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midibob

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Everything posted by midibob

  1. Frying tonight I think is the phrase! Not a clue on the Ohmage but just compare it with a good one.
  2. I've never been in the industry either but my first vivid memory that got me here some 60 odd years later was being at the local funfair in Haying Island. I remember the machine hadn't paid out or something similar and when the engineer opened the back and I saw all the coloured wires and relays I can't tell you how excited I was. The funny thing is I was only really ever interested in the innards, playing the games had no interest for me and still doesn't. Folks on here give me an odd look when I tell them that. Keep the stories coming Frank, it's always a good read and the techy stuff is a bonus.
  3. It sure is, maybe to stop any high frequency transients as the data rate is quite low. Who knows?
  4. No, it's just a ceramic cap.
  5. Hi Tony, If it's the small cap that's connected to IC7 (MC1488) pin 3 then it's 330pF. I assume it's the little square grey one with the purple stripe at the top just under plug Q?
  6. Fired up first time and ran without a hitch. Don't you just love it when that happens.
  7. Hi Ronnie, I used an Isopon body repair kit. If the hole is large enough I chop up some glass fibre strands to give it more strength. The only thing you need to be careful of is the temperature. It can go soft with heat so if you need to drill rivets through it with soldering a bit of care is needed. Not had any problems it has to be said.
  8. Some more boards giving me the run around or beyond economic repair. First one was a real pain, it wouldn't initialise and for the life of me I couldn't see why? Someone had been here before which is always a worry but they work seemed of a good standard. So the nitty gritty....on switch on there was just a short pulse to the RAM and then a few address lines died and it just sat there. IC9 (74LS138) and IC24 (74LS12) had been changed so I knew all was good in that dept and all the other usual stuff had been done. The first suspect was the CPU which was swapped but no difference. Next one was the 6840 as I've seen this stop boards booting before, but again nope! Not wanting to continue the wild goose chase I thought I'd try and think this one out. Next step was to tap out all the data and address lines to make sure there were no shorts or open circuits, which there weren't. Then it was the turn of all the other functions eg E, NMI, VMA etc. When I got to the R/W I found there was no connection from the RAM (pin 10) to the R/W line feeding the rest of the board? What a relief I'd actually found something. On the previous repair the two RAM sockets had been changed but because they were using the RAM daughterboard they had to be the stamped pin type as you can see in the pic. On removal of the socket in IC8 I found this... The via at pin 10 of IC8 had been ripped apart and consequently lost connection. So a quick rivet insert, a tack wire and a bit of solder mask to finish off and she's as good new. When all put back together it booted and ran fine. ....and the next one. This had already been deemed beyond economic repair as you will see from the pic.... The board was toasted right through just above the power diodes and various components further up the board varied in incinerated, well done to medium rare depending whether they caught the flame or not. As I was head scratching yet another board I thought, why not, and stuck it on the bench. First thing is to give it a clean and try and remove as much carbon as possible. Once done this left a sizeable hole in the board. This has to be done though as any carbon left will just track and start the whole process over again. I must admit it does look scarey but I've done this quite a few times now so it's pretty much business as usual. The next step is to make up some resin, seal the bottom with cellotape and then fill the hole. Once this has set the track needs to be re-made, holes drilled, rivets fitted and solder mask applied. New track cut and fitted and riveted. They do look close together but it's a trick of the light! I still need to drill and fit another rivet for the white power lead but that's tomorrows job. Then a bit of solder mask to finish off. All that's left is to swap out all the burnt components and the usual bits and pieces. I just hope after all this it doesn't have any obscure faults!!
  9. I think the surest way to prove this one way or the other is to beg, steal, borrow another board and see if the fault goes, at least then you'll know for sure where to carry on looking.
  10. A couple more things to check. Does the sensor lamp illuminate for reel D? Does the reel look like it's spinning correctly? I don't know if that was a video you posted but I don't see anything?
  11. You may have to be careful with the charging as the original is Lead Acid and the AA's are likely to be NI-MH so will have very different charge characteristics.
  12. It is on my Cabaret machine. It's on switch bank 2 (7). I've never used it to see if works though?
  13. Neccessity is the mother of invention, I think that's how the saying goes? Well done Rich.
  14. Don't know if this is any good? https://www.silicon-ark.co.uk/ped-63-150-332-380-relay?search=relay
  15. I've now managed to get the games running but it's been an uphill struggle. My main issue has been the test rig as the game software is quite fussy what it sees on certain switch ports. Also not having a proper reel deck caused loads of alarms till I worked out that on boot up it needs all photo sensors to be open and then all closed to run the game. The problem with the alpha must be a timing issue as I'm using a modern OKI printer one. This works fine with the diags but not with game software. Very occaisionally it will actually show proper text so I'll just ignore it for now. I also had to close 4 of the aux switches as these I know now are the coin inputs from the mech. My usual adage of 'I won't be beaten' has paid off yet again. I think it's put years on me though, I must be about 200 by now!
