If by the IF output you mean connection 5 on the IF module (Video-Sync-Chroma), that's where TP C1 is located, so I could clip the lead of the generator onto that point on the top of the chassis.

I have the two capacitors in my cart now and they are the part numbers from the SM and the C202 replacement is N750.

Here is the section of the generator instructions related to injecting the video signal. Maybe it will help identify exactly where it should be connected.

I'm assuming you have the set back up and running, and the jail bars are visible.

Try this:

1) Gently disconnect the IF Input cable from the tuner to the chassis. At the chassis it is very similar to an RCA connector. Power up, jail bars still visible? Power down.

2) Remove the IF Module. Power up, jail bars still visible? Power down. Leave the IF Module out.

3) Drive the video stages with one of your generators. Most generators will block a small amount of DC but to be safe, connect the 50 Ohm video output through a .1 uf or so capacitor to block the DC. Connect to the C1 test point you have identified. Shield to a nearby chassis ground. Power up, adjust video level from the generator, try different patterns, what do you see?

Safety-- This is a transformer based set, so you should be reasonably safe using grounded test equipment, unless something is seriously wrong.

I appreciate my Sencore PR57 everytime I use it:yes:

Set isn't together yet. I'm waiting for the C202 and 204 replacements. Am also going over everything under the chassis to make sure I didn't disturb something and create a short. Once that is done, it goes back together on Monday or Tuesday, depending on delivery of parts.

The instructions with the Hickok says to ground the generator by connecting black lead to chassis. I wish it had more details on that since I had assumed the black lead went with the red lead which is the trigger out for my scope. That and I'm sure it needs another adapter of sorts as my scope's trigger input is a 1Mohm 20pf BNC. But that's another day's battle.

Tried to pull C202 and 204 by heating up the bucket and pulling the leads out, but that only worked on one lead that was alone in the bucket. All the other leads were in one with multiple leads and I couldn't seem to get it hot enough as they all acted as heatsinks. So I cut the other leads.

I tested them and the 68pf tested as 56pf with an ESR of 21kohms and the .0047 tested as .0038 with an ESR of 411ohms. I tested them for value at 100Hz and ESR at 100kHz. That is correct? When the new ones arrive, I'll check them the same way.

Yeah, that ESR sounds way too high at 100kHz.

It's worth noting that you would have to have a fairly expensive and fancy tester to get a really accurate reading on something as low as 68pf, but I think it's safe to say that those are bad ~kohms, or 411ohms.

You should test the new ones before you put them in to see if your meter might be misleading you for some reason. Cheaper testers might not be able handle really small value caps. If the new caps also test crazy high ESR, then you know something's up

It was kohms. I did read that lower values and higher voltage ceramics don't measure will with basic ESR testers. I will definitely test the new ones and compare the reads to see if my tester isn't up to the task.

I do have a question you might be able to answer. The chassis is hand built, so when they are building them is there instructions on lead length for certain components, or is the length determined by fit and clearance? The reason I ask is the 68pf was pretty much bottomed out on the pad, so I had to clip it as high up toward the body as possible, leaving short stubs sticking out of the buckets. I plan on sitting the new leads into the bucket and using a small tip to reach the inside of the bucket and then flowing more solder into it. Since this cap had very short leads, do I need to do the same or can they be longer? I wasn't sure if they were short based on design or just that the cap fit better lower down. I know, odd question.

That would be determined by best practices at the time. Lead length could absolutely make a difference in specific situations, but I'm not familiar enough with the make of your TV in general to know all of the spots that would be sensitive. I would assume that anything involved in a trimmer circuit would be important as they could pick up interference.

The older guys in the Solid State forum will be able to tell you a lot better as they know the 70s US make stuff really well and I don't.

Manufacturing practice was to make a prototype agreed on by the engineering and production departments, and install it on the assembly line for physical comparison. The prototypes could range from individual modules to complete chassis in a plastic housing to illustrate it completely finished including things like lead dress of the wiring. No deviation was allowed whether it was actually important or not.

So in some cases, lead length was just a matter of neatness, and in others it had an effect on performance. Wiring harness lead dress could be important if it affected issues like jail bars, or it could just be an issue of neatness or easy order of assembly. And of course there were also consideration of tie-downs for long leads and heavy components to prevent breakage during vibration and shipping tests.

