1949 motorola table top - Page 6 - Videokarma.org TV - Video

timmy · #76 03-20-2015, 10:00 AM

well i have a verticle problem where it just wont stop rolling really bad after a few minutes on it starts, but now i lost alot of horizontal width dont know what happened so now i got 2 major problems, any hints out there...

timmy · #77 03-20-2015, 01:05 PM

well it appears that the horizontal size pot is getting hot and smelling bad so something went bad here. i had a spare and put it in but no difference so its staying off until i find whats happening here , it maybe a mica cap in that circuit maybe shorted, dont know. i have micas and compared readings in nf with the ones in the set and are good and seems to be no shorts so now it may be the horiz sweep transformer, again not sure.

timmy · #78 03-21-2015, 02:33 PM

ok found that problem but what would keep the horiz oscillator from running correctly. if i touch pin 1 of the afc- horiz oscillator with my dvom in voltage check mode the oscillator runs and the pic is ok. the pic is pulled in on both sides, horiz, when turned on then i touch that pin 1 a slight arc and its fine. something seems to keep the oscillator from running when turned on. and the voltages are high where they should be low like 70v is 200 v.

timmy · #79 03-23-2015, 04:01 PM

well nothing but trouble with this set now the hv shut down and the 100 ohm resistors at the hv oscillator tube are getting hot , dont know where to go from here. ok my mistake hv is ok but this horizontal issue where the oscillator for the horiz hold wont start unless i turn the horiz pot to one one to get it running and then its fine but i cant turn this knob every time i turn it on. at a loss, help

bandersen · #80 03-26-2015, 06:10 PM

I've never had a problem quite like this before, but I'd start by checking all the parts around the size control. It's got B++ on one side and the T-6 hor sweep output transformer on the other. The other side of that winding goes to some capacitors and T5. Assuming all the caps are OK, the only path for DC to smoke the pot is through T5 and T6 so I'd suspect those parts.

timmy · #81 03-26-2015, 07:43 PM

i even checked the ohms on all 3 transformers and they check right on. t-4 and t-5 have resistors a 15k and a 27k the 27k measures 37k , thats all i really found. and when i got done recapping this set had a verticle problem but no horizontal problem.

timmy · #82 03-27-2015, 06:52 PM

ok i found the problem, there is a 20mmf cap off t-5 that was bad however the parts chassis i have has a different cap, colors are not the same but it works horizontal oscillator is right there now but i dont know what value this cap is because i am alittle short left to right on the horiz size so this cap must set the frequency and must be right to have the right size on the screen. next is the verticle, maybe another cap as i think there are 2 or 3 in that circuit, non stop rolling but i can put a resistor from ground to the .004 can and stop the rolling but temporary. that cap is at pin 2 of v12 and this cap sets the oscillator in motion and if it dont run i learned that it will take out the horizontal size pot very quickly. this capacitor that went bad is a dogbone type and im wondering if a ceramic disc 20 pf can be used in place of this 20 mmf .

bandersen · #83 03-27-2015, 09:16 PM

The original ceramic tubular caps had an excellent temp coefficient and were very stable. Make sure you replace it with a C0G or NP0 type.

timmy · #84 03-28-2015, 02:37 PM

i know that resistor and the .05 cap and if i take them both off i still have 250 volts using the frame ground and b++.

bandersen · #85 03-28-2015, 03:38 PM

Think about it - what would you expect to see? 0 volts ? That would mean the frame was at the same potential as B++

Also what about that 0.01 off V11 going to the frame (chassi) ? Which schematic are you looking at - Motorola or Sams ?

timmy · #86 03-28-2015, 07:46 PM

Quote:

Originally Posted by bandersen

Think about it - what would you expect to see? 0 volts ? That would mean the frame was at the same potential as B++

Also what about that 0.01 off V11 going to the frame (chassi) ? Which schematic are you looking at - Motorola or Sams ?

well looking at sams and motorola schematics they both dont show a .01 at v11 but this set had one and it was original motorola cap never touched so i put a new one back i also checked it and its right on the money. so in taking one leg of that cap off gives me the verticle hold, and i think its excessive voltage on the frame from somewhere. befor i put the silicon diodes in i never checked if this problem was there befor and if the diodes were in wrong somehow the set im sure wouldnt work. i would have expected some voltage from static or leaking voltage from the rf section and beyond, like maybe 10 -50 volts maybe alittle more but not 250 volts dc. the .01 leg is off got verticle, the resistor from b- and the .05 disconnected i still have 250 volts , frame ground to b++.

stusnyder · #87 03-29-2015, 06:35 AM

Quote:

Originally Posted by timmy

well looking at sams and motorola schematics they both dont show a .01 at v11

So leave it out then. It might have been a revision.

timmy · #88 03-29-2015, 10:06 AM

Quote:

Originally Posted by stusnyder

So leave it out then. It might have been a revision.

problem is, it was in the circuit and there is a reason why it cannot be in there now, like the voltage on the frame ? im baffeled now....

timmy · #89 03-29-2015, 05:37 PM

ok so leaving the .01 disconnected didnt last its rolling again so i put it back. i looked at near everything here and it just wont stop rolling. i subbed tubes, mica caps, verticle hold pot, for the verticle and horizontal micas as well and all makes no difference. , there has to be a reason why it wont stop rolling all the caps that came out were put back with the same values. i went over everything i did and cant find a thing wrong. does anyone know where i can go from here because i am burned out at this point and maybe someone out here can mention something that i missed. i cant get an acurate voltage reading on tubes in the verticle circuit because the voltage is all over up and down as it rolls out of control. i dont know if the horizontal may have something to do with verticle or is upsetting it for some odd reason. right now the horizontal is ok just alittle short on the width. so maybe something is interfearing between both vert and horiz and the verticle is taking it the worst. HELP

timmy · #90 03-29-2015, 06:01 PM

i dont know if its possible if there is a problem in the video amp or video output since i was thinking that everything has to go into the video amp and output, just guessing at this point since i didnt check anything in those areas.is this at all possible ???