Spectravideo SV-328 Power Plug and Receptacle Replacement

[Nelno]

Back in 1987 my Spectravideo SV-328 got knocked off a desk (power cord was tripped over or something, I can't remember) and the plug receptacle on the motherboard was broken. Undaunted, my 16 year-old self cut off the plug and soldered the power cables directly into the motherboard. Unfortunately, I left a little too much wire on the bottom and it contacted the shielding when the case was closed. This fried the transformer.

 

Fast forward to 2020 and I got a 3D printer. I've kept my SV-328 all of these years and had promised myself I'd fix it one day. This is the result.

 

This is a plug and socket made to replace the plug and socket in an SV-328 computer.

 

WARNING: BY USING THIS PLUG AND SOCKET YOU ARE DOING SO AT YOUR OWN RISK. YOU SHOULD VERIFY THAT THIS SOCKET MEETS GUIDELINES FOR POWER PLUGS WHERE IT WILL BE USED.

THE SV-328 HAS AC POWER COMING DIRECTLY INTO THE MOTHERBOARD THROUGH THE POWER RECEPTACLE SO THERE IS A REAL RISK OF ELECTROCUTION IF YOU DON'T KNOW WHAT YOU'RE DOING.

 

This will only be useful to you if you no longer have a working original SV-328 power supply, receptacle and plug. If you have the original plug and socket you may be much better off reusing that with another power supply vs. printing this.

 

The plug is not compatible with the original SV-328 power receptacle on the computer. I did not have the original (that is the first piece that broke) to even attempt to make it fit. There is another project out there somewhere (sorry, I don't know the link) that is a replacement plug for the original socket.

This plug is designed to be used with 0.062 inch Molex connectors. The male connectors go in the receptacle and the females in the plug. This is important because YOU DO NOT WANT LIVE AC VOLTAGE ON EXPOSED PINS ON THE PLUG (POWER) SIDE!!

 

YOU MUST ABSOLUTELY VERIFY YOU HAVE THE PINOUTS CORRECT BEFORE PLUGGING IN. DO THIS WITH A MULTI-METER TO VERIFY THE CORRECT VOLTAGES ARE ON THE CORRECT PINS OR YOU CAN DESTROY YOUR SV-328.

 

Molex connectors

 

I opted for two separate wall transformers because these were easy to source on Amazon:

16VAC, 1000 mA wall transformer

9VAC, 1500 mA wall transforme

 

I've released all of the files, STL + FreeCAD, on Thingiverse here. I'm releasing this to the public domain in case it's useful to someone else later. This thread on AtariAge discussing Spectravideo power supplies was of great use to me in this project.

 

Anecdote:

 

When I first powered on my machine on with these transformers (and an a hacked up connector using a 4-pin DIN connector, which I later decided was a bad idea because it had the AC power on semi-exposed pins) it worked fine until I typed in the following program:

10 print "Hello, world!"

20 goto 10

 

Upon typing "run" the computer's video signal promptly died. I probably should have made it "Goodbye, world!" instead.

 

This turned out to be a bad transistor in the video out logic that was almost certainly an age-related failure and nothing to do with the new power supplies or connectors as nothing else on the board was damaged, and the power all checked out fine.

 

After finding and fixing that it's worked flawlessly.

 

This just goes to show you -- you never know what will happen if you decide to do this and it may just expose something else that's wrong with a 30+ year old computer that is completely unrelated, so do it at your own risk. I take no responsibility for what may happen should you decide to use or misuse of this project. Be careful not to fry your Spectravideo, as there aren't a lot of them around!

 

3D models:

 

 

Pinouts, as well as the installed receptacle:

 

\

 

Final plug:

 

 

The transformers I used:

 

[carlsson]

So to get this straight, you designed your own connector that roughly resembles the original one, but isn't a perfect fit so you need to replace both the connector in the computer and the one on the cable? FWIW, a small amount of people have replicated the original plug though those generally aren't available in finished form.

[Nelno]

6 hours ago, carlsson said:

So to get this straight, you designed your own connector that roughly resembles the original one, but isn't a perfect fit so you need to replace both the connector in the computer and the one on the cable? FWIW, a small amount of people have replicated the original plug though those generally aren't available in finished form.

Not quite. I didn't have a connector (i.e. the receptacle part) at all on the motherboard -- it had shattered and been removed back in 1987. Neither did I have an original transformer, cable or plug.

 

I didn't "have to replace both the connector in the computer and the one on the cable" because I designed a receptacle that didn't fit. I had to replace all of that because I had none of it, and I designed a receptacle that doesn't fit the original because I have no references or specs for the original plugs aside from the pinout voltages.

 

Like I said, this would only be useful to someone who's lost both the power supply and receptacle on their motherboard.

If I did have those specs, I'd consider designing a full replacement that matches the original parts. That gets tricky to do without the physical parts to test and validate with, though. Even with measurements it would be a guess as to the tolerances and whether or not it would really match the originals.

Edited April 29, 2021 by Nelno