2600 AC adapter disected

[SIO2]

 

Didn't see a photo of this around so here is one.

[Video]

Actually more in one than I expected. Most I've seen are little more than a ring of metal plates with wire wrapped around them

[+Stephen Moss]

It is just a transformer outputting around 9V AC with a discrete (four diodes) bridge rectifier to convert the AC to full wave rectified DC voltage of around 12V and a smoothing capacitor to reduce the AC ripple on the DC voltage. Although the components used may look different all unregulated, fixed voltage power units should have the those contents.

[danny_galaga]

It is just a transformer outputting around 9V AC with a discrete (four diodes) bridge rectifier to convert the AC to full wave rectified DC voltage of around 12V and a smoothing capacitor to reduce the AC ripple on the DC voltage. Although the components used may look different all unregulated, fixed voltage power units should have the those contents.

If it starts off as 9VAC should it not be around 4.5VDC after the rectifier?

[SIO2]

If it starts off as 9VAC should it not be around 4.5VDC after the rectifier?

 

Because of the voltage drop across the diodes?

 

Well, I would expect there would be a drop. Perhaps not that much. I think the usual voltage drop for this type of diode is around .7 volts. Not sure how that totals up in the bridge arrangement.

 

I suspect that the output of the transformer should be higher than 9v AC. When I try to measure this one, I get no voltage on the output so, I believe the transformer has failed which in my experience is odd.

 

Also, the cap tested high on ESR which is not too surprising given its age and the fact it was being baked in this little plastic box all those years.

 

Normally when I measure the DC output of these Atari wall warts they meter around 13 volts DC. I have read that voltage drops under load (when the machine is connected rather than the meter). However, the voltage regulator in the console still has to receive somewhat higher voltage than its nominal output in order to function. My understanding is that the voltage regulator basically blows off the excess through generating heat.

 

This is also probably the point where we should say, this discussion is for educational purposes only and fiddling around inside these things can be dangerous or deadly.

Edited September 19, 2016 by SIO2

[alex_79]

If it starts off as 9VAC should it not be around 4.5VDC after the rectifier?

Keep in mind that when dealing with AC, we refer to "root-mean-squared" voltage, not the peak voltage (not useful to compare power with DC), nor the average voltage (that would be 0).

In 9V AC, the voltage peak-to-peak amplitude is 25.4V (that is, the waveform oscillates between +12.7V and -12.7V).

 

[danny_galaga]

Ah, maybe I was thinking of peak to peak. My understanding of AC to DC and rectifiers comes from my auto electrical trade where we dealt with 3 phase alternators. Probably in trade school they talked about peak to peak. This was maybe 25 years ago so naturally things in my brain may have changed slightly since then

[+Stephen Moss]

If it starts off as 9VAC should it not be around 4.5VDC after the rectifier?

 

No, as Alex_79 stated when it come to domestic AC supplies, transformers and equipment the stated voltage relates to the root mean squared voltage, not peak, peak to peak or average therefore...

DC voltage = (AC x 1.414) - 1.4 (Voltage drop across two diodes)

 

 

 

I suspect that the output of the transformer should be higher than 9v AC. When I try to measure this one, I get no voltage on the output so, I believe the transformer has failed which in my experience is odd.

 

Also, the cap tested high on ESR which is not too surprising given its age and the fact it was being baked in this little plastic box all those years.

 

Normally when I measure the DC output of these Atari wall warts they meter around 13 volts DC. I have read that voltage drops under load (when the machine is connected rather than the meter). However, the voltage regulator in the console still has to receive somewhat higher voltage than its nominal output in order to function. My understanding is that the voltage regulator basically blows off the excess through generating heat.

 

This is also probably the point where we should say, this discussion is for educational purposes only and fiddling around inside these things can be dangerous or deadly.

 

Standard transformer output voltages are 3, 6, 9, 12, 15, 18 etcetera, 6 would be too small and 12 too high so in unregulated power units like these the AC output voltage of the transformer used is normally the same as the rated DC output voltage, in this case 9V AC but being cheap and cheerful the output of the transformer may be as high as 10.5V.

I do not know what ESR you measured for the cap but they would not have used a more expensive low ESR cap in such a cheap supply. The output voltage does drop under load because the current rating of the transformers used is insufficient, as the console draws more current than the transformer can supply while maintaining its output voltage the transformers AC output voltage drops resulting in a corresponding fall in the DC output voltage.

This is a cheap and cheerful method of pseudo voltage regulation has been around for decades and keeps the production costs down over using a larger capacity, heavier and more expensive transformer and a power resistor or primary internal voltage regulator to drop the excess voltage, the downside of those losses within the transformer (as with those of voltage regulator) is they generate heat which is why the power units get so warm.

[SIO2]

So, the wall wart pictured above is an original linear type but I see that there are some cheap adapters being advertised around as replacements for Atari AC adapters. These replacements look to be the light weight switch mode type. I have not tried one with an Atari 2600. Has anyone reading this tried one of the new adapters? Do, they create any noise that affects the Atari video display? The new ones are cheap but are they also cheerful?

 

BTW, I came across this interesting article about the switch mode power supply used in the Apple II and there is a link at the bottom of that page to another article about what is inside cheap USB chargers. http://www.righto.com/2012/02/apple-didnt-revolutionize-power.html

Edited September 20, 2016 by SIO2

[danny_galaga]

So, the wall wart pictured above is an original linear type but I see that there are some cheap adapters being advertised around as replacements for Atari AC adapters. These replacements look to be the light weight switch mode type. I have not tried one with an Atari 2600. Has anyone reading this tried one of the new adapters? Do, they create any noise that affects the Atari video display?

 

BTW, I came across this interesting article about the switch mode power supply used in the Apple II and there is a link at the bottom of that page to another article about what is inside cheap USB chargers. http://www.righto.com/2012/02/apple-didnt-revolutionize-power.html

Yeah I use one. I can't say for sure if it has noticeable side effects as I have an S-video mod. Although maybe with an S-video mod it would be more obvious? In that case it is fine

 

Incidentally, another article by that guy about chargers informed my decision on a 5V supply for my C64. I guess I should be as wary for my 2600, but somehow I think it is made of sterner stuff!

Edited September 20, 2016 by danny_galaga