B758 B754 drive jitter.

[allan]

Hi Guys.
Been frustrated with a problem that recently popped up. Hope to post some sample soon. I have 2 machines one 758 and the other a 754 each with around 1 mill on the counter with jitter issues.
It seems that some thing on the drive locks up for fractions of a second causing the printing to "compress" in a 5mm area on one place on A4 prints. Looks like the drum, transfer belt or paper transport to go slow.
If you print halftones at say 125 the area where that occurs makes a cross direction band of about 5mm (3/16 of an inch) that is darker. Looks like charge arcing to the untrained eye but its the drive going slow or the paper going faster in those areas.

Does not happen on the fisrt page and does not happen or display on double sided printing. Anyone seen this before.

Replaced drum, dev unit, sincro section and fuser so far. The TBU turns ever so freely but would need to replace that to eliminate that for sure.
Any clutches on the drive that could cause this? No jams and sounds ok.

[blackcat4866]

Re: B758 B754 drive jitter.

Hi Guys.
Been frustrated with a problem that recently popped up. Hope to post some sample soon. I have 2 machines one 758 and the other a 754 each with around 1 mill on the counter with jitter issues.
It seems that some thing on the drive locks up for fractions of a second causing the printing to "compress" in a 5mm area on one place on A4 prints. Looks like the drum, transfer belt or paper transport to go slow.
If you print halftones at say 125 the area where that occurs makes a cross direction band of about 5mm (3/16 of an inch) that is darker. Looks like charge arcing to the untrained eye but its the drive going slow or the paper going faster in those areas.

Does not happen on the fisrt page and does not happen or display on double sided printing. Anyone seen this before.

Replaced drum, dev unit, sincro section and fuser so far. The TBU turns ever so freely but would need to replace that to eliminate that for sure.
Any clutches on the drive that could cause this? No jams and sounds ok.

This is my first inclination. Even minor drag on the primary transfer drive will make the compressions that you describe. On Toshibas these sort of defects occur when the inner edge rubber of the primary transfer belt starts to break down (10+ yrs). The degrading rubber adheres in lumps to the facing roller, and the other transfer unit rollers. For a test original I use a print font page, A page covered evenly with small text will help you see the compressions more clearly.

Have you ruled out an optical problem (does it affect scans, or prints, or copies)? =^..^=

[allan]

Re: B758 B754 drive jitter.

I am also inclined to suspect the transfer belt. Will need to get a spare good unit to test that. Its from the engine for sure. The text is compressed on the internal PS font list printout.
Strange that its only from the second page onward. That too point to the transfer belt. Been looking at the timing diagrams to figure out what to eliminate. So far I am left with the main drive and the transfer belt.