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Tech Chat The Thorn 4000 Thread

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crustytv
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I've long sought a 4K, know where one is, and have been in negotiations with the owner for a long time, It may come to fruition, it may not, we shall have to see. Very little info exists out on the web with regard to 4000 repairs, so this thread will at least serve to plug that gap and detail some information about the infamous 4K.

Recently I was loaned the 4K service manual, now, I was aware there were a number of thick film units employed, but to my horror I discover there are over 22 of them!

Now foolishly I always thought, that despite these being prone to failure it should be possible with data, to fashion a replacement on a mini PCB, replicating the components that were in the TFU....... errr No! Looking at the circuit, Thorn failed to describe what the values are. Why would they, at the time you would just order up another and I doubt they expected anyone in the 21st century would be repairing one of their sets.

All you can tell from the cct is that they contain resistors, transistors, inductors, diodes and caps etc.

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The tally:-

  • 7 TFU's on the Hoz timebase
  • 3 TFU's on the Vert timebase
  • 5 TFU's on the signals board
  • 6 TFU's on the convergence Neck module
  • 1 TFU on the handheld convergence unit

I see no way out of this problem should I end up with a set having multiple TFU failures. I'll be scanning the 4K service manual in due course for the data library.

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Topic starter Posted : 10/09/2021 8:08 pm
Till Eulenspiegel, Jayceebee, freya and 1 people liked
Red_to_Black
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I think the Aussies (Irob ?) had some details for discrete replacements but no doubt that will now be lost to the sands of time!

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 10/09/2021 8:23 pm
Jayceebee
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It’s a long time ago but I thought I had seen manuals with resistor values for hybrid TF units but no details of semiconductor types, maybe I dreamt it or possibly it was only in early publications, possibly member jcdaze may be able to add to this.

Sadly due to these specialised and now unobtainable components restoration could prove very difficult. The most unreliable ones without doubt are the ones shown on the convergence neck module circuit, one on the handheld convergence unit and one in the PSU. Again it’s long ago but the I don’t remember having to change many of the ones which were just low wattage resistor packs similar to those in the 8k, 9k and 9k6 although the one used in the 9k PSU was known to give trouble but that was hybrid containing a single zener.

The most complex hybrid unit if I remember correctly was used in the frame generator stage. Back in the day I don’t remember ever having to change one, likewise with the similar type used on the very late 3k5 frame & sound board.

John.

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Posted : 10/09/2021 9:22 pm
crustytv
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You're right John, my bad, the details are in the manual, just not on the circuit, that'll teach me to skim read, Phew! As you say though, no info on the semi's

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Topic starter Posted : 10/09/2021 9:42 pm
Jayceebee
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That’s good news, gives you a fighting chance if you ever manage to land one. There is one very troublesome IC you need to check your stocks for, it’s a type TCEP100E used in the PSU/Line stage. By it’s type number I’m sure it was a special for Thorn and only ever used in the 4000, no idea who was the manufacturer.

John.

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Posted : 10/09/2021 10:36 pm
Red_to_Black
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If it was Thorn bought in then either Texas Instrument, or Motorola, then again they liked Plessey as well at that time.

Philips (Mullard) tended to use their own chips, I suppose what you would call a "vertical integrated" company today, but even they used Toshiba  TMP*** microprocessors in their sets.

Thomson was no better, even though they had SGS/ATES at that time etc. in their own stable, they still used both Hitachi. ITT , Mitsubishi  and a few other makers in their chip line up, no doubt whatever was cheaper.

I do realise Thomson did a reciprocal deal with Toshiba wrt the VCR manufacturing after the JT2 part ended but even so!

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 10/09/2021 10:48 pm
crustytv
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Would the TCEP100E be the same as the TCEP100 by Plessey, plenty of those. What was the significance of the 'E'.

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Topic starter Posted : 10/09/2021 10:49 pm
Red_to_Black
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God knows Chris, Philips were buggers for changing the N* version number of a chip where certain  component changes were required, but were not alone here, especially when you had for example the TFK version of the TDA3562A chip, as they were not exactly the same then why couldn't they designate a different number?

It got even worse with the "jungle chip variations" TDA4505 etc. where different versions existed "E", "M" and so on types etc, then different masked versions of base micro chips as well and so on.

