UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Reply
 
Thread Tools
Old 8th Nov 2021, 9:48 am   #21
Welsh Anorak
Dekatron
 
Welsh Anorak's Avatar
 
Join Date: Apr 2005
Location: North Wales, UK.
Posts: 5,649
Default Re: Bush Dual Standard Colour Restoration

As far as I know the tuners were more or less identical.
A local private rental company used to swap out the complete timebase unit in the field which wouldn't have been too difficult - I was given a lot of dead Mk3s timebases for parts in the late Seventies - obviously the TVs had mostly been scrapped by then and the Mk1 versions had been seen off long before for obvious reasons!
__________________
Glyn
www.gdelectronics.wales
Welsh Anorak is offline   Reply With Quote
Old 17th Nov 2021, 6:25 am   #22
Niechcial,Steve
Hexode
 
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 281
Default Re: Bush Dual Standard Colour Restoration

I've now been through the IF, decoder and colour/video output stages checking/replacing electrolytics and high value/high power resistors, quite a few of which were out of tolerance.
The result is that normal frame sync has returned, the luminance smears have gone, but verticals remain bent as does a colour fault whereby the top and bottom halves of the picture have a different tint (it's not purity- which is perfect). I will now get the scope out and do some fault finding
Niechcial,Steve is offline   Reply With Quote
Old 1st Dec 2021, 2:04 pm   #23
Niechcial,Steve
Hexode
 
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 281
Default Re: Bush Dual Standard Colour Restoration

I have now come back to this for some detailed fault finding. Just to summarise, scan, EHT regulation, convergence and sync faults are sorted, and electros blanket tested and replaced as necessary throughout.

I next tried setting up the grey scale and found that despite having the tube show near perfect on the B and K tester, the grey scale would not track over the usual brightness range. The problem was no clamping pulse on the three PCL84 colour difference amplifiers. Diode 5D12 on the convergence board, which feeds line pulses in, had gone o/c. Replacing that resulted in a very good definition black and white picture with correct grey scale

I am now left with three faults:
1) Bizarrely wrong colours on the colour bars.
2) Smearing/overshoot on the left hand horizontal lines of the test card into the grey area of the circle beyond.
3) Green tinted broad horizontal band over the middle (black and white part) of a test card.
Taking these in reverse order, shorting out the U and V inputs to the colour output valves confirms that the green tint is coming in mainly on the V (R-Y) channel from the decoder.
I am not sure whether the smearing/overshoot is coming is on the luminance output stage (which is largely rebuilt), or coming in from the IF panel. I donít suspect alignment, as the picture is otherwise good definition . I will feed in a video signal from another source into the output stage to test.
The wrong colours are the most interesting fault. For the colour killer to be switching the colour in (which it is), not only does the chroma derived bias have to be present but so do bistable pulses. The ident which syncs the bistable is there looking exactly as it should on the scope, but I guess there is the possibility of some strange phase error in there somewhere. I will start by viewing the individual blue and red channels on the screen to see if both are contributing to wrong colours. If so, I will start by checking out the sync of the reference oscillator and take it from there. I suspect and hope that the green tint will vanish once I have sorted out the more major decoder fault.
Niechcial,Steve is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 2:32 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.