Intracept Electronics N7118 TV Colour Pattern Generator

[Chris55000]

Hi!

. . .I thought all of these were long since extinct by now but a very yukkified one fell into my lap for a princely sum a few weeks ago!

. . .This was yet another of the failed Colour Bar & Pattern Generator Kits that ran away with all my Student Grant at the end of the 1970s and the beginning of the 1980s when I was learning the CTV trade – I don't suppose any Member has a copy of the original Intracept N7118 Construction Plans hidden away in a drawer or sheaf of paperwork by any chance?

. . .I suspect that this example might have been originally purchased "ready–built", judging by the paint sealing on the frequency trimmers and the PCB fixing screws and the relative (!) neatness of the many single–core PCB jumper wires!

. . .Rather surprisingly, the 6 cell 7.2 V rechargeable NiCad battery in it hasn't gone rotten, altho' I dare say at least one of the cells will probably be shorted by internal tin–whiskers by now!

. . .Can you still get these "Veroboxes" this was built in?

Chris Williams

[Chris55000]

. . .I discovered that Intracept Electronics also produced a later design called their "N7128" that rearranged the press–button switches to add a "dots" button, and the sound and video facilities, originally advertised as an extra "add–on" pcb costing extra, were included as standard in the N7128 – the N7128 had a black front panel lettered in white! Unlike the N7118, the N7128 appears to have only been available ready–built and tested!

Has anybody ever come across an N7128?

They began advertising in April 1980 and quietly disappeared from "Television" magazine in November 1983 and Street View now shows no evidence that there was ever anything electronics related there now – there's a gap on the odd numbers of Picton Road between 177 and 215 – their address was given as "203" and there is nothing on a Companies Search for them, even tho' they were advertised as "Ltd".

[Chris55000]

. . .Forgot to mention that I came a cropper with the original kit I purchased and built in 1981 because several of the resistors broke off the tags on the top of the press–button switch bank and I'd accidentally lost the original plans, and Intracept said they hadn't any spare copies when I wrote to them "but they would offer a repair service for £39.99 if I sent my unit back post paid!"

Chris Williams

[Philips210]

Hi Chris.

I too built the N7118 kit back in 1982 and it worked well for many years in my early TV servicing days. I also lost the original documentation in 1984 when we moved. I revisited the project several years ago and it still works well.

I can check my unit re component values and send you some pics if that helps. I will have to rack my brains as to where it is though! I've since obtained some unclear copies of the required data and willl send you a PM later.

Regards,
Symon

[Chris55000]

Originally Posted by Philips210

Hi Chris.

I too built the N7118 kit back in 1982 and it worked well for many years in my early TV servicing days. I also lost the original documentation in 1984 when we moved. I revisited the project several years ago and it still works well.

I can check my unit re component values and send you some pics if that helps. I will have to rack my brains as to where it is though! I've since obtained some unclear copies of the required data and will send you a PM later.

Regards,
Symon

Evening Symon!

. . .Excellent - even furry documentation is better than none at all as I can redraw to a very good magazine-publishable standard with my sPlan 8 software, and even a furry diagram will save me hours of tracing out!

. . .Part 22, Chapter 299 of my Gigantic T & M Theory & Repair Book covering the Intracept Electronics N7118 is now well in progress!

Chris Williams

[Philips210]

Hi Chris,

PM Sent.

Regards,
Symon

[andyt22]

I've got a N7118 which I too built from a kit and used in the 70's & 80's for TV servicing and I am sure I have the manual too so will look it out for you this week and send you a copy.

cheers, Andy

[Chris55000]

Evening Andy!

. . .Excellent if you can Andy, as it will save me a lot of re–drawing and tracing of the eBay pictures!

I can easily (and the work is in progress!) tap out all the original typed content, but as my question on "Modern Technology" details, its a lot of work correcting the perspective distortion of the eBay pics!

. . .It took me 4h to draw this block diagram of the N7118 to my satisfaction, including drawing all the little waveforms and the press–button switch legends!

Chris Williams

[Philips210]

Hi Chris

That's looking great and thanks for your efforts on this which is much appreciated. That's a good offer from Andy re the original doumentation.

My N7118 is due to be tested in the coming days after the battery leak and clean up.

Regards,
Symon

[Chris55000]

. . .There is much more currently in preparation that will be published as Part 22, Chapter 299 of my Gigantic Test and Measurement Theory & Repair Book, of which work has been carried on a further 110 Chapters, altho' they're not fully completed to my total satisfaction yet!

. . .As is the usual practice on a basic system block diagram I have drawn the Pattern Selector Switches in a simplified form for clarity – the Circuit Diagrams to follow will, of course, illustrate the exact switching arrangements!

