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Old 17th Mar 2019, 12:54 am   #70
sexton_mallard
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Join Date: Sep 2013
Location: Ellesmere, Shropshire, UK & Co. Cork, Ireland.
Posts: 499
Default Re: Kolster Brandes RV 10 (Crown)

The story continues... I have still not been able to get a raster.

As a recap ('scuse the pun) at this point I have:

1. Checked and measured all components and work done back to V6, the PCF80. One or two resistors that had gone 2x high have been replaced including R68, the PL81 screen resistor. Vertical and horizontal controls tested and are OK..

2. Replaced the boost cap C63 and C60 cap (cap in series with scan coils) once again.

3. Changed the PCF80, PL81, PY83 and the U26 EHT rectifier for all NOS ones. Valve holders checked.

4. Removed, examined and replaced the scan coils, removed checked the line and frame coil wiring harness for damage.

5. Run the set with the line deflection coils disconnected, boost voltage comes up to about 680volts and a tiny weak spark can be produced between the top cap lead and the cap of the U26 EHT rectifier. Vertical line on the screen (frame deflection coils still connected). Frame timebase working fine.

6. Line drive (with line whistle) appears to be OK with a reasonable scoped waveform and about -45v on pin 2 of the PL81.

7. With all connections restored, on switch on, the line whistle comes up, the boost voltage starts to rise to beyond 300v and the line whistle is loud, the line whistle then goes quieter but still audible and the boost voltage falls back to about 230V, no light on the screen and the PL81 start to red plate.

8. NOS replacement LOPT fitted which included NOS high voltage caps C62 and C64.

My gut feeling is a high voltage breakdown somewhere possibly in the deflection coils. I might try and 'ring' them but I doubt I will find the problem as it appears to be a high voltage breakdown.

Is there anything else I have overlooked?
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Last edited by sexton_mallard; 17th Mar 2019 at 1:01 am. Reason: correction to No.5 - Line coils not frame coils!
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