Canon AC/DC transformer with 24V CONT GND, CONT=?

[NielsVdk]

Hello

I did a tear-down on a Canon MP140 and I found a transformer from 220V to 24V, but there is a catch: it has 3 pins:
24V, CONT, GND

After googling I found that Cont stands for control and it is used to bring the transformer out of it's standby-mode (please correct me if I am wrong).

Well now to the question: how do I wire the CONT pin?
Some sources say they connected it with the pin 24V from the transformer (but with resistors in series).

Does anyone have experience with this? I don't want to blow up this transformer because it's the only 24V source I got.

Please note: I don't have a oscilloscope to read out anything nor a variable voltage source for testing the CONT connection.

[Cald0s]

Hi Niels,

Can you post a picture of the transformer? Also do you have a multimeter? We will get to the bottom of this yet.

[Mechatrommer]

its not a transformer, its a smps psu. it got a transformer inside allright, but thats not just it.. i dont think cont is to put the psu into standby or it will simply shutdown the printer hard-off'ed

[NielsVdk]

Hello

Here is a picture of the Canon AC adaptor K30270:

(it's just a plastic box with a power cord attachment, 3 pins and this text on it)

I do have a cheap (€5) multimeter, it isn't very good but it will do.
Measuring the resistance between:
24V and Cont: 27.6 K?
24V and Gnd: 11.70 K?
Cont and Gnd: 14.2 K?

Mechatrommer: Thanks for the info, then maybe the 24V connection is for the printer motors? Shutting them down with cont to save electricity?

[Mechatrommer]

(it's just a plastic box with a power cord attachment, 3 pins and this text on it)

no its not just a plastic box, you havent dig deep enough, i have trillions of this plastic box just not for the MP140 iirc.. i am a printer salvager nuts.

Mechatrommer: Thanks for the info, then maybe the 24V connection is for the printer motors? Shutting them down with cont to save electricity?

yes 24V is for printer motors, but depending on what is CONT really is (i'm not sure) 24V also possibly powering all the electronics and printer's brain. but if CONT is like 3.3V output, then it can be to supply them, hence no standby mode, as i'm expecting...

[rs20]

Resistance isn't terribly informative (the connections won't be ohmic). Can you plug it in and measure the voltage across the same pairs of pins? This is no different to plugging in the wall plug before plugging the plug into the printer; so it is sure to be safe.

[NielsVdk]

(it's just a plastic box with a power cord attachment, 3 pins and this text on it)

no its not just a plastic box, you havent dig deep enough, i have trillions of this plastic box just not for the MP140 iirc.. i am a printer salvager nuts.

Well with plastic box I meant it's a double insulated electric box. Opening it probably means destroying the box.

Resistance isn't terribly informative (the connections won't be ohmic). Can you plug it in and measure the voltage across the same pairs of pins? This is no different to plugging in the wall plug before plugging the plug into the printer; so it is sure to be safe.

I thought so too, but as it was the first time I would measure out a 'live' component I wanted to be awake and yesterday night I was too tired.

Voltages:
24V to GND: 7.2V
24V to cont: 7.0V
cont to GND: 0V

By looking at this: would it be correct to assume that CONT is indirectly connected with GND?

[rs20]

(Edited because I misread earlier)

Well, there could just be a pull-updown resistor from cont to 24VGND, and pulling the cont down up to ground24V turns on the 24V to a proper 24V. ATX power supplies have a very similar arrangement (albeit it's a pull-up resistor that you pull down to ground).

Just shorting it out with a wire is a bit risky, though. Try a 1k resistor from cont to ground24V, maybe? And see how both 24V and cont respond. That's what I'd do, not taking any responsibility though.

[NielsVdk]

Well, there could just be a pull-up resistor from cont to 24V, and pulling the cont down to ground turns on the 24V to a proper 24V. ATX power supplies have a very similar arrangement.

Just shorting it out with a wire is a bit risky, though. Try a 1k resistor from cont to ground, maybe? And see how both 24V and cont respond. That's what I'd do, not taking any responsibility though.

Resistor between cont and ground: no effect
Resistor between 24V and cont: voltage changes

When using a 100K resistor I get a voltage of 21.1V
................. 10K resistor....................... 23.8V
................. 1K resistor ........................ 24.6V

It could be that the voltage difference is because of my cheap multi-meter, but the results are clear
Connecting the 24V line with the CONT line does increase the voltage of the 24V line.

Maybe one last question: is this the principle of a pull-up or a pull-down resistor?

[NielsVdk]

That makes no sense. You said there was zero voltage between 24V and cont, yet connecting a resistor between 24V and cont causes an effect? V=IR, V=0 --> I=0, connecting a resistor between two equipotential points can't have any effect.

Actually I said 7.0V (=7,0V). Sorry for any unclarity on my behalf.

[rs20]

That makes no sense. You said there was zero voltage between 24V and cont, yet connecting a resistor between 24V and cont causes an effect? V=IR, V=0 --> I=0, connecting a resistor between two equipotential points can't have any effect.

Actually I said 7.0V (=7,0V). Sorry for any unclarity on my behalf.

Just looked back, and it was me that misread. My fault, sorry! I've edited and deleted earlier messages accordingly.

In summary, the results you see are consistent with the power supply have a pull-down resistor on the "cont" line.

[NielsVdk]

No problem Thanks for the explanation.

[Mechatrommer]

Voltages:
24V to GND: 7.2V
24V to cont: 7.0V
cont to GND: 0V
By looking at this: would it be correct to assume that CONT is indirectly connected with GND?

i managed to open a canon ip1880 psu, similar pin out as the OP, you maybe solved your problem by now but fwiw for future reference... cont is connected to a transistor base that is pulled down by resistors to GND... the transistor then will turn on something that is not my interest (optocoupler and then to the hot side). during turning on 24V pin will read 7V but if you pull up (short) the cont with this 7V output, you will get 24V output. so i guess cont is for control when we need high demand of 24V, during idle, cont is gnded and psu is low voltage mode of 7V. i believe it is safe to short 24V pin to cont, since cont to the transistor base has a resistor in the middle, not interested to now the value, only interested in making it output 24V or until it blows up, my spare is expendable anyway, i got many more spares. fwiw...

[teknosrp]

Hello

I just arrived to this thread looking for the pinout of a K30330 power supply, used in canon PIXMA MG2120 and MG3120 models. It works just the same way of the other models posted here, but this one hasn't got the pin names marked at the outside. After measuring and trying, this is the correct pinout:

(Side of the AC outlet) GND - CONT - 24V

And for powering it up, just short these last two pins.

[ccare]

Greeting and happy new year to all,

i have a question, on this thread.

it is possible to replace the original adapter with a regular one 24v +/- ?
the adapter just stopped working. i provide 24v to 24v - GND but i take no signal. only 0.003A. the machine does not turn on.
do i have to provide 24v to CONT aswell?

Thank you

[Munko]

Hello, I have the same source, I managed to open it, you just have to make a bridge between the 3v (Central Pin) and the pin on the left, the pin on the right is the GND, with that it activates the reference of the T431 and the output is from 24 - 25v, the center pin has a resistor that goes to a transistor that drives the negative reference of the internal transformer output

[Afinch56786]

THANKS FRIEND. YOU SAFE ME.