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Microsoft Windows 10 (64-bit)



I have a Plotter HP Designjet T790PS 44” which was working wonderfully, until one day I received a 79:04 error. I change the HDD but the problem persisted. At that point, I changed de firmware but the problem remained, afterwards I changed the Formatter and then the printer was working but another error appeared, saying that the printer didn’t recognize the Printhead MK-Y ( C9384A ). I replaced it with a  new Printhead, but the problem persisted. I performed a “ Carriage Assembly Test“ and then the printer didn’t recognize any of the three printheads. I bought the new printhead, but the problem remained the same. I also tried replacing the Carriage PCA but the problem remained the same, the printer didn’t recognize any of the three printheads.


Thank you for your help

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I'm having a similar issue.

Received the 79:04 error yesterday and cleared it by turning off the printer, unplugging/replugging it, and powering up. I think it was due to in incompatible size print being sent to the job queue.


Anyway, today I got the error to 'reseat' the MK-Y printhead. I just went through the steps to remove/reseat the printhead with the same part. After that, the 79:04 error returned so I went through the steps in the first paragraph (above).


When that finished, the message said "Printhead replacement incomplete" "error code 0x80000". Removed/Replaced and still = incomplete.


Next, I went into printhead replacement and removed all of the printheads then closed the compartment and the cover. I turned off the printer and unplugged it; I removed the paper roll. I plugged it back in and turned it on. It asked for paper; I installed it. Good so far.


Then it asked for the printheads and I put in each one and received a 'beep' before locking it in. Once again, it seemed to be going through the remaining initialization but ended with the "79:04" error again.


I again turned off/unplugged/plugged in/turned on. And again with the printheads, but this time the message is: "prnithead replacement not completed" -- on all three!


It's nothing but a 'door stop' right now so I guess I wil turn it off until I find a new thing to try.

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Having the same problem with a T790PS.  Replaced C/M and MK/Y printheads and have the same "...not complete" error message.


Anyone solve this?


Also put in all new ink cartridges and now am getting a message that the yellow is not working.  Argh!


Also posted a thread about erroneous dates showing up.  Yellow ink cartridge says the expiration date is 12/31/69!  How does that happen?

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So may have solved the mystery about the 12/31/1969 date showing up.  Has something to do with the Unix system.




So I'm thinking it's software that's the problem rather than hardware.  Not sure though.

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Mar 9
Having the same problem with a t2300. Replaced C/M and MK/Y printheads and have the same "...not complete" error message.

Anyone solve this
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Dear death master

the 79:04 error is firmware error, first of all you should to disconnected the power cord and wait for 5 minutes and then turn on ,

now you have problem with printhead, you should to going ink menu and choose printhead replacement, after few seconds you must open the upper door and see the condition of three printhead on your touch panel, if you dont see that , your door sensor have problem , solve that and try again.

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Has any one got this problem solved?

My Designjet T920 has the same problem: keep showing replace printhead 0x80000 error. I have replaced the printhead and the carriage PCA and latest firmware.

Any one can help please?
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I wish I could say that I've found the problem but I haven't.  We have a tech coming over to look at a T1200 that has a main pca issue and I hope to ask him about it then.  I'll post up what he tells me, if anything.

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Haha, myself is one of HP designjet 79:04 error victim.... I have 2 Z3100 44" & I could not solve this problem. here are the details :

#1... at least 2 years, I could not get it pass this error. This machine booted up all perfectly, as soon as I loaded paper roll

to align printhead, right away, 79:04 error.... I changed belt, check encorder strip. all cleaning, lubrication etc etc.

my original post is stiil on this forum.    unsloved.


#2 Z3100 44" it was working all fine. my daily use #3 Z3100ps had an error said MK ink was empty, so I replaced

with a brand new, genuine HP ink.... same & printer said empty.... so I replaced with another brand new one... same old, same ole.


So I pulled the new MK ink & plugged onto the #2.... same  error, shut off & turn it on few time.... same ink empty error.

I went back to #3  printer & tried all the possible way I could ever knew....


Unfortunately the #2 79:04 error came up, good bye.... never worked since. This week I recevied a brand new HD,

same old, same old. unsolved. 


This afternoon I went back to #2 & paid close attention when the 79:04 come up.... it came up right after 100%

& carriage box did not move at all.. Tomorrow I will replace the print mach board A version & see any different.


Then if nothing work, I will replace print mech board with B version, also B version of formatter board...


I will post if any news....

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I have some questions that found your problem, 1-did you change the belt with original part or Oem part? 2-when you want to load the paper and carriage going to check paper you see the 79:04 error or every time that carrige want move out service station?3-have you tried to update firmware?
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