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midibob last won the day on May 11

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About midibob

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  1. I can't say I ever get angry enough to do that. Normally just a shrug of the shoulders and go and make a cup of tea! And so on to the last one. After yesterdays success the first thing I thought I'd do was to check all the DATA lines but this time all were in order. They do say lightning never strikes the same place twice! So where do we go from here? ADDRESS and DATA lines are all running but there's no IRQ on the CPU (pin 20). This called for a quick check in the Midibob book of horrible faults. Page 1, don't jump in the Thames! (or 'DON'T PANIC' if you're a Douglas Adams fan) If th
  2. Down to the final two in this present batch and of course I always leave the worst till last!! This one wouldn't boot and I couldn't see why not? There was activty on all the DATA and ADDRESS buses but nothing happened. Someone had had a good go this already and 4 of the PIO chips had been socketed and swapped out. In the head scratching that followed I socketed the other two so that I could test all the chips in a good board. So all PIO's and SIO tested OK. The CTC was then swapped but still the same. The RAM was already socketed but a replacement also made no difference. Attention then
  3. .... and some more. On switch on the board would clock up 18 credits, in fact every time it was switched on another 18 credits? Sometimes just touching the coin inputs with the scope probe or the meter would clock up credits. This little head scratcher turned out to be the 12v supply feeding the coin mech. Transistor T95 had a broken leg and hence no 12v was delivered to the coin mech so the inputs were floating. This was caused by bad storage of the board and it's a real bug bear as I see so many faults similar to this with broken/crushed components, broken tracks due to a deep scratch e
  4. Another bizarre fault today. The board would boot sometimes, and other times only partially ie. the reels would index and then it would click to initialise but then just make a high pitch noise? Eventually I discovered that it was due to IC1 (Z80 PIO) by substitution but couldn't understand why. After much head scratching I found that if it was stuck with the funny noise just touching the chip would make it fire up correctly??? If that wasn't strange enough, only when it was touched in the middle. Further proding and poking led me to pin 16 and touching the meter on this pin would also fire it
  5. Nice to see more folks getting there sleeves rolled up and stuck in. 👍
  6. Procon boards seem to be coming out the woodwork at a great rate of knots at present. Looks like I'm going to be doing nothing else for the next couple of weeks! This one was a goodie. On switch on it would almost boot then make funny noises and lock up. If the board was flexed it would boot completely and then maybe lock up when pressure was released. It was all very hit and miss. Eventually I found applying pressure to IC3 (PIO) would make it go one way or the other. As this was a socketed chip suspicion was centered on perhaps a dry joint somewhere. As it happened lifting th
  7. Just looked at a board today that a member was hoping I'd be able to fix. It didn't have any bubbling at all but it was tracking all over the place and it's very dry today too. I scraped off a very small area of mask in the battery area and no reading whatsoever (which was good) so I had to relay the bad news, it is fixable but not by me. I don't do Scorp1 for this very reason.
  8. I'm assuming normal sound is OK? You have checked that T5 is being switched on? If it isn't you can always temporarily short that end of the pot to ground to see if that increases the volume. If it doesn't and normal sounds are OK then something wierd is going on. You'll need to put a scope on any of the ABC outputs from the 8912 chip and see what the audio levels are like there.
  9. 3 more boards have taxed the old grey matter no end. First had the usual bits corroded, triac drivers and Vbat supply transistors plus the little 1nF caps. Once done all booted and ran fine, all tests passed and left it running a soak test. I forgot to switch it off in the afternoon and only realised next morning. There it was, stuck in lamp test and on power cycle...nothing. After much head scratching everything seemed to be doing what it should do but it wouldn't boot. Then I checked the output of IC 20 (7425) and it was low! A new one restored operation. Next one failed with RS232
  10. Good stuff, I know how long that takes to do!! I've not found an easy method of neatly applying resist especially on a populated board. I suppose you could try a micro sprayer (if there is such a thing).
  11. Probably a good idea. I think I did mine, can't remember now it was so long ago. It'll be in the workshop thread though.
  12. Yep, still a fair bit of 'bubbling' to remove yet. It's amazing how the stray voltages can track across the board even when it's bone dry. The slightest bit of breath would cause havoc. Without the bubbled solder resist you should find it's fine. Try it with a meter on high ohms range, one leg to ground and the other to any part of the bubbled board (not a track) and then breathe on it slightly. You should see the resistance plummet! I can't remember if I showed this in a vid in my repair thread? It was a real eye opener.
  13. I've done so many I can't remember where they might be? Normally I'll follow the original track path (above or below) and solder a bare wire each side of the missing bit. Sometimes I'll completely strip the wire or if it's a long stretch just strip at each end. I use proper tack wire as it's very thin and the insulation is high temperature. Can't remember what it's called at the moment? All finished off with a coating of solder resist. If it's a long run then I'll fix the insulted wire with a little hot melt glue every inch or so. The specific situation dictates the process I use. An
  14. I managed to do mine with a screwdriver blade (carefully) as it can be chipped away to an open edge (if that makes sense).
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