RTS AIO-16 Technical Bulletin

TECHNICAL BULLETIN

RTS-TB-030 25-July-2014
AIO-16 Audio Port Noise Susceptibility

Issue Severity: Product(s) Affected:

High: URGENT – Immediate Action

Required
Medium: Bosch Security Systems,

Inc. strongly recommends you take
the action(s) described below.

Low: Advisory

Notification Applies To:

Technical Support (TSS)

Repair (ASA)

Sales (NSO / RSO)

 AIO-16s with manufacturing date codes

between June 2011 and August 2013 (approx.
1700 total cards)

Access Restrictions:

Internal Distribution ONLY

No Restrictions (Internal & External Distribution)

1.0 Issue

It was recently discovered that a portion of manufacturing test was omitted on AIO-16s made at the Bosch
Zhuhai manufacturing facility during the time period from June 2011 through August 2013. A series of
calibration steps related to Common Mode Noise Rejection (CMRR) optimization were omitted from the
manufacturing process. The result is that cards manufactured during this period have unbalanced audio
inputs that can be more susceptible to noise on the incoming audio lines. This allows noise to pass through
the input receiver stages of the AIO-16 and be heard by customers. In low noise environments, this may not
be detectable. However, any installation with noise present on the incoming audio (due to equipment
grounding issues, for example) may detect audible noise on these channels.

In general, since none of the 16 channels on the AIO-16 were properly calibrated by manufacturing, any
audio input may be vulnerable to this condition.

2.0 Resolution / Corrective Actions

In order to address this issue, the common mode rejection must be manually tuned on each of the 16 input
channels of the AIO-16. This is done by adjusting a potentiometer on each input audio amplifier circuit.
Bosch recommends that this adjustment be performed by an authorized service technician.

3.0 Detailed Rework Instructions

NOTICE! The following rework should only be performed by qualified repair personnel

operating according to proper safety, ESD and soldering practices

____________________________________________________________________________

Necessary rework equipment (no electrical parts are necessary):

 Small flat blade or jeweler's screwdriver
 Magnifying glass (if required for improved visibility)
 Digital Multimeter / Ohm-meter

The odd channels on the AIO-16 (1, 3, 5, 7, 9, 11, 13 and 15) follow the same layout topology around the op­amps on the PCBA. The even channels on the AIO-16 (2, 4, 6, 8, 10, 12, 14 and 16) follow the same layout
topology around the op-amps on the PCBA. For this reason, a detailed description is given for the calibration
of the potentiometers associated with channels 1 and 2. This same methodology can then be repeated for
the remaining odd and even channels.

3.1 Rework for Channel 1

In the schematic below, locate potentiometer R105, 19.6 kOhm resistor R104 and 20 kOhm resistor R106.
During the manufacturing process, the potentiometers (R105 in this example) were not properly calibrated.
To achieve optimal common mode rejection of noise, the potentiometer R105 must be adjusted so that the
sum of R104 + R105 = R106 within 40 Ohms.

Bosch Security Systems, Inc., 2014

12000 Portland Ave S., Burnsville, MN USA

ww.rtsintercoms.com

RTS-TB-030

echnical Bulletin

5-June-2014

age 2 of 7

TECHNICAL BULLETIN

FIGURE 1: The following assembly print shows a BOTTOM
of all eight dual op-amps in the AIO-16 design. Detail A circled in green shows the op-amp U101 associated
with the first two channels 1 and 2.

view of the AIO-16 Front Card and the location