[ICOM] IC775DSP display backlight problem

[Anders Janis SM4RNA]

The only problems with the backlight so far is that my and two other radion 
suffer from dry joint / bad soldering. In two cases it is the back of the 
display itself, the long row of with very thin wires and quite large holes 
in the PCB. When this problems appear the sub-VFO digits start to flicker. 
In my radio it was the transformer that I had to re-solder as the backlight 
it self started to flicker.

Will be intresting to herar from you when it works again.

de Anders SM4RNA


----- Original Message ----- 
From: "Martin Sole" <msole at loxinfo.co.th>
To: "ICOM Reflector" <icom at mailman.qth.net>; <sm4rna at telia.com>
Sent: Sunday, June 18, 2006 10:19 AM
Subject: Re: [ICOM] IC775DSP display backlight problem


> Anders,
>
> Many thanks for the reply. If the display backlight is indeed 120 volts AC 
> then this explains the significant power supply circuit used to feed it. I 
> will try to produce a simple 120 volt AC feed at low current to feed it 
> with and prove that it is working before proceeding further with the 
> supply problem. As you noted the transformer may be shorted but I have no 
> way to verify that so it may be that I have to order a new transformer and 
> a couple of transistors directly from Icom and replace all.
>
> It would be nice to know if others have experienced complete backlight 
> failure of this type before.
>
> Thanks again for the information and any other comments pertaining to this 
> problem would be greatly received.
>
> On a slightly unrelated note this is the first Icom other than a 706 that 
> I have played with in a long time and it does seem to be a very nice 
> radio. I have long avoided Icom's for their, to my ears, harsh sound, but 
> this one is very smooth sounding.
>
> Martin, HS0ZED
>
>
> Anders Janis SM4RNA wrote:
>> My supplier says that it is driven by 120V AC. In low light mode the Q19 
>> activates the voltage devider R200, R201 and R202 and then the voltage is 
>> lower.
>>
>> Have you disconected the wire to the light itself?
>>
>> My guess is thet the transforer is shorted or that there are any other 
>> flashover on the HV side.
>>
>> /Anders
>>
>> ----- Original Message ----- From: "Martin Sole" <msole at loxinfo.co.th>
>> To: <icom at mailman.qth.net>
>> Sent: Saturday, June 17, 2006 10:12 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
>>> ----
>>> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
>>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>>> Icom FAQ: http://www.qsl.net/icom/
>>
>> ----
>> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>> Icom FAQ: http://www.qsl.net/icom/
>>