Xerox DC 470 trouble

[xtech]

Hi all,
I have a Document Centre 470 with copies coming out way too dark (both image and background). It's not the Xerographic module, it has been replaced and didn't solve the problem. I also tried to adjust values of the potentiometers on the HV charge board, and the MAG/DONOR voltage board, but that doesn't seem to alter the image appearance at all - it almost seems as they are offsets and counteracted by feedback/software. When running the Xerographic Routine, it fails with code 09-324 (too much background), which doesn't get me any closer since we already knew that.
Does anyone have experience with this style of machines here? Is there a way to access the diagnostic routines from the UI or do you need that PWS thingy? Does anyone have a SM manual for this beast or similar series?
It doesn't look like a complex machine though, I mean it's big but no different from any other laser/copier in terms of functional parts, but with that few abilities to alter things it becomes like touching in the dark ...
Thanks a lot!

[edwin rocha]

Usually HVPS is having problem with high background on most Xerox digital copier/printer. Adjusting potentiometer at HV would not solve the problem, replace it as possible.

[OES TECH]

Your Problem Is Due To One Of The Following: Developer Housing, Toner Dispenser Or Btac Sensor.

[xtech]

Thanks for the replies, really appreciated.

OES TECH:

I think I can exclude the BTAC sensor since I cleaned that one (and opened it to check there is no toner dust inside). Since the Xerographic Routine fails with error code 09-324 (too much background), the sensor is likely to work because it is able to see the actual problem on the PR belt, i.e. too much toner on background.

Developer housing: what do you mean by that? Is there something which can go wrong with the housing itself??

Could it be the toner mix, wrong ratio of dev/toner?

One interesting thing is that the copies get somewhat darker when taking multiple copies, so for example comparing sheet 1 and 10 from a series of 10, the problem gets worse on sheet 10. However, this could perhaps be a false indication, it may very well be the normal PR belt recovery which may be more visible in case of excessive toner loading.

Another thing I recall is when I bought the machine (with the defect), the defect was very visible, the complete sheet looked gray. Only after running the Xerographic Routine copies became more acceptable albeit with too much background. So the system has probably adjusted itself to the lowest possible limit. This is another reason to believe the BTAC sensor is okay.

[OES TECH]

The Toner Dispenser Has A Senor That Determines How Much Toner To Dispense Which Sometimes Goes Bad Which Then Cause Black Background. Never Tried To Replace Senor.

[xtech]

Thanks OES TECH.

I just wanted to give feedback to the forum since the problem has been solved, and it's always good to have the solution posted so other people can take advantage of it.

It seems the problem was purely related to the mix dev/toner, with too much toner being in the mix. So no HVPS problem$$$ , luckily. I've been thinking a while how I could trick the machine into "purifying" its developer by freeing it from toner, without having to purchase a new can of developer dust from Xero$$ and this is how I did it:

- I removed the toner cartridge
- I opened the scanner lid and printed totally black pages, about 50 (one by one), until toner level went much more pale

This fixed it and after now 1000-2000 copies it seems to stay stable (which wasn't the case before).

The question is of course how the mix became wrong. So either the toner dispense sensor went bad, as you mentioned OES TECH, either the machine does replenishment with fixed adaptive amounts which over time eventually became inaccurate (unavoidable in such case) making the mix remain too rich in toner.

One very interesting reading on the subject is the Xerox US Patent 5890042 Hybrid jumping developer with pulse width compensated toner mass control Hybrid jumping developer with pulse ... - Google Patents
which describes more or less what happens in the DC470.