Motorola ts907 low hv

[timmy]

Originally Posted by Yamamaya42

That still does not change that a digital meter will give inaccurate readings in this situation with a active RF circuit, you must use a use a VTVM, or a FET VOM, to get correct readings.

I found that to be true using my other dvm but I use the new one that does give better reading. Well this IF is far from active.

[timmy]

I find it kind of odd that if I pull v3 tube the voltages on the b+ comes up nice and the 4.7k resistor that feeds v3 is a 5 watt and it only calls for 2 watt but this 5 watt resistor i put in gets really hot v1 and v2 don’t do this with the voltage drop I would think that v1&2 are conducting but maybe v3 is not causing the tube to be full on drawing down voltage if this is the case why is v1&2 not pulling voltage down IF signal goes down the line 123 then out to video amp.

[Yamamaya42]

V1,V2,V3 are tuned RF amplifier circuits, and are always active as long as the tubes are inserted and power is on, regardless of if there is any tuned signal or not, it is still active, the only way to render it not active is to remove a tube.

The tuned circuit is comprised of the tube, the adjustable coil, and capacitors primarily, and secondly resistors.
This area is extremely susceptible to external influence, as in anything hooked to any of the pins of the tubes will alter how it is working and change what you are trying to measure, this includes the meter and even the length of the test leads used.

Therefore, do not be fooled by these readings, because they can't be trusted, in this situation.

Known good, 275v source, R54 (4.7K 5w), R53, R52, C27,C28.
Variables, the overall out of aligned state of all 3 amps, any one or more of these can alter voltage readings, hooking a meter to the grids or plates of the amps under test, this will also change the state of them, like adding a resistor to ground, and change the voltage readings.

[timmy]

So how can I use a vcr with a tuner built in to be hooked up to the sets video amp

[bandersen]

Don't digital meters have a 10M input impedance same as a VTVM?

[Yamamaya42]

First you will have to build the video amp, this should be easy, I have made 2 before.
https://www.electronicsforu.com/elec...ideo-amplifier
Suggested parts are.
This includes replacing r5/r2 with trim pots to adjust gain and black level.
Also is suggested a 7805 regulator, for stable 5v power.
https://content.instructables.com/F2...bounds&frame=1

all mouser parts.

637-BC558A
512-BC547B
512-1N4148
531-N6S25T0C103-3030
531-PT6KH502A2020PM
511-L7805CV
594-MAL203851229E3 x2
647-UBX1V010MPL
854-SB404

[Yamamaya42]

here is v1 of the amp i made.

https://imgur.com/xYoNZOY

was unstable w/o the regulator.
thus v2

[Yamamaya42]

Originally Posted by bandersen

Don't digital meters have a 10M input impedance same as a VTVM?

Some, not all.
a high $ fluke or similar type would tend to be more trustworthy in testing an IF than one that's 15-20$.

for example, I did alignments with my Micronta FET Analog Multitester / fluke 77 multimeter, and not the cheap ones I have cause I knew they were not suited for the RF area.

[Electronic M]

Once you've built and installed the video amp connect the composite video output (yellow RCA cable) from your VCR to your amp, and the white audio output cable from your VCR to a point between the audio detector and the volume control through a .1uf 600 cap (you add that cap), power on the VCR and tune it to the channel you want and it should appear on screen.

[timmy]

R22 is an RF trap that is listed as being 200 ohms I get no reading whatsoever do these traps go bad ? And really what happens when they do go bad ?

[Yamamaya42]

41.25mhz trap, (sound modulated carrier), blocked in L6 and tuned by R22, after sound is taken off for process at V3 pin 7, if not working/ faulty, sound may be seen in the screen.

R22 can be tested by resistance check from L6 pin 3 and the junction of C30/C31.

[timmy]

Originally Posted by Yamamaya42

41.25mhz trap, (sound modulated carrier), blocked in L6 and tuned by R22, after sound is taken off for process at V3 pin 7, if not working/ faulty, sound may be seen in the screen.

R22 can be tested by resistance check from L6 pin 3 and the junction of C30/C31.

I tested there and I don’t get anything so I’ll lift L6 leg off to be sure but I don’t think it would show 200 ohms if it’s adjusted to something else.

[timmy]

Lifted one leg off the trap get zero no ohms ready at all.

[Yamamaya42]

If it does not read somewhere from 200-0, you may be able to clean it to get it working.
But you will have to pay close attention to where it's set before you start, get it really soaked in some kind of contact cleaner or isopropyl alcohol, so that the insides get good and soaked, then rotate it back and forth to each extreme several times, making sure it's put back in the original position, this SHOULD bring it back if it's not working.

but if that fails..
https://www.vivatubes.com/vintage-ma...ohm-shaftless/

[Yamamaya42]

Originally Posted by timmy

Lifted one leg off the trap get zero no ohms ready at all.

0 ohms?

This is OK, then, it has been adjusted to it's far extreme.
as long as you get a reading between 200-0, it is good.