mica capacitors

[timmy]

well when the verticle is fixed i will try this and see if those lines are gone. the circuit was for an admiral set with a 7jp4 and not a motorola. so ill try yours. the admiral one was to cut the ground and just run that pin 3 with the cap and resistor to pin 5 of 6sl7.

[timmy]

you say verticle 6sl7 tube , this tube is marked verticle sweep output tube and the 12sn7 is marked as the verticle sweep oscillator tube. i didnt see anything on the 6sl7 as an oscillator just making sure.

[Tom Albrecht]

Even 1/10 watt will be OK, so pretty much any size you have available. Typically one would use a 1/2 watt resistor.

Sorry for giving the 6SL7 the wrong name. It's the vertical output, and that's the one you want to connect the cap to.

[timmy]

ok tom , thanks alot for your time and effort in helping me out with this set.

[Gleb]

Originally Posted by timmy

there is a blanker circuit out there and was wondering if there is one for this motorola or maybe this one would work to get rid of those lines when the brightness is turned up. the circuit i saw was for an admiral set with a 7jp4 crt. its got a 250pf 1 kv cap and a 220k resistor in series from pin 5 of the 6sl7 to pin 3 of the crt. the crt pin 3 goes to ground and this wire should be cut off ground and attached to these 2 components to pin 5 of 6sl7. does this sound right for the motorola ts18 chassis. this setup is said to eliminate those lines with the bright up.

You'd better use a variable resistor of a bigger value, adjust the brightness control to get an acceptable picture, and then turn the variable resistor to eliminate the retrace lines. After that you can measure the value and use a fixed resistor of the closest value. The voltage rating of the capacitor should be at least 1000v.
Blanking intervals in modern video signals often carry some extra information (teletext, copy protection, etc), causing it's visibility on the retrace as bright dotted lines. It may be difficult to supress them completely, causing you to set much deeper blanking.

[bandersen]

There's no need to experiment with values. Motorola added retrace suppression to later revisions of TS-18 chassis as shown in this schematic. Earlier versions had pin 3 grounded. This version has pin 3 going to the junction of a 250pF (C-70) cap and a 220K resistor (R-90). That couples a pulse during the vertical retrace to the grid and blanks the raster.

I got this from Riders volume 4.

[timmy]

ok now i have more problems , i got the caps and i turned the set on to see if i was still where i was when i left it well when i left it i turned the vert size down and shrunk the pic and was able to stop the roll. so i turned it on befor doing the caps and now after leaving it alone doing nothing the vert size just makes it smaller and wont bring it big and i dont know why. i changed one cap at a time and with each cap changed the vert size still didnt work and i did this to make sure i didnt put a defective cap in and is always a possibility . so im done with caps except for the 900, 680, and the 200 mmf. what could this be the size worked when i left it waiting for caps and now it wont stretch the pic top to bottom to see if the caps i put in even helped. the other 3 caps will come tomorrow. what does this sound like ?

[Tom Albrecht]

Well, I would target resistors as the likely cause at this point. On the Sams schematic at ETF (not Bob's above - the numbering is different), I would check the following resistors:

R58, R59 - 2.2 meg
R61, R63 - 6.8 meg
R80, R81 - 2.7 meg
R82, R83 - 2.2 meg

In many of these sets, I find that some or all of the above have drifted to a larger value. Some of these can also affect the focus.

Also, you may have a whisker inside your vertical height control. Try removing it, cleaning up both the inside (remove the back cover) and outside of it, and reinstalling. Or sometimes something as simple as running a toothbrush between the chassis and the terminals of the control will do the trick (if the whiskers are between the chassis and terminals on the outside of the control). You might even be able to see evidence of whiskers by measuring resistances to chassis from the terminals (you may have to disconnect from the circuit to do so).

I presume you've swapped out both of the vertical tubes to make sure they are not the culprits.

[Electronic M]

A common problem on sets is infant mortality....Some parts test fine, but after a short time under rated load fail...Our sets usually have two periods of infant mortality, initial deployment when new, and during/soon after restoration. If you left carbon comp resistors in it, then one or more may have drifted or outright failed since you last ran it. Modern parts usually have a low enough infant mortality rate that you are unlikely to experience it. Another thing to be wary of in electrostatic sets is the tube sockets...They are often ran close to their insulation dielectric ratings in the HV and deflection stages, and thus internal arcing, carbonization (SP?), etc. can form and be hard to detect.

EDIT: Looks like Mr. Albrecht slipped a post in under me.

[timmy]

ok ill check those resistors but chances are i did already. i have tried another pot no difference. maybe you know , should there be around 250 volts dc on the frame of this set to positive of the b+ . i thought this was not right so i had look everywhere for maybe a shorted cap of some kind to the frame ground as there is an isolated ground on this set. i thought maybe this was causing problems. i have tried several tubes.

[Tom Albrecht]

R84 is a soft connection from the circuit common to the chassis. If you measure with a high impedance meter (like most modern meters), the chassis will behave more or less as if it is connected directly to ground in terms of measured voltage. So relative to the B+, you might see something like -250 VDC on the chassis. I would check the resistance from the chassis to the circuit common and see if you get the expected 470K from R84. If the resistance is lower, there is a short somewhere (solder blob, some wire touching, etc.).

Even if you checked those high megohm resistors before, as Tom C points out, they may have suddenly died in recent days. It's actually fairly rare to find those particular resistors still good in these electrostatic sets.

Also, check the voltages on the vertical oscillator and output tubes to see if they match the Sams chart reasonably well. Do you have a scope? If so, check to make sure that both triodes of the vertical output have a nice output waveform on the plates (huge sawtooth at 60 Hz, with opposite phases).

[timmy]

no i dont have a scope. and the resistance from both grounds are something like .530 meg is all i get between the both. the voltages look low where they should be high and others that should be neg 25 i get neg 12.50 so i dont know whats going on with this set.

[Tom Albrecht]

Can you measure the voltages on the tube socket pins for the vertical output tube and compare to Sams? If they are substantially different, tell us what you see, and it may provide a clue to the problem. Note that those voltage should be measured from the circuit common, not the chassis.

[timmy]

ok, will do and ill get back to you tomorrow. ill use the sams schematic voltages.

[timmy]

ok, i checked voltages on per sams, v9 , v11 , v12 ,
v12 6sl7 pin1- neg 1.6 to 1.8 v- pin2 140v- pin3 0 -pin4 -neg.936v pin5- 47.3v- pin6 0 , 7&8 i didnt check.
v11 pin1-neg 12.30v pin2 15v pin3 0 pin4 neg .551 pin5 71.8 pin6 0 7&8 did not check.
v9 pin1neg.7v pin2 17v pin3 0 pin 4neg 1.630v pin5 11.26v pin 6 0 , 7&8 not checked.


it looks like the biggest problem here is v12 vert output pins 2 and 5 measure very low unless i cant use a dvom on these pins. where does pins 2 & 5 get there hi voltages,pin 5 i think comes from the focus circuit and the resistors are fine and i also changed the resistors in that string. does pin 2 get this voltage from oscillations or the hv cap. i am lost at this point,lol,lol... one other thing i still did not change the 900, 680, 200, micas yet.