Bush TV22 Picture Fault - UK Vintage Radio Repair and Restoration Discussion Forum

Radio Tech · 16th Sep 2016, 8:15 pm

I am about to embark on help a good friend of mine in solving a picture fault on this Bush TV22, the problem being with a good signal from an arora standards convertor the picture is generally weak and has bars across the screen, it's as if there is sound on picture, however on saying this can't seem to find the problem.

Any Idea?

Regards

Ken

Boater Sam · 16th Sep 2016, 9:49 pm

Check all the HT voltages, this could be a smoothing cap problem putting "hum" into the video circuits.

stevehertz · 16th Sep 2016, 10:16 pm

If you haven't already, change all the wax paper capacitors - in any case. What's the state of the valves? all they all known good ones? Has the set previously been restored or is it pretty much original, ie potentially full of faulty components, bad connections etc. There's just so much to go out if the set has not been restored. I always used to to go 'all through' a newly acquired vintage TV, never looking for individual faults until all the basics were done.

KeithsTV · 16th Sep 2016, 10:32 pm

Check the 16uF cap C25 especially if the verticals are distorted. This cap decouples the line oscillator plus the RF chassis.

Keith

Radio Tech · 17th Sep 2016, 4:44 pm

Thanks everyone, and ok Keith all noted on that c25 cap

Will let you know how I progress

Ken

Radio Tech · 20th Sep 2016, 2:57 pm

Hi Keith

You were quite right about the 16uf, it measured only 9uf, somewhat different from what it is supposed to be, replacing this has improved the sets performance but still got to check out C25 which decouples the screen of V7 an ECL80

Ken

KeithsTV · 20th Sep 2016, 4:21 pm

That cap decoupling pin 7 of the ECL80 will be a wax paper type and will almost certainly be leaky. The screen grid is fed via a 1.5Meg resistor so the leaky cap will pull the screen grid voltage down affecting the sync separator performance.

Have you replaced the other wax paper caps as they will almost certainly be leaky after 60 odd years.

Keith

Radio Tech · 26th Sep 2016, 7:36 pm

Hi Keith and everyone

latest update on the progress, changed 16uf electrolytic and the decoupling cap on V7, found a few others that were up the creak in and around the sync circuit but I also suspect that metrosill so going to put a request on the want section, otherwise the picture and sound seem fine

Best wishes

Ken

KeithsTV · 26th Sep 2016, 9:57 pm

Have you changed C18 the reservoir capacitor for the A1 supply for which the metrosil is the rectifier. This is a very high impedance circuit and any leakage through C18 will cause the A1 supply to drop. Even measuring it with a DVM can load the supply. The Bush service manual says to use an electrostatic voltmeter to measure the voltage.

From memory C18 is hidden under the tagboard close to the metrosil.

Keith

Radio Tech · 27th Sep 2016, 11:21 am

Hi Keith

Not changed C18 but will do so on your advice thank you for that, will update as I progress

Ken

16th Sep 2016, 8:15 pm	#1
Radio Tech Nonode Join Date: Dec 2012 Location: Bocking, near Braintree, Essex, UK. Posts: 2,071	Bush TV22 Picture Fault I am about to embark on help a good friend of mine in solving a picture fault on this Bush TV22, the problem being with a good signal from an arora standards convertor the picture is generally weak and has bars across the screen, it's as if there is sound on picture, however on saying this can't seem to find the problem. Any Idea? Regards Ken

16th Sep 2016, 9:49 pm	#2
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Bush TV22 Picture Fault Check all the HT voltages, this could be a smoothing cap problem putting "hum" into the video circuits.

16th Sep 2016, 10:16 pm	#3
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,835	Re: Bush TV22 Picture Fault If you haven't already, change all the wax paper capacitors - in any case. What's the state of the valves? all they all known good ones? Has the set previously been restored or is it pretty much original, ie potentially full of faulty components, bad connections etc. There's just so much to go out if the set has not been restored. I always used to to go 'all through' a newly acquired vintage TV, never looking for individual faults until all the basics were done. __________________ A digital radio is the latest thing, but a vintage wireless is forever..

16th Sep 2016, 10:32 pm	#4
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,574	Re: Bush TV22 Picture Fault Check the 16uF cap C25 especially if the verticals are distorted. This cap decouples the line oscillator plus the RF chassis. Keith

17th Sep 2016, 4:44 pm	#5
Radio Tech Nonode Join Date: Dec 2012 Location: Bocking, near Braintree, Essex, UK. Posts: 2,071	Re: Bush TV22 Picture Fault Thanks everyone, and ok Keith all noted on that c25 cap Will let you know how I progress Ken

20th Sep 2016, 2:57 pm	#6
Radio Tech Nonode Join Date: Dec 2012 Location: Bocking, near Braintree, Essex, UK. Posts: 2,071	Re: Bush TV22 Picture Fault Hi Keith You were quite right about the 16uf, it measured only 9uf, somewhat different from what it is supposed to be, replacing this has improved the sets performance but still got to check out C25 which decouples the screen of V7 an ECL80 Ken

20th Sep 2016, 4:21 pm	#7
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,574	Re: Bush TV22 Picture Fault That cap decoupling pin 7 of the ECL80 will be a wax paper type and will almost certainly be leaky. The screen grid is fed via a 1.5Meg resistor so the leaky cap will pull the screen grid voltage down affecting the sync separator performance. Have you replaced the other wax paper caps as they will almost certainly be leaky after 60 odd years. Keith

26th Sep 2016, 7:36 pm	#8
Radio Tech Nonode Join Date: Dec 2012 Location: Bocking, near Braintree, Essex, UK. Posts: 2,071	Re: Bush TV22 Picture Fault Hi Keith and everyone latest update on the progress, changed 16uf electrolytic and the decoupling cap on V7, found a few others that were up the creak in and around the sync circuit but I also suspect that metrosill so going to put a request on the want section, otherwise the picture and sound seem fine Best wishes Ken

26th Sep 2016, 9:57 pm	#9
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,574	Re: Bush TV22 Picture Fault Have you changed C18 the reservoir capacitor for the A1 supply for which the metrosil is the rectifier. This is a very high impedance circuit and any leakage through C18 will cause the A1 supply to drop. Even measuring it with a DVM can load the supply. The Bush service manual says to use an electrostatic voltmeter to measure the voltage. From memory C18 is hidden under the tagboard close to the metrosil. Keith

27th Sep 2016, 11:21 am	#10
Radio Tech Nonode Join Date: Dec 2012 Location: Bocking, near Braintree, Essex, UK. Posts: 2,071	Re: Bush TV22 Picture Fault Hi Keith Not changed C18 but will do so on your advice thank you for that, will update as I progress Ken