Can some one decypher this???

sshaft

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In regards to Dragons Lair LED score disply:

The below was an online article:

Symptom: Score board displays dim F's when not displaying anything:

Fix: The cause is from pin 9 (mode input) of the ICM7218 display driver ICs being unloaded. Connect pin 9 of both display drivers together then connect one end of two 1k resistors to pin 9. Connect the other end of one resistor to +5V and then the remaining one to GND.

Is this on the main board???
What exactly is the display driver???

thanks


http://users.rcn.com/jenison/mars/trouble/man/cinemat/game/dragon.html
 

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Yes

It means that on the display board there are two IC's that drive the digits.... they are ICM7218's
Some versions have a built in voltage divider on pin 9 to maintain V/2 on the pin when it is in an 'open' condition... some don't... the ones that don't can cause issues in certain applications and in your case this is what you are correcting by adding an external voltage divider to take the place of the missing internal one.
You do this by connecting pin 9 on both ICs together and then connect those same pins to both +5 volts and ground via 1k resistors.

Don't mind the messy diagram.... I just scribbled it down.
 

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Last edited:
You're a badass Old Willy...

Does that mean i could pic up another pair of icm7218's that have the voltage divider included..???

If so where/how would i know?

Sketch was great i hung it on the fridge:)


thanks
 
The voltage divider is on the board, not part of the chips... swapping drivers shouldn't make a difference... but then again I've never seen a DL scoreboard that didn't have the resistors on it.
 
You're a badass Old Willy...

Does that mean i could pic up another pair of icm7218's that have the voltage divider included..???

If so where/how would i know?

Sketch was great i hung it on the fridge:)


thanks


There are four versions of this IC... ICM7812A, ICM7812B, ICM7812C and ICM7812D.
The A&B versions do not have the resistors, the C&D versions do.
The A&B refers to a common anode vs common cathode version and the C&D do as well, but the A/B versions and the C/D versions are not exactly the same.
So adding the resistors to the existing chips is likely your best bet.
 
Can someone post a pic of a Dragon's Lair w. the resitors on it....???!
(the pic i posed has them on the back but is a repro pic from the web)

I think i figured out where they were soldered off

thanks
 
dlscore.jpg


Resistors are right above the 'top' ICM7218D
 
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