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No modulation There is audio present in unit but does not modulate the carrier.

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Hello Rob55spiral, Most common malfunction in no modulation is the microphone. Swap out with a known working mic. #1 If problem is corrected, aquire a DVM and repair the broken cable connection in your microphone. #2 If still no modulation you have an internal componet malfunction. Please inform me of results.

Posted on Nov 04, 2008

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Posted on Jan 02, 2017

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Transmits and receives no modulation out


I am not an expert but I think there can be little or no modulation of the carrier wave unless there is an audio input to the modulator. Like any audio amplifier a transmitter modulator (amplitude modulation) is quiescent without an input.

If the modulation amplifier and audio pre-amp are working and modulating the carrier wave and the antenna is ok then audio modulated radio frequency must be being transmitted.

It would be an extremely good quality CB that had a modulation meter. Mostly all they have is a meter giving an indication of the rf power being sent to the antenna and that rf (radio frequency) power would be the same whether modulated or unmodulated.
The modulation envelope, incidentally, is traditionally viewed or measured with an oscilloscope.

The indicated rf power could be verified using a field strength meter but the only practical way to discover if a standard CB is transmitting modulated rf is to listen to the transmission on a suitable receiver. If the squelch is turned down it will be obvious if the rf carrier wave is being received as the hiss would be silenced. If no audio is received it can be assumed none is being transmitted.

I suggest you try another microphone and lead and if that doesn't work it is clearly a job for a repair shop.

Oct 28, 2015 | Radio Communications

1 Answer

What is the most likely cause an error code u1900 in a 2008 ford explorer xlt 4wd


Do you know what a serial data network is ? With all the computers car makers put on thier cars these day's they need a communication network for them to talk ,share info. on etc. U codes are codes for the network . A module could be down ,could be a wiring problem . A shorted module or bus wire can bring down the whole vehicle. Could cause the vehicle not to start ,systems not to function . How did you pull this code ,with what scan tool or code reader ? Did it come from the PCM - engine computer ? Need a up scale professional scan tool to check all module's on the vehicle , need to pin point the module that is causing the problem .
U1900 CAN Communication Bus Fault - Receive Error 4WD Control Module REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 . U1900 CAN Communication Bus Fault - Receive Error ABS Module REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 . U1900 CAN Communication Bus Fault - Receive Error DSM REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 . U1900 CAN Communication Bus Fault - Receive Error Instrument Cluster REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 . U1900 CAN Communication Bus Fault - Receive Error Occupant Classification Sensor Module REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 . U1900 CAN Communication Bus Fault - Receive Error Parking Aid Module REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 . U1900 CAN Communication Bus Fault - Receive Error RCM REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 . U1900 CAN Communication Bus Fault - Receive Error Retractable Running Board Module REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 .
016 CAN Communications

SECTION 418-00: Module Communications Network 2007 Explorer/Mountaineer/Explorer Sport Trac Workshop Manual DESCRIPTION AND OPERATION Procedure revision date: 08/02/2006 Communications Network Vehicle communication utilizes both medium and high speed controller area network (CAN) communications. CAN is used for many modules to communicate with each other on a common network. CAN in-vehicle networking, is a method for transferring data among distributed electronic modules via a serial data bus. Without serial networking, intermodule communication requires dedicated, point to point wiring resulting in bulky, expensive, complex, and difficult to install wiring harnesses. Applying a serial data network reduces the number of wires combining the signals on a single network. Information is sent to the individual control modules that control each function.
The vehicle has 2 module communication networks:
  • Medium speed (MS) CAN
  • High speed (HS) CAN
Both networks are connected to the data link connector (DLC). This makes diagnosis and testing of these systems easier by allowing one scan tool to be able to diagnose and control any module on both networks from one connector. The DLC can be found under the instrument panel between the steering column and the audio unit.
Network Topology

