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midibob

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  1. midibob

    Red Dwarf emulation now possible?

    Sorry to hear that Andrew, hope it gets sorted.
  2. midibob

    Tales from Midibobs workshop JPM MPS2

    Couldn't resist mentioning a couple of faults that might save anyone a fair amount of time and head scratching. It's well known how bad these boards can get with the green plague but here's one which shows you don't even need anything metallic for it to travel. This had got in to all the buffer chips too which is very common. A couple more boards later and I had the usual non booter but this one was a bit odd. The sound would come and go at random and this was due to the voltages on the sound o/p chip (pin 8 ) going up and down. Eventually it booted too which was good so I knew the basic system was OK. Anyway back at the ranch I looked deeper into the audio side. Being as I've seen similar faults like this with Scorp1 my first port of call is to use my straw!! As daft as it seems using a straw is a good way of directing moist air to a specific part of the circuit board or component. These faults are most often caused by board contamination even though they look clean. The slightest hint of mositure and stray voltages start appearing all over the shop. Using the slightest hint of breath through the straw around the three yellow caps (C13,14,15) or the three resistors (R28,29,30) caused the output voltage to go one way but the same method directed at IC6 caused it to go the other way. In both cases the audio would start to distort then disappear completely. The only cure I've found for this is too remove all 4 yellow caps, the 3 resistors the tant cap, C26/27, HD3 and IC3/ IC6. Then give the board a good clean with a cotton bud. I've found IPA doesn't shift it and you need proper PCB cleaner. The components also need cleaning or replacing. Once done I could huff and I could puff with no loss of audio. I also confirmed it with the meter whereas before just touching the bare board around that area was showing varying stray voltages and now nothing. Flushed with success I moved on to the boot issue, as I said it had started to boot but using the straw technique again any directed at the battery area or around IC35 would cause it to alarm and stop booting. Cleaning again as before and also removing IC35 prooved to be a cure. There has been some discussion on the removal of this chip but I have found that it suffers badly from contamination and you can sometimes measure voltages on it's case!! Removal is the only option and as these are obsolete there's no chance of a replacement. The technical merits of this have been discussed previously but for home users it's no big deal. Finally this isn't the board below, it's just to show the components involved. Having said that this one does suffer slightly to applied moisture so it will need a good rub down with the cleaner.
  3. R211 is 2.7R Get a single pole DIL switch for SW1. There's lots more info on my workshop thread for Scorp1. Good luck.
  4. midibob

    Socket Adapter

    You can of course just use double pin strips and cut them to size. I think they are only £1-2 a strip of about 20. Can't remember what they are called off the top of my head? This board is the master oscillator as correctly stated by various folks. I've put the diagram up for it in the downloads section, it's very simple.
  5. midibob

    Socket Adapter

    Here you go https://uk.rs-online.com/web/p/dil-headers/6007704/
  6. midibob

    De soldering station -pace

    Jamie, all I get is a disco in the background and no video?? I wonder if that's the same for anyone else?
  7. midibob

    Proconn 7 seg led displays

    Love it.
  8. midibob

    Proconn 7 seg led displays

    I wouldn't use second hand ones anyway as they are as likely to be as dull as the ones being swapped. Definitely not at that price either. Thanks for looking though. I've gone for the Kingbright ones which was my original choice. Not sure if they come with a pair of sunglasses!!
  9. midibob

    Proconn 7 seg led displays

    Thanks Louie. I'll revert back to plan A as trying to find the originals is an absolute pain.
  10. I'm working on a Proconn Plus at present which came in as a no boot. First thing to note was it had a master oscillator daughter board fitted, which I've covered in a previous article. On intial inspection all looked good, no signs of corrosion on the board which is always a good start. On switch on it did absolutely nothing, no address or data, in fact the CPU appeared dead. Reset was fine but there was no clock! Checking on the daughter board showed there was no power getting to the chips and after a bit of continuity checking there were a few tracks that didn't connect. Scraping off the solder mask explained why, all the copper had been eaten away!! This pic was taken after the repair to the board. Considering how good the main board is I suspect this daughter board has come from a different machine. Anyway, once repaired things started to happen but only to the point of getting an alarm and a P 60 error on the display? I'm running it with Reflex software but there's no game manual for this and of course no error codes.The nearest guess is a P600 which is a meter error on a different game. Further to this R18 (330R just to the right of the yellow wired meter connector) had been suffering from heat so a new one was put in. This is part of the meter circuit and the new resistor does run quite warm, warmer than I'd expect. Everything else in the circuit apears to test OK so I'm not sure as yet what the problem is? If somebody could confirm that it is a meter error at least I won't be chasing my tail looking for the wrong thing.
  11. midibob

    Proconn 7 seg led displays

    Ah, that's interesting. As it stands the modern ones won't show any decimal point at all as the DP2 connection isn't wired on the boards. Don't really want to mod them all so if they aren't used that's even better. Thanks Louie.
  12. midibob

    Proconn 7 seg led displays

    Hi chaps, I'm trying to source some of these at a reasonable price. Thought it would be straightforward and was just about to order a load of modern ones when I thought I'd do one more check. These are common cathode devices with 20.32mm character height. Plenty of red ones available everywhere and vary up to about £1.50 a pop in bulk. Looking at the data sheet they only have one right hand decimal point although it's looks like they have both from a visual perspective (SC08-11EWA). Here's the good bit, the original displays have both decimal points but only use one. Your probably miles ahead of me here but guess which one..... yep the bloody left one!! Looking for the other types that have a left one (or both) and they are about another quid a pop??? Work that one out? Anybody know a good (cheaper) source for these?
  13. midibob

    M1 Repairs

    For 68B09's I think you'd be better off finding some junk MPU4's with board damage. Usually the CPU's are fine and they are in sockets (mostly).
  14. midibob

    Help for my Spotlight

    Yep, that card is set up exactly the same as one of my pics. It's unlikely that's an issue as it runs and goes into attract. The MPU2 has a smaller white plug if I remember correctly although you could mod it although I woudn't advise it! I think the reel sets are identical (correct me if I'm wrong) so I would persevere as to why a: there's no power to reels 2,3 in the MPU2 and b: why your deck alarms in the MPU3.
  15. midibob

    Help for my Spotlight

    Chris, what type ROM cart does it use? Some use the MPU1 type or the later larger MPU2 type which may or may not have a battery on it. I think there may also be another variant with just two ROMs on it. Sounds like you've been round the block a few times with this one! First thing is to make sure the main smoothing cap is OK. If it's the original blue LCR then chances it's either knackered or well below par. (possibly on your spare boards too!) If the 5v is good, which it sounds like it probably is, then the 15v supply must be good too. If there's no power to any one of the reels I would suspect their transistors first and 6820 next. having said that if the 6820 was duff I would normally expect it to stop it booting. (never say never though!) This is assuming all connectors and cables don't have any bad connections! Dry joints on the connectors are very common. The only other thing with these old machines is the switch wiring. All the switches are break to operate (not the coins accepts). If there's a broken wire/switch then you can get the most weird faults. Not sure if any of that will help you but if you need a pic of the cart for comparison just let me know the type as I've got a selection of pics I've saved as they've passed through the workshop.
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