AR-285 (serv.man16). AR280 285 335 Service Manual-Operational Description - Sharp Copying Equipment Service Manual (repair manual). Page 5

Deterioration of developer leads to changes in the environmental conditions.

To solve the above problem, the developing bias voltage is changed according to the situation to maintain the proper density print and prevent
against background copy. 

(Operation)

1) Three toner image patches are made on the OPC drum with the three voltages Vdbc and Vdbc 

±

 (n)a. (a = 50V)

2) Connect the three points of three toner patch density points with strait lines, and check that it reaches the reference density "38" (set with SIM

44-4).

If the above condition is satisfied, obtain the correction developing bias voltage (Vdbc(n)) for the reference density "38" by linear approximation. 

3) Calculate the developing bias correction voltage (

 Vdbc(n)).

The developing bias correction voltage (  Vdbc(n)) is applied to the developing bias voltage correction in all the operation modes. 

If the condition of 2) is not satisfied, change the condition of 1) as follows and make three toner image patches similarly to 1). 

(Contents of change)

Change the three developing bias voltages of correction for making toner image patches to Vdbc + (n 

±

 1) 

α

, Vdbc + (n 

±

 2) 

α

, and Vdbc + (n 

±

 3) 

α

, and execute 1) and 2). (

α

 = 50V)

Repeat the above operation until the condition of 2) is satisfied. (n = Number of toner patch forming. 3 toner image patches are made for once.)

The correction operation of the developing bias voltage should be in the range of 0 

∼

 –750V. 

Develping bias voltage

Reference level
(Set by T.C 44-4)

Limit(-750v)

800

Vdbc

Vdbc + (n)

α

Vdbc - (n)

α

Vdbc + (n+1)

α

Vdbc + (n+2)

α

Vdbc + (n+3)

α

60

Lower

50

40
38

Image patch density

30

20

10

Higher

0

100

200

300

400

500

600

700

∆  

Vdbc(n)

α

 = 50

PT2/BS2(1D1)2

PT3/BS3(1D2)3

PT2/BS2(1D1)2

PT3/BS3(1D1)3

 

∆  

Vdbc(n)

CASE 1

CASE 2

Vdbc(n)

Vdbc(n)

PT2/BS2(1D2)2

PT1/BS1(1D2)1

PT3/BS3(1D1)3

PT1/BS1(1D1)1

PT1/BS1(1D1)1

Develping bias voltage

60

Lower

50

40
38

Image patch density

30

20

10

Higher

0

100

200

300

400

500

600

700

∆  

Vdbc(n)

PT1/BS1(1D1)1

PT3/BS3(1D1)3

PT1/BS1(1D1)1

PT2/BS2(1D1)2

PT3/BS3(1D1)3

∆  

Vdbc(n+1)

FIRST

SECOND

Vdbc(n)

Vdbc(n+1)

α

 = 50

Vdbc

Vdbc + (n)

α

Vdbc - (n)

α

Vdbc(n) - (n)

α

Vdbc(n)

Vdbc(n) + (n)

α

800

Reference level
(Set by T.C 44-4)

PT2/BS2(1D1)2

Limit(-750v)

12 – 3