Hi everyone,
I picked this set up from Mike T some time ago and have ben working on it, on and off for ages.
I am now stuck with a couple of issues that I think are possibly all linked, but Im stuck!
Am I being too fussy?? or is this how this set is?
I have been using trader sheet #1454 and the red book 1959/60 for circuit info.
When I first powered up the set, the the screen was quite dim with frame reduced/cramped at the bottom and line tearing. After changing most of the waxies/hunts and a few resistors the picture brightend up, a few more caps and resistors later I had a full sacn, but with terrible cogging.
A few of the components I changed were fitted with the wrong values ie. 17 inch values instead of 21 inch values, all of which are listed on the data sheets. So I guess someone has been repairing this set thinking it was a 17 inch set. (Not Mike T)
I have put all values back as per trader sheet.
The cogging on the picture would briefly go away if I adjusted the fine tune, but would return almost immediately, also any voltage measurements arount the video/AGC area would also have an effect on the cogging, I eventually found the cause of this to be R35 (trader sheet) was measuring about 1k5 and should of been 180R 
.
I now had a fairly nice and stable picture 
but.
Here are where my problems (if they are problems) lie.
The focus is quite poor. (control at one end)
The picture seems to be over bright on whites.
Flyback lines are visible on black/dark pictures.
(if you turn down the brightness the flyback lines and flaring go away, but you can only then really watch the tv in the dark)
I have also found that to get line lin correct (sliding shorted turn inside the scan coils) then leaves me with reduced width, and although the data sheets shows a coil labled width its not adjustable.
As you can see in the pictures I can get full scan, but I have to put up with linearity/centering errors, but the focus and over bright whites are annoying. (photos do not really show the faults very well)
The tube measures tip top on my leader and has no leakage.
The only thing I can find wrong now is the voltage at the junction of C49/R51 is high @ 550V should be 515V and at the junction of R51/R50 is also high @ 390V should be 270V. This is the A1/focus supply and goes to the frame stage. I think this is maybe why the focus is poor and the picture is over bright.
HT and all other voltages listed on the trader sheet are all with in spec.
Does anyone have any ideas as to what might be causing this? Or are these voltages normall? Apart from this fault the set seems to work a treat.
Am I being too fussy?
Best regards
Jon
Jon
BVWS Member
A couple of points.
Cogging is always due to video getting into the sync feed. This can be cause by the composite video being crushed at the bottom or biasing of the sync separator. The alternate black/white castellations at the side of the test card are the cause of the cogging.
The width is too low. You've made the common mistake of setting the width so that the castellations are visible at the sides. Many tubes, such as yours, do not fit the transmitted aspect ratio* and require to be over-scanned by about 10% to get the width correct. In your picture the width is too narrow, making the circle oval rather than round.
Hopefully, when you've set to the width correctly, the linearity will improve ...
* CRT development was still progressing from the round CRT of the early days towards the completely rectangular CRTs that eventually emerged but it was a long struggle. The slight rounding of the shape of your tube is because it is really a distorted circle. A really rectangular tube at that stage of development would have been too weak and in danger of (frequent) implosion ...!
When all else fails, read the instructions
Hi Terry,
Thanks for the reply.
I didnt know what was causing the cogging, but I thought it must be somethimg to do with the picture content as the gogging seems so regular and your description fits the bill.
On the width front, thats just about as wide as it will go.
As I said in my post there is no width control as such its just a fixed coil. Even if I remove the linearity sleeve from the scan coil assy the width does not increase and linerarity gets worse.
Jon
Jon
BVWS Member