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 10/09/2021 11:21 pm
Red_to_Black
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It was a PITA then, probably more so today, as if you didn't have the latest tech, bulletins (especially  not being a main dealer) you were pretty phooked without technical help.

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 10/09/2021 11:35 pm
Jayceebee
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It’s possible the E suffix may have been an improvement to the ICs design for better reliability or possibly a figment of my imagination 🤣 🤣 🤣

John.

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Posted : 11/09/2021 1:08 pm
jcdaze
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IC 301 (TCEP100E) was supplied by Plessey and did cause trouble early on by overheating. A clip on heat sink was soon supplied and with suitable heat sink compound became a must do mod for every set encountered. Also a couple of external components were added between 3 of the pins to help stop the IC being destroyed by crt flashover, which the crt's seemed to do quite frequently. The thick films in  the convergence circuit were modified with some external resisters fitted and by the time the 4,200 series came along most of the early these mods were done during manufacture but it never did lose it's reputation for unreliability. Multibroadcast had over 15,000 of the 4K out on rental at one time. They used the model number 7777. There were 4 Ferguson models made; 3C03-50cm, 3C05-67cm, 3C06-56CM and 3C07-67CM with different cabinet styles, a lot of which were exported to be used by Thorn rental companies with large numbers going to Denmark and Germany if my memory is correct. I have still got a load of circuit modification info as well as the 4,200 series service manual and other stuff which could do with being scanned at some point I guess.

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Posted : 12/09/2021 2:01 pm
crustytv
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Hi Jim, so if required, would the TCEP100 Plessey ic's I have in stock be OK for use in place of the TCEP100E? Obviously, with a heat sink attached as well.

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Topic starter Posted : 12/09/2021 2:36 pm
crustytv
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Whilst this thread is documenting info on the 4k, for completeness I might as well add the only part of the set I do have, that being the remote.

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Topic starter Posted : 12/09/2021 2:37 pm
jcdaze
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@crustytv Simple answer if that I don't know. I can't remember what the E stood for but I will go dig out my old info and see if it contains any clues.

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Posted : 12/09/2021 3:07 pm
Jayceebee
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Posted by: @jcdaze

IC 301 (TCEP100E) was supplied by Plessey and did cause trouble early on by overheating. A clip on heat sink was soon supplied and with suitable heat sink compound became a must do mod for every set encountered. Also a couple of external components were added between 3 of the pins to help stop the IC being destroyed by crt flashover, which the crt's seemed to do quite frequently. The thick films in  the convergence circuit were modified with some external resisters fitted and by the time the 4,200 series came along most of the early these mods were done during manufacture but it never did lose it's reputation for unreliability. Multibroadcast had over 15,000 of the 4K out on rental at one time. They used the model number 7777. There were 4 Ferguson models made; 3C03-50cm, 3C05-67cm, 3C06-56CM and 3C07-67CM with different cabinet styles, a lot of which were exported to be used by Thorn rental companies with large numbers going to Denmark and Germany if my memory is correct. I have still got a load of circuit modification info as well as the 4,200 series service manual and other stuff which could do with being scanned at some point I guess.

I had completely forgotten about the addition of the heatsink! We had two models both 26" in D.E.R. fitted with the 4000 chassis, the 5762 branded D.E.R. which was produced as a system I UHF only and the VHF/UHF 3C05 which was apparently originally destined for South Africa but were turned back because of the reliability problems supposedly.

I had heard of the 4200 but never encountered one, I have seen a picture of a 7C06 internals which appears to use the excellent multifunction remote control system from the early 9600 models, I wonder if that was it? It was still ultrasonic but with the ITT PCM (or was it PPM) chipset, the spot frequency type from the 4000 was terrible for random operation from extraneous noises.

ferguson7c06chassis

John.

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Posted : 12/09/2021 10:27 pm
crustytv
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Posted by: @jcdaze

There were 4 Ferguson models made; 3C03-50cm, 3C05-67cm, 3C06-56CM and 3C07-67CM with different cabinet styles, a lot of which were exported to be used by Thorn rental companies with large numbers going to Denmark and Germany

And here they are, many thanks to Hans from Germany 👍, who must have been looking in on the thread, he kindly provided the following flyer. I took it into Photoshop and translated parts of the text from German to English. I have also added this to the Ferguson Brochure.

I've seen the 3C06 before, but in wood finish, that's the one Mikey had that was destroyed in a flood 😥 .

Never seen the 3C03, 3C05 or 3C07. The 3C03 is a rather curious design, I quite like that it’s unusual. Have to say though, the HMV console (see above) is still the one I would like, closely followed by the 3C05. Though in truth I'd love and gladly take any, shame they have all but disappeared.

Have to say I like that portable (albeit wired) hand-held convergence unit, I'm surprised that idea did appear on more sets. Though a lot of manufacturers did provide front facing controls like Philips, B&0, Telefunken to name just a few  and Thorn/RBM and PYE had flip up boards. All saved you peering over the rear of the set into a mirror, or precariously reaching with one arm extend whilst trying to balance leaning round to see the front. But this extendable semi-portable unit is a very good idea.

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Topic starter Posted : 13/09/2021 8:46 am
Lloyd, Jayceebee, jcdaze and 1 people liked
jcdaze
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@jayceebee Yes the 4200 series had the 12 channel ultrasonic remote TX U703 and RX unit U706 and a lot of the circuit changes were to allow their use. The export models were designated as the 4200 series and the Uk version with a UHF only tuner was designated as the 4100 series. You mentioned the DER model 5762 and it jogged my memory because I mentioned the Multibroadcast model 7777 and I've checked back on old notes and Multibroadcast used the numbers; model 7719-20"(no remote), model 7758-22" (U701 or U702 remote options),model 7762-26"(U701 or U702 remote options) all of which were 4000 chassis and the model 7777 used the 4100 chassis. I hope that makes some sort of sense!

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Posted : 13/09/2021 2:09 pm
irob2345
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Ah yes, the Oz AWA / Thorn 4KA chassis looks just like that.

Except that they had much larger heatsinks for the Line Out and EHT transistors and an extruded finned heatsink just for the jellypot transformers. And an E-I lamination mains transformer screwed into the bottom of the case on the left hand side. No live chassis in Oz!

The RGB cable, where it loops around when the chassis was folded up, was held in place by an ordinary plastic clothes peg! Apart from on very early production units where the loop was taped up. Somebody on the assembly line had that idea apparently.

Early CRTs were Mazda. These were very uncompetitive for picture quality and brightness with Philips and Toshiba CRTs and domed badly on bright scenes. They were soon replaced by RCA CRTs which suffered from orange luminous reds and horrible white raster purity.

With a Kriesler sitting alongside one on the showroom floor, the AWA was well nigh impossible to sell. Except that you could have one immediately when most other brands had a 6 or 8 week lead time.

AWA were importing 3500s early on (the 3504 chassis) to try to fill the gaps. They were one of the cheapest CTVs you could buy but looked very dated style-wise.

How many different versions of the chroma board did you see?

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Posted : 15/09/2021 9:04 am
jcdaze
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@irob2345 I bet those AWA/thorn sets were heavy old lumps. I don't remember seeing different chroma boards but they did have mods along the way. The 4200 had different a different horizontal timebase/power board and a different vertical timebase board which could be used in a 4000 but not vice versa.

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Posted : 15/09/2021 2:27 pm
irob2345
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Posted by: @jcdaze

I bet those AWA/thorn sets were heavy old lumps

No not particularly, the mains transformer (made by A&R) was not huge and even back then they economised on the cabinet material thicknesses. All 4KAs were 26". They weighed about 50Kg.

You got me thinking about other differences. The small P/S sub board seen to the right of the vertical module wasn't in the 4KAs. Instead there was a much simpler board on the left hand side of the vertical that just contained the degaussing parts, a diode bridge, a few connectors, a fuse and a 470uF 350v cap. I guess the P/S board I see in the UK chassis contained an auxilliary power supply?

Oz was VHF only back then, the bands were crowded and from the early '60s until the late '70s we even used Band II for TV! So because no varicap tuner available at the time had the necessary performance (regional city viewers expected to be able to watch all the big city channels 100+ Km. distant as well as their much stronger locals), a rotary turret tuner was fitted. Made by Mitsubishi as I recall.

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Posted : 16/09/2021 11:52 am
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