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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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10th Apr 2021, 3:17 pm | #1 |
Triode
Join Date: Feb 2021
Location: Dunstable, Bedfordshire, UK.
Posts: 12
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Thorn / BRC850 repair
Hi,
I've recently been working on a BRC850 TV I've owned since the 1970's. Numerous capacitor and a few resistor replacements later I have a reasonable picture and sound. Despite reading OK, C86 and boost reservoir capacitor C89 went bang at first power on but no harm done. I only have a VHS player to use it with and would like to receive TV programmes. I am tempted to buy a PROception Promod1 UHF AV modulator, would this work with my Freeview box? I've attached a couple of pics, fortunately finding a tape that didn't involve some friendly girls and blokes with mullets Best wishes Graham |
10th Apr 2021, 5:30 pm | #2 |
Hexode
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
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Re: Thorn / BRC850 repair
Congrats on the picture! I have just started out on an 850 myself, and like you had the mains filter explode with a spectacular bang! I usually cut them out before plugging in, but forgot. The dropper on mine was like a Christmas Tree but I managed to find an NOS one on Ebay. I've just re-capped it and will be switching on again soon.
That modulator should work fine. I notice it's not in stock at Amazon presently |
10th Apr 2021, 7:41 pm | #3 |
Triode
Join Date: Feb 2021
Location: Dunstable, Bedfordshire, UK.
Posts: 12
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Re: Thorn / BRC850 repair
Thank you for the information on the modulator.
I removed and measured many of the capacitors but only replaced those out of tolerance which was the majority of them. The dropper in mine has one replacement resistor and that area could do with tidying. I see the part is currently available on Ebay so I think its worth buying now I know the set is basically good. Good luck with your 850. |
10th Apr 2021, 10:13 pm | #4 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,727
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Re: Thorn / BRC850 repair
Why not connect the AV of the Freeview box to the VHS?
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-- Graham. G3ZVT |
11th Apr 2021, 7:46 am | #5 |
Hexode
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
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Re: Thorn / BRC850 repair
The paper caps may read ok when cold and on low voltage but you may well find that they do funny things with voltage and heat, Progressive frame non-linearity is a common one on these sets
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11th Apr 2021, 8:44 am | #6 |
Pentode
Join Date: Jul 2020
Location: Staines, Surrey, UK.
Posts: 131
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Re: Thorn / BRC850 repair
Well done Graham
I had to take a second look as the chassis looked just like mine. (posted yesterday). Strange for another FM 850 to pop up next day. It does help with some confusion. Looks like someone bodged an RS R.21 dropper in mine whilst yours has an R.22. That is how it should be. What flavour is that 850? Ultra HMV Fergy The audio in these sets is rather good. In that separate sound box and good sized speaker. Still changing caps in mine. Simon |
11th Apr 2021, 9:01 am | #7 |
Pentode
Join Date: Jul 2020
Location: Staines, Surrey, UK.
Posts: 131
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Re: Thorn / BRC850 repair
Yes I use the Proception modulator. It has scart input which I currently feed from a cheap LG DVD which also has a USB port on which I have a stick of test cards.
I can recommend it. |
11th Apr 2021, 10:33 am | #8 |
Triode
Join Date: Feb 2021
Location: Dunstable, Bedfordshire, UK.
Posts: 12
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Re: Thorn / BRC850 repair
Thank you all for your replies.
The set is badged as 'Red Arrow' which I assume is a long defunct TV rental company. I agree, the sound is rather good and undoubtedly helped by a a decent sized speaker. Strange a similar 850 surfaces on here the same day! Despite only changing capacitors that read out of spec the the set has remained stable after 1 hour of use. Time will tell with further use of course. Obvious really, but the VHS works fine as a UHF modulator. I was rather slow there and I like the idea of getting a test card up as some linearity and picture positioning are still required. It looks like there should be some sort of cover over the LOPT and EHT rectifier. Is this correct? Regards Graham |
11th Apr 2021, 12:34 pm | #9 |
Pentode
Join Date: Jul 2020
Location: Staines, Surrey, UK.