You can see these kind of considerations in the old Heathkit assembly manuals, where you are told to connect this or that but not solder it yet because something else will be added in the net step.

Good information. I will try to keep the leads of the 2 replacement caps as close to original lead length as possible. They are in the Horizontal Blanking circuit tied to the diode and also to the setup side of the setup switch. As you may remember, I can't get the setup mode to produce anything but a faint blue line at full and nothing from the other guns at full. I have to adjust with a greyscale ramp pattern and with the setup in normal mode, same max rotation of the G2s brings up a super bright raster, so I know the controls work.

+1 old_tv_nut, duplicate what was there as much as possible.

Stay on the track you are working, finish, and then move forward.

and I remember. Alternative Ways of Adjusting G2, is only 4 threads away. IMO you never fully explored that issue. ElectronicM gave you excellent advice and recommended looking at the voltages associated with the CRT. You looked at a lot of things but it appears you never returned to that. The CRT and Video Outputs are supplied by the 3 boost sources that are Horiz derived. The TV needs to produce 3 pictures, a red one, a blue one, and a green one, of equal intensity dark to light (gray scale -tracking) on top of each other (convergence). Thats why in the immortal words of Zeno, start with a good black and white picture.

I concede that a really tired/weak CRT might not be capable of producing one or more RGB setup lines but from the brief pictures you have posted, your CRT actually looks really good. Did you ever test the CRT?

ElectronicM has also chimed in with soldering advice, I think in more than one of your threads. Do you think you have enough wattage in your soldering devices? You should be able to pull component leads from the solder cones (pots), and re-insert leads to the depth of the cone. I use a Weller gun. If I did this more often, I would use the higher wattage iron that he uses.

I figured that since I'm replacing the C202 and 204, and they are connected to the setup side of the setup switch, it might help with that issue.

In the past, I tested all those voltages and they all were good. Since I haven't had any new issues that might point there, I haven't checked them again, but I can once it's back together.

The CRT is good. I've tested it a couple of times and each time it tests good and strong on all 3 guns.

My iron is 200W, but I might need to put the largest chisel tip on it for maximum heat transfer. Should I be concentrating the heat on the tip of the bucket, or the side? I think the side give more contact surface, now that I'm thinking about it.

I think for the setup switch issue, I might bypass it for testing. I've cleaned it a number of times, but it might be extremely dirty, or damaged. What I want to do is put it in setup and jumper the connections on the back side of the switch. That should determine if the switch is good or bad. The other area I need to look into is are the Chroma Gain Taps. I accidentally found out that while in setup I couldn't get a red line adjusting the G2 control, but I could by pulling the lead off the tap. I realized I had the tap on low when it should have been on Hi, so I pulled it to move it and a red line appeared. When I moved to Hi, the line went away. I tested the resistors in that network, but nothing stood out. I tried deciphering the schematic for that section, but I'm not sure what I was seeing.

I figured that since I'm replacing the C202 and 204, and they are connected to the setup side of the setup switch, it might help with that issue.

In the past, I tested all those voltages and they all were good. Since I haven't had any new issues that might point there, I haven't checked them again, but I can once it's back together.

The CRT is good. I've tested it a couple of times and each time it tests good and strong on all 3 guns.

My iron is 200W, but I might need to put the largest chisel tip on it for maximum heat transfer. Should I be concentrating the heat on the tip of the bucket, or the side? I think the side give more contact surface, now that I'm thinking about it.

I think for the setup switch issue, I might bypass it for testing. I've cleaned it a number of times, but it might be extremely dirty, or damaged. What I want to do is put it in setup and jumper the connections on the back side of the switch. That should determine if the switch is good or bad. The other area I need to look into is are the Chroma Gain Taps. I accidentally found out that while in setup I couldn't get a red line adjusting the G2 control, but I could by pulling the lead off the tap. I realized I had the tap on low when it should have been on Hi, so I pulled it to move it and a red line appeared. When I moved to Hi, the line went away. I tested the resistors in that network, but nothing stood out. I tried deciphering the schematic for that section, but I'm not sure what I was seeing.

I have tested all the resistors in the setup circuit from the switch to the convergence board. So don't know enough about reading schematics to understand why setup connects the video outputs to the inductor coils on the convergence board. I'm pretty sure when you flip the switch it's main function is to disconnect all the video amps and collapse the vertical.

