[TenTec] Orion 565 LCD Contrast & Power Distribution Board

[Robert Mcgraw]

Excellent troubleshooting technique followed by equally good results.

Thanks for sharing.

73
Bob, K4TAX


> For the last several months my Orion (565) has had a screen contrast
> problem at start-up.  Last week I noticed that is was still there but
> somewhat quicker than it was in the winter months.  I thought perhaps I
> was imagining things so I shut down the rig and rebooted.  The screen
> came up at the correct contrast immediately. 
>
> What was going on?  The following morning when I turned on the rig I
> timed the process.  Virtually a white screen at start-up and then some
> contrast at 30 seconds and close to full useable contrast after 2
> minutes.  Putting all this together suggested something in the circuit
> was responding to ambient temperature.  It was time to dig out the
> schematics.
>
> The first thought of a culprit was C700 on the logic board (Schematic A7
> sheet 15 of 16).  C700 is in the contrast line to the LCD and immediately
> follows the hardware contrast adjustment pot. If this capacitor was
> leaking or had some temperature stability problem it could be the
> culprit.  I replaced the 4.7 uF @35VDC capacitor but nothing changed.
>
> I felt that my LCD screen was likely good since it was relatively new. So
> I began to look elsewhere and noticed that the "bottom" of the contrast
> pot and one end of C700 were tied to VEE.  
>
> VEE is generated on the infamous power distribution board and nominally
> is about -20.5 VDC.  So with the rig cool I monitored the VEE at
> start-up.  In a period of 2 minutes it slowly climbed from about -18.5
> VDC to -20.1 VDC and then stabilized.  This timing matched my Orion
> screen contrast.
>
> I looked at the power distribution board circuit (schematic A9) and
> replaced C1 (100 uF @35 VDC) and C3 and 4 (10 uF @50VDC).
>
> After an overnight cool down of the Orion I am happy to announce that
> this morning there is NO delay in reaching full usable screen contrast at
> start-up!
>  
> 73,
> Rick
> VE7TK
>
>
> Website:  http://www.ve7tk.com
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