silvertone roundie
 

hey all i have not got started on this silvertone ctc12 clone yet to find out why the hv jumps up and down with scene changes and the cathode current jumps as well. i will be checking the 390k resistor at the blanker tube to ground since it was said to do this if the resistor is out or the ground trace is bad. so with all the talk about the low hv on that ctc5 does this sound like anything to anyone? 24kv at the crt but it jumps around with scene changes as low as 19kv and with that the cathode current to. this set was not right from the beginning with the hv. all the caps in the horiz section was changed and more. i changed probably more caps then i should have. shunt tube is new , rect tube, resistors in the hv adjust string checked good, resistor at the 6dq5 was changed. the crt bias has to be all the way counter because if i raise it just a touch the whole screen turns to blurr and the hv takes a huge dive, any ideas befor i go ahead and look at something that will get me nowhere,lol,lol....:smoke: :D

Sounds like a bad brightness control (or that bias pot you mentioned) to me, the blooming is caused by excessive current draw so if the screen brightness is all over the map that's where I'd start.

What's the model number??

i think its stamped 3129 or 28 i think its 1963 with the ctc12 clone. its the one on this page on the left.

If it's a CTC-12 clone then you will not have the same problem with the blanker tube bias effecting the HV production, that did not happen until the CTC-15. It was a backup to runaway HV if the shunt tube failed.

If it has a 1.5 meg resistor from the control grid of the HOT to the term TT on the chroma board, then you have the blanker tube bias issue.

the 12 schematic shows the same 390k resistor off pin 2 of the blanker tube just as the 15 and 16.

I give up

Ok first forget the clone crap, thats something the super elite do so they have spare parts.

Whats the model number, its going to be something like 528.555555 and it will be on the back.

It may not be a clone at all, it may be a spinoff...how about that?

We need to start with the right model number and schematic and stop telling the tv what it is.

ok the chassis dont have a number on it but could use this number from the sams which is this chassis, 528.61110 hope this helps. and as far as this bias problem i had read a thread here on karma about this resistor from pin 2 of the blanker tube to ground and yes it was said that it started with the 15 chassis but no one knew if possibly it went for the 12 unless the sams was looked at for the 12 and it shows just that resistor in the very spot from the 12 to 16 chassis and there is no 1.5 meg resistor that i found on the 12.

Look very close at the boards, most of the time sears has a little metal tag soldered into the board facing back with the number stamped into it. It looks like a little flat capacitor or something.

ok ill have to get the chassis out and find this number. i was just fishing for maybe something i could have looked for as a simple fix without pulling the chassis.

You dont have to pull the chassis out. Its sticking up out pf the board facing back at you

Im working on getting our dearest timmy to get me a verified model number so I can get the correct sams and post a photo of the area of interest.
I went through a bit of trouble to compile a fairly complete set of sams and its ridiculous to be guessing what resistors it may have and what it may be a clone of. It takes me fairly little effort to grab the correct schematic and scan it.
We already left poor davewm in the oven to long on this one getting sidetracked on what might be

ok dan heres the chassis number 528. 61115 there was a paper tag on the back. i also checked the 390k resistor from the grid of the blanker tube to ground and its 248k its down from what it should be, dont know if this is a factor.

Very good, do you have a copy of 655-2?

yes that is the very folder i have 655-2:D:D

i dont know what this means but bwhen i raise the bias the rect tube filiment dims and the whole screen goes blurry and the hv drops way down.:no:

Ok I will look when I get home.

You are overloading the HV or there is lack of HV capacity. What is the screen voltage on the HOT and what should it be?

Hmm... Gassy CRT? I never had that symptom. Be interesting to find out what it's about. :yes:

screen volts on the hot ill need alittle help there where to measure but the rgb screen drives are to be 620-680 volts im getting around 600volts bg drives are to be 290v im getting 250-280 volts there. i also pulled the hot and measured the cap volts and thats 415v. horiz tube 6fq7 pin 6 is 280 volts. focus volts are 4500kv.

No No. the screen voltage on the horizontal output tube. Its usually around 190v. Its usually on the right side of the tube on the sams, opposite the grid which should be around -45v.

stromberg6; this is a fairly common problem on these old color sets. If there is excessive drive to the horizontal output tube or a bad capacitor, even a defective focus control causing the HV to run inefficiently it wont be able to keep up.
Kinda like if a car has a restricted exhaust it falls on its face when trying to climb a hill.
These can be difficult problems to diagnose because its half way working.

Some of the confusion with this thread is a problem thats related to the ctc16 chassis only. On the 16 there is a very thin trace on the edge of the board that fails and causes excessive drive to the output and results in lack of capacity.

ill try to get to those terminals the sams shows -50v and the other 140v. i did check cathode current its at 200ma and the hot is not red plating. ill check those voltages.

ok the hot screen volts sams shows -50v and i get -55.9v and the other sams shows 140v i get 140v. i had changed all the red caps in and around the horiz and many more.

55 is kinda high. I bet once its fixed it will be -50 @220ma and will work right. Yes 5 volts can make that much of a difference. Hang out till I can get home and look at the sams.

i checked these voltages with the set running normal i just put 2 wires in the socket and put the tube back in and waited about a minute then i checked.

