magnavox 24" b&w tv trouble - Videokarma.org TV - Video

63bird · #1 07-17-2010, 12:15 PM

ok i have a 1966 or 1967 solid state b&w tv U90801 FA date 10/66 i got it for 10.00 but of course it dont work.

well i jumped the circuit breaker to get it to turn on and there is a coil under the chassis that started to make noise and i saw the wax begin to bubble so i shut it down (it was on for about 10-15 seconds max).

so looking at where the coil wires go (yellow and red)
yellow wire goes to a 350uf 100v section of a can cap
red wire goes to a plug on the chassis that goes to the yoke

so i figured it had to be a bad can cap so i replaced the cap with the same values 100uf 75v
350uf 100v
350uf 100v

well fire it up and the same thing with the coil heating up.

so i checked the crt with my b&k crt 400 (i know most people dont like this model) well it read that it had a short (open G2 first anode) and no emissions.

so i did the rejuve and i cleared the shorts but emissions is about 200ua it says 300 -1000 is good. however ive been told my 200ua is decent for a old b&w tv.

i have pics i cant seem to be able to deleate my old ones to post these. so anyone curious i can email you pics.

im also ordering a manual for this tv but that takes about 2 weeks from mike at vintage audio manuals.

a little about me im a vintage nut ive worked on stereos a good bit but this is my first atempt at fixing a tv ive read a lot of books on vintage tv repair lately. im 27 and really want to learn this trade that some you have done for years mainly for myself or friends. ive been real heavy in to old cars and there has not been a real challenge for me in years. so i figure tv's are just cool i have learn more.

well i thank you all in advance for any insight to my problem.

DaveWM · #2 07-17-2010, 07:04 PM

you have a short in the B+ somewhere. I would have guessed a filter cap but it could be somewhere else.

most likely will need a schematic to find out where to look. Could be a shorted diode I suppose, feeding AC to the cap.

I would start by checking the resistance of the B+ with a mutimeter, should get an inital surge then the resistance should go up as the cap charges.

You may end up having to disconnect the B+ one at a time to find where the short is.

ctc17 · #3 07-17-2010, 07:56 PM

Im with you Dave, that selenium rectifier needs to go. You can put a regular silicone diode in there. You will need to put a resistor in series with the new diode because the new silicone diode is much more efficient that the old one. Usually 20-30 ohm 5 watt resistor would be ok.

As a test you could leave the diode, coil and cap hooked up disconnecting the power connections for the cap to the set and see if the breaker still trips, then you would prove its the rectifier.

63bird · #4 07-18-2010, 02:37 AM

ok the yellow wire on the coil has a blue clothlike coverd wire connected with it at the cap. that blue wire comes directly from the transformer. i dont know if this helps any?

Don Lindsly · #5 07-18-2010, 04:39 PM

Check B+ rectifier diodes and horizontal output transistor for shorts.

Measure HOT collector to ground. If it is 0 ohms, it is trouble. Remove the mounting screws. If short remains, the transistor is bad. If it disappears, it is likely a shorted damper diode or feed thru cap.

63bird · #6 07-19-2010, 11:10 PM

ok i traced the B+ untill i found the short and it leads to a very thin yellow wire that goes to the flyback. with it disconnected it dont trip the circuit breaker. so would that mean the flyback is bad?

AUdubon5425 · #7 07-20-2010, 01:35 AM

Does the chassis look like this?

If so, it may be a U44 - I scanned the Sams for it a while back. If it looks the same and you want a copy PM me your e-mail address.

63bird · #8 07-20-2010, 07:02 AM

the chassis is rectangle shaped and mounts to the bottom of the tv. the tag on the chassis read U90801 FA 10/66

also i forgot to metion the flyback has melted to where the black stuff touches the chassis and puddeld. i can email pics if anyone wants a look at it.

DaveWM · #9 07-20-2010, 07:27 AM

yes send a pic of the fly back. I does not mean its bad, ofte flybacks will drip and be ok, I have one that you would swear is bad, but still works ok.

you will prob need to wait for the schematic to find out any more.

DaveWM · #10 07-20-2010, 11:49 PM

house number 63N1 does anyone know a cross?

DaveWM · #11 07-20-2010, 11:53 PM

found it

NTE163A

DaveWM · #12 07-21-2010, 12:06 AM

this looks like a good cheap sub
http://www.surplussales.com/Semicond...str-BU208A.pdf

DaveWM · #13 07-21-2010, 12:08 AM

buy here

http://www.surplussales.com/Semicond...-Specials.html

DaveWM · #14 07-21-2010, 09:40 PM

I have been helping 63 bird on this on over the phone. Don nailed it, shorted HOT.

He is getting close, got raster, just need to a signal. I think he will be in business soon.

63bird · #15 07-22-2010, 07:36 AM

it was the horizontal output transistor that gort me working with out poping a circuit breaker.

new possible issue to me the snowy screen seems fine. but i tried to hookup a video source (dtv convertor box) from the left of the screen over to 3/4 to the right the screen is all grayish and the remaining 1/4 of the screen has a more black section. if you have seen a heart moniter it looks like that but going vertically up the screen.

now here is my fear. this set was in a small thrift store the lady said a guy had bought the other tv sets that worked. she also mentioned he took the back off of this tv and was trying to fix it.

my audio could be heard through the loud rushing sound. but not to loudly.

my guess could be this dipstick started to mess with all the knobs becuase i looked in all my books and cant find a picture that even looks close to my screen.

thanks for getting me this far this is awesome ive never worked on a tv before.