Help with Mystery -- Sudden changes in print densities Canon iR8500

**Juxta5** · 11-19-2015

Was performing PM and strung new wires: Primary, secondary, separation and transfer. Did not replace array it has about 300,000 copies on it.

I make a copy, it looks good but a bit light. Went through Image Adjustment Basic Procedure and made some very small adjustments to the wire heights. Make copies they look better.

Make a few more copies, get a paper jam, clear the jam, then instantly copies are EXTREMELY light, barely visible.

Turn machine off and on. Make copies they look fine again. Make about 50 copies and I notice they are slowly getting lighter. Another paper jam, clear the jam and instantly the copies are barely visible again.

So I check VDM it's okay at 390, but VL1M reading was 290! And I'm thinking cool.. possibly Potential control. Turn off and check connections just to be safe. Turn back on and suddenly VL1M is normal at 77.

and PG prints (4,5,6,7,8) look good.

I also pulled the developing unit and the roller could use replacing. I'm not certain how old the develop unit is.

So thoughts as to why the instant flip-flops between good image and super light images?

**Juxta5** · 11-19-2015

Oh, btw. No error codes with this one.

**teckat** · 11-19-2015

Dev Bias_😱

**blackcat4866** · 11-20-2015

Potential control can do this. You should be able to turn off potential control to use generic values, which should look much better temporarily. =^..^=

**Canuck** · 11-20-2015

Potential control is not done on the fly. Machine does it initially or when fuser cools down. Have you tried to replace the transfer/sep assembly? Check transfer current in service mode while it is running. Dev clutch slipping? HV leads?

**Juxta5** · 12-03-2015

Yes, developing unit.

When I tested this unit it could print single sided endlessly. In fact it printed 96,000 additional single sided sheets after my first post. But the minute it duplexed the image would become incredibly faint. I didn't make that connection when I first posted, ie that's why PG tests looked good.

I swapped out this machine's developing unit with a used spare and it can print both sides and maintain the density. But all said, it's best to retire this machine because parts are difficult to come by.

I get a sentimental over clean, well functioning machines and it's hard to let them go. This one was stellar, over 6 mil and if I could get parts... hell it just might double that.

**blackcat4866** · 12-04-2015

Congratulations. =^..^=

**KenB** · 12-04-2015

Glad it's working.

It's been years, but I got burned by slipping developer clutches and bound developer units enough times to look there first.

Also, it was more on the 8570, but some of the connectors on the DC controller were kinda touchy. I remember using a brass "toothbrush" and a can of spray contact cleaner to evict quite a few gremlins.

**blackcat4866** · 12-04-2015

Originally Posted by KenB

Glad it's working.

It's been years, but I got burned by slipping developer clutches and bound developer units enough times to look there first.

Also, it was more on the 8570, but some of the connectors on the DC controller were kinda touchy. I remember using a brass "toothbrush" and a can of spray contact cleaner to evict quite a few gremlins.

Yeah, NP8530 and NP8570 were the last machines to use Ultrex connectors. I don't miss them a bit. =^..^=