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Without your ability to keep finding these problems Bob, I think we would be in trouble! Quite good to see these write ups and what goes into finding the faults! Amazing 👍👍👏

Well at long last I've started delving in to the murky world of MPS1. First impressions, there's a bit more to get your head round than MPS2 but being as it contains nearly all discrete stuff repairs are easier to achieve as parts are still available. None of those horrible TIPP116 transistors for a start! Not sure if the PAL chip goes faulty though but I haven't come across that yet. The tester has come into it's own too. A few common faults have shown up starting with short circuit tants on the power fail detection supply. There's two in parallel C97 and C31 (10uF/35v) but so far only C97 appears to go short?? I'm changing them both as a precaution. Quite a few of the normal input output failures due to the 74LS541 chips running hot and others with the odd port failed. Output fails due to bad BCX38 transistors. Had one that didn't boot and my hand touched IC6 (TMS9902) which made me squeal as it was roasting. The board booted on removal and ran the diags OK without it. I suspect only certain games would need this chip fitted? Another board not going to reset was caused by IC27 (74LS04). This was an odd one as BCLKOUT was missing from IC15 (74LS541). As with MPS2 I went straight for this chip but in this case IC27 had gone bad and this controls the o/p from IC15. Funny thing is IC27 isn't connected to anything it just goes to the extension socket on the side so why it went bad is a mystery? Lots more sticky faults to tackle most seem to fall into the Watchdog and I/O failure so quite a bit of head scratching to come methinks. Watch this space.....

right go to the control panel and the two main timers nearest you as it shows on back door diagram look at the main control sequence timer. If it has it's grey cover it can be easily removed as just clipped on revealing the cams. With machine still switched on manually turn the timer by hand, it only rotates in one direction and the timer motor should take over and it should rotate one full turn and reels will start and stop as they would if a game had been played. See if this makes any difference?

This next one had me scratching my head a little. After changing a few chips, CPU buffers, and IC16 (near the battery) it still wouldn't boot. I eventually got down to IC30 (74LS32) which showed signals in on pins 12 + 13 but nothing on 11? Changed the chip but no difference? Time to bring the scope in. This showed a nice waveform on pin 12 but pin 13 it was only about 1.5v p to p? The logic probe was happy to display the pulse which led me up the garden path. So, where was the signal going? Checking the resistance to ground showed about 15 Ohms! Hmm, should be a few Meg Ohms. This is where things started to get tricky. The signal on pin 13 is BWE/CRUCLK and this is fed (or so I assumed) from IC29 pin 12 (74LS14). However this wasn't the case. On this chip it's shown on the diagram to have the same designation both sides and the 15 Ohm short was on the input side (pin 13)! This is then fed to all the I/O chips (8255's), the TMS9902's and a few other places I didn't bother with. So where does one start? I didn't want to start cutting tracks so Baldrick suggested a cunning plan. Checking the resistance it was decreasing by about 0.01 Ohm the nearer to the fault. I eventually ended up at IC38 (pin 36), there's an error on the diagram here as there's two pins marked 36!! (+ve and WR). Anyway with pin 36 disconnected the short disappeared. Without the chip in it actually booted and could run some of the diags so hopefully it should be a case of a new one and put it to bed.

....and another one. With this one I anticipated the worse as the power and ground would have gone up the wrong pins. After re-seating in the correct place it all burst in to life and passed the diags and game software!! If all faults were like this I'd be able to take the day off!

Cheers Nick yeah not as straight forward as thought, still mixing and trying wont post any pictures yet as it looks pretty tragic 😆 I can upload the before pic for now, will pop up some more when it's done

One on the bench this afternoon. Alarmed on boot up then after a while would magically boot but failed any tests (locked up) to do with switch or reels. I was just about to start removing the TMS9902's when I noticed this... Nice easy one for a change. Once the leg was reseated all the main tests passed with flying colours. Still one fault remains and that is it still fails the serial tests? Went back to IC5 (TMS9902) but it wasn't that so a bit more head scratching on this one.

hello and a very warm welcome to you . i can see your getting help from some of the forum experts already happy days

Look at the coin mechs first, sounds like a coin switch is stuck or held down by a coin. If a BF electro hold/nudge and variator timer start when machine switched on then it's a coin switch putting machine in credit, if switch jams and does not return to it's rest position it prevents the machine from accepting money and disables start button.

Agree with Chris,if it was working then cant be much.These are so much easier to fix than mpu versions.could also be a failed micro switch.ron will deffo know

For starters. Is the cams ticking over.? Can you put coins in? Are the coin mechs locked out. Check the coin mechs not jammed. Machine wont do anything when jammed but you'll still hear the cams ticking over like there are credits in it. Our resident expert Ron will know better .

welcome to the mecca every new member

welcome one and all