Ricoh A250 Service Manual page 693

Tech Service Bulletin No. A250– 001
Page 2 of 2
white data value as the background). Further, when making copies from an original, the machine will also
attempt to reproduce any small, white spots present inside the black areas.
For the purpose of confirming the image quality of black areas, please do not use the sky-shot copy.
However, if producing a sky shot becomes necessary, the Manual Image Density (Non Auto Exposure)
mode should be used (which turns off the background removing function). The image density of black areas
in Manual Image Density mode is higher than that of Auto Exposure mode. Also, dust or other particles
present on the contact glass will not result in white spots on the copy.
2. This symptom is also related to the mono-component toner developing system used by the A250.
There are two causes:
A. Image density is determined by the amount of charge that the toner holds. However, regardless of
whether the charge held by the toner is too low or too high, the resulting image density will drop. If the
charge is too low, the necessary static electricity and therefore the amount of toner used will also be low,
causing a lower image density. If the charge is too high, the developed toner will neutralize the charged
image on the OPC drum causing the static charge necessary for development will be relatively low. This
will cause the amount of toner used to be low, resulting in lower image density.
The reason for the initial low image density is therefore not related to the dual-component development
system. Rather, it results from a low initial static charge on the toner due to the use of a development
system where the uncharged toner is directly supplied to the development roller.
B. Generally, toner is initially supplied to the development roller starting with the smallest particles. If the
particles are relatively small, the image density will be relatively low not only because the toner density is
visibly low, but also because the amount of charge in the toner is higher. In the A250, image density
begins to increase after the smallest toner particles have been used up, approximately 100 to 250
copies. This symptom is not limited to the A250, and is present in machines of other companies that
employ the same type of development system.
It has been proposed that in order to increase the image density (i.e. improve the initial performance of the
toner), the development roller should be run idle. However, since the toner is not being used (as there are no
copies being made), the same toner will remain on the roller as it turns, subjecting the toner to stress (which
will cause the image density to drop). Therefore, although the symptom produces copies with slightly low
image density, it is limited to the first 100 to 250 copies, after which the image quality will improve.
A countermeasure will therefore not be applied to these symptoms. In addition, a test for image density was
performed using a new cartridge (AIO) followed by 10 days of no use. After testing, no change in image
density was observed.