Thanks for the explanation. So many things to go screwy in a horizontal output system that are related. Saving the comments for future reference. Thanks! :yes:

Yea exactly. Dont mention gassy crt to timmy or he will be at the local pharmacy looking for a fix.
Lets start by verifying the HV system has enough capacity.

Ok lets fix this thing....
The first thing I will say is the 390k resistor has nothing to do with it on this set. Its not even tied together like that. The thing calls for 200ma, if thats what you have and the screen is 140v I would wonder if you got the bias and the screens cranked up way to high. Check the HV reg current (it has a jumper) and see if you are getting the 1ma with a dark screen.
http://boxcarcabin.com/timmyss.jpg

ok, the crt bias is down ccw all the way the R G B drives are not even a quarter up they are very low, and the G B drives as well are really low. because i know if they are to high then sometimes you get the lines running across the screen like i have now faint but i see them and they each are a color.there are only 2 sets of lines running left to right and fades toward the middle. could you tell me where or what to break to check this hv reg current with the meter? would this be under the chassis or could i get to checking it behind the 6bk4. as far as a gassy crt i have looked in the dark for the dreaded glow of death in the neck and never seen any. as far as the crt testing, on the bk440 tester at 5v after a minute the needle bearly makes it close to the 200 mark which 200 reading or more is good. at 6.3v the needle just makes it over the 200 mark. at the color setting next to 6.3v it may be 7v i dont know it shows very good so i really dont know if the 6.3 reading would infact be good or if the crt is tired well then it is what it is if everything else checks out ok. the jumper in the sams for hv reg current is that jumper closed or is it opened all the time? the reason i ask is that jumper if i remember correctly was under the chassis and i think it was closed by means of a component where on the tie strap one leg was long and was tied together that way and i may have opened it thinking it was not to be closed and that it was open to put a meter across.should this spot be closed? i will look under to see if i had left it opened or closed. because i remember open or closed the set worked. ok 1ma bright down.:smoke:

IF for some reason the jumper was removed and left off, then you will have NO hv regulation, and you may have too high HV since the idea is the shunt tube should conduct at all times (bright and dark screen). How much current it shunts depends on the HV pot setting AND the overall load on the HV system.

hv is all over with scene changes, clearly hv cant keep up with demand for whatever reason so far.

I am not sure what you mean by "can't keep up" but if you mean the HV is not regulated then then the reason is:

1) HV shunt is not operating correctly (a missing jumper would for sure do this as an example)

2) there is not enough HV in reserve (so the shunt has nothing left to shunt, and the HV drops) this can be a weak tube or other problem in the HV system.

3) CRT load too high from incorrect setup or defect in circuit or bad CRT.


Answer the following please (in order)

What is the HV (in kV) with the shunt tube cap off and the brightness all the way down? Make sure the tube cap is not near anything as it will arc.

replace the shunt tube What is the HV now(in kV)?
brightness up
brightness down

with brightness down does the HV adjustment pot have any effect on the kV?


Its important to answer the all the above questions prefer in that order asked to try and figure out whats going on. It would help if you would quote this and answer each question.

i have done this in the beginning and the fly was said to be ok so the reg tube cap off was around 30kv alot of hiss. cap back on 24kv with the hv adjust at max if i turn it down it will lower the hv. bright up or down the hv adjust does work but to get just the 24kv it has to be maxed.

well the jumper was closed so i broke it put a meter in and im getting 5ma and hissing in the cage and sometimes an arc at the crt neck with the brightness not all the way down, the ma goes up if the bright is all the way down. ok im lost . i forgot to mention with bright up i get 1.2ma- 5.3ma it jumps from both readings.

That does not sound right. the shunt should be around .5ma on full raster, too about 1.5ma full dark. I suspect your are not reading something right or your meter is not working correctly if you are seeing 5ma

you need to put the HV meter on the CRT, put the current meter in the jumper and watch the HV vs Shunt tube current as you adj the brightness on a raster.

Set the HV pot for 24kv then adj the bright up and down note the shunt current, if it goes up as the crt goes dark and goes down as the crt brightness increases, then the shunt is working as it should.

If the above is correct (shunt working as it should) then you need to go back and recheck the HV setup, starting with the cathode current dip on the eff coil.

when you get all that sorted out and have the correct meter readings (.5-1.5ma shunt). Then you can restart the trouble shooting. One other thing, assuming the HV is ok is the focus voltage can cause what looks like blooming including complete darkness on the CRT. The pin and or the socket at the CRT sometimes fails from corrosion.

oh I would recommend an analog meter if you are not using one. Something like a simpson 260. I don't like to read current readings that move quickly with DMM.

also try a new HV rectifier tube.

well i did use a fluke digital meter and i do trust it but lowering the brightness is causing arcing and the ma does raise up the lower i put the brightness. so ok ill follow the above again. and i did have the meter in the ma setting. all i can do is leave the hv adjustment where it is now which is at max 24kv is all i can get. as far as the blooming with the hv probe in place if i just move the crt bias a touch it blooms and the hv drops dramatically.

where exactly is the arcing? you really want to avoid that.

I cant see enough of the schematic, but need to know where R135 goes.

some sets tie in the video signal from the video out tube into grid of the shunt. This is done for more rapid adjustment of HV.

Make sure C99 is not bad if you have HV reguation problems.