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CTV Philips G6 single-standard CTV, varying brightness.

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Till Eulenspiegel
(@till)
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This set is has a varying brightness fault.  Assuming the PFL200 video amplifier is OK, in order to carry out fault finding the operation of the brightness control should be studied first.   My take on the circuit is in the brightness control system a proper black level reference system is employed. Transistor T2146 conducts only during the back porch after the sync pulse. The negative going sync pulses from the anode of the sync separator are differentiated by C2002 and R2107. The result is a negative going leading edge and positive going trailing edge. Diode X2152 conducts on the positive going trailing edge of sync pulse and supplies the base of T2146 with the black level reference pulse. The voltage on the emitter of transistor T2146 determines the brightness control setting.

Lockfit transistors are becoming unreliable so T2146 (BC148) should be replaced first before any fault finding measures.

Till Eulenspiegel.

G6 Video Amplifier

 

 
Posted : 09/03/2022 12:13 pm
colourmaster
(@colourmaster)
Posts: 425
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Hi David

Many thanks for your description of the brightness circuit in my G6 . The brightness was varying for a couple of days then the picture went very bright . The brightness control works but even on minimum setting it's still too bright . The set has done well as it's over a year ago since it had a fault  and it's used at least 4 times a week 

 
Posted : 09/03/2022 3:31 pm
Till Eulenspiegel
(@till)
Posts: 4947
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Hi Gary,   it's possible the negative 24volt supply is causing the fault condition.  Check C1030 and X1114 in the power supply section and C2001 on the signals panel.

Till Eulenspiegel.

G6 Video 24V

 

 
Posted : 09/03/2022 8:27 pm
colourmaster
(@colourmaster)
Posts: 425
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Many thanks for that David , I'll get started with it on Saturday and post my findings.

 
Posted : 09/03/2022 8:32 pm
colourmaster
(@colourmaster)
Posts: 425
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Hi Everyone

I finally got to look at the G6 brightness problem, it turned out to be nothing more than a faulty pfl 200. I fitted a nos pfl 200 and the picture is back to normal. Now I'm wondering , should I log the repair on the mastercare repair card that came with the set of should I leave it with the last log which was 1981.

IMG 20220423 143633
IMG 20220423 141218

 

 
Posted : 28/04/2022 8:55 pm
Till Eulenspiegel, ntscuser, Nuvistor and 12 people reacted
Lloyd
(@lloyd)
Posts: 1897
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Make a copy of it and fill out the copy! Looks a good picture 🙂

 Regards 

Lloyd 

 
Posted : 28/04/2022 9:55 pm
colourmaster
(@colourmaster)
Posts: 425
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Hi Lloyd

I think that's a good idea , I will copy the service card and fill in the repairs done so far 

 

 
Posted : 01/05/2022 3:18 pm
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