[ICOM] IC775DSP display backlight problem

[Anders Janis SM4RNA]

Check Q19 on the main board that i gets the "low"-signal and that the 
transistor it self is ok.

If that works you can try this to find out if Q16 is ok.When enabeling 
"low"-light you sould see that the voltage is dropping at the emitter of 
Q16.

To get to the main board there is a lot of work and a lot of cables to 
disconect. If you are not used to work with complex radios, get help from 
someone that is.

GL

/Anders


----- Original Message ----- 
From: "Juan Pablo Mercé LU4DX" <lu4dx at hotmail.com>
To: "ICOM Reflector" <icom at mailman.qth.net>
Sent: Sunday, June 18, 2006 2:39 AM
Subject: Re: [ICOM] IC775DSP display backlight problem


>I have a problem related to the display in my IC-775DSP.
> This one works well and without intermittences but I cannot change the 
> intensity of the display, try to change the value to LO and HI into the 
> menu but nothing happens like the preset to change the low intensity.
> The level seems to be in the high position.
> The previous owner said to me that the display backlight was intermittent 
> and he resoldered the lamp's power transformer secondary contacts to the 
> printed circuit board.
> Does someone know where the problem can be not to be able to change the 
> intensity of the display?
>
> Tnx in advance,
>
> Paul LU4DX
>
> ----- Original Message ----- 
> From: "Martin Sole" <msole at loxinfo.co.th>
> To: <icom at mailman.qth.net>
> Sent: Saturday, June 17, 2006 5:12 AM
> Subject: [ICOM] IC775DSP display backlight problem
>
>
>> Dear Icom friends,
>>
>> I have a problem with an IC775DSP display that I would appreciate some 
>> assistance with. The owner noticed the backlight flicker a couple of 
>> times then go out. This was accompanied by a burning smell and some 
>> smoke. Investigation shows that both Q17 & Q18 in the backlight driver 
>> circuit have disintegrated.
>>
>> I would first like to know what kind of voltage the backlight is meant to 
>> be driven with? The schematic shows it to be simply an LED driven from a 
>> rather complicated AC source. I therefore assume that the backlight needs 
>> more than just a few volts at a few mA.
>>
>> My second question concerns the voltage source itself. This appears to be 
>> some sort of oscillator driven from the 14 volt line but I am unfamiliar 
>> with the nature of its design. I did replace the damaged transistors with 
>> similar items albeit 100 volt rated rather than 120 volt rated but they 
>> immediately self destructed so I assume I need to look elsewhere for the 
>> cause.
>>
>>
>> I can email scans of the circuit area if anybody would like to see before 
>> passing comment.
>>
>> Thanks in advance for any help.
>>
>> Martin HS0ZED
>> ----
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>>
> ----
> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
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