Motorola ts907 low hv

[Yamamaya42]

Originally Posted by timmy

So would using a 10% make that much difference in the oscillator circuit compared to a 5%.

The lower % part you can get, IE 5% 2% 1% and so on, the more stable it will be and less prone to drift with temperature change and age, and so on, you buy a 100 ohm resistor at 10% rating, expect it to BE within 10% of 100 ohms and stay there, 5% 2% 1% respectively.

[Yamamaya42]

when needed, I replace the carbon composite resistors with metal film 1% types.

[timmy]

The schematic shows only the .0039 400v but no % for that cap so how am I to know what was in there. The horizontal.

[Yamamaya42]

Originally Posted by timmy

The schematic shows only the .0039 400v but no % for that cap so how am I to know what was in there. The horizontal.

It normally has it listed on the part, if it has no listing, a general rule of thumb is that it's a 20% part, unless otherwise indicated, and as always in these cases, it always helps stability to put in a higher tolerance part than you remove, because back when it was made it was a cost issue, putting in 10-5% or more parts was costly, but now, those parts are very cheap and effective.

[timmy]

Well now I look closer and the 2- 0068 and 1- 0039 are all 10% and that’s what I put in the print was small.

[timmy]

I read an article about AGC that the agc is for antenna connections but it’s somewhat not needed for a cable or any other video source so I don’t know if the agc is not working will it still knock out the video and sound from another source such as vcr cable line dvd.

[Electronic M]

Originally Posted by timmy

I read an article about AGC that the agc is for antenna connections but it’s somewhat not needed for a cable or any other video source so I don’t know if the agc is not working will it still knock out the video and sound from another source such as vcr cable line dvd.

It absolutely will take out RF from a VCR or DVD player I've seen it happen on my own sets more than once.

The amp bias is controlled by the AGC circuit. If AGC is defective you can get absolutely no reception like the IF tubes are removed all the way to problems like signal overload and red plating IF tubes.

[timmy]

Ok I’m at it again the search continues for a cause for this horz oscillator agc problem I have yet to find anything obvious resistor or tube or anything else for that matter.

[timmy]

I don’t understand exactly if the 2 couplets or even one was bad if it would effect the horizontal drive because the 2 resistors within the couplet are 94k and 56k in series should be 150k it measures 114 and 115 k but the cap inside shows it should be .002 and my cap checker measures 3 times above the marked rating so I’m not sure at all if this would effect the horizontal drive along with the agc. Correction the 2 resistors do check ok at 165k and 170k so not so high on to the next.

[timmy]

One crazy thing after another this set is unreal it’s cursed. So now whatever was going on with horizontal oscillator it finally died and at the same time the 190 v source is dropping down to 38v and the 6hs8 is red plating. And yet again went over resistors and double checked the new caps I put in and nothing I can find. I hope the new flyback I put in is not defective.

[nasadowsk]

Get an oscilloscope, already

[Username1]

Well, Good. A dead ocs. is better than one that only works partly. Ok, No Scope, Go find
an amplifier, make probes, couple the input of the amp through a cap. to protect it.
Horiz Osc. is 15khz, take your amp and put it on the Horiz Osc. of a tube tv that works, See
if it delivers sound, and does not kill the osc. Then you can see if your tv from hell has
any osc. action at all. You might have to use a coupling cap, and big resistor, 50K?
so as not to load the test circuit with the amp input. Be aware of that...

Also Remove the plate caps from the H. Output tubes and focus on fixing the osc. And
only focus on fixing the osc. Now that I think about it, you should forget about the tuner,
and other stuff, and focus on fixing the Osc. Use Voltage checks, on the Osc. tube & the
AFC. tube. Use the amp to see if you can hear the osc. Test the sound against another
tube tv, if it sounds faster, or slower, etc.

When the osc. is dead, what happens to the -45V on G1's of the H. Output tube?

Also with this tv working some time, and not others, working in the cabinet, and then not
have you thought there might be some intermittent bad connection? Have you tried
whapping the chassis really good a bunch while it's on to see if symptoms change??

I mean whapping it like Onslow from Keeping Up Appearances......
Anything less is not considered a whap.....


.

[timmy]

A scope would help but it will tell you a tube is bad or resistor or flyback or capacitor or horizontal coil all of which i ruled out except the new flyback I put in. The ohms on the original flyback is different then the new one I won’t say drastic but different.

[Yamamaya42]

Notice pin 8 of V6 on the 6HS8, it gets power from 640v boost via R92, if the horizontal oscillator is NOT working, then this voltage is obviously not there for the plate to use, making the tube NOT happy, it will try to get power from someplace else, like the grids, this can overload and damage the tube.

From what I understand, V6 is not needed in the set for horizontal oscillation to take place, can be removed while you debug the horizontal oscillator circuit, it IS needed to sync it to incoming video however.

And as been stated many times by many here, an oscilloscope, even a crappy $35 one, would be a great aid to you at this point.

[timmy]

What if the ohms on the flyback were out to a degree would this prevent the oscillator from running. With the 6hs8 out the 190 rail is dropping bad down to 35 v. I think it’s obvious that whatever the problem was has now disabled the oscillator for good which is a good thing maybe now I can somehow track it down so now it’s a dead short probably between a resistor otherwise it would burn the fuse wire.