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Cobra 29 LX Repair: Display troubleshooting | Radioaficion Ham Radio

Cobra 29 LX Repair: Display troubleshooting

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Cobra CB Radio MODEL(s): 29 LX, 29 LX LE

DESCRIPTION: Display troubleshooting

ACTION: Does the backlight light up?

If the backlight lights up but the display is otherwise blank, then the ribbon cable for the display may have become dislodged.

Is the display active, but dark?

If the display is dark even when power is turned on, then it may be a problem with the backlight. Carefully inspect the display while power is turned on. Try changing the channels. It might be that the display is actually working but the backlight is out. If this is the case then the display will be dark but you should see all the various details (numbers, icons, etc.). If you find this to be true.

Is the display totally dead?

If the display is totally blank (no backlight, no details) then double-check whether the radio has experience reverse polarity. If the reverse polarity diode is blown (D23) then replace the diode and repair any associated damage.

If the problem persists

If you have gone through all the above troubleshooting tips and there is still a problem, then try replacing the CPU/WX board, Cobra p/n 300-009.

ADJUSTMENTS: None

NOTES: None

Ribbon Cable

There is a ribbon cable which runs from the display to the display PCB. If this cable becomes loose then you may loose the display. Or the display may become intermittent. The backlight will still illuminate, but the display will not show any information.

The following pages shows the location of the ribbon cable. Make sure that the cable is fully seated into the connector. Please note that the connector has a locking mechanism. Lift up on the top piece to release the lock, and push back down to engage the lock.

1. Lift up on the top piece to release the lock (see page 3).

2. Use the eraser end of a pencil to push the ribbon cable all the way down.

3. Push down on the top piece to engage the lock.

Cobra 29 LX Repair: Display troubleshooting

Cobra 29 LX Repair: Display troubleshooting

Cobra 29 LX Repair: Display troubleshooting

Backlight

If the backlight is out, then the display will appear dark but you will still see all the proper lettering, icons, etc. Here is an example:

Cobra 29 LX Repair: Display troubleshooting

If this is the case, then measure the backlight voltages as shown on the following image.

Cobra 29 LX Repair: Display troubleshooting

The backlight voltage should read between 5-18VDC depending on the DIM setting. If the voltages are not present then replace the backlight power supply, Cobra p/n 306-004. The backlight power supply is a metal can mounted to the side of the chassis:

Cobra 29 LX Repair: Display troubleshooting

If the voltage measure correctly but the backlight is still dark, then replace the backlight module, Cobra p/n 306-003.

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