I've also tested all the resistors in the gain taps and they are withing tolerances. So unless I'm missing something, my inability to bring up lines in setup looks to be either in the switch itself, or the connection of the outputs to the convergence board.

The side of the solder pot terminals usually works best. I recommend choosing the biggest tip for best thermal mass and conduction to the terminal.

Got the biggest chisel tip ready to go. Replacement caps will be here tomorrow, so I should be able to get them installed, check over the entire chassis for anything I might have disturbed in my work and all new transistors for proper orientation. Then it's time to reinstall the chassis and fire it up. Fingers crossed.

I managed to get the other 3 leads from the cut capacitors out. It seems a bigger tip and holding in on the side of the solder bucket helped, but I think extra pulling also helped. I'm attaching a pic of one of the leads I got out. I'm not sure what that stuff is, but it is hard and was on the three leads I couldn't get out, but not on the one I did get out. So maybe that's why only one lead came out.

Also note the crud on the lead. Is that old flux? I'm assuming the discolored lead is only from the removal and it wasn't that way in the solder. :lmao:

So when I work to install the new capacitor leads, should I put a drop of flux in the bucket first? I figure I'll let it heat up for about 20 to 30 seconds before trying to insert the lead.

Oh, and with the amount of time it takes to head up the bucket to melt the solder, is the heat transfer to other components like resistors bad? They get pretty warm/hot during the process. Should I clip a heatsink to the leads of the other components sharing the bucket?

Question about transistors. I've noticed that several transistors noted in the SM, each with different Zenith part numbers, have PNs for other manufactures, but those part numbers are all identical. Does this mean when you buy from another manufacturer you're getting replacements that aren't the exact specs, but close enough to work? For instance, transistors 695, 888, 931 and 447 replacements are all ECG123A or NTE123AP. The same happens will all other manufacturer's replacements (RCA RT102).

So the thing about transistors is that they have a lot of characteristics, but which ones make a difference entirely depends on your application.

When a manufacturer is deciding which transistor to use in which spot, they have an entirely different set of considerations than a general repair-person does, or in fact you or I have many years later.

Usually, they are working with a bunch of boxes of parts they buy in bulk, and that is all down to contracts and maybe just what's around at the moment. They try to make it as cheap as possible while still doing the job, but that might actually mean using a way over-spec'd part if that's what they have a whole lot of in the back room right now.

The repair manuals are looking at the whole field of parts available and giving you choices because different repair shops have their own stock and their own prices based on the volume of parts they can afford to buy at the same time.

Sometimes (a lot of times) the exact transistor you chose doesn't make a heck of a lot of difference. As long as it sort of fits the voltage and current requirements as the junctions, it's going to do the job.

Other times, the gain characteristics and/or the transition time of the transistor is going to make a big difference, and you have to pay attention to it in the circuit. In these cases, even a single transistor replacement can require reverse engineering the whole portion of the circuit that it is found in.

If you are seeing a single transistor type shown as a replacement for many different transistors in BOM, then it's likely that is a common replacement part used for a variety of transistors from different manufacturers. And so is more of a general replacement than an exact fit. They are usually pretty much okay, but I have seen situations in which Sam's replacements didn't work in a circuit. Not often, but I've seen it.

Got it. Was just wonder as I needed two 695s and found a seller with a lot of 10 for next to nothing. So I bought them and wondered what I could do with the rest. If the ECG123A is a basic replacement for a number of transistors, and one of those is the 695, then if need be, I can use the 695 as a replacement for those other transistors?

Well it seems the replacement caps won't be here until tomorrow. No biggie as I was cleaning the G2 pots with D5 and F5 and decided to give the setup switch it's 5th or so cleaning when I decided to look at it closely with my video microscope. I couldn't see anything but the pads at the end for the setup mode and the contacts on the slider. They were pretty much black and it appeared the slider part wasn't making full contact even though the spring in it was providing pressure. Not sure this at fault, but it got me searching for a replacement and I managed to find an NOS switch and bought it. Should be in by end of week. So I'm going to replace the switch while the chassis is still out.

The G2s now rotate much smoother than before, so it can't hurt to have clean pots.

If you show me a circuit (the schematic) with a transistor, and you give me both the original transistor and the one your are thinking about replacing it with (and their datasheets), then I can probably tell you with some confidence if it's going to work.

