You just bolted the new head in, pushed the dampers back on, ran two cleanings, and printed a nozzle check. Every row is there. No deflections, no gaps, nothing missing. Then you print a real file and the whole image looks washed out, like somebody knocked the density slider down overnight.
Most of the time the head is fine. The number on the side of it never made it into the machine. Every Epson printhead leaves the factory with a five digit ID printed on a label, and that ID tells the printer how hard to drive that specific unit. A new head running on the old head's number is firing at somebody else's voltage. It puts ink down, it does not clog, and it prints thin.
This is the order I work in after a head swap: the label first, because it costs nothing, then the ink path, then the alignment, then the head itself.
Start With the Label on the Side of the Head
Pull the old head out and look at its side plate before it goes in the bin. There is a label there with a string of digits. On the Epson heads most shops are running, that string is five digits long. The first two are the head ID for normal dots, the next two are the head ID for microweave dots, and the last digit is the rank value. Older service manuals spell this out line by line in the head voltage write section, and the layout has not moved much across generations.
Take a photo of that label with your phone before the head goes anywhere near the carriage. New ink on a new head smears the print fast, and a label you cannot read is a head you have to guess at. I have watched a technician burn an afternoon trying to decode a half dissolved label with a flashlight and a magnifier. The photo took four seconds.
Do the same with the head you are removing, even if it is dead. Two reasons. If the replacement turns out worse, you may be putting the old one back in to finish a rush job, and you will need its number again. And if the machine carries four or six heads, you now have a written record of what sat in each slot.
One number per head. Not one number for the machine. On a dual or quad head carriage, every head has its own printed ID and its own rank, and each one goes into its own position. I have seen shops clone the value from head one into heads two, three and four because it was faster. The result is a machine where one color looks right and the rest print like they are working through fog.
Where the label sits varies. On some heads it is a sticker on the metal side plate. On others it is printed on the housing and ends up under the damper once the head is installed. That is the case that catches people: everything is bolted up, the cover is closed, and the number is now behind hardware. If you cannot read the label with the head mounted, do not invent a number. Pull it back out. Twenty minutes of disassembly is cheaper than a week of faint prints you cannot explain.
Refurbished and pulled heads are their own problem. A genuine refurbished head should still carry a readable ID. If the seller cannot tell you the ID of the exact unit they are shipping, or the label has been cleaned off, you are buying a head with no way to set it up correctly. Ask for a photo of the label on the real unit, not a stock shot of the model.
Why a Perfect Nozzle Check Still Prints Thin
Here is the part that confuses people. A clogged head and a mis-set head both give you a thin print, but they do not look alike on paper.
A starved or clogged head shows up in the nozzle check. You get missing segments, half rows, a staircase where one side of the head drops out. You can point at the exact nozzles that are not firing.
A head running on the wrong voltage usually prints a clean nozzle check. All rows present. Then the real image comes out uniformly light, or the gradients step instead of blending, or a solid block of color looks grainy at the edges while the middle is acceptable. The nozzles all work. They are being pushed with the wrong amount of energy.
That one observation saves money. If the nozzle check is perfect and the print is faint, stop buying cleaning solution and stop running powerful cleanings. You are not fighting a clog. You are looking at a setup problem, and the cheapest place to look is the number you did or did not enter.
There is a second version of this on multi head machines. One color prints thin while the others are normal. If that color's nozzle check is clean, the head is probably running at a voltage that does not match the unit. Same cause, easier to spot, because you have three or five healthy heads sitting beside it as a reference.
The machine does not know which head you installed. It only knows what number you told it. Piezo elements vary from unit to unit even inside one production batch, and the ID is how the manufacturer passes that variation down to the driver board. Get the number wrong and every dot from that head lands with slightly the wrong energy, which reads as low density rather than as a hard failure.
That is also why a head can print fine for a week and then seem to fade. Nothing changed in the head. Somebody ran an initialization, a firmware update, or a head replacement routine, and the stored value went back to a default. If the machine has a service history you do not control, read the stored value before you touch anything mechanical.
Keep a note of the number you entered. If a machine that printed fine last month suddenly looks light and nobody touched the heads, pull up the stored value before you order anything. Ten seconds in the service menu tells you whether the number is still the one on the label. That is a free check, and it rules out the whole voltage branch of the fault tree.
Writing the Value In, and the Shutdown Trap
Every major brand has its own route to this screen, and the routes do not transfer. On Epson wide format machines it is done through a service or adjustment program on a laptop connected to the printer, in a menu usually labelled head voltage write or VH. Roland, Mimaki and Mutoh each have their own service utilities or panel level menus. Do not run an Epson procedure on a Mimaki. Find the procedure for your model and keep it in the shop folder.
