No. Look at the frequency. It's 60Hz. You're just seeing noise from the AC line.
Amplitude is pretty big too. What do you have the ground of your scope connected to?



Get that frequency dialed in to more like 45kHz or higher so you can see the horizontal sync pulses.

It should look something like this.
https://www.electronixandmore.com/pr.../tvscope14.jpg

Ground is connected to the chassis. I thought I was seeing AC when I saw that. The 60Hz pulse is what is going into the amp pin 1 from the detector.

No, the chassis is not ground - it's floating. Connect your scope to B-. Same place the negative leads of your electrolytics caps are going.

and make sure you have the TV running on an isolation transformer!

I don't have one...just a Variac but I ordered one so I'll keep away until it's safe!

Yikes! Remember B- connects directly to one side of the AC plug. If you connect that to ground on your scope - POW!

Scope is OK. I did try it (:screwy::screwy::screwy::screwy:), grounding it to B-, but the scope still works ok on my calibration generator. That's my issue with understanding parts of this hobby and being out to lunch with other things. I'm a science guy...a biology professor and researcher, but there are things about electronics where I have no idea what I'm doing. Feel pretty stupid at times working on these things...but I just learned B- connects directly to one side of the AC line!!!!!

You should also check continuity of the ground lead of your scope probe....The positive path can be OK at the same time the ground is open and the probe will still work on the scopes internal calibrator because they share an internal ground, but connect it to a working TV chassis and you'll get hum and weird behavior from the open ground...Ask me how I know!

I used an external frequency generator atom

Tom. Not atom!!!!

I am atomic! Lol. You can edit your posts if you want to there should be an edit button next to quote if you are reading this via a web browser.

It's encouraging that it was an external generator, but you can still get same false reassurance from an external generator if both the generator and scope have 3 prong power cords...Most test equipment that have 3 prong power tie the signal negative/ground to building ground and test equipment plugged into the same outlet can sometimes use that in lieu of the signal cable ground when it goes open.

They are both run off USB cables off non-grounded plug in transformer chargers...thank God

So when are we going to see a nice clear picture on that Motorola.

Just got the isolation transformer yesterday so I’m going to start back up again this weekend!

I give up. It's going back on the shelf again. All thumbs with the oscilloscope. Grounded to B- and the TV plugged into an isolation transformer, I get no signal off pin 5 of the video amp despite getting audio off pin 6. I've tried 4 different tubes, all tested good. I clip on the probe and the auto-read function gives me nothing...no signal. Before anyone wastes their time trying to help me go further with this, I'm going to put it up on the shelf and start working on something else. I wish there were some gurus around Philadelphia who would take it on and get it running for me. Tim and Chuck A. are in Northern NJ but I really don't know of anyone else who would be able to fix this and Chuck keeps his contact information very private as he should. I was so impressed with his take on the business of restoration during the February online meeting. Bob A.'s too! Anyway, thanks to everyone who tried to help this clumsy novice through this. Sorry if I frustrated you.

If you ever get back into working on the set, you always have the option of trying to direct feed video into the grid of the 6AU6, far side of point D on the SAMS, making very sure your video source is protected and isolated, ( TV on isolation transformer, video coupled via capacitor), according to the service manual, signal level out of video detector is 1.8v PtP, standard composite video level should be close enough to this to see SOMETHING W/O any amplification.

Thank you so much...yes I will try that. At the least, it will give me a reference as to what can be ruled out. Also, it will be so wonderful to see an actual picture on this!!! A few questions...what value capacitor...should the ground for the composite input be to the chassis or B- and, I have the variac set to 117 volts plugged into the isolation transformer so the setup is IT-Variac-Television. Is that OK? I know it makes sense to me but I trip over so much stuff in this hobby.

Hey Chris I’m up here in ferndale ny upstate probably 2-3 hours from philly if you give up take a road trip.

Well since C31 is a .1, most likely a film capacitor of the same size will work for coupling, but the value is not super critical, .1,.01 should not matter TOO much.

