I need help with IC signal. CD4075BE

Thread Starter

OG Style

Joined Aug 18, 2017
31
I have a crain machine that I'm am trying to work on. The marquee lights are controlled by its own board. I was able to figure out how to power the board and get the lights to function. There suppose to be different patters but I can't figure out how to change them. There is a connection that connects to pin 5 of a CD4075BE. I'm unable to figure out what type of signal it uses. It's the left pin on the connector. Can anyone help me to figure it out? I've attached pictures and what is supposed to be the schematic for the board.

Thank you
 

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dl324

Joined Mar 30, 2015
14,475
There is a connection that connects to pin 5 of a CD4075BE. I'm unable to figure out what type of signal it uses. It's the left pin on the connector. Can anyone help me to figure it out?
The schematic is barely readable.

CD4075 is just an OR gate. Any one of the three inputs will set A4 HIGH. The voltage levels on the inputs will be 0V or near 0V for a LOW and 5V or near 5V for a HIGH. That determines the address range that will be used in what appears to be a PROM.

There suppose to be different patters but I can't figure out how to change them.
The output of the OR gate determines the pattern. There are two patterns that you can't change.
 

MrChips

Joined Oct 2, 2009
26,124
CD4075 is a triple 3-input OR gate. The IC is powered with +5V. Hence the inputs will require 0-5V TTL digital voltages.
All three inputs on pins 3, 4, and 5 are already pulled LOW to ground. Thus any 5V input on pins 3, 4, or 5 will produce a logic HIGH on pin-6 of the OR gate. This will select the upper 16 words of the 32 x 8 PROM. This selects a different pattern.
 

Thread Starter

OG Style

Joined Aug 18, 2017
31
Ok. Let me make sure I understand. 0v is one patter and I can hook 5v up to it to get a different pattern? I'm not sure what digital voltage is.
 
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MrChips

Joined Oct 2, 2009
26,124
Ok. Let me make sure I understand. 0v is one patter and I can hook 5v up to it to get a different pattern? I'm not sure what digital voltage is.
Yes that is correct. Leaving it as is gets you one pattern. Applying 5V gets you another pattern.
Digital simply means that there are only two voltage levels to deal with, 0V and 5V.
 

Thread Starter

OG Style

Joined Aug 18, 2017
31
This board is from the 80s and hard to find. Luckily there's is 2 of them because someone tried to tackle this problem before.
 
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