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Is -5v absolutely useless on Colecvision?


7800fan
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Looking at schematic, -5v is used for RAM and controller but if one perform the RAM mod to replace it with more common 5v only version, that leaves only the controller port.

 

Is there any controller that needs it at all or can I just snip the -5v line and fix the "low" reading to ground instead? I wanted to use my Jaguar pad adapter but it's not designed to handle -5v and I'd need a few optoisolators to safely connect the adapters.

 

If I can leave out -5v it would also be easy to replace the big ass power brick with something a little more efficient. There's a 5v and 12v DC-DC converter and a cheap laptop power (15-18v) to supply it.

 

(there's also -5v on ext connector, is that needed for SGM or 2600 adapter? 12v would have to be left in as it's used by video circuit)

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I can tell you what I did.

 

I bought 3 el-cheapo chargers [uSB or otherwise], a 12V 1A, a 5V 2A and a 5V 1A.

Connected all of them and replaced the power brick entirely (I added a simple plug for AC on the chassis). I kept the -5V (juiced from the 5V 1A) in case I want one of the fancy controllers (I believe the roller controller may be the one using it or the steering wheel).

My RAM has already been replaced with +5V only so I'm good there too.

I had to use a 2A for the +5V as a 1A alone would get hot (and eventually failed on me), given as it is the CV rates the +5V at 0.9A and replacing the mem to +5V only may push it a little higher I kind of expected it.

 

I hid the 3 chargers/USB PCB-only in the front of the CV "under" the joypad, where there's enough space.

 

Connections are easy, the 12V 1A and 5V 2A have the GND in common and produce the +12V and +5V on the other wire, the 5V 1A instead has the +5V connect in common with the 2 GND already mentioned and its GND is the source for -5V instead. -5V has so little current requirements anyway that you can likely use a 500mA or smaller.

 

The CV ratings are +12V 0.3A, +5V 0.9A, -5V 0.1A.

 

I had no issue whatsoever, I was hesitant especially on the -5V connection but it worked.

 

I played a few hours the first time around (with the +5V at 1A) and then again a few hours with the replaced 5V 2A and have not seen issues since.

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