Posts: 131
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Re: Thorn / BRC850 repair
Yes Graham there is a cover on the EHT section.
Well done though I am cracking on with caps and resistors. Hopefull now as 405/625 working. Simon |
11th Apr 2021, 12:46 pm | #10 |
Pentode
Join Date: Jul 2020
Location: Staines, Surrey, UK.
Posts: 131
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Re: Thorn / BRC850 repair
Can I also recommend a Panasonic TU-CT20 freeview box?
Very cheap on Ebay but they do have a fully tunable UHF modulator. Mine looks very sad but does the business. |
11th Apr 2021, 1:08 pm | #11 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Thorn / BRC850 repair
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11th Apr 2021, 2:01 pm | #12 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,147
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Re: Thorn / BRC850 repair
Yes Lawrence. I would be happy with 50p! It's amazing how many of these chassis were produced. They would turn up in many brands including Decca.
This is an Ultra 6818. I have it has been hanging around me for about 30 years and still gives a good picture. It came straight on having been stored away for many years. You are lucky with that one Graham. Most of the ex Granada 850's were completely shot to bits by the time they were released from rental. As Stephen mentioned, every capacitor on the bottom chassis needs to be replaced if you want it to be reliable. The good old Dubiliar blue caps, after sixty years are leaking. Not really surprising, they did well! It's no use just testing them. Pay particular attention to the 2X.01uf usually small grey types in the frame circuit. They test ok but always give poor frame linearity. It should be 100%, no creep and plenty of spare travel with the preset pots. The 22k anode load, hidden behind the 1/2 frame oscillator 6/30L2 burns to powder but it has probably been replaced by now. The same goes for the 47K and 5.6K resistors in the video output bias stabilizing circuit. The same goes for the caps on the I.F. plate. The ones decoupling the AGC line go leaky resulting in the contrast control being unable to reduce the gain to a low level giving a 'soot and Whitewash' picture. Not a bad UHF performance but a pain to change standards. Regards, John. |
11th Apr 2021, 2:45 pm | #13 | |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,727
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Re: Thorn / BRC850 repair
Quote:
I started as a Junior Improver (apprentice teaboy) at a GTVR workshop adjoining a showroom in Salford in 1971. when not engaged in sweeping the floor or making the tea I must have refurbished thousands of 850's and 900's, so they are very evocative to me, but not entirely in a good way. Even back then they were getting past it, but we kept them going including fitting new CRTs when required in order to fuel the decontrolled TV rental market. The government mandated a hefty down-payment on any TV rented that was less than three years old.
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-- Graham. G3ZVT Last edited by Graham G3ZVT; 11th Apr 2021 at 2:59 pm. |
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11th Apr 2021, 5:57 pm | #14 | |
Triode
Join Date: Feb 2021
Location: Dunstable, Bedfordshire, UK.
Posts: 12
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Re: Thorn / BRC850 repair
Quote:
Regards Graham |
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11th Apr 2021, 6:05 pm | #15 | |
Triode
Join Date: Feb 2021
Location: Dunstable, Bedfordshire, UK.
Posts: 12
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Re: Thorn / BRC850 repair
Quote:
I'll have to try and find an EHT cover. I guess I removed it for some strange reason when I was a youth and is now long gone. Good luck with your recap! Regards Graham |
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11th Apr 2021, 6:54 pm | #16 |
Pentode
Join Date: Jul 2020
Location: Staines, Surrey, UK.
Posts: 131
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Re: Thorn / BRC850 repair
Thank you all.
So much invaluable experience on the forum. My pipe is lit and my iron is on as I currently do caps and so forth. I shall put up results presently. |
11th Apr 2021, 10:24 pm | #17 |
Nonode
Join Date: Sep 2017
Location: Stockport, Cheshire, UK.
Posts: 2,007
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Re: Thorn / BRC850 repair
Nice to see, was this Thorn's first dual standard chassis?
