CV Internal Power Supply Mod (no external brick)

[Ikrananka]

I am in the process of building an internal power supply mod for the CV. This is based on the open frame power supply that doubledown used for his internal power mods (http://www.cincon.com/data/products/cfm2_1/CFM40D_T.pdf). I have built and tested a prototype unit and it works great, is much lighter than the standard external CV brick and has the advantage of only requiring a standard household power cord to connect the CV to the mains supply. However, I am not an electrical engineer and have concerns over safety and grounding but do not know the answers. So, looking for some advice on the following (hope someone can help):

 

1. In one corner of the power supply PCB there is an earth/ground symbol marked with a trace running from a capacitor to a circular trace running around the adjacent mounting hole. I believe that I should have this connected to ground - is this correct?
   
2. One of the other mounting holes also has a circular trace running around it (connected to another capacitor) but does not have an earth/ground symbol next to it. There is NO electrical connection between the two circular traces - should this second trace also be grounded?
   
3. The other two mounting holes do NOT have traces around them. Nevertheless, I plan on mounting the power supply using metal screws and metal standoffs. The bottom screws will be outside of the CV case, can be touched, and so in theory there could be an internal short to these screws - do you agree therefore that all four screws/standoffs be grounded?
   
4. Do I need to provide some kind of physical shield in case a user pokes a metal objects through the CV air vents thus preventing them from touching the power supply? Or is this overkill? I can see quite a number of consumer electronic items that I have that I could easily poke something inside and touch the internals (not that I ever would mind you).
   

 

I plan on releasing details of how to do the mod once I have a final working model and a complete parts list. I may also provide an installation service if demand is there - let me know if you'd be interested.

Edited July 29, 2010 by Ikrananka

[retroillucid]

I'll use your service for modding my system

Let me know when its ready

[+5-11under]

Hi Ikrananka,

 

First of all, I'm not an electrician, so you shouldn't pay any attention to this ...

 

In answer to your four questions:

 

1. I would connect the earth/ground symbol point to the main AC ground (third wire, green, from the power cord). I would not connect this point to any point on the ColecoVision - there is no need for those two grounds to be connected.

 

2. I don't know what's going on here. Is this connected to the output's common, pin 4 and 5? Probably not? I would do some investigation, and perhaps contact the supplier on this one. Presumably, though, some customers are bolting these down, with standoffs of course, to a metal plate, so this would connect all the mounting holes together. Presumably, you could connect these two.

 

3. These mounting holes aren't an issue, of course. I don't think it matters if the accompanying standoffs are grounded or left floating.

 

4. A shield would of course be advantageous, but not necessarily required. You could find some fish paper, which is good for high temperature, just in case.

 

I'd be a bit wary of performing this mod for others. When you're dealing with high voltages, such as 110VAC, there's regulations and standards to follow (for instance, when we import equipment at the company I work for, we need to get an inspector to verify that everything is up to CSA or equivalent/local standards). If you're performing this mod for others, there's a liability issue if anything goes wrong in the future. Sorry to scare you, but better that you know this beforehand.

 

For your own unit, make sure the AC connections are secure, and make sure the cord coming out of the CV can't be pulled or twisted (disconnecting the connections to the power supply). I'd consider using the same type of cord that is on your computer, and installing a corresponding input jack and fuse into the CV (you can buy these).

 

Personally, though, I'd go with a +5V input, and use a DC to DC converter to obtain the +12V and the -5V. Unfortunately, there's a bit more involved, such as suppressing the switching noise, and probably converting from -12V to -5V, which, although simple enough, adds a bit of complexity to the idea.

 

Thanks,

5-11under

[Bruce Tomlin]

Does anyone have a circuit to generate the -5 volts from the +5 or +12 volts? There are a lot of switching power supply bricks for +5/+12 volts, but that -5 is the weird voltage, and it doesn't need much of it.

 

Or maybe replace the video DRAM with 4164 chips, most of which did not need the -5 volts.

[+5-11under]

Or maybe replace the video DRAM with 4164 chips, most of which did not need the -5 volts.

The controllers also use the -5V, I assume just for the spinners. I think the Atari expansion module may also be using it, for what it's worth.

[Ikrananka]

I'll use your service for modding my system

Let me know when its ready

I have decided that I will now not provide this as a service - too many safety and legal issues involved. If I knew what I was doing and could get the modification inspected and certified then that would be a different kettle of fish. In reality I do not know what I am doing and so will have to leave it up to individuals to do the mod themselves along with any associated risk that it may be unsafe.

 

That said, I am not stupid and am doing as much research and testing as I can to ensure this mod is as safe as I can reasonably make it. For instance, I will now be using nylon standoffs to mount the power board to avoid any possible electrical connection to the mounting screws.

 

My intent will be to finalise the design, develop a comprehensive parts list and installation instructions and then post them here with the appropriate warning of doing the mod at your own risk.

[+5-11under]

I'll use your service for modding my system

Let me know when its ready

I have decided that I will now not provide this as a service - too many safety and legal issues involved. If I knew what I was doing and could get the modification inspected and certified then that would be a different kettle of fish. In reality I do not know what I am doing and so will have to leave it up to individuals to do the mod themselves along with any associated risk that it may be unsafe.

