751 leaking toner and throwing malfunction code.

[nullskull]

I have a 751 that is leaking toner. I've replaced the developer, drum, transfer separation unit and cleaned the corona module. Even after all that it is still leaking in the same place. Before I replaced those aforementioned parts the machine worked albeit the prints were dirty. Now the machine will show a "malfunction detected turn on and off main power switch" message (doesn't show the error code). I booted into the admin mode and I believe the code it's throwing is C-2202. Which seems to be linked to the motor or circuit board. However, I believe the real culprit might be dirty sensors on the PRCB. Does anyone have suggestions as too which problem I should tackle first? The toner leak I'll leave pics of below. I wonder if it is the reason the PRCB sensors might be dirty acting up. As I know I cleaned them quite well before re-seating the drum and blade with setting powder.

Screenshot 2025-01-28 161330.jpg 1000131263.jpg 1000131262.jpg 1000131264.jpg
1st pic is of the dev unit. It sort of dribbles toner out in that messy looking area that lines up with the spill on the transfer separation unit in the 2nd and 3rd photos

[Albonline]

the h cut blades wore on these at high meter count , also there are a ton of mods and adjustments to be done to help with toner control. after market parts and supplies are questionable at best. if you need something you can count on without having to work on all the time sorry but the old 751 just ain't it.

[nullskull]

the h cut blades wore on these at high meter count , also there are a ton of mods and adjustments to be done to help with toner control. after market parts and supplies are questionable at best. if you need something you can count on without having to work on all the time sorry but the old 751 just ain't it.

Yes this machine seems to be poorly designed in some areas. You mentioned H cut blades do those go by another name i could look up? Or is that the cleaner blade?

[Synthohol]

only because you didnt mention it, when you replaced the drum, did you get the charge voltage off the back drum plate and set your charge voltage with a meter that goes to 800?
if not then nothing is gonna work right.
plus the
set charge voltage, run your LD adjustment until both lasers write just barely between the lines etc...
just follow the manual when replacing imaging parts. clearing appropriate counters and running process adjustments ensures a much longer life of components.

[nullskull]

only because you didnt mention it, when you replaced the drum, did you get the charge voltage off the back drum plate and set your charge voltage with a meter that goes to 800?
if not then nothing is gonna work right.
plus the
set charge voltage, run your LD adjustment until both lasers write just barely between the lines etc...
just follow the manual when replacing imaging parts. clearing appropriate counters and running process adjustments ensures a much longer life of components.

Ok that is a bunch of stuff I've never heard of before. My field service manual only mentions to reset the drum counter. I was wondering cause that sounded kinda too simple. As for the charge voltage stuff you mentioned would you have a guide i could look at? I'm just a teaching myself haha.

[blackcat4866]

These machines dumped toner and developer like it was going out of style. The symptom I would see first was a blank line, because the transfer wire was literally buried in toner. The separation transfer unit would fill to the top. At high volumes these machines did better, but al low volumes they dumped. Best spend your money on a different machine.

[nullskull]

These machines dumped toner and developer like it was going out of style. The symptom I would see first was a blank line, because the transfer wire was literally buried in toner. The separation transfer unit would fill to the top. At high volumes these machines did better, but al low volumes they dumped. Best spend your money on a different machine.

Is there a good fix to the dumping? Well I suppose this means that my issues with codes are because I didn't properly setup the new drum and not necessarily because of the dumping. Seems like the manual led me wrong in regards to drum replacement.

[blackcat4866]

At low volume it will dump toner and developer.

[Synthohol]

At low volume it will dump toner and developer.

this is very true, thats why i adjust the LDs just barely between the lines, it really helps.

[Synthohol]

i sent you my service manual nullskull

[wjurls]

The Bizhub 601/751 as well as their predecessors the 600/750's are the "Mufasa" of the Konica-Minolta lineup. They send chills down the spines of many a tech.

[nullskull]

i sent you my service manual nullskull

Thanks. So I should run the charging grid manual adjustment? From what i understand I should measure the voltage and then make adjustments to bring it to standard value (being 5V)? Like if it measures 10V I'd lower it by 5V?

[Albonline]

Yes this machine seems to be poorly designed in some areas. You mentioned H cut blades do those go by another name i could look up? Or is that the cleaner blade?

h cut/doctor blade. the series was built like tanks . after all adjustments/mods are done . they run if you run them, if you are low volume don't waste your time and money on it. we had quite a few of these run close to 5 million .

[nullskull]

h cut/doctor blade. the series was built like tanks . after all adjustments/mods are done . they run if you run them, if you are low volume don't waste your time and money on it. we had quite a few of these run close to 5 million .

Yes this machine will be very low volume so I should talk to the boss about selling it. But in the meantime what sort of mods can be done?

[Synthohol]

on the back of the drum there is a 3 digit number usually in the low 700s, this is the voltage you set the grid voltage to.
you measure from ground to the round shaft in the grommeted hole in the center and you run the adjustment in service mode and measure the voltage and + or - it to match whats on the drum.
did you do the developer calibration? the LD adjustment will help it less likely to overtone and spill as well.

look at the adjustment section, its all outlined what adjustment to do and in what order when replacing parts. (for best results of course)