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Old 25th Feb 2005, 7:40 pm   #21
davegsm82
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Talking Re: Fixing a Ferguson Colourstar

Oh well, happy days then. note to self BRC4443 = BT116 = SCR957 and probably most other SCR devices of this period. Ok, well, pyoor I need your addy and I'll send these bits and pieces off to you. After looking at the diagram, as a way of testing i'd like you to check C704 + C706 which are the main filter caps on the "secondary" (as it were) of the PSU. I'm not sure if they are the ones you replaced earlier (the ones you said leaked) but it would make sense if theyre drawing lots of current or have gone O/C. (also, erm, this may be a stoopid question, but er.. you havent got them in *backwards* have you?).

If you want to test to see if the BU208 is pulling the system down you can disconnect its collector feed, this is the wire which goes to the main outer case of the transistor, dont touch the wires leading to its pins. Make sure you insulate the wire once disconnected, it will be at the same potential as C704,6.

BTW I'll need to know if you definately what this seat and tank from the ETZ251 too, allthough i'll send these separately (obviously)

Good Luck.

Dave.
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Old 1st Mar 2005, 6:51 pm   #22
pyoor
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Default Re: Fixing a Ferguson Colourstar

Quote:
. After looking at the diagram, as a way of testing i'd like you to check C704 + C706 which are the main filter caps on the "secondary" (as it were) of the PSU. I'm not sure if they are the ones you replaced earlier (the ones you said leaked) but it would make sense if theyre drawing lots of current or have gone O/C. (also, erm, this may be a stoopid question, but er.. you havent got them in *backwards* have you?).
C704 and C706 are the two that were replaced, and then unreplaced in the quest to find out why the set had gone from sick to dead. 704 is the leaky one, quite definately signs of having expelled some electrolite, but it's still working-ish. C706 looks okay, tests okay, but we replaced it anyway. At the moment the original caps are back in the tele for the sake of debugging the new fault.

Quote:
If you want to test to see if the BU208 is pulling the system down you can disconnect its collector feed, this is the wire which goes to the main outer case of the transistor, dont touch the wires leading to its pins. Make sure you insulate the wire once disconnected, it will be at the same potential as C704,6.
Rightho, that I can manage

I'll be sure and update you, if coredump doesn't!
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Old 13th Mar 2005, 11:28 pm   #23
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Default Re: Fixing a Ferguson Colourstar

Progress, of sorts...

Changing the line output transistor (the one we took out was shorted) resulted in the set working(ish) for about half an hour.

The picture was in sync, monochrome, and sound was fine but there was a bright band vertically on the picture. The band was about 1/3rd of the way from the left hand side and about 1/5th of the width of the raster. The band had straight, stable edges and it appeared that the line scan had "folded over". That it is to say that the band was brighter, it appeared to be being scanned twice per line.

This implies that what should have been a smooth saw-tooth wave, was not; it must have returned to zero and started climbing again?

After about half an hour, the cut-out tripped. On reseting the cutout the fuse blew, and it appears that the line output transistor is dead again. However, on further examination it also appears that the Line Output Transformer is deceased - the top of the transformer has lifted away, and some insulating material has expanded into the space (line output transformer from the side).

Can anyone suggest where I might be able to obtain a suitable line output transformer (and another (few) BU208 transistors!). Also, is it separate from the tripler (shot of link to tripler) or do I have to get both (and should I get both?!)

...And is there anything else we should be looking at.

--
Kate E
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Old 14th Mar 2005, 12:30 am   #24
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Default Re: Fixing a Ferguson Colourstar

Hi There
Sorry to hear about your on going problems. But if you take a look at " Radio Sets offered" there is a Thorn 8500 on offer. I would not be surprised if the moderators moved it to the Vintage TV &Video list in the near future though!
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Old 14th Mar 2005, 12:53 am   #25
Danny
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Default Re: Fixing a Ferguson Colourstar

Hi the the eht tray is probrably ok but check the harmonic tuning caps as it sounds as if their is trouble in this neck of the woods. it could be the lopt though! i dont remember having to many go if i remember the eht tray contained 1 stick rect and the focus metrosil . the caps to check are the ones connected to the colector of the BU208 then replace the transistor and
switch on then switch off remove the mains plug and feel the lopt to see if its hot if it is hot then the overwind has shorted turns these lopts do turn up sometimes as NOS when tv shops close.
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Old 14th Mar 2005, 9:22 am   #26
Mike Phelan
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Default Re: Fixing a Ferguson Colourstar

