308 - Fully black prints

[tmmdmmm]

Hello guys! Somewhat stumped, and curious if anyone has seen something similar before

Customer called about their 308 with 48k meter (bought 2017) printing pure black. I get there with a PH and my font list is pure black. No codes, but possible P9. Swapped out the laser. First print is perfect, but quickly darkened into a pure black sheet after 10 pages.
Questioned the customer again and he mentioned when he lets it sit for a while it gets better for a couple pages. Saw the P9 and a TCR of 0.5%, toner was empty. Manual add toner from their empty bottle, got TCR to 6.5%. One page later it dropped to 4%. Put brand new toner in, started auto adding toner, after a couple minutes of adding it gave a toner empty screen. Opened and closed the front door and it continued adding. Repeated that add/empty three times. During all this TCR was rapidly fluctuating between 2% and 4%.
I have a new developer coming in this week, but I've never seen developer backgrounds get to a pure black, its usually a light gray that doesn't change regardless of how many pages printed. Any other ideas?

[blackcat4866]

I think the toner density issues you have documented are exactly what you might expect when printing 100% fill black images. So I think you've focused on a consequence, not a cause.

You did not mention that there were no page voids. If there were voids I would suspect laser or image processing ... but I suspect that there were no image voids, meaning that you're probably losing primary charge. Maybe at the contacts, maybe a primary charge short, maybe HVT.

Were it me, I'd start with a drum unit, check charge contacts, then HVT. =^..^=

[tmmdmmm]

I think the toner density issues you have documented are exactly what you might expect when printing 100% fill black images. So I think you've focused on a consequence, not a cause.

You did not mention that there were no page voids. If there were voids I would suspect laser or image processing ... but I suspect that there were no image voids, meaning that you're probably losing primary charge. Maybe at the contacts, maybe a primary charge short, maybe HVT.

Were it me, I'd start with a drum unit, check charge contacts, then HVT. =^..^=

Thanks, I did swap out the drum as a gamble before throwing the PH in. Wouldn't charge contacts/high voltage cause the opposite issue; Completely blank prints? And yeah, I'm sure the lack of toner and initial 0.5% TCR was a symptom of the original problem, but what's throwing me off is the rapid up and down of TCR while adding toner, w/out any prints

[blackcat4866]

... Wouldn't charge contacts/high voltage cause the opposite issue; Completely blank prints? And yeah, I'm sure the lack of toner and initial 0.5% TCR was a symptom of the original problem, but what's throwing me off is the rapid up and down of TCR while adding toner, w/out any prints

Back in the analog days, yes, high voltage loss gave blank images. But at the advent of digital copiers, high voltage loss presents as black images and no voids. Digital copiers charge the drum negative, then laser discharge the image areas to become less negative. Confusing, I know.

Did you say there are no voids? =^..^=

[tmmdmmm]

Back in the analog days, yes, high voltage loss gave blank images. But at the advent of digital copiers, high voltage loss presents as black images and no voids. Digital copiers charge the drum negative, then laser discharge the image areas to become less negative. Confusing, I know.

Did you say there are no voids? =^..^=

Thanks for the clarification, I think I'm just basing it off poor movers knocking those contact assemblies out of position, causing blanks across one or more colors. From what I can tell, no voids, its a pretty consistent gray that quickly turns black.

[tmmdmmm]

Here’s a reference immediately after the PH change, Left I had laying around from a different machine
49427

[blackcat4866]

If it was overtoning you would have edge voids. Concentrate on charge. =^..^=

[tsbservice]

What are voltages readings in Table number? I mean Vdc and Vg. Inspect closer developer and drum contacts machine side. If possible swap developer unit for a test.
Good luck.

[Zesti]

If it was overtoning you would have edge voids. Concentrate on charge. =^..^=
Not showing void edges clearly shows PH unit is fine... Check HVT...... A dumb question....do they have mice??????:rolleyes:

[emujo2]

KMs "write to black". The drum is fully charged, anywhere the laser writes, the charge is dropped (255 steps). No charge would show up as 100% fill, including edge deletion areas. Could be the drum itself, the rear contacts or the HVT. The intermittent copies lead me to think it's a contact block..E

[tmmdmmm]

What are voltages readings in Table number? I mean Vdc and Vg. Inspect closer developer and drum contacts machine side. If possible swap developer unit for a test.
Good luck.

I swapped out the Dev this morning and all seems good, but its also been sitting for the weekend so I'm not convinced its resolved. Vdc and Vg before were 457 and 607 respectively, after was 433 and 583, both a fair bit high. TCR was also 0.19 when I got back this morning and it kept fluctuating while adding toner, same as last week. Moment I swapped it jumped up to 6.5ish and was very consistent through my tests. I don't believe this was the issue, I think it was just a symptom, but at the moment all seems good.


If it was overtoning you would have edge voids. Concentrate on charge. =^..^=

I agree, I've seen it plenty with those smaller IUs. If the problem returns I'll be focusing on HV, but inspecting all the connections on both sides it seems fine.

[tmmdmmm]

Little update so I don't leave anyone with a false fix
I got a callback the next morning, swapped out the HVB and all has been quiet for a few days. Although it makes sense, all my issues with HV in the past has led to the opposite problem; faded prints in one color. Certainly didn't help diagnosing with this being a black only machine.
Thanks everyone for their help!