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midibob last won the day on January 22

midibob had the most liked content!

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About midibob

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  1. midibob

    mpu4 not triggering payout solenoids

    Well there's a coincidence, same happend to one of mine the other day due to a RAM chip going bad whilst testing. It didn't blow the fuse either (MPU3) and melted all the plastic bits on the payslide. Stunk and smoked the place out. Luckily no board damage barring a new triac.
  2. midibob

    MPU4 Motherboard Repair WELL ATTEMPT

    Early days yet, don't get dispondant after the first day. I've had faults take well over a week before, real stinkers it has to be said, but some are like that. Most folks will always be glad to offer advice especially as you've tried yourself first. If you're going to do more of this stuff get some loups or a microscope, it's amazing what becomes visible with a bit of magnification.
  3. midibob

    MPU4 Motherboard Repair WELL ATTEMPT

    You can always jump in the river, works for me. Good luck.
  4. midibob

    MPU4 Motherboard Repair WELL ATTEMPT

    You should have highlighted the word 'after'!
  5. You're probably correct Nick, I just can't remember.
  6. midibob

    Maggi Maggi multicash machine

    Shame, so near and yet so far.
  7. midibob

    Tales from Midibob's workshop. MPU3

    This one was a blinder... As per usual all the bits affected by the green plague had to be replaced and once powered up it was stuck in reset. That turned out to be all the transistors in the reset circuit were bad. So, it now comes out of reset and nothing! All the DATA and ADDRESS lines were running as shown on the logic probe, all CE lines were also OK so what's going on? Next thing is to scope all the D & A lines just to confirm things are correct. Ah ha...... This was A15, enough to show on the logic probe but way too low to work. It should be nearer 5v. Of course A15 goes to all the support chips so which one is bad? As someone had been so kind to put IC4 in a socket I thought I'd start with that one. With the chip removed the scope then showed ..... A vast improvement but still a bit on the low side. In with a new chip and .... no difference, back to 1.2v again? What's going on here?? At least I was at the right location though so without further ado I decided to check the adjacent pins for shorts and lo and behold pin 19 is short to pin 22! Out with the socket and what have we here.... You can probably see the whisker in the top right between the pad of 19 and the track of 22. Once that was scraped away and all cleaned up, the socket re-fitted it all burst into life. That just left me with a another couple of easy fixes as the sound was low and there were no sensor lamps running, both BCX38's were bad. Not a bad mornings work I reckon.
  8. midibob

    Maggi Maggi multicash machine

    Fresh head in the morning, that's always my motto. I'm sure you'll crack it Andrew. Probably the 'cashiers' codes have been changed for when it was last used so they could be anything. Have you tried the 'Total reset' to see if that defaults the passwords?
  9. Hmm, not sure about that but it could be the percentage if the dip switches are set? Normally it says 78% I think but only if the battery is flat. Mind you if it's Dutch it could be totally different software.
  10. midibob

    Maggi Maggi multicash machine

    I feel your excitement Andrew!
  11. midibob

    Maggi Maggi multicash machine

    Starting to look like a tortoise! Great if it works though.
  12. midibob

    Tales from Midibobs workshop, Sys80

    Putting my Sys80 hat back on. This one came in as a no boot. Didn't look too bad on first inspection but it was as stated dead as the proverbial Dodo! The tester showed there were a couple of Address lines missing and there was no IRQ activity. The quickest way to check out what's working or not working is to use a known good board. Firstly a transplant of the RAM which proved it was knackered. The sockets were contaminated too they were also changed. Next thing was the CPU.... When this was removed one leg decided it wanted to stay! Another leg was bent underneath and once I picked the chip up two more legs just fell off! With a replacement CPU it still did nothing although all Address lines were now pulsing nicely. Next thing was IC8 (74LS138) as this provides the CE pulse for the RAM but although it's inputs were good there was no pulse coming out. In with a new one and BINGO, it burst into life. IC12 was looking a bit rusty so for good measure that was changed as well even though it was working. Nice when it all goes to plan for a change.
  13. midibob

    Maggi Maggi multicash machine

    I've got one of those Timekeeper RAM modules if you need one. Don't know if there is any life in the battery though as it might be quite old?
  14. midibob

    Maggi Maggi multicash machine

    It's nice to see a bit of kit with all the IC's socketed.
  15. midibob

    Maggi Maggi multicash machine

    Didn't you have a set to with ABI a while back saying their new tester was pants! I can't believe they wouldn't have addressed that issue by now?