CTV [Sticky] 1974 HMV 2726 Coloumaster; Thorn 4000

This is what I was not getting across, that well, step 3 makes no sense.

Posted by: @crustytv

This is what I was not getting across, that well, step 3 makes no sense.

 

Short of relying on a 0.1uF cap to have sufficient self-inductance to just reduce the chroma rather than eliminate it entirely, it is pretty odd.

What's the procedure for the other chroma modules, Chris? Just in case there's a mistake!

Updated setup procedure in manual part 5. 

There is also a mention of a change in value of C953 from 33pF to 39pF inside the RCU handset to centralise tuning conditions.

I've just spent the last hour trying to get things back to where they were. It got into a complete mess. It's still not right, as the user colour control seems to shift colours on the colour bar, but less so on TCF.

When I follow the page 9 procedure 7V, 1.2V  etc, it's impossible to set up. Only just seen your post, John, I'll have a look tomorrow.

I'll be in decoder mode as I sleep tonight, trying to decode the decoder.

Oh, and I forgot to say, I think there is a component giving intermittent grief, possibly an electrolytic or preset. The width seems to occasionally increase, as though I've set the raster for overscan, then it will be back in, showing the TCF outer colour gratings.

I'm having flashbacks to the days of construction projects in Television and Practical Wireless where sometimes there was a supplemental piece to correct the errors that crept in to the main article.

I built the Television TV sound tuner, which didn't work at first - until you came to the supplement that said the 6MHz coil was wired in the wrong way round...

Posted by: @crustytv

Oh, and I forgot to say, I think there is a component giving intermittent grief, possibly an electrolytic or preset. The width seems to occasionally increase, as though I've set the raster for overscan, then it will be back in, showing the TCF outer colour gratings.

Now, I was going to ask you about that as some of the photos showed more overscan than others...

If I can get to the bottom of this decoder shenanigan, and the other niggles, I can get on with the ultrasonic. On the plus side, Grey-scale looks great and convergence too. I haven't figured out how to shift the picture up yet.

That's it for tonight, I'm pooped.

Posted by: @crustytv

 I haven't figured out how to shift the picture up yet.

 

TF403.

I've noticed the chroma path is a little more convoluted than I thought as it passes through IC155 for saturation control. There is a 0.1uF electrolytic C192 which decouples the slider of the saturation control and is definitely worth a look if it's not been replaced already.

How could I have forgotten that? Tired is the answer. 😴 

Posted by: @jayceebee

There is a 0.1uF electrolytic C192 which decouples the slider of the saturation control and is definitely worth a look.

tinsy winsy red tant

.1uf electrolytic !!!!! Ridiculous!

I've certainly none of those in stock, lowest I have is 1uF .47uF

Posted by: @crustytv

Posted by: @jayceebee

There is a 0.1uF electrolytic C192 which decouples the slider of the saturation control and is definitely worth a look.

tinsy winsy red tant

.1uf electrolytic !!!!! Ridiculous!

I've certainly none of those in stock, lowest I have is 1uF .47uF

I'd replace that with a small polyester - I have an aversion to tiny tants... 

It’s come a long way since I looked yesterday morning, good you have sorted out the shading on the left.

The cross colour perhaps looks worse with the camera artefacts and all CTV’s did show some. Something you may wish to check further down the line when other problems are sorted out.

Attached section from the student guide showing the 4.43 MHz trap.

Posted by: @jayceebee

There is also a mention of a change in value of C953 from 33pF to 39pF inside the RCU handset to centralise tuning conditions.

The remote already has that mod 👍 

@crustytv I also found this mod this evening regarding changing W308 to a silicon device.

Posted by: @crustytv

.1uf electrolytic !!!!! Ridiculous!

I've certainly none of those in stock, lowest I have is 1uF .47uF

I do now

Posted by: @jayceebee

@crustytv I also found this mod this evening regarding changing W308 to a silicon device.

The CG3 SinterGlass diodes arrived today from Poland, they certainly appear man enough both in specification and construction.  It's probably just me, but looking at the package of the BY184, I have great difficulty believing the BY184 is capable of 1.5kV-1.8kV @ 5mA. I guess the specs don't lie. Now I have to make a decision on what to use, CG3 or BY184 with a 2.7K series resistor, or just leave the AEG992

Back in the vertical timebase, trying to add a bit more stability by finally removing all traces of those ROE caps. Still undecided about W308, so for the time being, I'm leaving the selenium fart stick in place.

Time to put it all back and see if it still works.

Phew! Relief, I hate doing bulk changes, but it's still working, and look all the better for it.

I'd go for the BY184 as it's a contemporaneous mod.

Any reason you've not tweaked out the N/S bow yet? With every photo that set just looks better and better.

Posted by: @cathovisor

Any reason you've not tweaked out the N/S bow yet?

I have that's the best I can get thus far, need to look into that at some point, I've just not mentioned it.

Edit: 8/8/2022 @10:30pm

It's also still occasionally giving the overscan, another time it will be as before.

This afternoon

This evening

@crustytv     Vic Hallam Ltd also made cabinets for ITT/KB sets of the same era!