Picked up this rather interesting test card generator, yesterday, should hopefully arrive this week. I'm not certain, but I'm wondering if it is an early version, or is loosely based upon, the 'RT Russell' test card generator. Though I've never seen one, I believe the later RT units gave you the ability to connect to a computer via serial cable, to upload new test cards and even teletext pages.
This unit appears to have two outputs, one for PAL and one for B&W. There is also a selector, which I'm assuming selects test cards, much like my IMOGen which has a similar selector to choose between TCF and B&W TC, but I've no idea if that is the case with this.
It also comes with a physical BATC test card, card. Again, I'm assuming this might be one of the test cards preprogrammed into the unit. Due to this physical card It's a fair bet the unit came from the BATC or at least one of its past members. I found the exact test card online, with reference to a computer program from 1983.
All very curious, really looking forward to having the lid off to delve inside, to see exactly what is in there. I had a similar unit a few years ago, even the case was the same except it was blue. That unit was 405 only, had test card C programmed and had a built-in tape player for test card music, the tapes I still have.
This appears to be 625, anyway, more to follow once it arrives, and I get it up on the bench and see what is actually going on inside.
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Though I've never seen one, I believe the later RT units gave you the ability to connect to a computer via serial cable, to upload new test cards and even teletext pages.
They certainly did, as mine was one such example.
I wonder where it is? Mine was programmed with Test Card J.
Finally, after 10-days waiting, the test card generator has arrived. I wasted no time in opening up to see if there are any clues.
The unit is very well constructed, the central PCB is stamped © Broadercasting Ltd 1983.It is populated with teh following chipset
- Toshiba TC4051BP MULTIPLEXER
- Ti SN74LS368AN 6CH BI-POLAR INVERTER
- Motorola SN74LS393N BINARY COUNTER
- SGS T74LS377B1 FLIP-FLOP
- Motorola 74LS393N DUAL DECADE COUNTER; DUAL 4-STAGE BINARY COUNTER
- SGS T74LS298B1 JITTER ATTENUATOR
- SGS T74LS166B1 LOW POWER OSCILLATOR
- SGS T74LS298B1 JITTER ATTENUATOR
- SGS T74LS298B1 JITTER ATTENUATOR
The small board to the bottom left
- TEA2000 PAL/NTSC COLOUR ENCODER
- Ti SN74LS157N QUAD 2- INPUT MULTIPLEXER
The right-hand side appears to be half populated with 4 chips. The top states frequency gratings and lists them. The second chip states Colour Bars. The third Colour Bars and Overlay. The final BATC Colour.
The front numbered, dial selector appear to choose the chip populated in the bank for test card selection, in this case 1 through 4. I hooked up to a scope and indeed I can see the output of the generator and changes when rotating the selector. I'll leave it soak testing, it's likely not been powered on for many a year, it's possible electrolytics are reforming. There are also 18 blue tants (2.2uF 35V) on the main board, If things don't improve after the soak I may just blanket replace that lot.
Time to hook up to a test TV, and here are the test cards. There appears to be an intermittent fault, in that colour is missing randomly lost. It can be brought back by random rotation of the card selector dial. Not certain where the fault lies at present, will need to do some checks, but without a schematic this will be fun. Voltages to the TC chips, the selector knob or maybe over on the decoder board.
A nice bit of kit and will compliment the IMOGen providing another test card. I wonder who programmed the chips with all the test cards and how, are the PIC?
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If you're randomly losing colour I'd have thought realistically it could only be around the TEA2000: that chip accepts TTL-level signals to give you 64 colours (2 bits each of R, G and B) plus TTL-level syncs and blanking and you'll note there's a 2Fsc crystal adjacent to it.
The devices on the right look to be EPROMs - it would be interesting to find out what they are, especially the one that holds the frequency gratings in it.
After leaving powered on for an hour, it seemed to settle, or so I thought, it manifested itself again. I think a more accurate description of the fault condition would be colour shifting? The fault you quite rightly point out is on the little decoder board. Curious that running the TC selector knob through a few sequences can settle it for a short while. Connecting to the B&W output which takes direct video from the centre PCB results in a perfect static display.
I think a short video of the fault might be in order.
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The TEA2000 requires the sync feed to generate numerous signals that are part and parcel of a PAL encoder: it might well be that there's an issue with the feed as presented to the chip. The RGB, MS* and MB* signals will have been combined prior to feeding into the encoder to give you the B/W output.
The TEA2000 data sheet is on the web and I'd have a quick look at the feeds of sync and blanking into it.
Those blue tants have caused me endless problems in oscilloscopes over the years, the eproms will have a 5 volt and 12 volt VCC. Power supply ripple ?
