Granada Television Brochure, 1970s
Long Gone UK TV Shops
Memories of a Derwent Field Service Engineer
PYE Australia Circa 1971
Radios-TV VRAT
Fabulous Fablon
Thorn TX10 Chassis
Crusty-TV Museum, Analogue TV Network
Philips N1500 Warning!
Rumbelows
Thorn EMI Advertising
Thorn’s Guide to Servicing a VCR
Ferguson 3V24 De-Robed
Want to tell us a story?
Video Circuits V15 – Tripler Tester
Thorn Chassis Guide
Remove Teletext Lines & VCR Problems
Ceefax (Teletext)
Suggestions
Website Refresh
Colour TV Brochures
1970s Lounge Recreation
CrustyTV Vintage Television Museum
Linda Lovelace Experience
Humbars on a Sony KV2702
1972 Ultra 6713
D|E|R Service “The Best”
The one that got away
Technical information
The Line Output Stage
The map
Tales of a newly qualified young engineer.
Tales of a Radio Rentals Van Boy
Sanyo SMD
Disastrous Company Rebranding
1969 Philips G22K511
Memories Of The TV Trade
Crazy house
Dirty TV screens
Dual Standard and Single Standard CTV’s
Radios-TV on YouTube
The Winter of 62/63
A domestic audio installation
1979 Ferguson Videostar Deluxe 3V16
Music centre modifications
Unusual record player modification
B&K 467 Adapters
Mishaps In The Trade
1971 Beovision 3200
1971 Bush CTV1120
Granada Television Brochure, 1970s
Long Gone UK TV Shops
Memories of a Derwent Field Service Engineer
PYE Australia Circa 1971
Radios-TV VRAT
Fabulous Fablon
Thorn TX10 Chassis
Crusty-TV Museum, Analogue TV Network
Philips N1500 Warning!
Rumbelows
Thorn EMI Advertising
Thorn’s Guide to Servicing a VCR
Ferguson 3V24 De-Robed
Want to tell us a story?
Video Circuits V15 – Tripler Tester
Thorn Chassis Guide
Remove Teletext Lines & VCR Problems
Ceefax (Teletext)
Suggestions
Website Refresh
Colour TV Brochures
1970s Lounge Recreation
CrustyTV Vintage Television Museum
Linda Lovelace Experience
Humbars on a Sony KV2702
1972 Ultra 6713
D|E|R Service “The Best”
The one that got away
Technical information
The Line Output Stage
The map
Tales of a newly qualified young engineer.
Tales of a Radio Rentals Van Boy
Sanyo SMD
Disastrous Company Rebranding
1969 Philips G22K511
Memories Of The TV Trade
Crazy house
Dirty TV screens
Dual Standard and Single Standard CTV’s
Radios-TV on YouTube
The Winter of 62/63
A domestic audio installation
1979 Ferguson Videostar Deluxe 3V16
Music centre modifications
Unusual record player modification
B&K 467 Adapters
Mishaps In The Trade
1971 Beovision 3200
1971 Bush CTV1120
Thorn 8000A troubles.
Hoping that there's a few people around as it seems to have gone a little quiet in this colour tv section of late ☹️
Anyway...one of the sets that gets used on rotation in the kitchen/diner in our house is this Baird 8770 which is fitted with the Thorn 8000A which uses a upgraded signals/chroma/video panel designated PC856. This was one of the latest versions and had all the improved performance mods. The set is also fitted with a varicap tuner and a six button selector bank.
The problem is that there is an intermittent fault which can only be described as a picture disturbance somewhat akin to the aerial plug being wiggled around. It does not always do it and is highly intermittent in nature. The fault can be cleared temporarily by very quickly switching on and off.
I had some time today to sling the set on the bench and see what could be done. The circuit in the signals path is quite different to the original panel but applying heat and freezer to the IF amplifier transistors (all Lockfit types) and their nearby components could not tempt the fault to show itself, surprise, surprise! Moving across to IC1 a TCA270S which contains the functions of IF AGC, vision detector and various other associated duties and a blast with the hairdryer caused to fault to happen but not for very long. Alternate sprays of freezer and hairdryer could not provoke this to happen again.
What I did notice though, its how hot this IC runs. It is almost too hot to touch. Surely for a small signals type of IC, it shouldn't be too hot should it? Any thoughts on this?
Meanwhile, here's a few shots of the set on the bench.
All the best for now,
Tas
Posted by: Tazman1966
What I did notice though, its how hot this IC runs. It is almost too hot to touch. Surely for a small signals type of IC, it shouldn't be too hot should it? Any thoughts on this?
