View Full Version : Dumont RA-109A help needed - very little high voltage


kramden66
05-27-2013, 08:32 PM
Its been recapped and finaly ready to go , well the sound works but no raster or sound of horz sweep , i tried the probe and theres maybe 1kv on the anode , tried the 1x2 that is v31 it has a connection from pin 1 according to sams it goes to a doorknob and to ground , it has more voltage when doorknob disconnected (2kv ) i tried replacing the doorknobs it made no change , sams shows a doorknob from pin 9 of v32 (1x2) to pin 1 of v31 (1x2) and there is none in the set nor signs there ever was one , also observed v31 gets hot fast , replaced the 1x2 tubes and no change , if you measure pin 1 of v31 when set turned on it shoots up and almost gets to 5kv before it quickly drops to 1kv , fly seems ok , any ideas where to go from here ? horz out or osc area ?

i did notice i didn't hear vertical roll or anything like that , will double check
thanks
mike

kramden66
05-28-2013, 12:50 AM
the vertical is working i can hear it when i rotate the vert hold , starting to wonder if the horz freq and hold control/transformer could be at fault ? or the horz lin or horz size ? this would cause not enough voltage on the anode right ? i ask because i did go over all the resistors and replaced any that where not right , there is one other thing , horz reactance tube v25 in sams it says 6BC5 is installed in the set , 6AG5 is listed as an alternative and theres a 6AG5 in the set , i wonder if i were to put a 6BC5 in if it would correct this ?

mike

Zenith26kc20
05-28-2013, 09:08 AM
If the 1X2 is getting hot I would suspect something is loading the high voltage down. Have you checked the picture tube. If it is "gone to air" it may be loading down the high voltage. What is the normal high voltage (KV) on this set?
Are you sure the doorknob caps are OK? They do tend to breakdown under load. Check the 1X2's after you have run them hot. They are not a robust tube and die fairly easy if loaded hard.

John Folsom
05-28-2013, 09:11 AM
If one or more of your 1X2s are getting hot, you have either a bad 1X2 or a overload on the hot tubes output (filament).

If a 1X2 tests good on a tube checker, it can still be bad under actual operating conditions.

kramden66
05-28-2013, 10:50 AM
i tried changing the 1x2 tubes and no change , the crt has not gone to air , i will have to take voltage readings on the horz out tubes which wont be easy since the set has the crt and yoke mounted in the cabinet of the tv.

mike

wiseguy
05-28-2013, 11:25 AM
I have the Same set and it's the A version, and I would agree with the other 2 members about about something loading it down if one of the 1x2 tubes get hot,
try measuring HV with the CRT 2nd Anode disconected, and probe right into the connector coming out of the HV cage.
I am due for open surgery this week so I cant pull the set out and compare for you..
(open hernia surgery sucks,I tend to lift way over my limit and I'm trim and fit !)

Zenith26kc20
05-28-2013, 12:13 PM
Years ago to check to see where the overload was, we would remove the cap from the 1X2 to the flyback and let it hang in mid air. Using a well insulated screwdriver NOT connected to ground, bringing it near the cap should make a fairly long spark to jump to the screwdriver. If the spark goes way down when the cap is reconnected, it means the overload could be from the 1X2 on to the CRT. If I remember right, this set has a high voltage doubler so arc over of the flyback may not be as possible as with some half wave setups. Don't leave it on long, just enough to test the spark. Check for pinholes in the 1X2 filament windings. This usually makes a burning smell unless they are carbonized badly and are really loading the high voltage down. From your description, as horizontal output starts working the 1X2 filament starts warming up and a leak path to ground will get worse as the tube warms up.

kramden66
05-29-2013, 02:19 AM
i will do all these things and check the horz section voltage - now can i leave the 1x2 or 1x2's out so i can run the set to get voltages ?

will report back with more info wed

mike

Zenith26kc20
05-29-2013, 08:43 AM
remove the caps from the 1X2 tubes. One of them will have the RF from the sweep circuit on it. Using a well(!) insulated screwdriver, just go near the cap from the flyback and if everything back from the flyback is good a spark should jump to the screwdriver tip. If this spark is less than 1/4 inch I would look to horizontal/damper/yoke circuit. If it is good, look for troble in the 1X2 circuitry.
Don't ground any part of the screwdriver. Hold the plastic end and just go near the cap with the tip. Don't leave the set on a long time as the flyback will be unloaded at the time of testing.

kramden66
05-29-2013, 12:51 PM
with the anode disconnected from the crt the voltage shoots up to around 14kv , so its obvious the metal part of the crt is somehow being grounded ? does that make sense ? so time to try to figure out how , if theres something wrong with the crt itself it will be a shame because it has good emissions

mike

kramden66
05-29-2013, 01:18 PM
getting resistance readings from a couple pins of the yoke to the anode / metal part of the crt , so i guess the yoke is shorting to the metal cone of the crt ?

mike

wiseguy
05-29-2013, 02:08 PM
there is a ground strap that sort of curls upward on the lower left side of the CRT, this grounds metal parts around the front of the cabinet, and there are some sort of insulators between the brackets that hold the Yoke and hold the CRT in place.
somehow one or all of them are not assembled correct and it is shorting the lip of the CRT to ground . I would remove the CRT and or see what the HV connector is touching on the CRT itself..

Zenith26kc20
05-29-2013, 03:55 PM
I assume this is a metal cone CRT?

Zenith26kc20
05-29-2013, 04:06 PM
the yoke is on the glass part of the bell (?). Possibly dirt/grease has become conductive and leaking to the metal bell.
Also, does the emission start slowly and rise rapidly when you test the tube? My T-933 CRT checked incredibly well but when the set was turned on the neck went purple:tears:

kramden66
05-29-2013, 04:06 PM
loosed the yoke bracket , moved the yoke back and no resistance , so i put the chassis in i have a picture , i do have an arcing sizziling issue in the hv section that stops if brightness turned up all the ay , so i have to figure out whats happening there and how the yoke is making contact with the cone , no its not the ground straps .... well this will answer the clean or not to clean post - no choice

mike

John Folsom
05-29-2013, 06:44 PM
Clean the glass at the end of the bell between the yoke and where the metal bell attaches to the glass, this should cure you leakage from the metal bell to the yoke.

Use a piece of plastic hollow flexible tubing like a stethoscope. Stick one end in an ear, and use the other end to listen around in the HV cage to find the location of thee HV sizzle. Of course, often you can see it in a dark room.

kramden66
05-30-2013, 12:27 AM
Gonna try shortly to see if i can see the hv problem , also paper towel cardboard tubes help in a pinch to locate noises , from what little i could see this set has a great picture , no wonder why its 35 tubes and dumont went out of business.

mike

Zenith26kc20
05-30-2013, 08:21 AM
mighty glad the CRT is good! A quick look at the schematic shows that set to be.... complicated!

kramden66
05-30-2013, 11:58 AM
can't see or locate the arc , if i move the board where everything is hooked up the sound changes , could be on the other side but tough to see and can't pull the chassis out far enough to look , i guess i could coat everything , whats good and cheap i can apply , a rubber sealent or silicone ?

it may look complicated but everything is spread out so room to work on it.

mike

John Folsom
05-30-2013, 12:46 PM
I do not recommend coating to try and resolve HV arcing/corona issues. First identify the actual source/cause of the problem, then you will know how to resolve it. Use the small flexible hollow tube method to locate the actual source. The paper towel cardboard roll is too big and not flexible. You may have to remove HV covers, or pull the chassis to locate it. If you pull the chassis, you will likely need to have the focus coil and yoke hooked up. You need not have the CRT HV hooked up.

kramden66
05-31-2013, 12:22 AM
there was a tube shield ( not from this set i don't tink ) it was under the rim of the crt , so that must have been what caused a short through the wood , i moved the yoke back to where its supposed to be and it works but still have to locate the arc issue .

so your saying i can leave the second anode unhooked and run the set ?

John Folsom
05-31-2013, 10:50 AM
Yes, just make sure you manage the loose end of the HV lead. I like to tape the end inside a glass container so it is shielded from causing trouble. Running with the lead unhooked is the same as just turning the brightness all the way down, so there should be no issues.

kramden66
06-02-2013, 01:51 AM
i haven't had time to try or do anything but read this in the riders tv trouble cures vol one , breakdown between chassis and flyback tranformer lead .. in order to eliminate electrical breakdown between chassis and red/white wire from the fyback the red/white wire to the capacitor end of the clip on v230 ( 1x2 ) is removed and replaced with a white wire to the tube end of the clip on v230 .... perhaps this is my issue ?

mike

wiseguy
06-02-2013, 05:47 AM
on my RA-109A I had the same corona/discharge issues, and it was the small doorknob caps for sure, it was a light "tick Tick noise, but enough to bother me so I replaced them
this is my 2nd home dy from suregrey and want was supose to be a 1" cut turned out to be a little of 3".. so now I will watch how I carry heavy things and always ask.!

kramden66
06-02-2013, 11:39 AM
Wow hope you feel better soon , i don't have a tick tick i have a rappid sound that causes the image to get in and out of focus and slight chage in brightness and it jitters the image , you can see on the probe the voltage drops and rises , so whatever it is it has moments where it slows and almost stops or just keeps going , i can try replacing the doorknobs again , i have ceramic disc caps that are 470pf at 15kv , i tried them before but that was when the lead was being shorted , now that it is not maybe they are the cause.... btw it looks like i will only have to do a little touch up on the vertical , looks close and the horz might be ok , once i lick this issue it wont require extensive linerty / width issues.. i hope.

mike

old_coot88
06-02-2013, 01:13 PM
...i don't have a tick tick i have a rappid sound that causes the image to get in and out of focus and slight chage in brightness and it jitters the image..
mike
What you describe sounds like one of the leads going into the CRT socket is broken loose from the lug. Have you checked there? Or maybe one of the lugs is not making contact with the CRT pin.

ggregg
06-02-2013, 03:31 PM
My RA-109 had a similar issue. It was coming out of the doubler circuit. Cleaning eliminated the issue, for now anyway. It was up by the caps things that attach to the top of the tubes. Carbon traces, I assume.

kramden66
06-03-2013, 12:41 PM
Yes virginia you are a doorknob .... it was the doorknob connecting the tops of the 1x2 tubes , i wasn't sure until i felt the doorknob and it was hot , so i swapped it with the one going to ground and the one at the caps of the 1x2 tubes remained cool , the one now connected to ground was getting hot , replaced the ground one with a ceramic disc cap rated at 15kv and then there was no arcing at all , the only issue that remains now is theres the anode wire where it connects to the pin on the 1x2 , it has a nice field around it , the wire has a couple threads that are loose and they stick up like moe's hair when he is scared , so i just have to insulate that area.

All agree its ok to leave the ceramic in ?

this motivates me , i may yet remove the crt to clean it and the glass

mike

John Folsom
06-03-2013, 01:27 PM
That wire with the broken strands, better to replace it, or at least coat the brea of the broken strands with a smooth bead of solder. Any sharp points will create corona, and will likely continue to cause problems even if you attempt to insulate them

kramden66
06-04-2013, 12:08 AM
theres a weird pattern on the side ( first picture ) that will pretty much go away when you fine tune (if you look closely you can still see it when tuned out but barely ) , here i made it as noticeable as possible in the picture so one can see the pattern and visable when screen is black , also you can see little ghosts/shadows on the letters , thats an if issue ? the ifs need to be realigned ?

its coming along atleast i've got a picture , the vert and horz are almost right without tinkering but for a better overall picture i will tweak them.

mike

Electronic M
06-04-2013, 01:26 AM
Might be barkhausen(I think I misspelled that) oscillation from the horizontal output tube.

wiseguy
06-04-2013, 06:03 AM
that is not barkhausen, but its just prob something within the i.f or tuner, try tuning to channel 4 instead, and make sure all tube sheilds are seated and the twinlead to the tuner is dressed away from other things, what I did was add the 300-75 ohm transformer/adaptor right in place of where the twinlead used to go. so if I want to tune FM I just turn off the TV converter box and it still passes a signal for FM.
did you notice that hole cut out under that chassis which looks like it was for shipping the Yoke Assy? the bolt pattern aligns up on the wood support

kramden66
06-04-2013, 09:57 AM
It doesn't have twin lead it has a direct 75 ohm ( i think 72 ohm ) rca phono connector to a shielded cable to the tuner , i tried tunning and hen the image is tuned right that pattern really isn't noticeable , i do have to try to align the if adjustments , if you look close at the not so good picture after the last letters you can see the shadoes/ghosts of the letters , so i'll see if i can eliminate them , if not it plays well as it is.

so thats what that big round hole is for , i couldnt figure out what its purpose was

mike

old_coot88
06-04-2013, 12:29 PM
If there is a shielded coax running from the tuner output to the IF strip, check to see if there might be a broken ground at one end of that cable.

kramden66
06-07-2013, 01:43 AM
I'm slowly but surely getting there.

mike