Service Bulletin

Service Bulletin
Power Resistor Hot Spots
Title:
Models Affected:
PLC0002
PLX, CX, DCA
Production Range:
04/98 - 10/99
Bulletin #:
Issue Date:
09-22-99
Bulletin Revison:
A
Description
PLX, CX, and DCA amplifiers produced from 04/98 through 10/99 have several resistors located on the main printed circuit
board (PCB) that may radiate or conduct too much heat. Left uncorrected, the resistors may eventually dissipate enough heat
to damage themselves or the PCB underneath them.
Only amplifiers with date code prefixes (the first four digits of the serial number) within the range of 0498 through 1099 are
affected. Amplifiers outside this range are not affected.
On PLX amplifiers, this service procedure is a low priority and should be done only in conjunction with other requested
service work.
This service procedure is mandatory on all CX and DCA amplifiers within the affected date codes. Among these models, the
CX 302V and CX 602V show the highest susceptibility to this condition. Models CX 502, CX 1102, CX 1202V, DCA 1622, and
DCA 3422 are moderately susceptible. The CX 302, CX 701, CX 902, DCA 1222, and DCA 3022 have a low susceptibility.
Therefore, when prioritizing amplifiers for this service update, we recommend that you assign priority so it corresponds with
susceptibility.
The resistors are grouped in four locations on the main PCB, all located toward the front of the amplifier. The resistors
affected are of the miniature 2-watt type. Depending on the various amplifier revisions, some resistors may be mounted so
they touch the PCB, and others may be standing slightly away from the board (called a “stand-off prep”).
The resistor groupings are as follows:
Group
Group
Group
Group
1:
2:
3:
4:
R251, R256, R257, and R378 (R378 may not exist in some models.)
R96, R105, R219, and R228
R276, R277, R278, 279, and 280 (R279 and R280 may not exist in some models.)
R274, R275
As an example, Figure 1 shows the location of the
resistors in Group 1. Further resistor details on
these and other resistors are shown in a matrix at
the end of this bulletin.
Symptoms
1. The amplifier remains in protect mode or has no
power at all.
2. The main PCB may be discolored or burned
around the resistors listed.
3. Some or all of the mini 2-watt resistors listed
may show signs of overheating, exhibited by a
washout of their blue markings.
4. Occasionally an amplifier at idle may emit a
burning odor.
Figure 1. Mini 2W resistors with accompanying PCB discolorization
1
Instructions
Updating the CX, DCA, and PLX amplifiers involves replacing the resistors listed above. The main PCB does not need to be
removed from the chassis. The resistors are all replaced from the component side of the board. The entire process should
take less than 30 minutes.
Tools required:
•
•
•
•
1.
25W soldering iron
Desoldering tool or equipment
Long-nose pliers
Small diagonal cutters (optional)
With the soldering iron, heat each resistor's solder connection until the solder re-flows and you can lift the resistor lead
out of the hole. If the resistor is mounted close to or touching the PCB, it may be easier to cut the resistor leads off
using small diagonal cutters and then desolder them. Be careful not to cut or damage any traces on the PCB.
2.
After the resistors and/or leads are removed from the PCB, use a desoldering tool or desoldering station to remove any
remaining residual solder from the solder pads.
3.
Once the solder pads' holes are clear and unobstructed, you can insert the new resistors. Make sure the leads will not
protrude more than 1/8" (3 mm) beyond the solder side of the board so they will not short to the chassis underneath the
main PCB.
Mount each resistor with a "stand-off prep" so the body of the resistor does not touch the board. Resistors supplied by
QSC will have leads already prepared, which will facilitate this type of mounting.
Hold each resistor in place with long nose pliers when soldering the leads to the solder pads. Because this is a twohand operation, you may find it necessary to first apply a small amount of solder to one of the solder pads, re-flow it
with the soldering iron, and then insert the resistor lead as a temporary connection; after that, hold the resistor in place
while the solder hardens, then solder the other lead properly. Wait for the solder to cool and harden sufficiently, then
re-heat and properly solder the temporary solder joint.
4.
After all the resistors are replaced, inspect the amplifier for and scraps or pieces of leads or components that may lie
inside the amplifier chassis. Remove or clean as needed.
5.
Install the amp's cover and verify that the amp works correctly before you return it to its owner.
There are as many as 13 different resistors in each amplifier that may need replacement, so see the matrix on the next page
to determine the specific changes for each model.
Note: Some amplifiers have no resistor R378. On these models, you must use two resistors for R257. Use the same
value listed in the table on page 3, but install two of them. One should be mounted with the “stand-off prep”
described above, and the other should be soldered as a parallel “piggyback” above the first one.
