7805A on a screen

SpearMan74 · Post by **SpearMan74** » Sun Apr 30, 2006 7:23 pm

I'm really excited because i found something. On the back of my Verge Gamecube screen i found 2 7805A regulators, which output 5v. Does that mean the screen runs at 5v?
It's confusing, because the power already runs through an unknown regulator with an inductor before hitting the screen, where the 2 7805s are.[/img]

Post by **Skyone** » Sun Apr 30, 2006 7:27 pm

Eh, it probably doesn't run off of 5v. You see, the PSOne screen also has 2 7805's, but it requires 7.5v-9v input. This is because certain parts of the board need more than 5v. So, in short, probably not, do some tests.

codeman · Post by **codeman** » Sun Apr 30, 2006 7:28 pm

Certain parts of the board need more than 5v? Which parts?

SpearMan74 · Post by **SpearMan74** » Sun Apr 30, 2006 7:28 pm

Yeah i ask all these stupid questions because i don't have a multimeter.

Thats what i need, right?

Post by **Skyone** » Sun Apr 30, 2006 7:33 pm

Ya, a multimeter is a great tool.

@codeman: I think the video drivers need 7.5v.

codeman · Post by **codeman** » Sun Apr 30, 2006 7:45 pm

huh....that explains some things. While i'm at it, any particular reason why there are two 7805s? too lazy to try to trace stuff myself

Post by **Gamelver** » Sun Apr 30, 2006 7:59 pm

it has two to provide enough current.

The chip for the video requires 7V-9V...

codeman · Post by **codeman** » Sun Apr 30, 2006 8:12 pm

yeah, i figured it was a current thing. I want to bypass any 7805's that I can so they dont eat all my battery power. As for the video chip needing 7v...that would explain the problems I was having, thanks

Post by **marshallh** » Sun Apr 30, 2006 8:16 pm

One of the two 7805s powers the audio amp, the other runs various 5v circuitry. The chroma decoder (actually it does more than that) runs off the unregulated input. That's why it has to run at a certain voltage to work correctly. Consequently, this is the part of the screen that is fried when you apply too much voltage to the screen.

Post by **Triton** » Sun Apr 30, 2006 8:18 pm

that gets me thinking, couldnt you with some hacking add a regulator to the chroma decoder or something to limit the voltage so as not to fry screens accidentlally?

Post by **Gamelver** » Sun Apr 30, 2006 9:00 pm

eh, just use a 7808 if you're gonna go higher than 9V, I say...

Warrior_Rocker · Post by **Warrior_Rocker** » Sun May 07, 2006 12:51 pm

Yea, the 7808 powers the ps1 lcd just fine, good if you are doing a 12v based system because this means you have 3 volts to drop before you get to where the regulator might fail...

codeman · Post by **codeman** » Sun May 07, 2006 8:07 pm

Ok, so one more question. How much current does the 7.5v line on the screen draw? It can't be that much since an unmodded screen takes about 750mA total, and the thing needs two 7805's to source current for the 5v line. I like power electronics, so I want to figure out a way to increase the battery life by bypassing the 7805s all together.

Anyway, I just need to know the current draw before I can choose components for what I'm thinking of doing. Thanks.

daniel3843 · Post by **daniel3843** » Wed May 17, 2006 1:22 am

marshallh wrote:One of the two 7805s powers the audio amp, the other runs various 5v circuitry. The chroma decoder (actually it does more than that) runs off the unregulated input. That's why it has to run at a certain voltage to work correctly. Consequently, this is the part of the screen that is fried when you apply too much voltage to the screen.

i'm building an NESp and today i plugged a 9.6v battery to the screen. all the colors were wierd so i'm assuming this ment bad chroma decoder. does this mean it's bad now, or could it still be fine? i dont have the 7.5v plug to test it as i lost it long ago. if it's bad, is it easy to place? i dont want to buy a new PSOne screen. Also, the 7508 regulator, should i just plug it into the main power going into the screen? (as in, between the battery and the screen)

vskid · Post by **vskid** » Wed May 17, 2006 6:47 am

The 9.6v itself might have been ok, but batteries are usually higher voltage than what they say, and that would most likely have fried it. There are fuses though, so it might have blown those.