I can see from the label it was made even before BBC2 started, though some dual standards were made for the Irish market before then, normally with the option to tune VHF on 625 lines. It's not been locked onto 625 lines, which seemed to happen to many dual standard sets to improve reliability.
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11th Apr 2021, 11:56 pm | #18 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,727
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Re: Thorn / BRC850 repair
Well, sort of.
There was an earlier 700 "convertible" chassis with a functioning time base system switch on the side of the cabinet, but a 405 line only signal board. I don't recall ever seeing an official conversion kit to dual standard though, perhaps someone could confirm if there was one.
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12th Apr 2021, 12:28 am | #19 | ||
Heptode
Join Date: Aug 2009
Location: High Wycombe, Bucks. UK.
Posts: 811
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Re: Thorn / BRC850 repair
Quote:
All of the secondhand ones I've come across have out-of-date software in them. There is a serious bug. If you live in most of the UK, the box will crash during re-tuning and will be unable to complete the tuning procedure, making it useless. The problem seems to be caused by some of the COMmercial Freeview multiplexes having a lot of channels on them. Many of the "channels" are just data or links to on-demand services which the box can't receive anyway, but this doesn't matter. If a multiplex contains too many channels, the box suffers a memory overflow and crashes before it can store them. There is a way round this, but you won't be able to receive ANY of the channels on the affected multiplexes. You need to connect the box via SCART to a TV with SCART or an external modulator - the built-in modulator is turned off during tuning so you can't otherwise see what's happening. Start the tuning process and watch the progress bar on the TV screen. At some point it will stop completely - the box has crashed. Mark the point on the screen. Unplug the box from the mains, start tuning again, watch the progress bar and very quickly unplug the aerial lead from the box just before it reaches the point where it crashed last time, then plug the aerial in again after it has gone past the crash point. It may crash at more than one point during the tuning process. If necessary, repeat the unplug the aerial step until the tuning is finished. At the end, you should have some Freeview channels, usually in random order, but better than nothing. Panasonic broadcasted an over-the-air software update to fix this problem, but the update did not install automatically - the user had to be watching a BBC channel and click OK to accept the update which would interrupt their viewing - many people didn't. The last update was broadcast in 2009 and of course over-the-air software updates for Freeview boxes have ceased, so there is no way to update an old Panasonic box now. There is a software update option in the menu, but it will search and wrongly tell you that the software is up-to-date even when it isn't - it just means the box couldn't find any newer software on-air. You may be lucky to buy a secondhand box that has been updated and will tune in properly. If you live in an area like High Wycombe where you can't receive any COMmercial Freeview multiplexes, only BBC, ITV, C4 & 5, the box will still tune in and work even if it has old software. Even then, I don't really recommend it, especially not if you want to use it with an old black-and-white TV. The menu colours make it very difficult to see which option is highlighted, also the modulator gets turned off during tuning and is reset to a random channel afterwards. I've had lots of frustration with these boxes and want to warn people. This is a shame, as the hardware (box and external power supply) is otherwise very reliable. Some Freeview boxes with built-in modulators that work well: Goodmans GDR10 and GDR11, Humax F2-Fox-T and PVR9200T , Thomson DTI2300 (these are all old, and may need power supply capacitors replacing, but that's an easy job for a vintage TV restorer!) |
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12th Apr 2021, 10:52 am | #20 |
Hexode
Join Date: Jan 2007
Location: Beckenham, London, UK.
Posts: 373
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Re: Thorn / BRC850 repair
Interesting crop of 850s . I have fully recapped mine and put the repaired LOPT back in (someone had obviously caught one of the lead out wires and snapped it off half inch from the core. A very delicate repair), also a NOS dropper as there was a complete bodge up mess of resistors all over the original. I haven't seen a picture on it yet because the tube is out of the cabinet while I do some woodwork repairs, but the EHT meter is showing a hefty 16KV + and the tube reads good on a tester.
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