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1977 Ferguson 3734 ColourStar: Thorn 9600 Chassis

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Jayceebee
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Ok that's good at least we know the SYCLOPS board is capable of attaining a decent output. I still think it's the rubbish on the overcurrent trip feed pulling down the rail via VT607 but it's impossible to tell from here whether is due to excess load, possibly a beam limiter issue as I mentioned earlier or supply rail noise being fed back.

Can you tell if you can see any beam limiter action when you over advance the brill/con settings? Without a good deal of experience it may be difficult for you to spot, with max contrast what should happen is as the limiter kicks in the brill should stop increasing as the control is advanced.

If it is just excess current I would have expected some more severe symptoms on the picture qualty than we are seeing at the moment, is there any signs of anything anywhere getting hotter than it would be expected?

W807 would be a suspect if the beam limiter isn't working but the flutter is the strangest symptom, as VT607 begins to conduct it should just shunt the charging volts to C606 without the effects on picture stability we are seeing. I can't really see it but you could try replacing C520 which is across the current sensing resistor. Of course as I said it could be noise from one of the supplies getting back into the drive, it's all a bit chicken and egg and to prove requires breaking the feedback paths and feeding in external supplies which could be risky. 

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Posted : 27/06/2018 9:48 pm
Jayceebee
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Not sure what I did there. Duplicate post deleted.

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Posted : 27/06/2018 10:25 pm
Jayceebee
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Ah tried to add a PS and I did something wrong.

PS. Here's something to try if you're willing which might be a good idea, to lighten the load on the chopper disconnect the feed to VT812 collector the 24V regulator and feed your new variable PSU set to 24V of course into the emitter? Might be wise to include a beefy diode in series with the +ve supply to prevent the possibility of any feedback. If you do try it keep the bri/con very low and also the set EHT before slowly advancing.

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Posted : 27/06/2018 10:30 pm
crustytv
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In response to a guest post (not approved), yes I have replaced C606, ages ago! and no I'm not just concentrating on semiconductors, I've been checking all suspect (to me and those suggested by John and others) components. If you're finding it frustrating reading then I suggest you avert your eyes elsewhere.

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Topic starter Posted : 27/06/2018 11:30 pm
crustytv
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I thought I'd recheck W529 & W530 both 6.2 zeners, using the test procedure I showed with a power supply.  W529 zener effect kicked in at 6.2V, good, however W530 did not until it reached 10.1V, next test 4.7V and the next all the way up to 20+V its very intermittent.  I replaced and hoped it might be the problem but no, the fault still persists.

I think after spending a month on this now I'm going to put the back on and come back to it much later. I want to move on to another set as frankly I had my fill of the 9000 chassis and I have plenty of other sets waiting in the queue. You can't win all the battles.

 

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Topic starter Posted : 28/06/2018 9:22 am
Nuvistor
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A rest is a good idea, find an easy one for your next assignment. The 9000 will keep you company this winter when it’s snowing outside.

I have always been of the opinion that no one can fix all the faults they are presented with, or was that just my excuse when I couldn’t fix something without help.  ? 

We had a manual at work and in was the message, if you get stuck, walk away for 15 mins with a tea/coffee, if that does not work call in another set of eyes on the job.

Not sure with the low level of patience that seems to be around when the internet fails that it would be accepted now.

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Posted : 28/06/2018 12:13 pm
crustytv
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Indeed Frank, I've done my best with this set, its in a far better state than when I first started so that's a positive I can take away from it. Not sure I have any easy sets as most of mine are ravaged by time, storage or past bodgers so I'm not sure what to tackle.

I was thinking of going back to my favourite the 3000 series and crack on with the Marconiphone 4711 PSU and LTB rebuild, that's been long overdue. However I'm quite tempted by the set I was going to start instead of this 9k6, that being the cable version of the Rediffusion MKI CH2213 which also involves a Frequency Translator box.

I think a few days break and then I'll decide.....

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Topic starter Posted : 28/06/2018 12:50 pm
Jayceebee
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No problem Chris, a better line of approach can be made if and when another set comes along and substitution can be made to narrow down which PCB the fault or faults are located.

Fault finding at a a distance is always going to be more difficult and I can understand some people becoming frustrated as everyone has there own methods.  I wish I had had the time to see the set first hand, sometimes you spot things that someone else may think insignificant or unconnected but could have a huge bearing on where the problem lies. Also on some occasions you need all of your senses to find some faults (yes, even taste sometime but I won't go into that one). At least you've learned that sometimes what appears to be a raster isn't i.e. due to the DC flowing through the scan coils caused by that s/c cap, you won't forget that one.

Better luck with the next one whatever it is but please don't a complex about the 9000 and 9600, you've just been unlucky. The former, yes a bit quirky but the latter a well sorted set. If Thorn had gone with Mullard instead of RCA, fitting a 20AX and updating the decoder chipset (the original lifted straight out of the 8500/8800) then I think it would have been held in much greater regard, up there with the G11.

John.

