Decca Bradford 1830 no raster - UK Vintage Radio Repair and Restoration Discussion Forum

System A · 19th Sep 2006, 10:10 pm

Hi
I have an 18" Decca Bradford model CS1830 it has no raster, but if I short the RGB leads to chassis I get a bright screen of the colour shorted.
I suspect the MC chip - any ideas ?

Focus Diode · 20th Sep 2006, 9:38 am

Hi GP,

Is the sound OK with signals present? The 3rd IF transistor might be responsible but this would usually result in distorted/low sound and an unmodulated raster in a darkened room. If all is ok here the MC does seem suspect.

Ironic how the valves are easier to obtain than the ICs!

Cheers,
Brian

Focus Diode · 21st Sep 2006, 10:10 am

Further to the above the J.McCourt "Comprehensive Colour TV Manual" gives TR 201, TR 202 (both BC148) and C200 (12.5uF) as possibles for the no raster with EHT condition.

Cheers,
Brian

Hybrid tellies · 22nd Sep 2006, 12:08 am

Hi GP
If you have got sound, and you have already proved the CRT and EHT are OK, then the fingure of suspicion points to a possible fault around the luminance circuit which on these is part of the MC1327 IC.

I also remember dry joints around the luminance delay line could cause similiar effects but sometimes with this you would see just the chrominance; ie just the highly saturated coloured areas of the picture. It looked quite weird.

19th Sep 2006, 10:10 pm	#1
System A Pentode Join Date: Feb 2006 Location: County Durham, UK. Posts: 234	Decca Bradford 1830 no raster Hi I have an 18" Decca Bradford model CS1830 it has no raster, but if I short the RGB leads to chassis I get a bright screen of the colour shorted. I suspect the MC chip - any ideas ?

20th Sep 2006, 9:38 am	#2
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: decca bradford Hi GP, Is the sound OK with signals present? The 3rd IF transistor might be responsible but this would usually result in distorted/low sound and an unmodulated raster in a darkened room. If all is ok here the MC does seem suspect. Ironic how the valves are easier to obtain than the ICs! Cheers, Brian

21st Sep 2006, 10:10 am	#3
Focus Diode Octode Join Date: Jan 2006 Location: Borough of Gateshead, UK. Posts: 1,420	Re: decca bradford Further to the above the J.McCourt "Comprehensive Colour TV Manual" gives TR 201, TR 202 (both BC148) and C200 (12.5uF) as possibles for the no raster with EHT condition. Cheers, Brian

22nd Sep 2006, 12:08 am	#4
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,965	Re: decca bradford Hi GP If you have got sound, and you have already proved the CRT and EHT are OK, then the fingure of suspicion points to a possible fault around the luminance circuit which on these is part of the MC1327 IC. I also remember dry joints around the luminance delay line could cause similiar effects but sometimes with this you would see just the chrominance; ie just the highly saturated coloured areas of the picture. It looked quite weird. __________________ Simon BVWS member