-1
6) Out-2
7) Out-3
8) Out-4
9) Out-5
10) Out-6
11) Out-7
12) Out-8
13) Out-9
14) Out-10

15) Out-11
16) Out-12
17) Out-13
18) Out-14
19) Out-15
20) Out-16
21) Data-In
22) Data-Out
23) Out-17
24) Vcc (5V)

Does anybody know of a chip like this that they possibly just re-branded?? My problem is I can not get it to output anything at all. I took a 1KHz clock and some push buttons and tried to get something to display but it just did nothing. I figure the 4 signals are DI, DO, /OE, /MR or /Latch as that seems standard but I tried many combos but that can take quite a bit of time seeing how 4^4=256 combinations here.

Any ideas?? Thanks!

Good work. Don't know that I could have deduced as much as you did.

1.

Did they get rid of it because it stopped working? There's a chance the chip is kaput.

2.

Do you get different readings for one side (2 digits), or the same results for both sides (4 digits)?

3.

Could it be an octal 1-of-16 decoder or a close cousin? Maybe you ruled it out since you mentioned one of those already.

4.

Do the output pins source current, or do they sink current? Are you using pullup or pulldown resistors?

5.

Could it be a specialty chip that does marquee effects, dashed lines, flashing, etc? In which case you might want to dismiss it and hook up your own clock driving circuitry.

Thanks,

1) It works but got smoked with a basketball so about 15 LED's are smashed. Three and a half of the panels work fine though and the LED's are in series so a simple fix.
2) I do not get readings or anything at all! Nothing I do to the 4 inputs causes any of the outputs to change.
3) I don't think its a 1:16 decoder as they have quite a few 7-seg displays in one scoreboard and to create a 60Hz "All On" pattern they would be driving it around 20KHz. That and each display section is fed from its own port on the mainboard (which I do not have) and then one bit from that chip and three of the inputs carry on to feed the next section so it couldn't be a decoder.
4) The unknown IC sinks current. Each output segment is 6 LED's in series and three of those sets in parallel. So assuming 1.7V/LED @ 10mA then it needs a minimum of 10.2V @30mA per segment. I am powering the board with a current limited 12V 200mA supply.
5) The board does do marquee effects but I am sure its the main brain that's creating them. If it did anything fancy I would think it would have been an SPI interface and that one pin coming out of the chip going to the next doesn't go well with any of the communication protocols I know.

I hope to get it working as is because its fed from an ethernet jack and I could toss on a cheap ATTiny without having to make my own board.

From your description it looks that you have HC595+ULN2803 combo, twice, in that SOIC. The four inputs could be OE (Output Enable), Serial Clock, Serial Data ant Latch, as you stated that the 3 input lines are carried out to the next stage (Clock, Data and Latch), and the fourth line is carry out from the last stage to next board. Unfortunately, you will have to figure out the function of the pins :sad: