1977 Ferguson 3734 ColourStar: Thorn 9600 Chassis

VT814e 18.1V, VT803b 16.1V? Something wrong there as they're directly connected to each other. Also there's a big discrepancy between TSA/4 and the emitter of VT803 as TSA/4 has only 10K between it.

The first was a typo, if you look at the post it was edited to correct

Yes, I see the corrected version now but TSA/4 to VT803e is very wrong. What about the volts across W523?

Posted by: Jayceebee

 Also there's a big discrepancy between TSA/4 and the emitter of VT803 as TSA/4 has only 10K between it.

I'm confused, what discrepancy? I just checked TSA/4 and its 16.7 same as VT803/e

Posted by: Chris

Posted by: Mikey66

I'm clutching at straws I guess but with the peak flyback still at 540V and the tripler input disconnected the EHT facsimile voltage dropped to 16.31V. Might be worth disconnecting the tripler and see what voltage you get at TSB/4 if it is 10-14V lower than your earlier reading youcould try turning the peak flyback up towards 650v and see if the set still trips?

I think you might be onto something here.

When I disconnect the input to the tripler TSA/4 (EHT facsimile) unlike yours it does not drop but remains unchanged, it still sits at 33.4V. However what does rise is TSA/9 (Peak fly-back), that goes from 537V tripler input connected, rising to 609V with the tripler input disconnected. I cannot adjust R613 to obtain higher as its at max extent.

Out of interest whilst monitoring TSA/9 I tried adjusting R612 (currently at mid point), this only seemed to have the effect of loading the PSU and I heard the channel lock go as the 80V (67V rail in my case) collapses.

 

 

See above. Previously you stated that the volts at TSA/4 didn't fall when the tripler was disconnected?

Posted By: Jayceebee

Previously you stated that the volts at TSA/4 didn't fall when the tripler was disconnected?

I know I did but that was then not now...... this set has a life of its own! I've also had components in and out for testing since responding to Mike VT803, VT814, W520, W521, W523 C830 and I've replaced W528.

I've just connected the tripler back up and you should see what I'm getting now! At least now the raster reflects the low EHT, whereas before it filled the screen despite being low. If I adjust the SET EHT the picture starts to try and fill the screen but goes off into the disturbance I demo'd before. So conditions have somewhat changed.

I really have just about had it with this set......

I feel for you Chris, as I've said many times "You don't 'arf pick em". What is the voltage at TSA/4, the anode and cathode of W520 now and can you get a swing at TSA/4 now with the tuning coil?

Hi Chris,

Is that apparent ghosting a camera artefact, or an on-screen aberration?

It's due to the fact that is a back silvered mirror I think, that's why they used front silvered types on projection TV's. Very easy to damage when cleaning

The mirror is probably misted over with Chris's perspiration. 

Seriously though, this would beat the best of us. (And I'm quite a way down the line there).

Yes Andrew, this one is real pain (or Thorn) in the bum. I even found myself downloading and looking at back copies of TV mag to see if I could glean any sort of clue or ideas but there a precious few references to the 9600, nothing anywhere near what we are seeing here. They were a pretty decent set, CRT apart back in the day but of course now a long way past a normal service life.

Posted by: Jayceebee

What is the voltage at TSA/4

25V

Posted by: Jayceebee

What is the voltage at the anode and cathode of W520

A=40mV, C=27V

Posted by: Jayceebee

 can you get a swing at TSA/4 now with the tuning coil? 

minimal 24.9V - 25.1V
 

Well I suppose in a way you have made progress. EHT facsimile won't case an issue at that voltage. 

I take it you still can't get 80V rail anywhere near?

More tomorrow if I can as it's my on call week.

80V rail is now up from 67V to 72V

That's encouraging news and only .04V on the trip rail is good so it definitely seems that something from the compensation circuit was causing VT607 to conduct, not heavily though. Let's go a stage further and see if we can pinpoint the source/cause of the disturbance.

Could you scope and meter VT607 base at both a low and high set EHT, advance to the point it becomes very unstable and note what happens. I don't need to see any defined waveforms as such I just want to see both and also the DC levels at low and high EHT values, I'm looking for noise so slow the timebase down to say 1mS.

Yes, there certainly appears to be over 800mv of ripple at 24kV which will begin to bias on VT607 and remove the possibility of C606 achieving the correct charging volts to open up the chopper for 80V, that's if I'm reading your scope correctly. But where is it coming from, the chopper emitter I suspect but it's a bit of a chicken and egg situation? I've looked back through previous post but don't know if you've checked W514, I'm sure you will have but give it another look anyway.

Another thought is that to start the chopper driver it is initially run from the rather dirty supply from the main smoother via R533, once the chopper is running it's fed from the cleaner more regulated 240V rail via W512. Might also be worth a check.

Just a small interjection here, I noticed wayback earlier Chris posted a diagram  of the syclops board  PC 891 -001, now looking through another diagram I noticed an extra transistor namely VT610 in the comparator stage, with an associated 1,5 uf C614, as I understand it there were more than one type syclops board fitted to the 9k6 , can we just confirm that we are talking about the correct board here.

Apologies if side tracking somewhat

Posted by: Red_to_Black

can we just confirm that we are talking about the correct board here.

I can confirm the sysclops module fitted in my set does not have VT10 fitted.

Posted by: Jayceebee

I've looked back through previous post but don't know if you've checked W514, I'm sure you will have but give it another look anyway.

[..] it's fed from the cleaner more regulated 240V rail via W512. Might also be worth a check.

Both previously checked and found OK, to be doubly certain I removed them again, tested and they are both still OK.