Television Magazine Testcard Generator

[Philips210]

Hi.

A bit of a long shot request.

Has anyone built the "Colour Pattern Generator" testcard generator by Malcolm Burrell? It was in the May to July 1979 issues of Television magazine.

It is a fairly complicated circuit using many TTL ics (45 in total) plus a ZNA134 line/field/sync ic and a couple of colour ICs, TBA520 and TBA540.

I have all the issues to hand for reference. I noticed there are a few mistakes in the circuit diagram. A number of these were addressed in the June '79 issue but I've found at least two more errors. I'm comparing the circuit diagram with the PCB foil print.

Unfortunately, there wasn't a foil layout for the top of the board, The solder side foil wasn't provided either but is visible though the given component overlay. Not having the top foil pattern makes it difficult to make comparisons with the circuit diagram. Apparently the PCB is correct, the errors are on the circuit diagram.

If anyone has built this project then a couple of pics of both sides of the board could be really helpful. I can't imagine many were built but fingers crossed someone may be able to help. Thanks.

Regards,
Symon.

[Wendymott]

Hi Symon. Yes I built it.... infact I built 3...... but I reversed engineered the pcb's... I made my own using Protel. It was a "learn Protel" and make the generator... I bought one set of ROMS, then copied...... all strictly "in house"..... I dont have any EPROMS anymore... I offered them on here.... no response, I have one or two ZNA234's One of my main pcb's had an intermittent fault, put down to not using PTH. One was built into the TV Factory signal system..one was my own, and the other was in the lab.
For its time, it was a great piece of kit. We eventually morphed into the Philips PM5518 test card.

[Philips210]

Hi Wendy.

My project uses just plain TTL so there are no EPROMs in the design. I remember a couple of TV magazine EPROM based testcard generators. One was in 1984 and the other much more recent. It is the 1979 circuit I need the PCB info for.

Regards,
Symon

[dsergeant]

I had the Manor Supplies version which I remember was similar. Disposed of (to our tip) when I had a clear out a while back when I no longer saw TVs which required it.

Dave

[Dave Moll]

Here is my Manor Supplies unit:

[Dave Moll]

I notice that the scribbled label fails to mention that -/-/OUT/OUT gives a plain raster for purity checks.

[Philips210]

When time permits, the plan is to draw the full circuit diagram and design the PCB layout with Kicad and then have the PCB made.
As it uses a substantial number of ICs there is no room for error. I intend to first build the circuit on breadboard to prove it is fault free. The breadboard is actually twelve small breadboards interlocked so the layout will essentially be the same as the component placements in the TV magazine's PCB.
There is also a second PCB which contains the analogue circuitry including the power supply, colour processing and the UHF modulator.

One component I can't find any data on is a thermistor type G23 or GL23. It stated this was available from Maplin so if anyone has a 1978/9 Maplin catalogue it would be great to find out the properties of this thermistor so I can select an alternative. I have the vast majority of the components for the project but short of a few 7408 and 7411 TTL chips. The original UHF modulator which was from Manor Supplies will be replaced by an Astec UM1286 unit I have to hand. This also has an audio input facility which I intend to use.

The project is quite sophisticated in that it has a large component count but it's very interesting to see how the various sections of the testcard are built. It looks to be flexible in that modifications to the card structure should be easy to experiment with. I intend to make some patterns independently available besides the testcard so will involve additional gating/switching.

I've seen a number of pattern generators by Malcolm Burrell, he certainly likes using 74121 monostables. I remember being told at polytechnic never use a monostable unless you have to. There are seven in this design! It's an interesting old tech project that will be a challenge to build.

Incidentally, does anyone know if Malcolm is still around?

Regards,
Symon

[See_Mos]

I built one and it has served me well for many years. I used it for TV and video repairs and still use it occasionally for monitor repairs.

The PAL generator was not very good and tended to drift when not used for a few weeks so I built a replacement using a TEA1002 IC I also changed the modulator for a better one with sound carrier and added an audio input. The replacement circuit board is quite crude as this was before affordable PCB CAD programs became available.

One time not long after it was built I caught the coaxial lead on a TV chassis and although the TV was on an isolation transformer the ZNA134 sync generator blew. At the time they were about £28 each, probably about £200 in today's money, so I was not happy. After that I fitted a TV aerial isolation socket to the generator.

I used an RS 'wind your own transformer' kit to replace the original and help reduce dissipation in the regulators by splitting the 12v and 5v supplies.

IC31 has a tendency to break down occasionally causing 'cogging' on the verticals.

I recently bought a couple of AD723 PAL-NTSC generator IC's to build an even better PAL generator after seeing it featured in Nuts & Volts magazine September/October 2018 but I never got around to designing the new board.