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Posted : 28/06/2018 8:07 pm
PYE625
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Posted by: Chris

I was thinking of going back to my favourite the 3000 series and crack on with the Marconiphone 4711 PSU and LTB rebuild, that's been long overdue.

That's probably a good idea because it will provide something familiar and will help restore a sense of pleasure, rather than frustration in the workshop.

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Posted : 28/06/2018 8:30 pm
neil1974
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If you feel the need to fix another similar set I have a 9650 here waiting ? .

Cheers

Neil.

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Posted : 29/06/2018 12:23 am
crustytv
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Posted By: Neil

If you feel the need to fix another similar set I have a 9650 here waiting ? .

Cheers

Neil.

Hi Neil, 

That's a lovely little console set, if I remember correctly that 9650 appeared on e-bay about 3-4 years ago and you saving it.

What I would really like if you can help are spare 9600 panels, specifically scanning, PSU, Syclops II (not 9000 syclops I) and Oscillator modules. If you have any I'm prepared to pay.

https://www.radios-tv.co.uk/community/sales-wants/thorn-9600-spares/

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Topic starter Posted : 29/06/2018 6:50 am
neil1974
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Hi Chris, Unfortunately the set is the only thing I have left as far as the 9000 chassis is concerned. so if you wanted to break the set for parts then I wouldn't mind as it saves me worrying about it like I seem to do with most of my stuff ? .

 

Cheers

Neil.

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Posted : 29/06/2018 11:07 am
crustytv
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Hi Neil, 

Well I'd love to take it off your hands and I wouldn't even need to break it for spares, I could just swap boards in and out between the two sets to isolate faults in either TV. So if you could reserve it for me that would be fantastic, its a lovely looking set too. ? 

Now the problem is how to get it from you to me, I'll put a transport request in you never know who's passing by and maybe we can get a chain from you to me. 

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Topic starter Posted : 29/06/2018 11:29 am
crustytv
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Yesterday I was at Mikey66's gaff to collect another TV, I also took with me the suspect boards from this troublesome 3734 to try in Mikes working 9600.

Remember, my fault is very low peak-flyback and a significantly reduced raster.

The following was the order of events and the results.

  • Tried my Sysclops in Mikes set, no fault present: Syclops eliminated as cause
  • Tried my Syclops and my oscillator, no fault present: Syclops and osc eliminated as cause
  • Tried my PSU, my Syclops and my oscillator, no fault present: PSU, Syclops and oscillator eliminated as cause
  • Tried my scanning module, fault present but raster not drastically reduced (odd). Peak flyback is reduced

 

** Established fault now lies somewhere within the scanning module **

 

  • Tried my scanning module with Mikes e/w module, fault still present. Peak flyback still reduced. E/W eliminated as cause
  • Tried my scanning module with Mikes tripler, fault still preset. My tripler eliminated as cause
  • Mike finds a couple of dry joints, re-flowed, fault still present. This time the heavily reduced postage stamp raster made an appearance. Good!
  • Tried my scanning module with Mikes LOPT installed, fault still present. Eliminated my LOPT as cause

 

At this point Mike Gary and myself all agreed that we had eliminated the PSU, the oscillator, the syclops, the e/w module, the tripler and the LOPT. It now only remained to component level fault find the scanning module back at the crusty workshop.

Mike removed his LOPT and refitted my original LOPT. Mike also decided he wanted to check his work at refitting the LOPT and reinstalled my scanning module, PSU with syclops and osc and powered up one last time. To our collective surprise and synchronised jaw-drop, we were presented with a stable virtually full screen raster. Mike set the Peak flyback adjusted width and height and  left it running for 20 mins or so, it remained stable as did the peak flyback volts.

I've just this minute installed the modules back in my set and can confirm all is now OK here too. The back is swiftly going on and the set will be prised from its sedentary position on the bench, finally!

What, why and how? Don't ask, none of us had a clue either.

fix

 

 

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Topic starter Posted : 05/08/2018 3:18 pm
PYE625
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"To understand the black art of electronics is to understand witchcraft."

Surely it proves an intermittent somewhere on your scanning module Chris?

 

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Posted : 05/08/2018 4:21 pm
crustytv
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Posted by: PYE625

Surely it proves an intermittent somewhere on your scanning module Chris?

One might have assumed that, only it never showed as an intermittent before and its certainly not intermittent now.  No amount of flexing or vigorous, bordering on aggressive tapping with an insulated screwdriver, could bring it on again at Mikes or today in my workshop.

Anyway, its done and to be honest I'm glad to see the back of it on it  ? 

 

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Topic starter Posted : 05/08/2018 6:12 pm
Jayceebee
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Well that was an adventure, shame we don't know the full reason. It may only last a few days/weeks or may never rear it's ugly head a gain. At least you learned a lot about the 9600, I hope it hasn't put you off as your symptoms were very unusual.

You now know your way around ready for the day your 7132 arrives. It's remote control/ramp tuning circuitry introduced us to digital techniques.

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Posted : 05/08/2018 9:37 pm
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