Chris Williams

[Chris55000]

. . .A further update on this project :–

. . .I have just discovered there are TWO different versions of the N7118 Pattern Generator PCB in existence, there is the version with the pictures uploaded by Symon that has a PCB silkscreened in white that has three 1N4148 diodes W12, W13 and W14 fitted between IC4 and IC5, and the version of the PCB from the unit that I have, which is silk–screened in yellow, that omits these diodes, and my version has many differences in the gating and connections associated with IC6 and IC7, that aren't shown on the eBay listing pictures that Symon emailed me, so that means I have TWO complete circuit diagrams to prepare, as there are many other component reference and component value differences between them as well!

Complete Circuit Diagrams for both of these PCBs will be drawn and posted!

Chris Williams

[Chris55000]

. . .Whilst I'm waiting for further information, I have started drawing out the different yellow silk-screened PCB of my unit, and I attach the circuit diagram of the U.H.F. Modulator and battery input sections here!

Circuit Description :-

Section 1 Circuit Description of the UHF Modulator and Battery Circuitry

Fig. 1 below shows the circuit of the U.H.F. modulator. A single AF 139 P.N.P. germanium screened U.H.F. transistor TR1 is employed as a common-base oscillator whose frequency is tuned to approximately Channel 45 by the preformed wire loop inductor L1, (which is a piece of 1 mm diameter tinned copper wire formed to an 11 mm diameter loop with ends spaced approximately 10 mm apart), tuned by a 4.7 pF ceramic capacitor C8.

The oscillator feedback is provided by the 2.2 pF capacitor C11 between collector and emitter of TR1, with neutralisation provided by capacitor C16 (4.7 pF) to prevent oscillation at unwanted frequencies. Base bias is provided by the potential-divider R23 and 29.

Two slightly forward-biassed silicon diodes W7 and W8 are used to couple the modulated U.H.F. from the modulator output, and the modulator input to the incoming video and chroma signal from C19 and the pattern selector switches, via C10 to TR1 emitter to provide amplitude modulation of the carrier, with a U.H.F. choke (L2) and a 4.7 pF capacitor C20 provided to isolate the U.H.F. oscillator from the rest of the pattern generator circuitry.
L2 is simply 5 turns of insulated single-strand 1/0.6 connecting wire wound the blade of a small electrical screwdriver or drill-bit about 3/32” in diameter.

Capacitor C19 couples the chroma signal from the PAL encoding circuitry to the composite-video summing point at the junction of R19 and R20, whilst the two OA 90 germanium diodes W4 and W5 feed in the crosshatch, colour bar and red raster signals, together with the composite sync. and blanking from the remainder of the pattern generator circuitry – the diodes prevent unwanted interactions between the various waveforms. The U.H.F. output is taken from the junction of W8 cathode and R28 via the 33 pF capacitor C21 (47 pF may have been supplied in some kits) to the coaxial output socket SKT1 mounted on the back panel of the instrument.

The complete modulator circuitry is powered by the battery supply “+Vdd” via a decoupling network R25 and C9 plus C22 directly across the battery supply to minimise unwanted U.H.F. feedback.

It should be noted that the simple modulator circuit employed here does not contain any “sideband filtering”, so care should be taken to tune the TV to the correct sideband, which is normally on the higher frequency side of the channel concerned in most cases.

The battery supply is from an 8.4 V 150 mAH “NiCd” type cylindrical battery secured to the PCB with a cable tie, and for mains or external 12 V operation, a 2.5 mm jack socket SKT2 is mounted on the rear panel.

The original maker’s instructions gave information on modifying the mains adaptor originally supplied, which was a multi-voltage simple unregulated type.

Resistor R34 (100 ohms) limits the charging current when used with a 12 V mains adaptor. Fig. 2 below shows the battery, charging input circuit and on/off switching.

WARNING !!

On NO ACCOUNT must the original battery be replaced with the modern “800mA high capacity type” – these are almost always of the “lithium-ion” chemistry type which needs a special voltage, current and time-regulated charger circuit to prevent dangerous overheating of the battery – if the old battery is unserviceable (as it almost always will be !) a PP3/1604 or 8.4 V cylindrical cell type specifically advertised as “Nickel Metal Hydride” should be fitted, these have a nominal capacity of about 200 mAH when new, and are quite safe to use in this instrument.

.

[Philips210]

Hi Chris.

Great work and really clear diagrams. Thank you for all your efforts on this and I look forward to seeing the rest of the circuit.

Regards,
Symon

[Chris55000]

. . .Next Circuit Diagram Section, for the 4.43 MHz Oscillator and Line Sync. Generator now complete !

. . .I need to take, and draw, some additional wave-forms, as indicated by the blue pentagons on the diagram, before I can write the full circuit description for this circuit !

Chris Williams