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AR8200 function button failure
On a few sets we have seen a failure of function button operation. This is mainly on older series 1 units that have seen a lot of use but is equally likely to occur on any series 1 or 2 set. The problem can also be induced by the use of large antennas due to increased flex at the BNC socket.
The problem is due to diode D520 becoming disconnected from its solder pads on the PCB. D520 is a diode in series with the function button switch. It is located on the small side panel board next to the function key.
The failure is due to its close proximity with the antenna socket shielding plates. The diode is almost touching the shield which normally doesn’t cause a problem. Any movement can cause the shield to push the diode away from its connection on the board. One or two of the diode connections may be lifted away from the board but it will probably still be more or less in the correct position.
Cure:
Usually no components are damaged and the diode can simply be re-soldered to the board. At worst, the diode legs may have been broken and it will have to be replaced.
Prevention of a repetition of the problem is simple – bend the offending edge of the antenna socket shield a few millimetres inwards. It is usually possible to see a small mark where the diode has rubbed on the shield so it is easy to see which area requires bending. Note that it really does only need a small amount of movement to clear the diode. If the set is a ‘well used’ example, this is a good opportunity to check that the shield is still soldered to the PCB.
Diode D520 is a dual diode surface mount package (4 legs) - 1SS319.
To carry out the work:
A small cross point screw driver and a fine soldering iron are the only tools necessary although a pair of fine pliers and tweezers may come in handy.
Remove all of the case screws – 5 long self tapping and 2 small threaded screws.
Split the case halves. Take care that the two ribbon cables between the front and back are not damaged – there is only enough length on these for the case halves to be hinged apart.
The side switch panel should remain with the front panel.
The area to be worked on is now exposed although if better access is required, the ribbon cables can be removed. To do this, gently lift the dark brown section of the clip – this hinges around the centre.
The side panel can also be removed if required. The easiest way to do this is by lifting the front control PCB slightly by undoing the 4 screws and de-soldering the speaker wires. The side panel can then be pulled from its connector.
D520 is located on the side panel switch PCB. It is to one closest to the top of the set. It should be quite obvious as it will be broken away from the board slightly.
Re-solder the diode or fit a replacement if necessary. All of the diodes are physically orientated the same was on this board, so just ensure that the writing on the package is the same way as the remaining diodes.
Re-building the set is the reverse of dismantling with two possible areas to watch;
Firstly, hold the two rubber covers out of the way when placing the case halves together. Secondly, Make sure that the battery contacts stay in position as the case halves are brought together. These should be trapped between the small plastic pillar and the PCB contact. They should also run in the groves on the side of the case.
Now power up the set and check the function button operation.
Check that operation is also still possible from the batteries.
Zitieren
Zitat von Sir Quickly (Irgendwie und sowieso)