Module Name Network Type Termination Module Anti-lock brake system (ABS) module HS-CAN No Audio control module (ACM) MS-CAN No Digital versatile disc (DVD) player (if equipped) MS-CAN No Driver seat module (DSM) (if equipped) MS-CAN No Electronic automatic temperature control (EATC) module (if equipped) MS-CAN No Four wheel drive (4WD) control module (if equipped) HS-CAN No Instrument cluster (IC) (gateway module) HS-CAN
MS-CAN Yes
Yes Occupant classification sensor (OCS) module HS-CAN No Parking aid module (PAM) (if equipped) MS-CAN No Powertrain control module (PCM) HS-CAN Yes Power running board (PRB) module (if equipped) MS-CAN No Restraints control module (RCM) HS-CAN No Satellite digital audio radio system (SDARS) (if equipped) MS-CAN No Smart junction box (SJB) MS-CAN Yes Transmission control module (TCM) (if equipped) HS-CAN No
MS-CAN Network Operation
The MS-CAN network communicates using bussed messages. The MS-CAN has an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, this network allows sharing of information between all modules on the network.
The MS-CAN is a medium speed communication network used for the following modules:
  • SJB
  • Audio unit
  • Instrument cluster
  • DSM (if equipped)
  • DVD player (if equipped)
  • EATC module (if equipped)
  • Parking aid module (if equipped)
  • Satellite audio receiver (if equipped)
  • Power running board module (if equipped)
HS-CAN Network Operation
The HS-CAN network communicates using bussed messages. The HS-CAN network uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, this network allows sharing of information between all modules on the network.
The HS-CAN is a high speed communication network used for the following modules:
  • PCM
  • TCM (if equipped)
  • RCM
  • ABS module
  • Instrument cluster
  • Occupant classification sensor module
  • 4WD control module (if equipped)
Network Termination
The CAN network uses a network termination circuit to improve communication reliability. The network termination of the CAN bus takes place inside the termination modules by termination resistors. Termination modules are located at either end of the bus network. As network messages are broadcast in the form of voltage signals, the network voltage signals are stabilized by the termination resistors. Each termination module has a 120 ohm resistor across the positive and negative bus connection in the termination module. With 2 termination modules on each network, and the 120 ohm resistors located in a parallel circuit configuration, the total network impedance, or total resistance is 60 ohms.
Network termination improves bus message reliability by:
  • stabilizing bus voltage.
  • eliminating electrical interference.
Gateway Module
The instrument cluster is the gateway module, translating HS-CAN to MS-CAN and vice versa. This information allows a message to be distributed throughout both networks. The instrument cluster is the only module on this vehicle that has this ability.

Aug 30, 2017 | 2008 Ford Explorer 2WD

1 Answer

I have a Realistic TRC-457.It has very low power and modulation.It is a virgin radio other than someone has replaced the final and driver.I noticet that I cant set the modulation and swr levels on my dosy...


How many watts does it do? If it swings say: 1.5 watts up to 4 watts, someone has installed a swing kit which has a very small carrier. In AM, carrier is not important, its modulation and swing that makes it loud. If its low Audio modulation then it may be that final has went bad too.

May 31, 2011 | Radio Shack TRC-503 CB Radio

1 Answer

Hi there. there is no spark to ignite the gas in oven.


You will need to replace the spark module if you don't hear any clicking, or there is no spark present when trying to ignite the gas.

To test the Spark Module:
When properly operating, the spark module repeatedly produces a spark at the ignitor accompanied by a sharp snapping sound.
  1. Turn off gas and power supply to unit.
  2. Check wiring diagram to verify all terminals and wire connections are correct and tight with no cuts in the wiring.
  3. Prepare to measure voltage on spark module from terminal L to N.
  4. Turn power supply back on.
  5. Turn top burner to LITE position.
  6. If no voltage is present on the meter, this will indicate the electrical circuit is interrupted before the spark module
  7. If voltage is present, then check ignitor.
  8. If ignitors are ok; then replace spark module.
To access the Spark Module:
  1. Turn off electrical power and gas to the range.
  2. Disconnect gas and power from unit.
  3. Remove screws securing top surface burners.
  4. Remove surface burner and disconnect spark ignitor wire from surface burner.
  5. Raise and remove maintop from unit.
  6. Remove screws securing spark module bracket.
  7. Disconnect wire terminals from spark module.
  8. Replace and reassemble in reverse order.

May 18, 2011 | Amana Ovens

1 Answer

No modulation with strong carrier


sounds like your Audio Output went out......not audio chip....may be your voltage regulator also....your voltage regulator IC is heat sunk....do you have a schematic?

Jan 23, 2010 | Cobra Radio Communications

1 Answer

Carrier Performance Edge Programmable Thermostat


Are you a qualified refridgerator mechanic with an eletrical liscence? If not get someone who is because doing it yourself will not only void the warranty of the unit but will also void your house and contense insurance in the event of a fire.

Feb 13, 2008 | Heating & Cooling

2 Answers

142 GTL Good AM Carrier Weak Modulation????


you may have to scope the finals circuit on the modulation to see if all the "inline" caps are installed correctly... be sure your pc board is grounded in all areas as required by specs in your manual. Make sure there is no bleedover and you are sheilding your crystals from the modulation platform. al

Mar 24, 2007 | Cobra 148 GTL 120-Channels Base CB Radio

5 Answers

Cobra 148gtl


i am having this trouble as well. The ics was my thought too, but I think it is in the modulation circuit somewhere. another article i read said to check this. "Look for the collector of TR-23, you should read about 4.5 V with a dead key. If you find that this voltage is not present, check on the opposite side of R-120 for 6.5V. Most likely this voltage will not be present; if this is the case, C18 has shorted and needs to be replaced. This is a 330uf, 10V electrolytic capacitor beside L31. To prevent "future" problems, replace with a 16V unit." As of yet, i havent gotten that far. note this is from the cobra 2000, but they are very much alike. you might cross check the resistor capacitor numbers though. btw, isnt the mb3756 the pll ic?

Jan 28, 2007 | Cobra 148 GTL 120-Channels Base CB Radio

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