[ICOM] IC775DSP display backlight problem

[Anders Janis SM4RNA]

I have a weak and unverified memory that it is 60Hz. But as the circiut is 
built it is not very frequency stable.

I would recomend to measure it on a working 775.

Do not expect sine wave.

GL

/Anders



----- Original Message ----- 
From: "Martin Sole" <msole at loxinfo.co.th>
To: "Anders Janis SM4RNA" <sm4rna at telia.com>
Cc: "ICOM Reflector" <icom at mailman.qth.net>
Sent: Tuesday, June 20, 2006 3:36 AM
Subject: Re: [ICOM] IC775DSP display backlight problem


> Hi again,
>
> I haven't had a chance to look at the display problem for a day or so but 
> I am beginning to suspect the transformer as I stated before.
>
> Your earlier message mentioned that the display itself is 120 volt AC. I 
> wonder if this needs to be at a specific frequency or if I could use 120 
> volts at 50 Hz in order to prove the display element?
>
> Martin, HS0ZED
>
>
> Anders Janis SM4RNA wrote:
>> 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/
>>>>
>>