 

That said, I am not stupid and am doing as much research and testing as I can to ensure this mod is as safe as I can reasonably make it. For instance, I will now be using nylon standoffs to mount the power board to avoid any possible electrical connection to the mounting screws.

 

My intent will be to finalise the design, develop a comprehensive parts list and installation instructions and then post them here with the appropriate warning of doing the mod at your own risk.

 

Sorry for putting a damper on things. It's definitely a nice, small power supply. When I was looking for one a few years ago, I couldn't find anything quite like that one.

 

Good luck on your mod. With the proper precautions, it should be just fine.

5-11under

[Ikrananka]

1. I would connect the earth/ground symbol point to the main AC ground (third wire, green, from the power cord). I would not connect this point to any point on the ColecoVision - there is no need for those two grounds to be connected.

I now believe that the two "ground" points are circuit common grounds and NOT mains safety grounds (both grounds are connected to capacitors). I have tried the unit without a mains ground connection and it works fine.

 

2. I don't know what's going on here. Is this connected to the output's common, pin 4 and 5? Probably not? I would do some investigation, and perhaps contact the supplier on this one. Presumably, though, some customers are bolting these down, with standoffs of course, to a metal plate, so this would connect all the mounting holes together. Presumably, you could connect these two.

Pins 4 and 5 have no direct electrical continuity to either of the "grounds". I do intend following this up with the supplier though - will be phoning on Monday.

 

3. These mounting holes aren't an issue, of course. I don't think it matters if the accompanying standoffs are grounded or left floating.

As I now believe that the "grounds" are circuit common grounds I will not be electrically connecting them to anything. I will use nylon standoffs to isolate any connection to the mounting screws.

 

4. A shield would of course be advantageous, but not necessarily required. You could find some fish paper, which is good for high temperature, just in case.

I've decided to eliminate the shield - I suspect this is overkill. If you're poking things through the vents of any electrical device that is plugged into the mains then you're an idiot and deserve the shock

 

I'd be a bit wary of performing this mod for others. When you're dealing with high voltages, such as 110VAC, there's regulations and standards to follow (for instance, when we import equipment at the company I work for, we need to get an inspector to verify that everything is up to CSA or equivalent/local standards). If you're performing this mod for others, there's a liability issue if anything goes wrong in the future. Sorry to scare you, but better that you know this beforehand.

Excellent advice - I have indeed decided to not offer the install as a service. I'll post instructions on how to perform the mod and will include a "do this at your own risk" warning.

 

For your own unit, make sure the AC connections are secure, and make sure the cord coming out of the CV can't be pulled or twisted (disconnecting the connections to the power supply). I'd consider using the same type of cord that is on your computer, and installing a corresponding input jack and fuse into the CV (you can buy these).

I will indeed be using a power entry module - although finding a suitably sized one with a fuse is not proving too easy - further searching required. At the moment I have a standard 2-pin power entry module installed and have been testing with the power cable for my printer. The power entry module is secured to the CV by screws and is firmly mounted.

 

Personally, though, I'd go with a +5V input, and use a DC to DC converter to obtain the +12V and the -5V. Unfortunately, there's a bit more involved, such as suppressing the switching noise, and probably converting from -12V to -5V, which, although simple enough, adds a bit of complexity to the idea.

I really want to eliminate any external power adaptor which is why I'm going down this route. If someone wants to progress the +5V input and conversion option then I'd love to see it.

[Ikrananka]

I'll use your service for modding my system

Let me know when its ready

I have decided that I will now not provide this as a service - too many safety and legal issues involved. If I knew what I was doing and could get the modification inspected and certified then that would be a different kettle of fish. In reality I do not know what I am doing and so will have to leave it up to individuals to do the mod themselves along with any associated risk that it may be unsafe.

 

That said, I am not stupid and am doing as much research and testing as I can to ensure this mod is as safe as I can reasonably make it. For instance, I will now be using nylon standoffs to mount the power board to avoid any possible electrical connection to the mounting screws.

 

My intent will be to finalise the design, develop a comprehensive parts list and installation instructions and then post them here with the appropriate warning of doing the mod at your own risk.

 

Sorry for putting a damper on things. It's definitely a nice, small power supply. When I was looking for one a few years ago, I couldn't find anything quite like that one.

 

Good luck on your mod. With the proper precautions, it should be just fine.

5-11under

No need to be sorry - your sage advice was most gratefully received.

[+5-11under]

1. I would connect the earth/ground symbol point to the main AC ground (third wire, green, from the power cord). I would not connect this point to any point on the ColecoVision - there is no need for those two grounds to be connected.

I now believe that the two "ground" points are circuit common grounds and NOT mains safety grounds (both grounds are connected to capacitors). I have tried the unit without a mains ground connection and it works fine.

That sounds like you've got it right. If it's working fine with the nylon spacers, and these two mounting holes left floating, I'd likely just leave them alone, then - there's two "commons" on the output strip that will be more useful, of course.

5-11under