That's about the extent of my knowledge with this stuff; one at a time. I can't sign off on blanket replacements between transistors regardless of the use case. I'm not that good at it.

Sounds good. I've tried to figure out which transistor package is from what year and if one is better than the other. For the 695s, I received 3 different package types, There are round white ones with black tops, black round ones that look like a water tower and the TO-92. I tried looking up the other 2, but I found no package numbers for them. I'm assuming the ones not TO-92 are earlier versions and might be of lesser quality.

The ones I'm looking at are the water tower looking one on the Horizontal module Q804 (121-447). Also, the Horizontal module is supposed to have a 121-931 (Q801), but there's a 447 in its place. Is this a suitable replacement, or is the 931 the best choice?

Do you have the datasheets for the transistors? I looked around for them, but I can't find anything. I even went as far as doing a cross-reference on the an archived version of the NTE part cross-reference tool, but those numbers don't come at all.

I'm good enough to have an idea of which specs would be important to adhere to, but I can't tell you what the specs of the original transistor are without a datasheet.

In general though, both Q804 (waveshape) and Q801 (AFC) are not in super critical spots for either speed or gain. I would think that almost any decent modern transistor with the correct voltage requirements would do the trick. Something like a 2N4401 could work probably. Q801 would be more likely to have possible issues if the gain was too high because the AFC circuit might rely on the gain characteristics to lock in, but I can't tell you that because I don't know the gain of the original transistor.

It is ususal design process in transistor circuits to design for proper operation whenever the transistor current gain (beta) is above a certain minimum.

Looking at Q801, you see that the peak to peak waveform on the base is twice the size of the DC voltage, so this stage is being overdriven to clip the AC waveform. The DC bias uses feedback from the collector load. Given all this, it's likely that any general purpose transistor with a beta of say 100 or greater would work.

Ok. That's really cool of you to explain that. I think I get it.

I think what you're saying here is that because the voltage threshold is so low, the transistor is only going to turn on when the waveform crosses the conduction threshold. Which would be ~0.7V if the emitter was tied to ground, but it has a 270 ohm resistor there, so I guess it would actually be a little higher than .7 it starts, depending on what the voltage is on the emitter at any given time.

So that means the collector probably has a ~10Vpk squarish waveform with fairly short negative-going pulses when Q801 is in conduction, right?

I won't try to guess what the duty cycle is. I haven't seen this sort of frequency control before and I'm not sure how it works - maybe by varying the duty cycle?

If the collector is sitting at 8.72V, fed by the 23.5V, then I would assume that the resulting waveform is determined by the narrow window that the base waveform allows for Q801 to be turned on.

If the base is at .54V, and the emitter is at .27V, and the waveform on the base is 1.5Vpkpk, then that means the top of the waveform swing is like 0.90-1.29V, where Q801 is turned on I would think.

The collector is providing some weak feedback by being attached to the base through the resistor, so I suppose that would help with changes in current draw due to the reactance of the hor osc coil on the other side of the collector.

Maybe?

Well something happened that usually never does, but I was wanting replacement transistors for the horizontal and vertical boards, for now or the future. I kind of want OEM parts, but finding them all from once sources proved impossible. I could find them all, but buying individually with shipping on each was way more than I was willing to pay. Then it happened, something very rare. I searched for a 931 transistor and came across a listing I couldn't ignore. Not only did it have every single transistor I wanted, I also had a red G2 pot! It had a few other items that I might find a use for, but even if I don't, I got the entire lot for 16 bucks! I don't know if I need the red G2 pot, but now I can disconnect the current one for full testing and know I have a replacement if needed. I tried testing in place, but the readings were odd as it would go up, then down and back up again pretty consistently during testing. Not sure if being in circuit was the reason.

I got the new C202 and 204 capacitors yesterday 68pf and .0047pf. They test dead on, but still show a high ESR, so I now know my tester isn't up to the task for these values.


Tomorrow I carefully plan and execute the installation. I have my liquid flux, 200W iron and largest chisel tip I have and a couple clip on heat sinks for the leads of the resistors already in the solder buckets. Then by Friday I should have the new setup switch and have it installed same day. Once I go over all components to make sure I didn't disturb routing or created a short, back in it goes and I'll fire it up.

