Copies come out with splotches

OEM (pronounced as separate letters) is short for original equipment manufacturer

The Cartridges for the HP DeskJet 3740 InkJet Printer are:

HP 27 Black Original Ink Cartridge
HP 28 Tri-color Original Ink Cartridge

These can be purchased from your local store that sells HP Printers & ink or by going to HP.com and ordereing direct from the Manufacturer

simply replace the cazrtridge with an OEM ( original manufacturer supply) cartridge and dispose of the third party cartridge- I haven heard of one instance where cheap ink refills have worked continuosly without destroying the Printer

Not sure about Epson but I had the same problem and the store where I buy my ink said that a lot of the printer companies require all the color cartridges with ink in them to work. My color use to disappear even if I just pushed black and they said that was the way they were made . They sell printers quite cheap but make their money on the ink. I got rid of mine and purchased a black only ink jet and it hardly uses any ink at all. Its a powder. You can copy many copies on eighty dollars worth of ink where the cartridges I went through several hundred dollars a year.

Try this: take a small, sharp knife and make sure the air slit on the top of the cartridge goes all the way through the plastic.
You know that little tab you have pull off the top of the cartridge before inserting in the print head? There is a tiny slit under the tab to let air in, which is necessary to let the ink flow out. The slit is made very small so ink won't leak inadvertently out the top. Sometimes the slit doesn't go all the way through the plastic. When that happens, the ink can't flow.
I blew through that slit on a defective cartridge and no ink came out. I used a pen knife to open the slit (it doesn't take much) and then blew again. This time ink spewed out the bottom. My print test showed the black ink coming through. It was a bit spotty so I cleaned the print head and now the black ink comes out just like its supposed to.

The small black tank is called "Photo Black Ink Cartridge" and is usually only sed when printing color pages or photos. There is no way to bypass that. Use the ********* ink since it is a cheaper cartridge judging by volume. Sets can be purchased on ebay for very low price. Link below:
7 BLACK Printer Ink with chip fits Canon PGI 5 MP600 MP800 MP830 MX850 eBay

If you need further help, I’m available over the phone at https://www.6ya.com/expert/alex_22751bbefa74c3d0

Canon PIXMA MX850 Multi Function Printer Printer Canon MX850 will not print from... Answer Canon MX850 will not print from small Black Ink Cartridge - 8BK. It only uses the large black ink... (More) Canon MX850 will not print from small Black Ink Cartridge - 8BK. It only uses the large black ink cartridge and I have a drawer full of small 8BK cartridges. How can I get it to use the small black cartridge and not the large black cartridge? Thanks

If you were using an original cartridge, contact HP and they will probably ask you to mail in the faulty cartridge.

If you were using a refilled cartridge you might have to buy a new printer.

This is a known problem with this printer, functions such as fax and copy will also be unavailable if the ink is low.

The low ink alert will appear even though the cartridge is not empty.

Here is the solution:

The ink cartridge has a sensor on the bottom, between the nozzles.
cut a small piece of tape and tape over the sensor.
The printer will now think the cartridge is full.

This will allow you to use every function of the printer regardless of how much ink you have. The cartridge will truly be empty when your print outs come out blank.

If you are making copies or sending/receiving faxes Press Black Start or Color Start. Make sure your ink cartridges are fresh. Cartridges remain fresh for up to two years if kept in their original packaging, after that the ink may become clogged. Cartridge expiration dates are printed on the package.

According to " HP Officejet R, PSC 500 and Color Copier - General Copying Issues and Solutions", under the problem heading "Black is not Black", notes that:

"The unit will perform mono (or black) copies using the color cartridge to create a composite black in Normal and Best modes. This is necessary to create the correct grayscale shades. NOTE: The HP PSC 500 all-in-one product cannot perform black copies. Scan the image in and print it out in greyscale.

The color cartridge may be out of one color of ink. Run a self-test page to verify that all the colors are there. Replace the cartridge if they are not."

In other words, the device only uses the black ink cartridge when used as a computer printer. When used as a stand-alone copier, it uses the color ink cartridge, and all three ink colors must be present and working to give a black and white copy. Perhaps you can refill the color cartridge with black ink in all chambers?