No Green on Thorn 3000 - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

HurtyAC · 17th Jan 2016, 11:08 am

Hi All,
From what you describe it sounds like the connection to the green cathode pin of the CRT may be open circuit? The only thing that goes against this is the bright green raster when you take the green cathode drive to ground. If you have 80-120 volts on the cathodes and 400 volts on the A1's and the red and blue drive is o.k. (seen on the screen) then you tube biasing is correct. Did this fail over time or all of a sudden?

Adrian

pastyboy · 17th Jan 2016, 12:19 pm

What a ROTTER !!!!! L802 was oc the coil in series with the green K

talk about a red herring but there was volts and a video drive waveform on a 3 cathodes

thinking about it now maybe the scope WF was being induced by the other guns ??

other red herring is the a1 volts didn't seem to tally should be 1kv from LTB to conv board pin 3 but only 670v this may be because I don't have an avo and its a rough dc line with sprogs on it...

I shorted the cathode pin to deck and had a green raster but then should of decked the other end of the video drive plug (with it unplugged of course)

Thanks to all that helped out with invaluable suggestions.

There is the convergence to set up - what a joy and I still don't think the brightness cct is right - will set up as per the posts, but as the preset is right on max I think there is something lurking.

At least me tube is OK !!

MALC SCOTT · 17th Jan 2016, 12:46 pm

There are quite a few of those black Callins electrolytics in these sets, best to change them all, Malc.

FERNSEH · 17th Jan 2016, 1:04 pm

Including C215, C227 and C231. These will be 2mfd Callins electrolytics. Replace C223, 10mfd in the base circuit of VT210. Replace C211 and C229 as well.
As Malc suggests, change the lot.

DFWB.

pastyboy · 17th Jan 2016, 2:14 pm

yes will look at them, think most have been changed ! there are a few lurking though. Now the lack of height and convergence to have a go at ! I have the circuit and there are plenty of stock faults mostly the dreaded callins again.

I'm a callins get me outta here !

17th Jan 2016, 11:08 am	#21
HurtyAC Tetrode Join Date: May 2009 Location: Ware, Hertfordshire, UK. Posts: 75	Re: No Green on Thorn 3000 Hi All, From what you describe it sounds like the connection to the green cathode pin of the CRT may be open circuit? The only thing that goes against this is the bright green raster when you take the green cathode drive to ground. If you have 80-120 volts on the cathodes and 400 volts on the A1's and the red and blue drive is o.k. (seen on the screen) then you tube biasing is correct. Did this fail over time or all of a sudden? Adrian

17th Jan 2016, 12:19 pm	#22
pastyboy Hexode Join Date: Nov 2015 Location: Cornwall, UK. Posts: 270	Re: No Green on Thorn 3000 What a ROTTER !!!!! L802 was oc the coil in series with the green K talk about a red herring but there was volts and a video drive waveform on a 3 cathodes thinking about it now maybe the scope WF was being induced by the other guns ?? other red herring is the a1 volts didn't seem to tally should be 1kv from LTB to conv board pin 3 but only 670v this may be because I don't have an avo and its a rough dc line with sprogs on it... I shorted the cathode pin to deck and had a green raster but then should of decked the other end of the video drive plug (with it unplugged of course) Thanks to all that helped out with invaluable suggestions. There is the convergence to set up - what a joy and I still don't think the brightness cct is right - will set up as per the posts, but as the preset is right on max I think there is something lurking. At least me tube is OK !!

17th Jan 2016, 12:46 pm	#23
MALC SCOTT Octode Join Date: Aug 2006 Location: Willington, County Durham, UK. Posts: 1,499	Re: No Green on Thorn 3000 There are quite a few of those black Callins electrolytics in these sets, best to change them all, Malc. __________________ Malc Scott

17th Jan 2016, 1:04 pm	#24
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: No Green on Thorn 3000 Including C215, C227 and C231. These will be 2mfd Callins electrolytics. Replace C223, 10mfd in the base circuit of VT210. Replace C211 and C229 as well. As Malc suggests, change the lot. DFWB.

17th Jan 2016, 2:14 pm	#25
pastyboy Hexode Join Date: Nov 2015 Location: Cornwall, UK. Posts: 270	Re: No Green on Thorn 3000 yes will look at them, think most have been changed ! there are a few lurking though. Now the lack of height and convergence to have a go at ! I have the circuit and there are plenty of stock faults mostly the dreaded callins again. I'm a callins get me outta here !