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


It is currently Dec Wed 11, 2019 8:01 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 5 posts ] 
Author Message
 Post subject: Predicta princess flyback overheating?
PostPosted: Jun Tue 04, 2019 4:39 am 
Member

Joined: Apr Sat 29, 2017 6:22 pm
Posts: 135
Finished recapping, changed two of the couplets in the vertical section And checked resistors. It works good, vertical hold is very touchy but after about an hour of watching it I noticed a crackling sound. The flyback was sizzling and bubbling, I shut it off immediately. What would cause this? I've heard predictas have overheating problems, but the chassis was out of the cabinet on the bench so it should have gotten plenty of airflow.


Top
 Profile  
 
 Post subject: Re: Predicta princess flyback overheating?
PostPosted: Jun Tue 04, 2019 3:52 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2004
Location: Lafayette, CO
The wire insulation inside the fly may be breaking down or there might be more current than designed running through that winding. Are there any red-hot elements in the horizontal output tube, besides the cathode? Craig


Top
 Profile  
 
 Post subject: Re: Predicta princess flyback overheating?
PostPosted: Jun Tue 04, 2019 7:10 pm 
Member
User avatar

Joined: Nov Thu 11, 2010 6:03 pm
Posts: 968
Location: Pewaukee, WI
Compare horizontal output cathode current to what is on the schematic. If close and the set was stored for a long time In a humid environment it may have been accumulated moisture boiling out.


Top
 Profile  
 
 Post subject: Re: Predicta princess flyback overheating?
PostPosted: Jun Wed 05, 2019 6:59 am 
Member

Joined: Apr Sat 29, 2017 6:22 pm
Posts: 135
Swapped the horizontal output tube with another, seems to have fixed it. Cathode current is now where it should be. The tube must've been partially shorted or had some leakage not sure there but its working well. Thanks!


Top
 Profile  
 
 Post subject: Re: Predicta princess flyback overheating?
PostPosted: Jun Wed 05, 2019 3:33 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 293
It could also have been moisture in the flyback windings. It's a good idea not to run a newly restored set for long periods at first. I like to do a few short runs of 30-45 minutes before trying a long run. Even then, it's a good idea to keep a close eye on the flyback. It's by far the most vulnerable part in most vintage TVs. The windings are usually insulated with paper and wax, just like all those leaky caps we replace on sight.

Choosing a HOT that has the lowest current, and possibly reducing the line voltage a little can also make a big difference. One of my first vintage sets was a late 50's RCA portable. I noticed than when plugged directly into the power line, the flyback would start to sizzle, but when I used my isolation transformer, it was fine. Sometimes 5-10% less line voltage will keep it from going into thermal runaway.


Top
 Profile  
 
Post New Topic Post Reply  [ 5 posts ]  Moderators: 7jp4-guy, Mr. Detrola

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 5 guests



Search for:
Jump to:  




























Privacy Policy :: Powered by phpBB