I got the COM-14970 thermal printer a week ago. I’m using it with the TOL-15312 5V 2A power supply.
Out of the box the printer was working great. I was getting nice, dark prints. I’m almost at the end of my starter roll now. Starting yesterday, I started getting very faint prints, and longer lines would fail to print. I also couldn’t get the selftest to work; the printer would just repeatedly print the first half of the “Selftest” header over and over.
I suspected it was due to some kind of current issue, however I’m not sure why this would have changed over the week. The printer is plugged directly into the power supply and I’m using serial from the computer, so nothing else should have been drawing any kind of current. To check this, I plugged a 9v battery into the printer. This allowed for the selftest and for prints with more than a few characters to print, however the printing was still very faint.
I’m not sure what other steps I could take to resolve this. Is there a chance I got a defective printer, or maybe is something mechanical sticking causing a higher current draw? My multimeter doesn’t update super quickly but I don’t see it ever cross over about 1.8A at 5V.
The first photo shows how longer lines get cut. The second photo shows a self test at 9V where everything is printed very faintly. The self tests I printed when I got the printer were very dark.
Can you share some pictures of the printing or even video? It’ll have to be hosted on Google Drive, Imgur, or another service to share via a link. There is a small bug currently with uploading photos.
Generally, these printers have been reliable. Most likely, it could be an issue with the paper.
Oh, I didn’t notice the photos didn’t get uploaded. Here’s an album link: https://photos.app.goo.gl/vz2SSDJKu2cBY2E78 . I’ve put comments on the pictures with more information.
I’ll be able to get a video uploaded this evening, but it’s not going to show much. The printer more or less looks normal, but I think the controller inside the printer is resetting itself because immediately after a failed print I get the green LED flashing once like it does at power up.
I have some fresh paper coming this afternoon I can try with too. I tried re-printing over a “known good” section of paper that printed well before but I saw the same failure.
One other thing: when I request the status from the printer with 0x1B 0x76, 0x20 is returned. This doesn’t seem to match up with anything in the datasheet. If I remove the paper and request status I do get the correct status message for that.
Let’s see how the new paper performs. You could also try disassembling the printer to do a quick clean out of any dust or debris at your own discretion.
The new paper came in. At 9V on battery I’m getting the same results as before. Funny enough my 5V prints are looking much better now, though still not as good as they once did. In this picture, left is 9V, middle is 5V, and right is an old messed up (but very sharp print) on the original Sparkfun paper at 5V. https://photos.app.goo.gl/hYswEMo8iJuxG57o9
As an aside, I think my printer came with firmware that isn’t entirely compatible with the documentation. My firmware version is GV2.16.08 20191121_R. The heat time & interval commands (27 55 n1 n2 n3) seem to have no effect. I can send the minimum value of 3 for heating time, which supposedly will print a blank page, but the output looks no different from the heating time set to 255. If I trigger a self test from software the “Heat Configure” section remains unchanged.
I really appreciate your help and I hope you have a great (hopefully long) weekend!
Re: trying it with a 9 volt battery, if this was the common rectangular type you find at the grocery store, it is unlikely to be up to the task.
Those 9 volt batteries are generally designed for relatively low output current - on the order of 10 to 100 ma. The thermal printer can draw up to 1500 ma. They are available in different chemistries - carbon-zinc, alkaline, and lithium. The lithium ones are the only ones that typically even show currents over 100 ma on the data sheets, but would likely be used up in about 45 minutes at 1000 ma drain current, and would have dropped to a little over 7 volts within the first five minutes at that rate. (see https://data.energizer.com/pdfs/l522.pdf)
Be aware, too, that if you have your meter in series with the supply to measure the current, there will be some voltage drop across the current shunt in the meter. Depending on the quality and sensitivity of the meter, and what range you are on, this could reduce the output enough to degrade print quality some. (Possibly the difference between the original sharpest output and the not-faded-but not quite as sharp output with the replacement paper.)
Also double check for a good connection to your 5 volt supply. You might also look at how the supply voltage is holding up when the printer is printing.
I think you hit the nail on the head. I’ve never really dealt with something that pulls this much current, and I’ve been out of the hobby for quite a while so I was a bit rusty.
When I started tinkering with this I had the printer more or less directly wired to the the wall wart power supply. Later in the week I changed my power connector up and it looks like I didn’t have a good power connection any more, but I never put two and two together on that being the cause of the problems.
I just got a bench supply to mess with and I’m getting great prints again with the printer plugged into the terminal on the new supply. That said, the printer does seem to be wanting to draw more than 2A: if I have over current protection turned on it will trip.
Thank you both very much for your help. I think we can consider this one closed.
Just for fun and to hopefully learn something I hooked my scope up to the power supply during a print. It looks like the voltage is dropping down to 3.66V at worst during a print and when the power supply is in constant current mode.
