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Thermal Printer not feeding paper

Los_

Nov 6, 2022
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Good morning,
My thermal printer stopped working recently and I was wondering if there is a way to test the paper sensors or if there is any other motherboard component I should start troubleshooting first.
It would be great if I could learn something from this.
I appreciate any feedback!

Unit info:
Model: D4602B
VRETTI PRINTER
 

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kellys_eye

Jun 25, 2010
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My thermal printer stopped working recently
What level of 'not working'?

The subject title infers a simple refusal to feed the paper? Is it just that or more?

Have you checked the obvious - correct paper feed, paper type, cleaned the rollers, cleaned the sensors, checked the manual feed etc?

After that you could measure the voltage on the paper feed motor with the manual feed button pressed to check for a dud motor or a missing signal. Thereafter we can proceed to a potential repair.
 

Los_

Nov 6, 2022
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Thank you for your reply, Yes I checked the obvious as mentioned above.
The printer turns on and it goes "offline". The manual feeder button/light just blinks indicating what may seem to be a paper error or a mobo error.
Pressing the manual feed button doesn't seem to work at all =/

-los
 

Delta Prime

Jul 29, 2020
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Are you using Windows ,Mac, Linux, proper drivers, recently purchased?
 

Los_

Nov 6, 2022
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Are you using Windows ,Mac, Linux, proper drivers, recently purchased?
I'm using Win11.
The printer used to work just fine until last week. I have the correct drivers but it seems like a mechanical issue. The reason I know is that anytime you turn on the machine, the paper motor pulls in and out 1 sheet of paper, I believe it is some sort of initial test to see if the sensors and motor are working OK. That no longer happens and the status light turns solid for a second then blinking constantly.
The unit is over 1 year old, I just wanted to see if there was a simple way to test the motherboard and learn something while I'm at it :)
I read about MOSFETs and it seems like the D and S are shorted, They both are giving me a read which I think it only should work one way only but I'm no expert, not sure if I'm testing properly.
 

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kellys_eye

Jun 25, 2010
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I read about MOSFETs and it seems like the D and S are shorted, They both are giving me a read which I think it only should work one way only but I'm no expert, not sure if I'm testing properly.
Pretty meaningless without some context i.e. where is that MOSFET?, what does it control? A 'short' will read '0' both on continuity and on voltage so reading 'something' doesn't mean a short per se.

The reason I know is that anytime you turn on the machine, the paper motor pulls in and out 1 sheet of paper, I believe it is some sort of initial test to see if the sensors and motor are working OK. That no longer happens and the status light turns solid for a second then blinking constantly.
Now that is a proper symptom! and potentially an issue with the power supply. Show more pictures of the board - 'up close and personal'.

Also check the paper feed sensor (the one associated with detecting paper actually exists in the mechanism).
 

Los_

Nov 6, 2022
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Good morning, @kellys_eye
The MOSFET is near the power source but I have no clue what is controlling =/
It looks like there are 3 sensors, is there a way to test those individually? I also checked the PSU, I'm getting the correct voltage (24v)
I added a few more pictures to see if that helps.
 

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kellys_eye

Jun 25, 2010
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The 24V input will use the 24V for the motors but reduce the 24V to 5V (or maybe 3.3V) for the electronics side. Sadly, if there is any issue with the 5V (or 3.3V) side of things you're unlikely to affect any repairs without some sophisticated test equipment and (probably) some dedicated soldering equipment to remove/replace parts.

Your best hope is that there is an issue with one of the sensors - either with a blocked sender (usually an Infra Red LED) or faulty receiver (IR detector). In either case, if it's not a simple 'dirt' issue then testing/replacing (even FINDING) the sensors may be more troublesome than just replacing the printer.

You can 'see' Infra Red LEDs if you view them through a phone camera (in video mode) - try this by looking at your TV remote whilst pressing a button - you'll see the IR LED show on the phone but you won't see it with the naked eye.

Use the phone to view the senders on the printer and see if they light up.
 

Los_

Nov 6, 2022
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Thank you for the explanation @kellys_eye
I don't want to waste any more of your time but last question, Is there a chance that the MOSFET is breaking down the 24V to the 5V or 3.3V as you mentioned above or that is not the use case for those components?

-Los
 

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kellys_eye

Jun 25, 2010
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The MOSFET may indeed be the switching component of the power supply to derive the 5V supply the rest of the circuitry needs. Difficult to tell from the images currently available to me.

If you look up the data sheet for any of the other multi-pin devices you may find one that shows the power supply to its supply pin and, from that, determine what voltage is actually there by measuring it. I suspect all is ok and that the fault is more basic than that but without physical access to the printer I can't be of any more assistance.

Is there any 'hair trigger' wire that detects the paper presence as it enters the feed path? your image ki3 shows a detector right at the edge so this one would be the main area of concern - perhaps check out the cable to it as it looks to pass across a hinge and it might have fractured a wire through movement?
 
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