Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Jan Fri 21, 2022 1:35 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 11 posts ] 
Author Message
 Post subject: Hoffman EasyVision Flyback noise?
PostPosted: Jan Fri 14, 2022 11:24 pm 
Member

Joined: Apr Thu 15, 2021 4:32 pm
Posts: 98
Hi guys,

Just got this TV to show a picture, but currently the flyback seems to make an arc sound, and its whining weirdly. It seems to sound "crackly" of sorts. What could be going on and first places to look for trouble?

https://imgur.com/a/P2pURPx


Top
 Profile  
 
 Post subject: Re: Hoffman EasyVision Flyback noise?
PostPosted: Jan Sat 15, 2022 1:32 am 
Member

Joined: Apr Sat 06, 2013 2:18 pm
Posts: 694
Location: New Hampshire
Usually a mechanical problem. If its true arcing you should smell ozone or something.
Probing around & listening with a paper towel tube can narrow the area down.
Tighten all hardware in the HV area. IMPORTANT if you tighten the flyback core do it
just a little. Too much can crack the ferrite core !
You may also be sensitive to the hoz freq. I couldnt hear it myself unless it was screaming.
So usually the repair went to another tech.

73 Zeno 8)
LFOD !


Top
 Profile  
 
 Post subject: Re: Hoffman EasyVision Flyback noise?
PostPosted: Jan Sat 15, 2022 1:42 am 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 3767
Location: Dallas, TX
You can turn off the lights and see if you can see an arc. Don't blink or you may miss it.

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: Hoffman EasyVision Flyback noise?
PostPosted: Jan Sat 15, 2022 2:15 am 
Member

Joined: Apr Thu 15, 2021 4:32 pm
Posts: 98
I'll take a look. I know the HV rectifier cap is kinda crusty, and I heard that can cause come strange sounds.

In the mean while just off topic to this. The CRT currently only shows a dim glow with the brightness maxed out, but there's no video signal and I believe the cathode will have a high voltage on it. I haven't adjusted the ion trap magnet. Don't I have to ground the cathode to see if it'll make a bright picture or not?


Top
 Profile  
 
 Post subject: Re: Hoffman EasyVision Flyback noise?
PostPosted: Jan Sat 15, 2022 2:31 am 
Member
User avatar

Joined: Mar Sun 01, 2009 10:27 pm
Posts: 6071
Location: Ann Arbor, MI
Some sets are set up so that the screen is dim with no video. What does it look like when given a signal?
In general the brightness is set so that dark areas of the picture are dark and the contrast is set so that bright areas of the picture are bright.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: Hoffman EasyVision Flyback noise?
PostPosted: Jan Sat 15, 2022 2:38 am 
Member

Joined: Apr Thu 15, 2021 4:32 pm
Posts: 98
Okay so it looks like the screen is getting real bright, and then something is making that arc/pop noise, and the screen goes dim.

https://imgur.com/a/3PRiB3x

What could be causing this to happen? I can post the SAMS if needed.

Okay the TV does NOT do this when the variac is set to 110V. My current wall voltage is 123, I think its upsetting the TV which is rated for 115.


Top
 Profile  
 
 Post subject: Re: Hoffman EasyVision Flyback noise?
PostPosted: Jan Sat 15, 2022 3:40 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2238
Location: Waukegan, IL
Do you know how to measure cathode current on the horizontal output tube? Do you have a high voltage probe to measure voltage at the picture tube anode? Lets see if this in spec. My flyback used to whine until i realized ibwas drawing way too much cathode current and readjusted the horizontal drive and horizontal linearity coils.

_________________
Tony Pignaloni


Top
 Profile  
 
 Post subject: Re: Hoffman EasyVision Flyback noise?
PostPosted: Jan Sat 15, 2022 3:45 am 
Member

Joined: Apr Thu 15, 2021 4:32 pm
Posts: 98
Don't have anything to measure either of those. I know how to do the cathode current but don't have a socket for it.

Also my linearity adjustment seems to be seized up, so not sure what I'm going to do about that.


Top
 Profile  
 
 Post subject: Re: Hoffman EasyVision Flyback noise?
PostPosted: Jan Sat 15, 2022 4:15 am 
Member
User avatar

Joined: Mar Sun 01, 2009 10:27 pm
Posts: 6071
Location: Ann Arbor, MI
If there is a cathode resistor on the horizontal output tube, you can measure the voltage across it. Take a piece of wire, strip some insulation from the ends, take out the horizontal output tube and wrap one end of the wire around the cathode pin and put it back in the socket. Now connect your voltmeter from the wire to ground.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: Hoffman EasyVision Flyback noise?
PostPosted: Jan Sat 15, 2022 5:39 am 
Member

Joined: May Sun 07, 2017 11:35 am
Posts: 1585
Location: Belrose, NSW, Australia
When looking for the cause of 15kHz whistle, don't forget that ceramic caps can exhibit piezoelectric behaviour. I have heard (well actually the younger engineers in my office have heard!) loudly-whistling ceramics in power converters. We call them "chatty"!

And the 1956 Astor SJ TV had a notoriously screaming ceramic in it when new. I remember this from many years ago before my hearing was 35dB down at 5kHz!

_________________
Wax, paper, bitumen, cotton, high voltages - what could possibly go wrong?


Top
 Profile  
 
 Post subject: Re: Hoffman EasyVision Flyback noise?
PostPosted: Jan Sat 15, 2022 7:31 am 
Member

Joined: Apr Thu 15, 2021 4:32 pm
Posts: 98
I installed all the tubes and the B+ came down. Flyback is pretty quiet now, well by 1950s TV standards. But no odd noises. Its been on for ~30 minutes and probably power cycled a dozen times tonight, and I haven't seen any startling sounds from the flyback.

Also good news: the CRT is very strong! Very bright picture from it.


Top
 Profile  
 
Post New Topic Post Reply  [ 11 posts ]  Moderators: Mr. Detrola, 7jp4-guy

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 7 guests



Search for:
Jump to:  






































Privacy Policy :: Powered by phpBB