Atari Video Music - 3 wire Power Supply Replacement ???

[KLund1]

HI,

  I have a Video Music with its original Atari 3-wire power supply that appears to only output 5v and 10V. The label shows 16.6 vac.

When I test with a multimeter, I assume that the middle wire is ground, I measure the other two wires and get 5vac and 10vac.

This is a 3 wire very tiny power brick. Obviously I need a replacement. I am still not too good with power supplies, and this 3 wire psu has me stumped. 

First where can I find a 16.6 psu, then one with 3 wires? Oh, and only 100mA.  Or can I make one a 3 wire psu from a 2 wire unit? if so, how?

Thanks

[+Stephen Moss]

Hopefully you will get an answer from some who knows about these, but if not...

Did you measure it with the power on or off? Having seen a video of it the power unit looks very small and so I suspect that 16.6VAC is the off load (unit off) voltage and it drops to 5 & 10 on load. Still 16.6 seems a slight odd value, plus the power unit does appear to indicate it is 6W which usually refers to the output in which case I would expect 300mA, not 100, assuming the 100MA is referring to the output current.

 

You cannot make a 3 wire PSU from a 2 wire one.

If you wanted to make a new power unit from scratch then you would need a transformer with either two secondary outputs (i.e. 0-6, 0-6) or centre tapped (i.e. 6-0-6). If using a twin secondary you connect the two middle output pin (9 & 0) together to make it in to a centre taped transformer. I would suggest a 6W/6AV transformer.

 

A quick search and this schematic shows it to be centre tapped, additionally this modification description and clearer schematic appears to confirm that and the author indicates that they used an 18V (0-9, 0-9 or 9-0-9) transformer being the nearest in a standard voltage and that it worked. Although looking at the supply voltage on the schematic I would think a 12V (0-6, 0-6 or 6-0-6) transformer would be better.

As it is a centre tapped transformer, I would expect that what you measured as 5V should the be centre tap (GND) connection...

Actual --- Your measurement

6 --- 10

0 --- 5 --- Centre Tap

6 --- 0

 

But you can verify that by seeing where it is connected to in the schematic, I hope that make sense.

[KLund1]

Many thanks for the detailed replay. Very much appreciated.

It looks like I bit off a little more than I can chew on this. From what I can understand is that you agree that this current transformer is not up to spec.

Do people sell 3 wire wall warts? If so, what would be the best search terms too find a proper replacement?

Again thanks

[+Stephen Moss]

On 6/19/2022 at 2:31 AM, KLund1 said:

From what I can understand is that you agree that this current transformer is not up to spec.

Well I find the spec a little confusing at best as the apparent stated wattage of 6W (6VA) and current 100MA if referring to the output do not tie up as 6W/16.6V = 0.361A (361mA), additionally it is unclaar if the rated voltage is the onload or off load voltage. Usually it would be the on load voltage so certainly it would appear that you are getting insufficient voltage out if you measurements are correct.

 

However, again it depends of if that voltage was measured with Music Video units power switch in the on (on load) or off (of load) position, if it was measured off load there is defiantely a problem with the power unit as you should be measuring at least the specified voltage. If it was measured on load then it is possible that a fault with the unit is resulting in excessive current draw from the power unit which would drag the voltage down, so it would be less certain that the issue lies with the power unit. 

 

On 6/19/2022 at 2:31 AM, KLund1 said:

Do people sell 3 wire wall warts? If so, what would be the best search terms too find a proper replacement?

I do not know, however unless someone here knows otherwise, I think you would struggle to find a replacement center tapped AC output unit off the shelf. Most power units that plug into a standard wall output provide a DC output and are only single sided, GND and positive voltage. Which is why, if a replacement power unit is required I think you would have to make it yourself.

An 6-0-6 (or 0-6, 0-6) transformer = 12V ac, when converted to DC = 16.98 - 1.4 = 15.56 / 2 = +/- 7.78V DC which falls within the voltage ranges indicated in the schematic, but potentially a little low for the votage regulator.

An 8-0-8 (or 0-8, 0-8) transformer = 16V ac, when converted to DC = 22.62 - 1.4 = 21.22 / 2 = +/- 10.61 DC which theoretically falls a little outside the ranges indicated on the schematic but probably not enough to cause an issue.

An 9-0-9 (or 0-9, 0-9) transformer = 18V ac, when converted to DC = 25.45 - 1.4 = 24.05 / 2 = +/- 12.06V DC falls further outside the ranges indicated on the schematic, would not be my choice unless no other option.

 

If you want to do a search for a suitable transformer then parameters to look for are...

Single Primary

Twin secondary (more readdly availability than center tapped)

Output Voltage 6 (2 x 6), 8 (2 x 8), or 9 (2 x 9)

Power 6VA