Motorola ts907 low hv

[Electronic M]

Originally Posted by zeno

Timmy
At this point I really think you need to invest in a MODERN analyst such
as the Sencore VA48 or VA62. That will give you a stable known source
that was built for your sets era. A scope is nice but an analyst
helps with other projects & do more than trace & show freq.

This is long distance servicing. VERY hard to do. A lot of us that
spent time in the biz fixin 10's of thousands of TV's could spend a
few mns looking , twisting & observing a set & know where to go.
You have stuck it out well & the next one will be easy.

BTW vid det diodes are usually in a can. Often the can has two parts
& if you pull the top half off the diode is there. You can always nip one end
of the diode & hang a new one in on the bottom for test.

73 Zeno
LFOD !

+1 a Sencore analyst or B&K 1077 analyst and a scope are things to have if you own more than 2 vintage TVs that you plan to maintain.
A daily driven tube TV is going to fail every 12 months give or take 6...If you get tricky troubles every 3rd time, the time you save with good equipment will pay for that equipment and it's storage several times over.

[Yamamaya42]

A cheap used VCR is the best choice for setting it up for direct AV input, cause as mentioned, they are still very easy to find, and have good stable tuners and output composite A/V, that Sony portable would not be a good choice cause it would need major adapting to be used, the schematic shown does not list any signal levels, but only the DC voltages at those points.

It should be easy enough to find a VCR, build the video amp, and adapt to A/V input until a future point you have the equipment or can get someone to help repair the IF section.

[timmy]

Using that small tv it wouldn’t take that much adapting it would need to be grounded to the chassis probably a single wire to get the sound and another singly wire to test point B and wire in the power source to the switch and make sure it’s tuned to channel 3 and forget the rest. Mount it on a small board out of the way. The antenna input would be setup on the tv board. Again just another thought.

[Yamamaya42]

Too many unknown factors with that, what is the peak to peak output at that point on that video buffer chip? You need 5v, is it inverted or not inverted?

The Sony schematic gives no clues as what the video signal is, only hints of a 5v vertical blanking pulse at q402.

The idea of this seems much more trouble than it's worth over a VCR.

Cable boxes do sometimes have composite A/V output that can be used for this such a thing, but you also need to input test patterns for convergence, so a VCR'S tuner is more flexible.

[timmy]

Well I do have the complete schematic for this Sony. I figured if it were that easy to get video from a DVD player I thought I could use the IF from that little tv and just input the cable to it and get video and maybe work out any other things after.

[Yamamaya42]

DVD players & VCRs have composite level video output, (positive 1v ptp), however, what that Sony has at that buffer chip is an unknown factor.
By adding that simple video amp listed before to boost it to 5v it should give it what the TV needs.

[timmy]

Originally Posted by Yamamaya42

DVD players & VCRs have composite level video output, (positive 1v ptp), however, what that Sony has at that buffer chip is an unknown factor.
By adding that simple video amp listed before to boost it to 5v it should give it what the TV needs.

So are you saying that using the little amp to boost to 5v and putting the IF from the Sony into it would it work is that what your saying?

[Yamamaya42]

What is unknown about the Sony, is what the peak-to-peak voltage of the video signal out of the buffer chip is, and if it is positive or inverted, chances are that one is positive, one is inverted (11,12) but w/o an oscilloscope to look and see what they are, this is a risk factor that it may or may not work due to the unknown factors of not really knowing what is being put out of the IC, for example, if you knew that it was putting out .5v positive peak-to-peak, then you could build an amp with enough gain to boost it to 5v.

On the other hand, a DVD/VCR always has an output of 1v peak-to-peak, thus you make a amp with a gain of +5, more or less.

[timmy]

Originally Posted by Yamamaya42

What is unknown about the Sony, is what the peak-to-peak voltage of the video signal out of the buffer chip is, and if it is positive or inverted, chances are that one is positive, one is inverted (11,12) but w/o an oscilloscope to look and see what they are, this is a risk factor that it may or may not work due to the unknown factors of not really knowing what is being put out of the IC, for example, if you knew that it was putting out .5v positive peak-to-peak, then you could build an amp with enough gain to boost it to 5v.

On the other hand, a DVD/VCR always has an output of 1v peak-to-peak, thus you make a amp with a gain of +5, more or less.

Ok but I’m looking for the cable input I don’t need vcr or dvd I just want to be able to watch regular tv and I would use the cable box remote change the channel. So in the end I could always try it there’s nothing I have to do to the set to try except try one of those wires or just take it from the 3rd IF and see what happens.

[Electronic M]

I'd just build the little 5V video amp and feed it with an RCA composite cable. That way I could plug a VCR in or any other device I want. If you find a good line level output point on the Sony later if there's an RCA composite video cable coming out of the moto you can plug it into the Sony later.

[timmy]

Here’s the full schematic notice after going along to 2 transistors it shows 5v p-p well it’s not clear enough

[Yamamaya42]

Originally Posted by timmy

Here’s the full schematic notice after going along to 2 transistors it shows 5v p-p well it’s not clear enough

I have the same schematic, that does not look like a video signal there at the collector of Q402, but looks more like a blanking pulse, from q401 or d301, which will only mess up the video out .

[timmy]

Originally Posted by Yamamaya42

I have the same schematic, that does not look like a video signal there at the collector of Q402, but looks more like a blanking pulse, from q401 or d301, which will only mess up the video out .

Then what about taking it directly from v3 ? Although I don’t see any kind of diode

[timmy]

This Motorola has the thermistor is it absolutely needed if it were taken out and jumped would this affect the transformer so many other color sets don’t have this thermistor and they survive. I put higher amp b+ diodes in so they should hold up from a heavy jolt.

[Yamamaya42]

Originally Posted by timmy

This Motorola has the thermistor is it absolutely needed if it were taken out and jumped would this affect the transformer so many other color sets don’t have this thermistor and they survive. I put higher amp b+ diodes in so they should hold up from a heavy jolt.

Normally the thermistor circuit is added in color TV if the auto degaussing is built in, not sure why it's in your set.