[ICOM] IC775DSP display backlight problem
Anders Janis SM4RNA
sm4rna at telia.com
Sat Jun 17 04:53:18 EDT 2006
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/
More information about the Icom
mailing list