SHARP SP1576 Technical Report

Date: Apr. 30, 1993

COPIER : SF-7800

No. : SP-1576

TROUBLESHOOTING POWER SUPPLY BOARD
DAMAGED BY OVERCURRENT (Q301, SCR301)

1.Model name: SF-7800/7850

2.General: It may possibly happen to damage the transistor (Q301) or the thyristor

(SCR301) of the DC power supply board caused by overcurrent owing to an
abrupt voltage fluctuation. If Q301 was damaged, a voltage above 30V is
added on the 24V line (VB) which may cause to damage IC25 of the main
PWB. To avoid this, these parts (Q301, SCR301) are replaced with new types,
the DC power supply is provided by other vendor, C316 is changed for 100V
series of the domestic version of SF-7870 to prevent a damage caused by a
voltage fluctuation owing to an abrupt service interruption. (for a communal
use of the power supply PWB)

3.Reason: The problem is eliminated f or the DC power s upply PWB t o resist the abrupt
voltage fluctuation.

4.Description: The voltage withstanding property is c hanged for t he Q301 transistor from
100V to 200V, the amperage is changed f or the S CR301 thyristor from 6A to
8A, and the capacity of the C316 capacitor is changed from 3300µF to 4700µF.
However, the change in C316 applies only to t he 100V series machines. The
structure of the heat sink (A303) i s also c hanged to improve the wi re harness
routing job.

Current New Note

Transistor, Q301 0CBUAC0107AZ/ 0CBUAC0247AZ/

Thyristor , SCR301 0CBUDA0063AZ/ 0CBUDA0076ZZ/
Capacitor, C316

(100V series only)

0CBUGAC222GQ/ 0CBUGAC472GQ/

Voltage withstanding
property changed from
100V to 200V.

Amperage limit changed
from 6A to 8A.

Changed from 3300µF to
4700µF.

This change of C316 is for preventing a damage owing to an abrupt service
interruption for the domestic version of SF-7870 only. C316 of SF-7850/7800
are also changed due to a communal use of the power supply PWB. (The
current capacitors of SF-7850/ 7800 have no problems.)

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SHARP CORPORATION Reprography Division

Green

C

Change in the Q301 transis tor

* For the pin layout of the Q301 transistor is changed after the change, the new

transistor cannot be inst alled on the current t ype PWB. Considering t he field
work, the transistor (400V) of the same pin layout is supplied as a service
parts. The circuit pattern of the PWB is also changed to meet the change in the
Q301 pin layout.

4.Action: (Factory action)

Since mid-October 1992 for the 100V series SF-7800 and SF-7850, while Q301
and SCR301 changed since Januar y 1993. S ince September 1992 for the 200V
series SF-7800 and SF-7850. Since December 1992 for the SUKM production.

Current New

100V rated 200V rated

(Field action)

When the problem is met for Q301 or SCR301 on the field, the replacement of
C316 is not required. They must be replaced wi th the new items. P lease note
in this case that i t needs to replac e with the 400V rated Q 301 because it has a
different pin layout from the ex isting Q301. A lso, it needs to use the new heat
sink added besides t he existing heat sink (A 303) as i t needs to enhance the
heat releasing effect as the new Q301 has more heat generation.

Field action Q301 transistor VS2SC3572-/-1 Q’ty=1
Field action heat sink LPLTM4470FCZZ Q’ty=1
Field action screw (M3x8) XBPSD30P08K0D Q’ty=2
Field action SCR301 thyristor 0CBUDA0076ZZ/ Q’ty=1

Notes on replacing Q301

1) Q301 and, D302 and IC302 found besides the Q301, must be in contact
with the A303 heat sink surface.

2) You must add the extra heat si nk (LPLTM4470FCZZ) to t he existi ng heat
sink when replacing Q 301. The exist ing heat sink (A303) mus t be in contact
with the new heat sink in their surfaces and the new heat sink must be
fastened with the existing heat sink using screws (M3x8).

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Q301 and SCR301 replacement procedure

1. Remove the screws from the power supply PWB and remove the baseplate

and the heat sink. (➀ through ➅ in t he figure.)