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Old 21st May 2019, 9:12 am   #9
Mazda Man
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Join Date: Feb 2017
Location: Poole, Dorset, UK.
Posts: 44
Default Re: Bush TV53 hum bar problems

so the Hum bar problem when the Bush set is powered on raw mains is now solved!
As I had just overhauled the set replacing all suspect caps etc I was pretty sure that there were no faulty or missing caps that were causing the hum fault.
First I tied another set on the bench and connected the aurora up to that to see if if it was the set or the signal source. No hum was visible on the substituted Tv so it looked like the signal source was not to blame after all.
Reconnecting the Aurora to the Bush and the hum was clearly visible. even though the aurora / 9v power supply combination worked ok on the other set.
Just to be sure I decided to substitute the 9v Aurora power supply for one of a different brand. these little Ac to Dc power packs are the plug in the wall type and use a little switched mode converter inside them. As they are a high frequency type power supply I did not think a replacement would solve it as the ripple appeared to be low frequency and beating with the frame timebase.
A different branded substitute power supply however reduced the effect by about about 50% with it being much less visible but not gone.
Feeling like I was on to something I next fed the aurora from my variable DC bench power supply which uses a standard linear power supply.
Switched on the Bush and the hum was completely gone, not a trace of it! Bizzare why this Bush set should be sensitive to this effect whilst other sets using the same signal source are not. So now Ive Just got a very intermittent line twitch to sort out!
Thanks to all for their input, particularly Argus25 and McMurdo who got me thinking along the right lines to solve the problem.
Regards, Dave
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