Leaderboard

The 4081B that drives the transistors in the top right corner is a quad AND gate chip, and each gate receives an output from 4001B and another signal which comes from the 4011B in the top left corner (more on this later). Each output from the 4081B that is logic '1' turns on the appropriate transistor which fires the triac and turns on the output. The mystery signal that goes to the AND gates in the 4081B is a zero crossing signal that is generated by the top-left 4011B from the incoming mains supply. The idea is that the zero-crossing signal is generated when the AC mains voltage is at it's lowest level. By switching the triacs on and off when the mains supply is a zero volts (or very close to it) the amount of interference generated is kept as low as possible. The zero-crossing signal is only at logic '1' when the mains voltage is practically zero, which is 50 times a second, the rest of the time it's at logic '0' and when AND-ed with the outputs from the 4001B, ensure that the outputs can't be turned on. In other words, each output channel can only be on when it gets a logic '1' signal from the 4001B AND the mains voltage is at (well, near) zero. As for what's wrong with this particular board, there are a couple of possibilities: 1) All of the outputs on the 4017B are stuck at logic '0', which would leave all four outputs of the 4001B stuck at logic '1' and all fours output on all the time. This could be because the 4017B is faulty or because it's not getting a clock pulse on pin 14 from the 4011B next to it. 2) The outputs of the 4017B are sequencing properly but all outputs on the 4001B are stuck at logic '1' because it's faulty. My money would be on the 4011B clock generator being faulty, but given the age of the chips on the board I'd be tempted to replace all five for the sake of future reliability. It is nice to be able to say what's causing the fault though

The power section of the circuit is the two large resistors at the top of the board, the capacitor and a few other components. It generates a DC supply of probably 12 to 15 volts which supplies all of the logic chips. As they are CMOS chips, a logic '1' is at least two thirds of supply voltage up to the actual supply voltage. A logic '0' is one-thirds supply voltage or lower. The supply voltage can be measured across the power pins (16 is +ve and 8 is ground) on the 4017 but it is not isolated from the mains and could kill you if you're not careful! Certainly don't go probing around using a mains-powered oscilloscope on it.... The 4011B in the bottom left-hand corner (next to the pot) is configured as a square-wave oscillator which generates clock pulses for the 4017B decade counter. The 4017B has ten outputs that go high one at time in sequence on receipt of a clock pulse on pin 14. As only four outputs are required, the fifth output is connected directly to the reset pin, so that the first output goes high directly after the fourth one and the sequence is repeated. The outputs from the 4017B (pins 3, 2, 4 and 7, in that order) then go to the 4001B in the bottom right hand corner, which is a quad NOR gate chip. Each NOR gate has both input pins connected together and they come from the outputs of the 4017, so the NOR gates effectively invert the logic level of the outputs from the 4017B. This will eventually give three channels that are on and one that's off at any one time, which is going to look more impressive than having only one channel on and the other three off! The other two chips on the circuit, The 4011B and the 4081B, will take a bit more explaining, so I'll do that in another post below.

Another nice original example, still on old coins and 5p tokens... https://www.ebay.co.uk/itm/284456581506?hash=item423aeef982:g:6iAAAOSwE2FhRbxl

ARRIVED! This one is the Super 500. It only has the 5p play, no 2p game, but the jackpot is variable. It changes between £10, £15, or £25 seemingly at random. It doesn't change every play. It SEEMS to dwell on an amount until a WIN is registered, then re-selects from the three values. I'll get a picture of the device which does this, as soon as I've got the back open...

Cheers I have ordered some of them on ebay likes of RS and CPC don't do that stuff these days! I will fit sockets in case they are duds! Cheers Ronnie

You're welcome It does sound like your 4017 has died if all the outputs are floating. Try replacing that first and you may be lucky! I may have some NOS 4017 chips in my stash. I'll have a look next time I'm in the loft. If I have, I'll send you some. There seem to be a lot of people selling them on eBay but you never know whether you're getting fakes or not...

CanonMan, what a gent you are, thanks so much for this explanation, that is sheer genious! Right the 4017 is getting it's pulses which I can vary with the pot, but it's outputs do nothing on my probe neither state hi or lo, I see these 40XX series on ebay are cheap so I may just replace as you said but could try the 4017 first to see? I have another one to test and get working if needs be but one of it's TIC206 is bad, well I had to rob it for this board as I shorted it by accident and killed it! Thanks Ronnie

I'm going to attempt an explanation of how the circuit works. To make it a bit easier, I'll rotate the photo through 90 degrees....

back on again... https://www.ebay.co.uk/itm/384344727207?hash=item597cbb1ea7:g:I1gAAOSwIbRhIKES

Well that has to be one of my most disappointing wanks ever.