I also bought a switch mode power supply to replace the original because all of that TTL is quite hungry and the regulator IC runs quite hot.

I will get some pictures later.

[Philips210]

Hi See Mos.

Sounds great. I'm pleased to know someone actually built one and it's interesting to read your experience with it. Good idea to use a SMPS for the TTL power requirements. Did you also notice the errors on the circuit diagram and does your pattern generator use the TV magazine issued logic PCB?

I look forward to seeing some pics. Thanks.

Regards,
Symon

I am amazed that the AD273 is still in production, I went looking for the datasheet for a read (one of my foibles).

[loulou31]

Hi

For PAL/NTSC composite video from RGB, there is also MC1377 from Motorola.

Jean-Louis

P.S :I was product line engineer for consumer TV products that included MC1377 when I was young and worked at Motorola Semiconductors.

[See_Mos]

Hi Symon, Yes, initially I used both of the original boards and still use the logic one. I also did all of the mods and added the video level buffer and a multipole switch to give me testcard, colour bars, R, G, B, and cross hatch.

I have also been toying with the idea of using a PIC microprocessor as a substitute for the sync generator and as the basis for building a generator with the same facilities entirely using a PIC device but monitor repairs have dried up so I don't really need one.

The MC1377 looks interesting and there are some available on Ebay and they are not expensive so I just ordered a couple. Being DIL package they will be easy to experiment with.

[Philips210]

Hi See Mos.

As I will be using the Astec modulator the analogue board will need to be modified in any case so I may as well use an alternative PAL encoder. I see you mention the Philips TEA1002. Malcolm Burrell used this IC in his "Simple Pattern Generator" TELEVISION February 1990. I'd be interested to see your modified circuit for the encoder. I see Jean mentioned the MC1377 in post #11. I also thought about the later Philips encoder, TEA2000. I have some of each so have various options.
I think it's good to have the option of separate patterns besides the complete testcard.

Did you use the recommended thermistor to stabilise IC5's pulse width output?

If it's not too much trouble, could you please take some pics of both sides of the Logic board? It would be a great help as there are quite a few errors on the circuit diagram that I need to sort out. I need to check the foil layouts against the circuit. Thanks.

Regards,
Symon

[Philips210]

Regarding the expensive ZNA1034, Malcolm Burrell came up with a cheap alternative circuit with a slight drop in performance. It was in the August 1979 issue of TELEVISION. It was the "Simple Sync Pulse Generator" and used 5 TTL ICs and a couple of 555 timers.

I have a few ZNA1034s to hand but don't know if they're OK. I'll have to build a simple test circuit to check the available waveforms.

Regards,
Symon

[Wendymott]

Hi SeeMos. In Oct 2002 TV Mag published my TV Pattern generator based on a PIC. Fully interlaced, Colour bars, Red raster with underscan markers and centre cross, Cross hatch, Split grey for colour balance / greyscale. It has a 20 Mhz clock, thus 250 n/s accuracy.
The colour encoder is a CXA1645 and the RF Modulator is a TDA8722.
Unfortunately the software was lost in a computer failure, and the backups were lost. I still have two copies of programmed PICs though.

[See_Mos]

@Wendy, I had forgotten about that one, any relation to the author? I'll read the article later.

@ Symon, yes, I did use the recommended thermistor. I saw the simple generator but as I wanted to use the unit for video work I opted for the expensive version. If you send me a private message with your email I can send you the set of higher res' pictures.

While looking for data on the MC1377 I came across a circuit for another encoder, AD724, and then I found a kit for it on Ebay. At less than £10 including delivery I ordered one.

The first picture shows the start of 'cogging' as it warms up the effect becomes worse then gradually clears, as it does if a new IC is fitted. The second is from a small flat screen TV.

Most of the parts for the replacement encoder came from scrap gear. The modulator is an ALPS one and has a JVC part number on it. The toggle switch was intended to switch between audio and sine wave but the sine generator was never completed.

[See_Mos]

Two more

[peterpixel]

Hi Symon,I've found some info on a G23c thermistor in a mid 70s ITT catalogue which may help.Bead type,max bead temp 125degC,resistance at 20degC 2000R,min operating resistance at max bead temp 113R. Peter.

[Philips210]

Hi Peter.

Thanks very much for the data on the thermistor, much appreciated.

Regards,
Symon

[Philips210]

Hi See Mos.

Your pattern generator looks great. I'm pleased how well defined the testcard is. Interesting to note the cogging effect due to IC31 playing up.

Thanks very much for uploading your pictures that's very helpful. It has given me a lot of encouragement to tackle building mine.
It must have cost a fair amount to build in 1979!

Thanks for the offer of the high resolution pics, I'll send you a PM later on.

Regards,
Symon