Motorola ts907 low hv

[Yamamaya42]

The reason for the bad video is that there is something out of tune between the input from the tuner, to the grid of V2, AGC has nothing to process, and therefore has no reference to set the gain of the circuit , but it is not an AGC fault, as was shown by the override test, the heating of L42 and any HV related issues, if they exist, are a separate issue entirely.


"The difference between v1 and v2 is that v1 8.2 resistor goes to ground the 8.2 don’t go to ground directly on v2. "

since the measurement is not taken from ground reference, but from the main power point, this difference is infinitesimal, very high chance the SAMS is wrong and the 6k reading is correct for both.

[timmy]

Ok so let’s say it’s a sams mistake and leave it at that I already mentioned that the video would pop in clear and then gone so v1 there’s really nothing there except a few resistors and a few coils so I can’t believe that those coils were touched because the video at random would pop in and then be gone again. So what’s really left to check. Perhaps the .001 cap in L4 is bad the coil couldn’t conduct properly if that cap is bad.

[Yamamaya42]

The IF is the most sensitive tuned area of the set, having RC constant circuits, that are going to react to voltage and temperature, and you have no clue as to what was done to it before you got it.

It's not unusual for something that is out of alignment to briefly pass a signal as it starts up while voltages and things are cold, but stop as it gets into normal ranges.
Thus alignment is done when the set is warm.

HELL, all my sets that are able to tune in stuff take 60-90 seconds before the can tune correctly, then they run OK for hours, what you see in the first few moments does not mean anything.

[jr_tech]

Have you cleaned the tube pins? Is the socket ok?

jr

[timmy]

Originally Posted by Yamamaya42

The IF is the most sensitive tuned area of the set, having RC constant circuits, that are going to react to voltage and temperature, and you have no clue as to what was done to it before you got it.

It's not unusual for something that is out of alignment to briefly pass a signal as it starts up while voltages and things are cold, but stop as it gets into normal ranges.
Thus alignment is done when the set is warm.

HELL, all my sets that are able to tune in stuff take 60-90 seconds before the can tune correctly, then they run OK for hours, what you see in the first few moments does not mean anything.

Oh I understand what you’re saying but this is when it was already warmed not just turning on so I don’t know I have new .001 caps maybe I’ll try one in L4 and see what happens. If that don’t work then maybe I’ll disconnect L4 and check resistance and see what comes up.

[timmy]

Originally Posted by jr_tech

Have you cleaned the tube pins? Is the socket ok?

jr

I checked the pins and tightened them a bit move the tube side to side no change

[timmy]

Would an RF fixed 3600uh inductor the same is a peaking inductor 3600uh

[timmy]

I kind of overlooked at L4 that it has 2 .001 caps where L5 only has one the 2 in L4 one is red and the other is regular color ceramic disc the red one may be a mica won’t know til I get up close a personal with it. So now there’s 2 possible reasons for no video.

[Electronic M]

If it's intermittent it could also be one of the tuner inductors has a lead that either isn't soldered or corroded badly enough that it's effectively open and only gets continuity occasionally. Intermittent conditions often spawn in unusual places.

[timmy]

Since mica caps are used a lot in rf circuits it looks like it’s probably a .001 mica cap is on the primary of L4 makes sense to have a perfect signal to send down the IF line.

[Yamamaya42]

The difference between ceramic disc capacitors and mica is easy to spot, a pic of the caps in question would help.

But do remember, if you ARE thinking of replacing the .001 disc capacitors, don't use any old caps, but be sure to get C0G (NP0) type, it will save you from a whole world of pain down the line.

[timmy]

Well I was not going to touch L5 cap seeing it works already and the questionable problem is in v1 L4 hopefully. All I can say at this point is the primary side of L4 has a red cap and the secondary side has a regular color disc cap and it’s so tucked in there tight I can’t even get a picture to show it. So I’ll try the secondary side cap first if it Works then great if not then I may have to take the coil out of the housing that it’s in.

[timmy]

I don’t even have a 1000pf mica I have micas that I can make up a 1000pf but then I have to leave it out of the coil housing don’t know if that’s acceptable or not.

[Yamamaya42]

Before doing anything to L4, you should try what others have suggested, V1 removed, and feed in the tuner subber into pin 7 the same as you did before, through a isolation capacitor, to see if you can get any signal through, you may have to adjust the gain on the subber a bit.

[Yamamaya42]

possible choices.

https://www.mouser.com/ProductDetail...znO8lXZA%3D%3D
https://www.mouser.com/ProductDetail...dco7WMcA%3D%3D


Mica caps are NOT cheap!