Been an interesting journey so far. Hopefully I've made things better, not worse. :thmbsp:

So now from update to question. I want to test voltages to the CRT and will pull socket back just enough to clip leads on all three of the screen drivers. Since they are driven by the 750 boost, I should get no reading higher than that and the SM has the voltages noted for each gun. However, if the G2s control those voltages, what is the purpose of noting those on the CRT part of the schematic? Since they G2s are adjusted for greyscale, doesn't that mean those voltages will be different based on current adjustment position? What exactly should I be looking for? Also, if I do the same for the cathode and G1? Are any of the values given in the SM a for sure value or will any of them vary and I'm looking for values close to what is stated?

Thanks!

Voltages given for the G2's are just what was measured on the particular set that was used and will vary with adjustment, as you said.
Voltages on the cathodes also vary with video content, so may be quite different if you use a different test pattern from the one used in the service info.
Volatages on the G1's also vary with video content in sets where the color difference signals drive the G1's.

So basically I'm just looking for something way out of the ordinary? :lmao:

I reinstalled the chassis after inspecting all components. I connected all internal cables and verified proper locations based on pics taken before removal. I plugged it in and it immediately started a deep buzz from the speaker. I unplugged it and double checked everything and it is all correct. Plugged it back in and it did the same thing. I have it unplugged now and haven't tried turning it on until I find out why it is making this sound while off. Any ideas?

Never mind, ground loop. First time it's ever happen. Rotated plug and it's gone.

I haven't gotten around to doing any real adjustments as the room is too bright. I'll do them this evening. The new setup switch is late, so I left the old one in for now. Still won't bring up any lines from the G2 controls. Hopefully the new one will fix that issue. As for jailbars, here's hoping the new caps will fix it. If not, I'm going to look at removing the IF module and injecting my generator directly into the circuit on C1. Was told these bars can also come form bad RF, IF, etc.

We're getting there!

I've done all the adjustments. I got the convergence pretty much dead on, except for a little blue horizontal on the very right edge. Seems the 2 new pots and a very extensive D5 and F5 cleaning of the other pots helped greatly. It is the best I've been able to get it and I'm more than happy with it and will not touch it again.

I'm starting to think the jailbars are coming from some other source (IF?). They are still there with all new electrolytics using SM part numbers, new diodes and new ceramics in the horizontal circuits. I disconnected the tuner to IF and I got a bright white raster, so no way of telling if the jailbars were there or not. My next step is to remove the IF module and connect my generator directly to C1 and inject the signal. I'm not sure if I can bring up anything that will show if the jailbars are there or not. What about a direct composite feed? I'm sure it's not as simple as connecting the composite out signal to C1 and ground, right?

As for the peak pix control... Is that off fully counter clockwise, or does that over soften the image? I really can't tell, but it seems soft CCW and noisy fully CW. So maybe the center is where it should be?

Attaching a couple of pics. They're from a laserdisc.

Peak pix action was designed to be default at center, with CCW notably softer and CW notably crisper.

Question about 23.5V in the set. How important is this? The reason I ask is I tested the regulator and it seemed fine. However, what I noted was the installed regulator is 121-808 and the sheet attached inside the set has it as being 121-966. In order to find the differences between them, I had to compare the part numbers from the other manufactures listed in the SM. That lead me to compare ECG152 (121-966) to the ECG184 (121-808). I found datasheets on them from AllTransistors and they are definitely different, but I don't know what those difference would translate to or if it's even an issue. Since this voltage is in just about every circuit of the TV, it must be important.

Can someone with the necessary knowledge take a look?

Thanks!

Since this TV has a transformer, it should be possible to bypass the IF and inject composite video and audio. If I understand this correctly, I should be able to remove the IF module, connect the composite to C1 and ground, then connect the audio to connection 4 of the sound module and ground. To reverse it, I just remove connections and reinstall IF module.

The input voltage of the sound module is .25V, down from the SIF out of .47V going through L215. I believe the fixed audio out of a DVD player can be as high as 2V, so will something need to be added?

I'm attaching the relative portion of the schematic and circled the points of connection.

I removed the IF module and connected the video out of my generator to C1 which is noted as being the picture detector output. The generator's manual says to connect its video output after the detector, so this is the correct point. When I did, I had to set the output on the generator to max in order to see anything. What I got was dim and the horizontal and vertical was not stable.

