Motorola ts907 low hv - Page 3 - Videokarma.org TV - Video

timmy · #31 08-12-2022, 10:17 AM

Chassis on off switch jumped on the bench no tuner no hv hot caps off no convergence none of this is plugged into the chassis. Best way I can define unloaded. I checked the voltage on the b+ line no run away voltage I had new caps that seem to be bad 2 more caps seem to fix the low b+ I had.

Yamamaya42 · #32 08-12-2022, 10:37 AM

The only TRUE way to insure that it's really unloaded is to unhook one side of the choak (L54?), that will make certain that there is no slight draw anyplace, but there is most likely no real reason to do so, it's rather normal for those diodes to get a bit warm under normal operation.

timmy · #33 08-12-2022, 01:44 PM

2 new old stock tubes for video IF both don’t even read on the tester I still have low hv I don’t think these 2 tubes have anything to do with hv. If I turn the horizontal frequency which is also the horizontal hold in about 5 turns the screen fills and I get good hv but the slug is halfway out of the coil not sure that is correct. I’m lost at this point.

Yamamaya42 · #34 08-12-2022, 02:28 PM

If you have to back it that far out, there is clearly a problem with the horizontal oscillator/AFC , this can include the phasing det and feedback loop ( winding on FBT), SOMETHING is causing it to be way off frequency.

Yamamaya42 · #35 08-12-2022, 02:38 PM

If you have a good digital o-scope, it may be a good time to see what your horizontal frequency really is right now.

timmy · #36 08-12-2022, 02:44 PM

No don’t have a scope. The flyback is new I put that in and are you talking about the chroma phase detect with the 6al5 tube. And all the caps were replaced and every resistor around the horizontal oscillator was perfect if only I could find a possible bad resistor.

Yamamaya42 · #37 08-12-2022, 03:10 PM

Quote:

Originally Posted by timmy

No don’t have a scope. The flyback is new I put that in and are you talking about the chroma phase detect with the 6al5 tube. And all the caps were replaced and every resistor around the horizontal oscillator was perfect if only I could find a possible bad resistor.

I'm not sure how it's done in this set exactly but the horizontal oscillator is norm always phase locked, look for telltale shark fin waveform on the schematic for the area, you are in a level of complexity now that w/o a oscilloscope you are basically working with your hands tied and one eye shut, you really need to get one to track down problems such as this, they are that complex.

timmy · #38 08-12-2022, 05:14 PM

One thought I had was one of the 3 caps in the yoke may be bad I can check NF but not PF so I’m not sure and there are 2 560 mmf 2.5 kv ceramic disk caps on the horizontal side of the yoke.

zeno · #39 08-12-2022, 08:03 PM

Quote:

Originally Posted by timmy

2 new old stock tubes for video IF both don’t even read on the tester I still have low hv I don’t think these 2 tubes have anything to do with hv. If I turn the horizontal frequency which is also the horizontal hold in about 5 turns the screen fills and I get good hv but the slug is halfway out of the coil not sure that is correct. I’m lost at this point.

Keep it painless first. Change hoz osc tube ( 6BL8 ? ) first.
If slug is way out but HV OK the hoz osc is way off the norm. Recheck caps
& VALUES used. In theory at this point the sweep is giving full width & HV
Try hooking up a source & look for clues. Hoz AFC can be defeated by grounding it out at the right point & will give a "floating" pix. I dont
have schematic so cant say exactly where. Never seen H AFC or the feedback from the FBT cause this prob. BUT ??

BTW if this set uses 6BL8's or 8BL8's just swap them out to test.
It was Motos 6GH8 but a better tube.

73 Zeno

LFOD !

damen · #40 08-12-2022, 10:56 PM

Horizontal drive circuit

timmy · #41 08-13-2022, 06:06 AM

Already swapped tubes no difference at all and every component within the horizontal oscillator circuit was either changed or checked but ceramic disc caps certain ones I cannot check. Discs are reliable but do go bad.

timmy · #42 08-13-2022, 08:41 AM

How much hv should be present at the anode without crt and yoke in circuit.

old_tv_nut · #43 08-13-2022, 10:37 AM

Quote:

Originally Posted by timmy

How much hv should be present at the anode without crt and yoke in circuit.

No telling what the answer is without the yoke in circuit. It is a vital part of generating the high voltage.

timmy · #44 08-13-2022, 10:43 AM

So if I plug in the yoke for hv testing but not the crt it should generate the proper hv long as all is good I know the crt acts like a capacitor but will it generate full hv without the capacitance of the crt. Chassis on the bench and these motorolas are different and I don’t have the pin out for testing on top of chassis at lots of test points.

Yamamaya42 · #45 08-13-2022, 11:04 AM

Quote:

Originally Posted by old_tv_nut

No telling what the answer is without the yoke in circuit. It is a vital part of generating the high voltage.

Exactly!

It's all part of the tuned circuit mentioned before, a big feedback loop, I kinda think they made it that way to protect the CRT if something were to fail, if the horz sweep was not right, the HV would shut down and protect the face of the tube from burn.