Motorola VT-71 K Chassis Restoration Issue

[kvflyer]

Chris, I will send you some diodes. I checked them with the diode function of my Fluke meter and they seem to be OK. They are new, probably new manufacture. I have had them for a while. Hope this fixes your set.

[timmy]

I did have an unusual problem with one of my vt71 and after putting the new diode in it turned out that someone didled with the alignment screws at the head of the chassis IIRC the 4h or 4j has those adjustments but the ts18 don’t if the diode don’t work and everything else is good to go then check the schematic for channel 3 slug on the chassis it didn’t take much to get it working. Just another thought on these sets. Those germanium diodes should check under 3 and indicated good.

[Chris K]

Originally Posted by kvflyer

Chris, I will send you some diodes. I checked them with the diode function of my Fluke meter and they seem to be OK. They are new, probably new manufacture. I have had them for a while. Hope this fixes your set.

Can't thank you enough!

[mrjukebox160]

https://www.ntepartsdirect.com/ENG/P...hoCeeIQAvD_BwE

[Chris K]

Originally Posted by kvflyer

Chris, I will send you some diodes. I checked them with the diode function of my Fluke meter and they seem to be OK. They are new, probably new manufacture. I have had them for a while. Hope this fixes your set.

I do have some 1N4148 diodes and put one in...still no change...tried both channel 3 and channel 4 signal output.

[timmy]

Originally Posted by Chris K

I do have some 1N4148 diodes and put one in...still no change...tried both channel 3 and channel 4 signal output.

Get any sound ? Are all the tubes good?

[Chris K]

Originally Posted by timmy

Get any sound ? Are all the tubes good?

All the tubes tested good on a Seco 107. Yes I get sound that responds to volume changes specific to the channel I'm feeding through so if I'm feeding the crosshatch into channel 3 and I flip the TV tuner to channel 4, the sound disappears. Mind you, as I posted before, my Leader LCG-396 does not produce an audio tone along with the video pattern but, something is getting through to the audio...a high pitched dirty tone that goes up and down with volume changes and fades in and out if I move the fine tuning. I have moved both the channel 3 and 4 adjustment slugs around a bit but not so far I would lose my frame of reference of their initial position. At most it was half a turn for each in either direction. The audio sound faded in and out when I moved them and then returned them to original position. No picture or a hint of a picture in there. I've also played with the horizontal and vertical hold controls. Still, no image.

[Chris K]

Just for additional info and to be certain I dont have the feed into the TV moronically incorrect, the leads on my coaxial converter are connected to the two terminals on the back of the TV marked "A" which I assume means antenna. There is a third screw terminal marked "G" between them I assume is ground. I do not have anything connected to that.

[timmy]

Yes I remember there is 3 screws and you are using the 75-300 matching transformer with cable screwed on to that. Long as the 3 6ag5 tubes are good and if the diode is good and all else failed I would trace back from pin 2 of the crt and look at what it passes maybe you can pick something up along there and as for the slug yes keep good track where you are when turning them. Those sets are pretty simple I’m sure you will nail it shortly. Don’t remember which tube is the video out but check around that tube. Things that are responsible for video. 6au6 video amp.

[Electronic M]

May want to use a sound capable signal source to check sound circuits are functioning properly.

Also not really important but this set can directly accept 300 or 75ohm antenna hookups. The outer screws are for 300 and IIRC the top screw and center G terminal are used for 75 ohm center and shield respectively. (I may have too and bottom mixed up, check literature before using the 75 ohm direct connection.) Not really that important, but interesting.