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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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26th Jun 2022, 2:54 pm | #1 |
Heptode
Join Date: Aug 2016
Location: Dumfries, Scotland, UK.
Posts: 549
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Royal Star a bit of picture bother HELP please
Don't ask why but ever since I first saw one I'd wanted a KB royal Star I finally managed to get one two months ago I have the set up and running but can't seem to cure an issue with the picture on it. The bottom half of it is fine the top half I have wider lines causing an egg shape on test card ( see photo ) the very top of the test card is squished when I bring it down on to the screen. All out of spec resistors have been done all the control pots are fine the valves are good so I assume it's scan coil position related ??
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26th Jun 2022, 3:13 pm | #2 |
Octode
Join Date: Feb 2007
Location: Harrow, London, UK.
Posts: 1,493
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Re: Royal Star a bit of picture bother HELP please
Hi Lloyd
Do you have the schematic? If not Google: "kb pvp20 royal star service manual," scroll down to radio-tv.co and the field (frame) circuit is shown on that site. Which controls are fine? Is the frame linearity preset R101 working as it should? If not the capacitors C84,85 & C86 should be checked. Chris |
26th Jun 2022, 3:16 pm | #3 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
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Re: Royal Star a bit of picture bother HELP please
What have you adjusted? Does the frame linearity control have any effect? Have all the wax capacitors been changed in the frame osc/output stage including the ones that look like resistors and the brown mini Hunts and are they the correct values? Is the cathode bias resistor the correct value? What is the effect of reducing the height and recentering the picture/raster?
Horrible to work on. Removing the 4BA screws that mount the mains dropper and moving it out of the way helps. Good circuit but nasty construction. John PS Sorry Chris we snapped! |
26th Jun 2022, 3:23 pm | #4 |
Heptode
Join Date: Aug 2016
Location: Dumfries, Scotland, UK.
Posts: 549
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Re: Royal Star a bit of picture bother HELP please
Everything on the board is either new or within tolerance it's all been checked and checked again against the original KB service manual and that included checking everything was through the correct holes in the board as the KB data comes with a rather handy board layout diagram the picture shows the set with the linearity control doing as much as it will to correct it .
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26th Jun 2022, 3:26 pm | #5 |
Octode
Join Date: Jul 2004
Location: Evesham, Worcestershire, UK.
Posts: 1,422
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Re: Royal Star a bit of picture bother HELP please
Looks like the frame linearity pot just needs a tweak.
Greg.
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Picture, sound?, DOOR. |
26th Jun 2022, 7:06 pm | #6 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,567
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Re: Royal Star a bit of picture bother HELP please
The linearity on mine is perfect. It has to be a capacitor or resistor problem. Make sure any capacitors replaced are correct value. Does the linearity control work correctly? The old pre-sets can change in value so it might not be able to cover sufficient range....just a thought.
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26th Jun 2022, 7:09 pm | #7 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,567
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Re: Royal Star a bit of picture bother HELP please
Another good point....
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There are lots of brilliant keyboard players and then there is Rick Wakeman..... |
26th Jun 2022, 7:30 pm | #8 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,567
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Re: Royal Star a bit of picture bother HELP please
Here's a quick picture of mine....the tube isn't brilliant and this was taken just after a gentle boost. If anything the line linearity needs adjusting on mine but frame lin is fine
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There are lots of brilliant keyboard players and then there is Rick Wakeman..... |
26th Jun 2022, 10:46 pm | #9 |
Heptode
Join Date: Aug 2016
Location: Dumfries, Scotland, UK.
Posts: 549
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Re: Royal Star a bit of picture bother HELP please
Sideband as mentioned the resistors and caps are in the correct place and the correct value checked multiple times against both the factory data and the trader sheet the linearity control measures 32.3K which should be near enough and has an effect centering the picture makes no odds the height control works fine what I have noticed is when it's as near as I can get it the lower half of the picture is slightly compressed. The only caps that haven't been changed are anything measured in PF everything else is new and was tested before fitting just because a component is new doesn't mean I trust it.
One last thing Spike Milligan's grave does and doesn't say " I told you I was ill" the cemetery wouldn't allow it and half the family were against that inscription it is therefore inscribed in small lettering on his stone in Gaelic not English. |
27th Jun 2022, 7:23 am | #10 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,431
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Re: Royal Star a bit of picture bother HELP please
The width seems a bit short, see photo in post #8 for comparison, is the HT voltage correct?
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Frank |
27th Jun 2022, 10:59 am | #11 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,431
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Re: Royal Star a bit of picture bother HELP please
Another thought is to check the boost HT, the boost voltage is used through the height control to supply the charging capacitor, hence the sawtooth waveform,
The boost HT is used as the charging voltage to allow a more linear scan, a low voltage will affect the linearity more at the bottom of the scan.
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Frank |
27th Jun 2022, 3:12 pm | #12 | |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,567
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Re: Royal Star a bit of picture bother HELP please
Quote:
That's a good point....I hadn't noticed the lack of width. Check the HT first and if that is OK check the boost HT. If the boost is low, try a boost diode. If the boost is OK, try normal width adjustment. If still insufficient width then it could be the line output valve (think it's a PL36). Either way, more width is required which will affect the overall picture shape. Has the boost capacitor been changed?
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There are lots of brilliant keyboard players and then there is Rick Wakeman..... |
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