Looking over the schematic, the detector out is 6.99V. From reading up, the composite signal is a max of 1V. The detector's out also feeds the video processor module and that is 6.24V. The video processor module sends out H and V synch as well. So does the composite signal I'm feeding it need to go through the video processor as well to? I see 3 destinations for the detector output.... The video processor module, the chroma module and the section with the video amps, vertical blanker, blanker amp, etc.

So am I correct that the composite I feed needs to hit all those points and can't just simply wander into the video outputs. The signal needs to drive the vertical and horizontal modules, etc?

If this is the case, how do I duplicate the voltage on the detector output for all the other modules? The odd thing is, the manual for my generator says nothing about removing the IF module or anything other than connecting the lead to a point after the detector. So maybe there is something in the circuit of the generator to allow it to inject its signal over the detector's?

Such a crazy day.

Troubleshooting 2 issues, jail bars, unable to produce one or more service lines in setup.

When you disconnected the IF input from the tuner, jail bars yes/no?
When you removed the IF module, jail bars yes/no?
When you inject the video source from your generator at C1, IF Module out, jail bars yes/no?

The 6.99v shown at C1 in SAMS is a DC value, to the right 1.4v P2P is the waveform involved and is roughly what your generator is supplying. Not every set has a IF Module that can be removed.

The 24v DC supply is very important, 121-808 looks like a good sub for 121-966. Higher values and a different case, but looks good. You noted in prior threads the voltage at the test point was good. Did you replace this transistor before?

What is the "ground loop" you are referring to?

The strategy behind measuring the DC values on the CRT is to rule out a circuit issue and unfortunately implicate the CRT. You appear to have good gray scale with what you have, good focus, convergence is really good.

I've never worked on an Avanti, which I believe your set is, do these NOT have a Service Saver plate on the bottom?

Might be interesting to test your setup switch with your ohmeter before you go to the trouble of replacing it.

When I disconnect the tuner to the IF, I get a bright white screen, and see no jailbars, but I don't see them with any of the bright test patterns, so I can't say for certain if they are still there.

When I remove the IF module, the screen goes completely black like the set is off, so no way to tell if jailbars are there.

Connecting to C1 with IF module removed doesn't bring up the pattern from the generator and if I increase the signal on the generator I get a scrambled image like there's no horizontal or vertical sync. Adjusting the vertical and horizontal hold makes it more stable, but it's not a useful image.

Since the manual for the generator doesn't specifically state the connection for injecting their signal needs the one from the IF be disconnected, I'm tempted to just leave the IF module in, disconnect the tuner and connect the generator to C1. The worst that can happen should happen to the generator, not the TV. I can't imagine they'd make such a feature and not implement safeguards in their system. Also, having the IF module removed might remove the 6V needed for something else in the video chain?

The regulator installed is what was installed when I got the set. Since it didn't match the paper in the set, I got the correct one. Never got around to installing it, but did so this time round as I had it. And yes, the voltages from the installed were correct and still so with the new regulator. I know I didn't need to change it, but it bothered me it wasn't what was called for.

I'm assuming it was a ground loop. After reinstalling the chassis and making all the internal connections (and double checking), I plugged it back in. It immediately made a deep buzzing from the speaker and possibly other sources. I immediately unplugged it and check all connections again. I plugged it back in and it still did it. I left it plugged in and tapped on all connections in the area of the tuner, IF and sound. I found that just my hand touching certain areas was enough to make it stop. That's what made me think it was a ground issue. I reverse the plug and it stopped and hasn't come back since.

What is a "service saver plate"? Never heard of it. Only thing on the bottom of the set is a removable metal cover to access the underside of the chassis.

I just got the new switch in the mail today. It is identical except for the fact it is much tighter than current one. The one in the set not only slides up and down, but in and out as if there were a spring between the slider and brass contacts. The new one has no play at all. Since all the resistors and capacitors on the setup side of the switch have been replaced, I don't know where else to look and changing the switch is an easy task that will help rule out another piece of the chain. This would also allow me to disassemble the old switch to inspect.

Tomorrow I plan on getting all the voltages from the CRT. I have it dialed in pretty well and thought I'd display the color SMPTE pattern with the pluge stuff on the bottom. That should keep voltages stable so if I test again I know the video information sent to the CRT is the same and any changes in voltage aren't from displaying different signal.