Hi Kate
To test the EHT tray, just disconnect it from the overwind or take the final anode cap off the CRT and see if you can draw a spark from it without earthing it (careful!!). From your symptoms, though, it seems as though there may be something wrong with the line drive to the base of the BU; if it is not being switched on and off fast enough, it will overheat and fail. ISTR a few official mods to the base circuit. Indeed, it could also be the 5th harmonic tuning cap breking down - usually green, and mounted on BU heatsink. Value and type are critical.
HTH
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Old 14th Mar 2005, 7:57 pm   #27
pyoor
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Default Re: Fixing a Ferguson Colourstar

Quote:
Originally Posted by Hybrid tellies
Hi There
Sorry to hear about your on going problems. But if you take a look at " Radio Sets offered" there is a Thorn 8500 on offer. I would not be surprised if the moderators moved it to the Vintage TV &Video list in the near future though!
Cheers for that; I tend to feel that 15 quid is a bit steep though, for a non-working set (being as I've had 2 of these, the most expensive of which cost me a quid).

The problem as I currently see it is that without replacing the BU208 we can't do any more testing; and if I do buy a bunch of BU208s, and it turns out to need a new lopt, then I'm pretty much stuffed and I'll have spent money on a telly that I can't really afford to spend. That and the fact that in the time it was on it's managed to sprout more than one set-killing fault perturbs me.

It must be said I'm erring on the side of ditching it in favour of a new set (I realise this is probably some kind of sin). I think I'll maybe have a look at this harmonic tuning cap and if it's dead then I might fork out for another BU208 (or a couple)... but I'm yeah. Hrm. Thinking (<--- poor nursing student who's money really *should* go on food!).

Cheers for all your help guys!
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Old 15th Mar 2005, 1:48 am   #28
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Default Re: Fixing a Ferguson Colourstar

Try CPC or RS for starters for replacement BU208's. In the meantime check the Harmonic tuning cap C406 as previously mentioned and on the line driver side check C408 & R466 which are mounted between the base and emitter legs of the BU208, R408,R406 & C410 which are on the timebase board. Also look for dry joints particularly around the line driver transformer.
If you do replace the BU208, fit a 220 ohme 15w resister in series with the HT line and turn the set eht control to minimum. On switching on if the HT across C704 is 150v,or more, then you have a fault in the power supply. If it is low bring the voltage on the power supply up to 170v and if all is well you should have a picture but with lack of width. Then you can remove that 220 ohme 15w resister from the HT line. But if you still have a fault then you will still see that band and line foldover without blowing another BU208A straight out.
As an ex Radio rentals engineer I seemed to remember the Jelly potLine output transformers on these Thorn sets were very reliable and I have never seen one split like this before. If the line output transformer is faulty (which I suspect it is) it could be very difficult to source. The only chance would be from another scrapped set or perhaps someone who has got one stashed away in their loft or garage.
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Old 15th Mar 2005, 11:19 pm   #29
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Default Re: Fixing a Ferguson Colourstar

Quote:
Originally Posted by Hybrid tellies
As an ex Radio rentals engineer I seemed to remember the Jelly potLine output transformers on these Thorn sets were very reliable and I have never seen one split like this before.
Well, the internal "Jelly" was making a desparate bid for freedom, and had managed to pop the top off its little "pot"! I suspect that the LOPT will need to be replaced. We'll have a closer look at it because it may have a part number on it somewhere. I've seen lists of LOPT spares on web sites where the only identification is a part number. There seem to be entire factories in China that make these things and nothing else, and they go by the part numbers!
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Old 16th Mar 2005, 1:21 am   #30
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Default Re: Fixing a Ferguson Colourstar

Let us know how you get on. It could be you have found a source of line output transformers which could be useful for many of us.
Good luck.
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Old 19th Mar 2005, 12:49 am   #31
davegsm82
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Default Re: Fixing a Ferguson Colourstar

Incidentaly, SEME sells LOPTX's identified solely by the part number, usualy something like xxxx.xxxx or similar, i know this set is old, but you never know, i was repairing those DORIC/Rediffusion sets up to about a year ago (now who DID that chassis belong to originaly?) and some parts were still available for those.

Good luck...
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