Leaderboard

The board with the resistive capacitor has been giving me the run around for quite a few days now and what with the silicon count getting progressively higher I was beginning to wonder if I'd ever get working. To recap most of the logic chips had been changed in the area below the battery and there was activity but not enough to boot completely. Basically the watchdog would kick in after about a second or two, reset and start again etc.... Disabling the watchdog proved that it tried to boot but then hit something it didn't like and froze the CPU hence the watchdog kicking in. A bit further down the board are all the switch buffer chips (74LS541) and most of these had crumbly solder. Voltage checks on the outputs showed almost all of them to be low and with no switches thrown they should be high! Another 6 chips to join the silicon waste pile. Once these were swapped out it burst into life and was I pleased!! The bottom 8way DIL switch was seized up so this was also changed. So, now it was running it was time to start the tests. Everything was going swimmingly until the lamps tests. Lamps 58-5F wouldn't light. This proved to be IC27 which didn't look too bad under visual inspection but it's output didn't go low enough for logic zero and consequently didn't switch on the 74LS259 (IC37) chip that drives the lamp outputs. This is before, should have taken it of the whole board! What it's like now. The two right hand PIO chips IC40 + 41 look like they've been in the wars but appear to be working fine at present. I think a fairly long soak test will be in order though just in case! Finally, I tried it with game software and it dosen't complete the boot cycle.That's it for today, I'm sure I'll crack it tomorrow.

Well another interesting day in the workshop. The weird fault of not running game software I think I've solved. I hit on something last thing yesterday and confirmed it this morning. The farting noise during boot up is the same noise as a coin stuck alarm! Although most of the boards ignore this and carry on some don't. I've found, by chance, that booting the boards with the reel sensor switches closed they boot every time and play faultlessly. Why some need this and some don't I haven't a clue but "that'll do for me Tommy"! If I was using a real machine I would never have come across this unless all the reel sensors just happened to be blocked by the reel tabs.

Yes, ages to boot if there is no battery, if not that then a faulty board

Recently bought some non working impact cards, so thought I would start them today. 1st one not too bad, usual corrosion pattern, plug has 3 pins broken off and PAL chip socket pins under the battery area is totally eaten away! 2nd one A lot of work been previously done to this one!! New Pal chip socket and cpu socket had been fitted, Q1and Q2 look like they have been replaced, similar battery damage pattern to usual too

Thank you mate will take a look much appreciated

the 625 is the one I use the most, the 624 is good for the bigger wires like program cart plugs / sockets

Thank you Vecs

IMG_6205.MOV

When is a 0.1uF capacitor not a capacitor? When it's a 20 Ohm resistor!! This has been an absolute swine to find. The resistance was across the 5v rail and you would have thought something would have heated up enough to be able to detect it by touch, but no! Testing across the 5v should be 300-600 Ohms on a good day and I wasn't looking forward to this one. Most of the IC's have the 5v rail along with all of the decoupling 0.1uF caps and plenty of tants. I had already removed/replaced most of the logic chips below the battery but I shall come back to that one another time. The only way of finding this type of fault is to break the tracks in the 5v supply, isolating parts of the board as you go. When I eventually got to the line of chips that was suspect I knew it had to be a cap as all the IC's had already been replaced. There were 4 in the run so I swapped them all even though the others tested OK. I need a glass of wine (or three) after that one.