Motorola TS18A

[AnthonysTV]

I have a TS18A I am restoring
I have it runing
but there is excessive noise in the video
looks like an Spurious Oscillation in the pix
I have not changed the Selenium Diodes although they apear to be working fine
there is no AC ripple on th efilter capacitors (The Oscillation seems to be much higher freq than 60 hz anyways
I did replace the 37 Ohm Resistor section of the ballast that powers the B+ to the chassis with a 37 ohm resistor 5 watt becuase it was open
the rest of the ballast seems ok
and the filaments seem normal


I will attach a pix later to show you what it looks like
I have changed all of the High Voltage Caps and this restored the pix
but now although the pix locks Horiz and Vertically there is an overlay of noise I cannot track down
but it seems to come from the H osc circuit
I have scoped the video off the sync sep and it looks clean at this point
also the noise seems to be in the raster not the video
Any help anybody can offer is greatly apreciated
The unit is missing the cover to the HV section and was wondering if that could be the cause?
I have jumped in several of the .05 caps and they make no diff in the noise
I have swapped tubes around the sync clipper and the horiz osc and the v osc
are all the same and that makes no difference in the symptom
I have a SAMS for TS18 seems close enough to work with
The pix is bright crisp and in focus
just too much noise over top of it
and if you tune to blank station the noise is there

[John Folsom]

Your missing HV cover is almost certainly the source of your noise. Unlike flyback powered sets, the very high frequency of the RF HV power supply will inject noise into your video IF without the cover in place.

I bet one of our forum members will have a junker chassis with a HV cover...

[Eric H]

I 2nd the cover being the problem.
The CRT itself is also supposed to have a metal (Aluminum) shield around the neck and part of the bell.

[AnthonysTV]

You are right I errected a metal shield between it and the crt and the noise just about dissapeared so that is that ...now i have a linearity issue with the top being stretched and some weak sync
I swapped the sync clipper the H osc and the V out 6SN7 I think (off the top of my head )
The tubes are all the same swapping them around will give me short vert or short horis or weak sync so at least one is weak... I have some picts ...
The first pix is What it looks like with the metal shield i layed in as you see it in the sec pix
the 3rd pix is the noise
without the shield
the thing i was working on it flipped on its side
so it had not occured to me the noise might be the shield untill late in the day just before I got your post..!!! LOL
The CRT realy looks good any advice on sync? weak coupling caps maybe?
or linearity ?? resistor off value on a plate?

[AnthonysTV]

Ok Here is where we are at today
I tried another 6SL7 and the picture did not change
Granted its used from my bin of toys but it gave me the same exact symptom
the bottom of the pix is compressed I can stretch the top right off the screen
I can move the pix up and down it moves freely so it is not a wapred plate in the crt
but when i ge to certain point the wavefome (Sawtooth) gets distorted on the tops its like it hits a wall
I also get a bout 250 V on pin 5 Plate and 185 on Pin 2 Plate
there is over 700V feeding the 2 6.8 M resistors from the focus supply
It seems like the tube may just be weak
but I also notice the compression going in on on pin 4 and 1 of the 6SL7 when you try to expand the pix
I also notice the other side of the 05uf Cap that comes from the Vert OSC Does NOT compress when you push the vert so it is def in the output stage Anybody Dealt with this?
Or Am I on my own?
Im ready to wrap this thing up If i can just get the compression out of the bottom of the pix

[Electronic M]

Have you replaced the mica caps in the deflection stage and checked the resistors? Those can cause all kinds of trouble.

[AnthonysTV]

Thanks for the reply


Are you reffering to the Square ones?
I already change all the black cats
I have jumped over them with other caps
and I dont even see a blip of gain on the lower part of the pix that was not there before jumping it
I did find 2 open 4.7 MEG although this fixed the centering action
did nothing for the gaiin on the output

[Einar72]

You have to REMOVE the Black Cats when you install the new caps, otherwise, they are still leaking between the various stages or to ground. The new caps will restore the DC isolation needed for the various circuits to work together and have the correct waveform and/or output level the design should be delivering...

[AnthonysTV]

The Black Cats have all been replaced
I am Jumping over the Square Caps
and the .05 and the .1uf 600v Caps in the vert osc deflection circuit
the HV circuit has been reworked from one end to the other
I have changed 5 of the HV caps
The HV seems to be there
the problem seems to be in vert deflection circuit
The way i see this is the waveform comes from the tube plate coupled through the HV caps and kicked up to 6000v to the plates in the CRT
the HV side is good IM sure of it
also H DEFLECTION works perfectly
lots of gain!!
IM looking at the low plate voltages on the V OUT 6SL7 tube
the schematic shows 420V and 350 V I show 250 and 185
Yet the volts from the HV section is well over 600V on the volatge divider(the 2 6,8M ) resitors so the power is there the tube is not using it ??????

[Einar72]

Replace ALL caps you still have jumped. You DOUBLE the value when two caps are in parallel. Check the resistors in the vertical circuit very carefully, remove one end before you measure unless it dead-ends by itself to a tube-socket pin. It's a Catch-22 either way you go, heating one end when removing it (or replacing caps) can change the value either temporarily or permanently. If a resistor changes value appreciably when heated, it's probably bad anyway. Measure the voltage up and down the B+ divider as well, if everything else fed after the Vert stage is low as well, that may indicate a problem. It's been 20+ years since I worked on mine and I just can't recall the schematic...

[Electronic M]

Replace ALL original caps with the exception of the Domino looking caps which are mica type (and any other types of PF or MMF rated) in the tuner, IF, and video amp stages.
If you left any original non-ceramic disc type caps in the deflection stages the set will be unstable if it can be made to operate properly at all.

[bandersen]

Beware! Some of those domino caps are actually micamold paper caps in disguise! As I recall, if the first dot is silver, it's paper - black and it's mica.

[AnthonysTV]

After going over this circuit again I have decioded to order 2 12SN7 and 1 6SL7
NEW and replace them and then see where I stand
I came to this conclusion becuase I swapped the SYNC sep 12sn7 with the HORIZ OSC 12SN7 and could not get the HORIZ to go Full width
so I am going to replace the Vert OSC 12sn7 and the SYNC SEP 12SN7 and the Vert OUT 6SL7
then if it dont work I am going to SHOOT IT !


I did find a 10Mohm Resitor open off of pin 1 of the 6sl7
after cutting it out and installing a new one
NO CHANGE! GO FIGURE!

[AnthonysTV]

Found a 22 MEG Resistor from the plate of the V out to the Grid of the Second section of the V out driving the lower half
completely open
22 MEG
Now I have a full pix
YAY!!!!
but now I have a sync issue
I can only sync the pix if the contrast contol is all the way up
if i lower the contrast
it bends the sync
any ideas here?

[tvtimeisfun]

Lets see a picture did you check all your tubes ? if not that would be a good place to start..