Colour TV IF Alignment Practice: Test Subject: 3000 IF board using PM5334

It looks good to me Chris and at the moment I can't see a reason why it shouldn't give some output although you may have to experiment with output level and the Y amp of the scope as I suspect the gain of the VIF in this configuration will be quite low. It also looks as though you may have to invert the scope display.

The simulation of the set white switch being operated can be done by grounding PL11/8.

John.

As you will no doubt be aware, with no tuner attached the output of the generator will need to be fed in at the IF input pins for the second part of the procedure.

Posted by: Jayceebee

The simulation of the set white switch being operated can be done by grounding PL11/8.

John.

Simulating the set white switch by grounding pl11/8 shuts the whole trace down, it just flat lines.

Further to this, I have a radio on in the workshop, when the gen is running and hooked in circuit I can hear buzzing being picked up by the radio and of course I can see the very minimal IF trace on the scope. When the the PL11/8 is connected (set white simulation) the buzzing on the radio stops and the trace flat lines.

Posted by Jayceebee

You may have to experiment with output level and the Y amp of the scope as I suspect the gain of the VIF in this configuration will be quite low

I have already tried adjusting the scope in an attempt to amplify, no go I'm afraid. What you see is the best I can get. Here's the trace with the invert actuated, that was something I had missed.

I think, but don't know for sure, that this is all we can hope to attain when trying to run an IF  board out of a TV, via a bench supply. Of course I'm happy to stand corrected if somebody knows differently.

Posted by: Chris

It has been suggested that a good way to practice CTV alignment is on a 3000 IF module. This module in theory, can be supplied via a 30V bench supply.

What better and safe way to do it than inside a set. Excellent !

Posted by: Chris

 

Either I've hooked up something wrong, the IF panel is duff or you cannot align the module this way, out of the set.

I've looked very carefully at your pic of the hook up and I can't see anything wrong there, the second and third parts of your comment are probably the most likely. If you haven't already done so it would be a good idea to try it in a set, I'm looking at C177 with deep suspicion. Remember your 2708?

Edit. The only other thing is that VT105c is floating, for the life of me I can't see it making a difference but try tying it to ground with a 1.2K if that board is working ok. When I mentioned doing it this way I was thinking out loud never having tried it before.

Hi John,

I checked C177 and although gone high (doubled in value to 70uF) was OK, I replaced it whilst it was out with a 33uF ( nearest), np change in response curve amplitude. I'll try tying the collector to GND via a 1.2K and if that does not work I'll remove a known working IF panel from one of my 3K sets. The latter part, if required, will be tomorrow though.

Adding the 1.2K from VT105(c) to GND did open up the trace, not a great deal but some, it also distorts the base line.

If I adjust the dB attenuation I can make it larger but the base line distorts and the traces tilts.

Posted by: Jayceebee

Posted by: Chris

 

Either I've hooked up something wrong, the IF panel is duff or you cannot align the module this way, out of the set.

I've looked very carefully at your pic of the hook up and I can't see anything wrong there, the second and third parts of your comment are probably the most likely. If you haven't already done so it would be a good idea to try it in a set, I'm looking at C177 with deep suspicion. Remember your 2708?

Edit. The only other thing is that VT105c is floating, for the life of me I can't see it making a difference but try tying it to ground with a 1.2K if that board is working ok. When I mentioned doing it this way I was thinking out loud never having tried it before.

Not being very familiar with this chassis and just having read John's suggestion of tying the collector of VT105 down via 1.2K and looking at the circuit, I have a question. Does the ground connection just under VT105 on the schematic need to be connected to ground or is that just there to feed ground to the video PCB??

No idea Jon, I didn't even know I could attempt what I'm trying out of a set until John suggested it this morning, even John is not certain its viable.

Posted by: Chris

No idea Jon, I didn't even know I could attempt what I'm trying out of a set until John suggested it this morning, even John is not certain its viable.

I would have thought it should be, as long as you can simulate the board being in a set.... just thinking whether you need a tuner connected to provide the right IF input coupling conditions?