What's important is taking the same safety measures that were in place when the oscilloscope was used, MY guess would be to use chassis gnd, but someone who has worked on the set, and knows it a bit more may know more info on how it's to be done.

I have 6 of those Motorola sets and had one that had audio but no video had my share of problems with those sets. I can get a picture on your set I’m sure. A lot easier then a color set lol….

Thanks Timmy. My guess is you have a good 7JP4 to use? Unfortunately, you're 3 hours away by car. PM me and let's see if we can work something out!

I have a 3fp7 same base as a test tube and a numbers matching with box 7jp4.

Ground for the composite source connects directly to B-. Anything 0.01 and up for the connection between the composite signal and tube grid as Yamamaya42 said.

So what I'm thinking is that the 6AU6 plate is being shorted to something and the screen is acting as the plate to get a signal for the audio. What voltage do you have on the plate and screen (pins 5 and 6)? How about the 6.8K, 4.7K resistors and 20uF cap?

Good luck!

Thanks Bob and I will check those values and post later tonight. Do you want to know voltage on the resistors? They have been replaced already with 5% value resistors. I did that after I started troubleshooting issues from the video amp to the CRT, and the originals were spot on anyway. Timmy has graciously offered to get it going and we've worked out a shipping scenario but I'm willing to give it one more shot before bubble wrap, Styrofoam and a corrugated box!

There are other tests you can do! First, get a .01 to .047 uF film cap (greater than 250 volts) and connect the 6.3 volt filament line to pin 2 of the CRT (point C on Sam's) with it. This should generate a substantial hum bar on the screen.

You could also try connecting the 6.3v through that cap to pin 1 of V6 (video amp) as that should product a really strong hum bar.

enter confused mode---:scratch2:

The heaters are series wired in this set, so which point in it would be a tie reference to give the 6.3v for a hum bar pattern to show on the screen?

Jesus...I have -0.5V on the plate and 180V on the screen. 180V through the whole circuit all the way to the 20uf electrolytic. I'm grounded to B-

250V going into the detector and nothing coming out

First IF amp, 6AG5, I have no voltage on pins 1 and 2...around 100V on 5 and 6.

so, now you have a fault to track down! Congratulations! :D

this seems normal

Like I keep suggesting - do the resistance checks. Should be around 11.5K between pin 6 of the video amp tube and B++ (pin 4 of the ballast tube).

https://www.earlytelevision.org/pdf/..._sams_83-6.pdf

Looking at the schematic, the 20mfd electrolytic that goes to the screen grid on the 6AU6 only has three parts that bring plate voltage to the 6AU6. A 6800 ohm resistor, and two coils. I would bet the 6800 is good as on my set it is a two watt. The small coils could have some corrosion where they connect to the leads. Looks like they are wound on resistors.

Timmy has the VT71 but he has questions as to the chassis designation. It does say TS-4H on the chassis but it's hand written. I've looked at a couple of sites for manufacture date and serial number (including VK), and I think it's a TS-4H but I'm wondering if there are sources in this community who could venture a guess. The chassis was manufactured in June 1948 with a SN#38069. Oh and BTW, I think my work is giving Timmy angina!!!!! Thanks all.

Vt71 4h 4d 4j
 

Is there a way to differentiate between the ts 4j 4h 4d they all use the same ballast but there are slight changes between them is there any concrete tell tale that would identify any differences.

Hey Chris I believe I found the voltage and resistance chart

Great Tim!!! Thanks for trying to undo my mess!!!

Serial # 38069 would be TS-4H. The TS-4H does not use the same ballast as the TS-4J late. It uses the older '303 type

Really wow I have 4h 4j and 4d schematics and from what I see it shows r80 for all 3 look the same. Ok great now we know that this set is infact a 4h thanks bob for that info. The 3 ballasts seem to show the same resistances but I think the ts-18 is different with one less resistor.

Hey Chris the ballast you made is that design for this ts-4h ?