Motorola ts907 low hv

[timmy]

It does have a spring it’s tight and the tube is clean. Is it at all possible that the hv could do what is is from a possible heater cathode short in the 6bk4.

[Yamamaya42]

It seems like a short like that could risk smoking R141, and R213, so it's unlikely.
6bk4 pin1 at 380v via R141 (1k) heater z to gnd via R213 (68k) , if shorted, I think something would have to give.

[timmy]

Well maybe this is pulling the b+ down.

[timmy]

Well there is one 450v 80uf cap for the b+ that I’m going to change because I already changed the 160uf caps thinking maybe they were bad but made no difference so I’m going to change that one since even if it checks good it could still be bad don’t know the esr of the cap and maybe it cooked inside from the frequency of the b+ circuit. And after all the cap has a name I never heard of, cheapy.

[timmy]

Changed all power supply caps now all nichicon caps big increase in the b+ but it’s still being pulled down to the point where the horizontal oscillator won’t run then it draws even more and the hot tube again red plates so on the bench this don’t happen but after I put it back in the cabinet and plug everything in this is when it happens so at this point I’ll have to sit on it for now. Baffling to say the least when the oscillator runs I have excellent hv but that’s only when I first plug it in once warm up pull plug put back in no oscillator and big draw. Oh well. The veritcle centering pot after turning more then half then it varies very little I have to think maybe it’s shorted it’s wire wound and has a 385v feed to it or possibly a shorted turn on one of the sections of the verticle output transformer got to think of everything at this point.I guess now I’m going to check voltages on the tubes.

[timmy]

Does a 1n60 diode go partial bad or it’s good or not good. And with the mention of injecting a composite video source does that mean like from a vcr with a .1cap. As for voltages they are there now after changing the damper. Pin 7 of the 6aw8 shows 13v so at test point b is that supposed to be 5 volts to say the diode is good?

[Username1]

Originally Posted by timmy

Changed all power supply caps now all nichicon caps big increase in the b+ but it’s still being pulled down to the point where the horizontal oscillator won’t run then it draws even more and the hot tube again red plates so on the bench this don’t happen but after I put it back in the cabinet and plug everything in this is when it happens so at this point I’ll have to sit on it for now. Baffling to say the least when the oscillator runs I have excellent hv but that’s only when I first plug it in once warm up pull plug put back in no oscillator and big draw. Oh well. The veritcle centering pot after turning more then half then it varies very little I have to think maybe it’s shorted it’s wire wound and has a 385v feed to it or possibly a shorted turn on one of the sections of the verticle output transformer got to think of everything at this point.I guess now I’m going to check voltages on the tubes.

Good Morning:

After reviewing the posts since I was away, All I see of any significance is this
post about Horiz. Output tubes overheating.

You don't need to look anyplace else. If the 6JM6 is so overloaded that the
plates glow red then this is a problem. Max ratings for that tube are 175ma
cathode current, The tv schematic shows 120ma each tube cathode current.
I would assume around 220ma it will begin to overheat, 260ma maybe red
hot plates?? This would be a source for lowered power supply voltages. If
only 1 tube overheats that means only 1 has a problem, Possibly not the
Osc. but you have to figure it out. Cathode current readings for each tube
will show what's up.

6JM6 Specs: https://frank.pocnet.net/sheets/127/6/6JM6.pdf

This tv uses 2 6JM6 tubes in parallel, so 2 nearly identical circuits that should
have the exact same voltages on all the tube pins - This is a place to start.
Also cathode current and screen grid currents are printed on the schematic.
You need to check them and see what's going on there.

-45V on G1's most important voltage to measure. You should check all the
parts in the Horiz Osc, & Output section, All Voltages, & Sorry to say but
at some point the wave shapes at input of 6BL8 & 6JM6's. Be sure there is
no DC component making it's way to the G1's.


I would focus my attention here. If an Osc. sometimes does not start, then
you can be sure it's not running properly when it does start, lower output,
possible misshapen signal to the 6JM6's.


I gotta go, see you later on.... Good Luck....



.

[timmy]

What was happening is I was turning the horizontal hold- oscillator and that’s what was making the oscillator stop or not start so both hot are at -45v I adjusted the coil voltages look good on the oscillator tube but now I’m trying to figure out why I cannot get an image on the screen so I’ll have to figure out a video source to try or the video detect diode may be bad. But I fear that the L6 may have been fooled with because inside looks like it has been turned but I do get something on the screen but can’t make out if it’s a distorted image it changes using the fine tune and it comes close. I still have sound. If L6 was turned from what I see on the screen then it may not be to far out. And b+ voltages are good now since I changed the damper.

[Yamamaya42]

If you do indeed have stable HV, (congrats on that! ) , you should now try what both I and EM has suggested, feed in a composite video signal to Point B, from a VCR or DVD, through a isolation film cap of .01 or so, the level will be lower than the set needs, but you should see something, and be able to get lock, also, removing the 3rd if tube V3 when you try this, don't focus on sound or getting a signal in from the tuner yet, see how it looks with video input, then go froward from there.

[Yamamaya42]

The input at point B is based on this, https://antiqueradio.org/A-V_AdapterForVintageTVs.htm
I used this for reference several times, as when the status of the tuner/ IF is unknown, I have always used video input as a starting point.

[timmy]

Ok it worked out good so now the video amp and output works so now I’m looking at possibly the 1n60 or L6 was touched.

[Yamamaya42]

Good! Very good!
That means everything from that point forward is OK, including color.
Now all back from that point should be looked at, like the resistors in the IF, especially the ones on the cathodes, they love to drift out of tolerance the most for some reason, and yes, sometimes the detector diode does go bad.

[timmy]

You mean the resistors going to ground.

[Yamamaya42]

Yes, realistically, all of them should be checked to see if they are still in tolerance, but I have seen that the lower value ones on the cathodes are the ones that tend to drift the most in sets, this may not be the case here, but I have seen this 85% of the time, and it's always good to check for this, as if resistors are out of tol in the IF, it will make tuning in things nearly impossible.

[timmy]

Ok well I’m off to finding bad resistors hopefully and not the video detect diode which is almost impossible to reach. I was a bit amazed at how decent the picture was. These resistors I should check are off each IF tube ?