Read JBL SCS 138 Sub (serv.man17) Technical Bulletin online
Service Bulletin
Harman International SNC - Harman Consumer International 2, route de Tours 72500 Château du Loir -FRANCE-
Service bulletin # JBL2001-002
November 29, 2001
To:
all JBL Service Centers
Models:
SCS138 SUB and SCS178 SUB
Subject:
Hum noise
In the event, you receive a SCS 138 SUB or SCS178 SUB with the complaint: Hum noise in Standby
Model
Serial number
SCS138BE/230
ME0246-06006
SCS178BE/230
ME0252-03045
The cause of this hum is due to the sensitivity of the pre-amplifier circuit. The result is that in certain areas the pick
up from the surrounding environment is sufficient to cause an audible hum.
The modification will decrease this sensitivity and
up from the surrounding environment is sufficient to cause an audible hum.
The modification will decrease this sensitivity and
in addition, disconnects the speaker in standby and decrease the
time before goes in standby.
Component needed: Part number:
138/178Berepkit
Quantity
Name
Item
Value
2
Resistor
New (across pot. UR202/A-B)
2,2k ¼ W
2
Resistor
R226 and R227
1k ¼ W
1
Capacitor
C217
470nF 50v
1
Capacitor
C218
1uF 50V
1
Diode
New
1N4148
1
Capacitor
C233
33uF 16V
Step by step:
1a Remove the amplifier from the cabinet, 10 screws
1b Dismantle the black box from amplifier, 4 screws
1c Dismount the input PCB from back panel and disconnect P101 and P102 on the Output PCB.
1b Dismantle the black box from amplifier, 4 screws
1c Dismount the input PCB from back panel and disconnect P101 and P102 on the Output PCB.
Now is the unit is in it’s service position.
2a Place the two 2K2 ohms resistors across the pot.meter UR202 A and B (see picture 2A and input schematics)
2b Change the other resistors R226, R227 and Capacitors C217, C218 on Input PCB.
2b Change the other resistors R226, R227 and Capacitors C217, C218 on Input PCB.
3a Cut resistor R263 on the input PCB (see picture 3A)
3b Change C233 from 220uF to 33uF.(see component location on picture 3A)
3c Add the diode on the output PCB. Place the diode anode on J121 and the cathode on D108’s cathode.(see picture 3C)
3b Change C233 from 220uF to 33uF.(see component location on picture 3A)
3c Add the diode on the output PCB. Place the diode anode on J121 and the cathode on D108’s cathode.(see picture 3C)
Picture 2A input PCB
See next page for lager view
See next page for lager view
Picture 3A input PCB
Picture 3C output PCB
Service Bulletin
Harman International SNC - Harman Consumer International 2, route de Tours 72500 Château du Loir -FRANCE-
New Schematic:
Schematic of new C233
Schematic of new diode (output board)
Schematic of new resister and cap’s ( input board)
Picture 2A input PCB
Picture of Service position
Display