The shape of the job is the same everywhere:
- Connect the laptop and let the service program see the printer.
- Open the head voltage or head ID menu.
- Pick the head position, starting with the one you replaced.
- Type the five digits exactly as printed, one at a time.
- Confirm, then move to the next position if you replaced more than one head.
- Exit the menu properly. Do not kill the program or shut the laptop.
- Power the printer off with its own switch, wait, then start it again.
Step seven is the one people skip, and it is the one that decides whether the job worked. On the Epson machines documented in the service manuals, the adjusted values are not written into the EEPROM until the printer is powered off. The program sends them, the screen says done, and the machine is still holding them in volatile memory. Pull the plug, lose power, or shut down in the middle of the write and you can end up with a stored value that is neither the old number nor the new one.
Two rules follow. Do the write on a stable supply, not on a circuit shared with a laminator or a heat press that gets switched on and off all afternoon. And after the write, do a full normal shutdown, count to ten, then start up and print a test file before you run production. Not a nozzle check. A real file with a gradient and a solid block, because that is what exposes a density problem.
Write the numbers on the service sheet and tape it inside the machine cover. Next time the head comes out, or the next technician walks in, the history is there instead of in somebody's memory.
One more thing about the first start after a write. Most service routines push an initial ink charge at some point, either inside the menu flow or as a separate step. That charge pulls a lot of ink and it hides problems for the first meter or two, because the head is wet and the dampers are full. Judge the result on the third or fourth meter, not the first. If density is still falling at that point, the value is wrong or something else is starving the head.
If the Number Is Right and It Still Prints Faint
Assume the ID is entered and confirmed. Now work in the order that costs the least.
Start with dampers and the ink path. A new head pulls harder than a tired one, and a damper with a partly collapsed mesh or an air pocket starves it in a way that reads as low density. Pull each damper, hold the mesh against a light, and check the ink level in the chamber. If one sits lower than its neighbors, that is your suspect. This step costs a pair of gloves and nothing else.
Next, check that the head actually got primed. A head pulling air will print a reasonable nozzle check and a weak solid block, because the check uses very little ink. Print a small solid patch of each color on scrap media and look at density across the patch. A patch that fades from one end to the other is a supply problem, not a voltage problem.
Then look at alignment. Every manufacturer says the same thing in their service documentation: after replacing a printhead, head angle and position have to be adjusted. A head that is slightly out of square lays dots in the wrong place, which reads as softness and, in bidirectional mode, as light banding that looks like low density. Run the angle adjustment first, then the position or alignment routine.
Only then question the head. If the machine carries other heads of the same color, compare the stored values. A single head sitting far outside the group, say more than about ten percent away from the others, is a signal worth raising with your supplier before you commit a production run to it. Some new heads also print poorly for the first few hundred milliliters and settle in with use. Give it a day of real work before you pull it back out.
On machines that show a voltage figure instead of a raw ID, read every head and write the figures on the bench sheet. Two heads of the same color normally sit within a few points of each other. You are not hunting a perfect match, you are hunting the one that broke away from the group. That spread is the fastest read on whether you have a mismatched unit, a tired unit, or a board pushing one channel harder than it should.
What you should not do is raise the voltage by hand to compensate. If the stored ID is correct, adding voltage on top of it drives the piezo harder than the design allows. You get density back for a while and you pay for it in head life.
The Bench Checklist
Keep this where the service laptop lives.
- Photograph the ID label on the new head before the rest of the box comes apart.
- Photograph the ID label on the head you are removing.
- Write both numbers on the service sheet, with the slot each one belongs to.
- Mount the head, but do not close the covers until you confirm the label is still legible.
- Enter each ID in its own position. Never copy one value across several slots.
- Exit the service menu properly, then power off and back on.
- Print a gradient and a solid patch, not just a nozzle check.
- Record the stored values inside the machine, not only on paper.
Two buying notes, since this is where most of these jobs start. When you order a head, ask the seller to confirm the ID label is intact and readable on the unit they are shipping. A label washed off by cleaning fluid turns a twenty minute job into an argument with your machine. And if you are buying a pulled or refurbished head for a machine that is already running production, price the downtime, not just the part. A head that arrives with no readable ID costs you the gap between a scheduled swap and a lost afternoon.
Questions that come up at the bench:
Can I run the machine on the old value while I wait for the service program? You can, and it will print. It will also print at the wrong energy for as long as you leave it, which is the exact problem you are trying to fix.
Do I need to redo alignment after every head swap? Yes, if the head moved. Most service documentation treats angle and position adjustment as part of the replacement, not as an optional extra.
What if the label is unreadable? Ask the supplier for the ID they hold against that serial number. If they cannot provide it, send the head back before it goes in the machine.