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Yes that’s the thought I had, just checked the specification.
https://www.digchip.com/datasheets/parts/datasheet/1019/TCA270S-pdf.php
Perhaps worth checking the components around the chip before condemning the chip.
Frank
Thanks Chris, thanks Frank.
I'll have a further check on it in a little while and see how the land lies.
Tas
Back in from the workshop and I've checked the components on the periphery of the IC and all is okay. The voltages on the pins of the IC are all roughly correct as per the circuit. Obviously the 25V rail is also spot on - well, it's actually 25.2V! I did change a couple of the decouplers as in the words of the late great Les Lawry-Johns "beware the blue tants"! He was also referring to this type of board!
A further development now though is that I cannot for love nor money provoke the fault! Should I wrap it up and hope for the best? Anyone else got an 8000A/8004/8800 with this designation of signals/chroma/video board that could check the operating temperature of the IC. The PCB is slightly darkened in the vicinity of the IC so I reckon it may always have been like it...
Tas
I might be tempted simply to replace the IC as they may be had for a couple of quid from ebay and it would rule it out.
To understand the black art of electronics is to understand witchcraft. Andrew.
Hi Tas,
my 8800 signals panel is not the PC856 but the previous incarnation the PC819. Like yours it uses the multi-signals processor TCA270s. There's no darkening of the surrounding PCB on mine and I don't recall it being too hot to touch when I was mapping voltages during diagnosing a fault on my 8800. I remember this because I removed it and installed another to eliminate it from suspicion and it was not hot.
I can't imagine Thorn would have a cool running PC819 signals processor, then move to a hot running one for the modded PC856 version, still you never know. I can't get to my 8800 it present but here's a photo I took at the time of the signals PCB, as you can see, no toasting around IC1.
CrustyTV Television Shop: Take a virtual tour
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As Andrew said it is worth changing, it is in a socket as well so it’s an easy test.
Frank
Thanks chaps!
I'm going to pop down to Cricklewood Electronics after work tomorrow and pick one up and also a couple of other bits and bobs. They're only just down the road from where I work in Edgware and their stock is really good indeed. Not many shops like this left nowadays.
TTFN,
Tas
Ah ! Cricklewood.... been using them since the early 90's for mail order bits and bobs.
To understand the black art of electronics is to understand witchcraft. Andrew.
A thumbs up here also for Cricklewood Electronics. Managed to source NEC transistors for the reel drive bridge and also belts for my 8924.
Just for completeness the 8770 uses the 8004 chassis, it should be fitted with the PSU from the 8800 with the overvoltage circuit.
John.
Sure enough, I did pop to Cricklewood Electronics and got the required IC plus a few more bits and bobs.
I put the new IC in and switched on and as far as can be seen, the picture "disturbance" has gone. The IC does still run very warm but not too hot to touch now. All this was done a few days ago but it's only now that I had the opportunity to post on here.
I really do like this little set and I know it would be even better with a first class CRT like my 17" Ferguson 3727 (Thorn 8004). I'm still after an HMV version of the 8000 with the gorgeous bevelled edged real wood cabinet. One day maybe...
I dare say the thick film resistor just below the IC generates a fair proportion of localised heat, judging by the discolouration of the pcb and that of the yellow wire above it.
A cracking little set and one to be proud of. ?
To understand the black art of electronics is to understand witchcraft. Andrew.
You're right. That gets hot too!
Nice bright picture, glad the chip sorted it out and was easy to obtain.
Frank
Looks very good ? . That later PC856 five IC decoder was a big improvement over the earlier three IC version and performance more uniform, although with a good signal the three IC type performed reasonably well it was not so good in marginal areas. Does anyone remember the white inverters hung on the back of sets with it's edgewise volume control in Rediffusion cabled areas used to feed aerial sets? These did not not sit well with the early 8000/8500 decoder.
I have to say that from your pictures the raster correction doesn't look too bad at all even though there's no circuitry fitted.
John.
One of my first jobs when i started work for Rediffusion in 1975 was fitting inverters to aerial sets. Went round customers homes fitting improved audio t/x to them in cases of low volume, Malc.
Thanks for the comments, chaps! We had relatives over a couple of weekends ago and this set was trundled outside into the garden and had Glastonbury on it and it performed impeccably even in the strong sunlight. No lumbering of sets for me though for the next couple of months though following a groin hernia operation on Monday just gone.
All the best,
Tas
Speedy recovery Tas, feet up for now.
Frank
Thanks Frank 🙂
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