Page 4 of this bulletin lists the part numbers and descriptions for the replacement resistors. To expedite processing, please
refer to the part numbers when ordering resistors from QSC. You can order the replacement resistors and any other parts by
contacting our Technical Services department at 800-772-2834 or 714-957-7150, or by fax at 714-754-6173.
Contacts
If you need assistance with this service procedure, contact us at
QSC Audio Products, Inc.
Technical Services Group
1665 MacArthur Blvd.
Costa Mesa, CA 92626 USA
Telephone: 800-772-2834 (USA only)
E-mail: [email protected]
2
714-957-7150
Fax: 714-754-6173
3
470
820
150
150
300
1K
1K
n/a
470
820
150
150
300
470
820
150
150
300
5.1K
8.2K
5.1K
5.1K
8.2K
15K
15K
8.2K
5.1K
8.2K
5.1K
5.1K
8.2K
5.1K
8.2K
5.1K
5.1K
8.2K
CX302
CX502
CX702
CX902
CX1102
CX302V
CX602V
CX1202V
DCA 1222
DCA 1622
DCA 2422
DCA 3022
DCA 3422
PLX 1202
PLX 1602
PLX 2402
PLX 3002
PLX 3402
2.4K
1.6K
1.6K
2.7K
2.4K
2.4K
1.6K
1.6K
2.7K
2.4K
2.7K
3.9K
3.9K
2.4K
1.6K
1.6K
2.7K
2.4K
R257*
2.4K
1.6K
1.6K
2.7K
2.4K
2.4K
1.6K
1.6K
2.7K
2.4K
2.7K
3.9K
3.9K
2.4K
1.6K
1.6K
2.7K
2.4K
R378*
8.2K
5.1K
5.1K
n/a
n/a
8.2K
5.1K
5.1K
n/a
n/a
8.2K
n/a
n/a
8.2K
5.1K
5.1K
n/a
n/a
R96
Value: New value, with component lifted from PCB
n/a: Not applicable or no change
R256
R251
MODEL
GROUP 1
SERVICE BULLETIN PLC0002
NEW RESISTOR MATRIX
8.2K
5.1K
5.1K
n/a
n/a
8.2K
5.1K
5.1K
n/a
n/a
8.2K
n/a
n/a
8.2K
5.1K
5.1K
n/a
n/a
R105
8.2K
5.1K
5.1K
n/a
n/a
8.2K
5.1K
5.1K
n/a
n/a
8.2K
n/a
n/a
8.2K
5.1K
5.1K
n/a
n/a
R228
820
470
470
1K
680
820
470
470
1K
680
820
1K
1K
820
470
470
1K
680
R276
820
470
470
1K
680
820
470
470
1K
680
820
1K
1K
820
470
470
1K
680
R277
n/a
n/a
n/a
1K
680
n/a
n/a
n/a
1K
680
n/a
1K
1K
n/a
n/a
n/a
1K
680
R278
GROUP 3
* See note on page 2 regarding R257 and R378
8.2K
5.1K
5.1K
n/a
n/a
8.2K
5.1K
5.1K
n/a
n/a
8.2K
n/a
n/a
8.2K
5.1K
5.1K
n/a
n/a
R219
GROUP 2
470
470
470
n/a
n/a
470
470
470
n/a
n/a
470
n/a
n/a
470
470
470
n/a
n/a
R279
470
470
n/a
n/a
n/a
470
470
n/a
n/a
n/a
470
n/a
n/a
470
470
n/a
n/a
n/a
R280
680
680
470
n/a
n/a
680
680
470
n/a
n/a
680
n/a
n/a
680
680
470
n/a
n/a
R274
680
680
470
n/a
n/a
680
680
470
n/a
n/a
680
n/a
n/a
680
680
470
n/a
n/a
R275
GROUP 4
4
QSC PART #
RE-015004-10
RE-030003-00
RE-047002-00
RE-068002-00
RE-082002-00
RE-110009-00
RE-116002-00
RE-124005-EM
RE-127003-00
RE-139003-00
RE-151002-00
RE-182005-EM
RE-215004-00
VALUE
150
300
470
680
820
1K
1.6K
2.4K
2.7K
3.9K
5.1K
8.2K
15K
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 15K OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 8.2K OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 5.1K OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 3.9K OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 2.7K OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 2.4K OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 1.6K OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 1K OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 820 OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 680 OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 470 OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 300 OHMS
RESISTOR, METAL OXIDE, 5%, 2W, AXIAL, STAND-OFF PREP 150 OHMS
PART DESCRIPTION
SERVICE BULLETIN PLC0002
NEW RESISTOR DETAILS