(Sorry Jon....I interrupted the flow)

Posted by: Chris

No idea Jon, I didn't even know I could attempt what I'm trying out of a set until John suggested it this morning, even John is not certain its viable.

I can't really see any reason why it should'nt work, although I have never done anything like this before either! I was just wondering if all the grounds on the I.F. all goto/come from one place and does that extra ground connection need to be connected to the ground your using or is it already made by a bit of track?

This is the connection I am refering too (in red), in case my ramblings are not making sense.

Hi Jon, the earth connection you are referring to which R201 is connected to is actually on the video board. As we are attempting to power just the IF out of a chassis then effectively R201 and R279 are missing hence the idea of terminating VT105c with a 1.2K on the IF. I didn't think adding the resistor would have such a marked effect so maybe were on to something here.

By the way although you're probably aware, components beginning 1 are on the IF, 2 for the video board.

Hope my ramblings make sense also.

You do realise Chris I'm not going to get any sleep tonight, this is going to be on my mind all night.  ? 

John.

Posted by: Jayceebee

Hi Jon, the earth connection you are referring to which R201 is connected to is actually on the video board. As we are attempting to power just the IF out of a chassis then effectively R201 and R279 are missing hence the idea of terminating VT105c with a 1.2K on the IF. I didn't think adding the resistor would have such a marked effect so maybe were on to something here.

By the way although you're probably aware, components beginning 1 are on the IF, 2 for the video board.

Hope my ramblings make sense also.

You do realise Chris I'm not going to get any sleep tonight, this is going to be on my mind all night.  ? 

John.

Hi John,

Yes I see that R201 is connected to that ground and I understand the purpose of the experiment. What I was asking (badly) was, is for example R125 and components to the right of it actually grounded on the IF PCB or do the recieve their ground from the video PCB? I can see that the way the circuit is drawn they are grounded on the IF, but is that really the case when the PCB is in the set as a whole TV and a PCB on its own?

I'll get my coat.

Sorry Jon it's late, I think I see what you're getting at now. Yes I'm pretty sure all the grounds on the IF are connected together but I can't be certain as I have no set or boards to check. The gap shown in the ground on the circuit is just to show clearly the connection of VT105c to SK10/2 (I hope).

Posted by: Jayceebee

Sorry Jon it's late, I think I see what you're getting at now. Yes I'm pretty sure all the grounds on the IF are connected together but I can't be certain as I have no set or boards to check. The gap shown in the ground on the circuit is just to show clearly the connection of VT105c to SK10/2 (I hope).

I'm sure your right John, but you know how some things are not always as they appear. It was just an observation and thought that it was worth an ask. If the output end of the IF is floating then Chris will not see what we think he should see. I do have a 3000 chassis but it's buried at the moment so I cant check it for myself.

The IF board like all the others would have been aligned and tested as an individual unit in the factory so it must be possible.

The hard part is working out how they did it.

I have been following the thread but unfortunately not too closely, hands full with other jobs.

I grabbed another IF panel from stock, again another unknown. This gives better results but still not what I would expect.

New panel, all links and connections added as per service manual instructions

The initial result this time is a little better than the previous board but still not a great amplitude.

So following Johns previous advice I ground VT05 collector via a 1.2K resistor. This makes the amplitude greater but in a negative direction.

Finally I select invert and we have correct orientation. 

However the IF response curve bears little resemblance to the expected response curve and little sign of the rejecters. Unless the large hump to the left is the sound rejecter and the tiny blip to the far right the vision.

Something is still not right and begs answers to previous posters questions about grounding or if it is indeed possible to do what I'm attempting to do. 

Sometimes I wonder if the illustration in a manual is an ideal theoretical curve, but in practise, only an approximation can be achieved to a certain extent. There are limits of course, but is it really possible to achieve a perfect curve? 

I suppose the tricky thing to decide is how much of a deviance from the ideal can be tolerated before the picture/sound is adversely affected.