Notifications
Clear all

Forum 2

CTV [Sticky] 1974 HMV 2726 Coloumaster; Thorn 4000

387 Posts
21 Users
519 Likes
4,216 Views
crustytv
(@crustytv)
Illustrious Member Admin
Topic starter
 

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

 

 
Posted : 05/08/2022 8:32 pm
Cathovisor
(@cathovisor)
Illustrious Member
 
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!

 

 
Posted : 05/08/2022 8:39 pm
Jayceebee
(@jayceebee)
Noble Member
 

Updated setup procedure in manual part 5. 

decoder

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

 
Posted : 05/08/2022 9:24 pm
crustytv
(@crustytv)
Illustrious Member Admin
Topic starter
 

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.

20220805 223351

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.

 
Posted : 05/08/2022 9:42 pm
crustytv
(@crustytv)
Illustrious Member Admin
Topic starter
 

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.

 
Posted : 05/08/2022 9:45 pm
Cathovisor
(@cathovisor)
Illustrious Member
 

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 : 05/08/2022 9:47 pm
Cathovisor
(@cathovisor)
Illustrious Member
 
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...

 

 
Posted : 05/08/2022 9:48 pm
crustytv
(@crustytv)
Illustrious Member Admin
Topic starter
 

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 : 05/08/2022 9:48 pm
Jayceebee
(@jayceebee)
Noble Member
 
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.

 
Posted : 05/08/2022 9:54 pm
crustytv
(@crustytv)
Illustrious Member Admin
Topic starter
 

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

 
Posted : 05/08/2022 10:02 pm
crustytv
(@crustytv)
Illustrious Member Admin
Topic starter
 
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 : 05/08/2022 10:04 pm
Cathovisor
(@cathovisor)
Illustrious Member
 
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... 

 
Posted : 05/08/2022 10:16 pm
Nuvistor
(@nuvistor)
Illustrious Member
 

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.

86402E01 F1C6 4311 B9FE ADE01FE71D2E

 

 
Posted : 06/08/2022 6:52 am
crustytv
(@crustytv)
Illustrious Member Admin
Topic starter
 
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 👍 

c953
 
Posted : 06/08/2022 9:25 pm
Jayceebee
(@jayceebee)
Noble Member
 

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

W308mod
 
Posted : 06/08/2022 9:30 pm
crustytv
(@crustytv)
Illustrious Member Admin
Topic starter
 
Posted by: @crustytv

.1uf electrolytic !!!!! Ridiculous!

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

I do now

20220807 150736[1]
 
Posted : 07/08/2022 2:10 pm
crustytv
(@crustytv)
Illustrious Member Admin
Topic starter
 
Posted by: @jayceebee

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

W308mod

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

20220808 113703

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.

20220808 145153

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.

20220808 155157
 
Posted : 08/08/2022 10:47 am
PYE625, PYE625 and PYE625 reacted
Cathovisor
(@cathovisor)
Illustrious Member
 

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 : 08/08/2022 3:13 pm
crustytv
(@crustytv)
Illustrious Member Admin
Topic starter
 
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

20220808 155157

This evening

20220808 222450
 
Posted : 08/08/2022 3:37 pm
Visconol
(@visconol)
Active Member
 

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

 
Posted : 08/08/2022 6:43 pm
Page 13 / 20