  16. It's been a while since I wrote an MPU3 fault up. Just when you think you've seen it all yet another one comes along to bite you in the bum? This one came in as not working/untested and after the usual suspects had been swapped out I noticed that IC23 (74LS08) was burnt! Swapping this out and then powering up on the test rig I was pleased to see the reels moving and the lamps flashing. The triacs were all pulsing correctly too. So moving on to the switch test and ....nothing?? Now IC23 is fed from IC11 (74LS138) and here there were no outputs because there were no inputs! Hmm what's going on here? The inputs to this chip come from 3 of the 6821's IC3,4 & 5 and there was nothing leaving on all three on pin 39. A quick resistance check to ground showed 2.1 Ohms 1k Ohms and open circuit (should be approx 5K) so although all 3 PIO's were working in their other functions all the pin 39's had popped!! What a bummer. IC21 (9602) is also connected to pin 1 of IC11 and this had also popped. With all parts replaced things were back to normal thank goodness.
  17. Interesting stuff Frank, thanks for going to the trouble of typing it all out. Playing machines is not my thing and I get totally lost when folks quote all the names of the games and nod to each other. My interest is in the technology and it's so great to hear it from the horses mouth, if you'll excuse the saying. Bob
  18. OK, done the mod and the games now boot. I'm running these on the test rig and unfortunately all I get is garbage on the alpha, ALAA06 on the 7 seg and the alarm. I can see reel activity and I can also throw a couple of the switches which causes a reboot so I assume they are probably the door ones. I have managed to get it into self test as well so it all appears to be running but it won't run the game. I'm using High Rise £6 and I've knocked out the CHR and Checksum checks. Can't find the game manual for this so it's all a bit uphill at present.
  19. That's brill and just what I suspected. The manual is definitely wrong and without that mod these carts won't work with 27512 chips. Talk about a head scratcher!!
  20. Thanks Tony, might be getting somewhere here. Hmm the plot thickens! That first pic of the V2 cart looks like it's been modified. My cart is exactly the same number 16539/2 but doesn't have the extra link holes between LK7 and LK5A in fact it's the same as pic 3. Now I can't see from pic 1 but I suspect IC3 has had it's pin cut away from the 5v rail and then goes to that extra link. Both these extra links are marked on the V3. Could you confirm that for me Tony? Probably a tac wire underneath. In which case the manual is wrong!!!
  21. Some really contaminated boards I've stuck in the dishwasher on a very gentle wash and they've come up pretty good with no damage to the silkscreen either. You just need to make sure they have dried out completely before powering up. https://www.fruitemu.co.uk/ib/topic/20787-tales-from-midibobs-workshop-sys80/page/5/?tab=comments#comment-332275 I did ask about cleaning baths a while back which is here.... https://www.fruitemu.co.uk/ib/topic/24350-thoughts-on-ultrasonic-cleaning-baths/?tab=comments#comment-363361
  22. I've been going demented trying to get a ROM cart to run with a 512K chip in it. I'm using the three ROM type one and using the link settings as per the manual. The cart says it's Ver2. After a good fair while of swearing and hair ripping out I realised that the socket IC3 which is meant for the 512K chip has address line 15 (pin 1) permanently connected to 5v? Now the version 3 cart has an extra link which looks like it handles this pin but of course that isn't mentioned in the manual as it was probably printed before it was made. I could easily mod my cart as it's only for testing bizarre faults that don't show on the test rig but I can't help think I'm missing something here being as it's documented in the manual for a 512K chip? Anyone care to comment...... As an aside the cart runs fine with a 256K chip in IC3, which it would.
  23. The scope should have a very high impedence input to ground! The only thing you might need to look out for is there are two grounds one for the high level supply and the other for the low level. I can't remember if they are joined back at the PSU? When I was faulting the MMM I used the -ve of the big smoothing cap for the ground connection. I would have thought putting the scope ground on anything but ground would drive it potty/blow fuses/plumes of magic smoke whatever! Not something I would do. I've found most issues in these boards are caused by rotten components in the battery area, much like any other tech really. I think it's all in my workshop threads a way back.
  24. Well had a few of these in lately and although I decided quite a few years ago not to do them as someone else had picked up the baton but I was made an offer I couldn't refuse (Godfather LOL) Anyway I didn't have a proper rig to test them with so I'm half way constructing one which is now functional but not complete. More of this in later tales. So one chassis I looked at today was listed as dead, which it was. Just the two 12v led's and one of the relays appeared live. On opening up it had the dreaded battery backed RAM board in it!! Without this board most chassis I've seen are in very good nick but this one, although not too bad, had definitely suffered the green plague. Here's a pic of the RAM board and It may not be salvageable especially if I can't get the old components off of it! The rot has travelled right up the wire and ate into the connector at the far end. It's also got into some of the IC sockets on the main connecting board although hopefully not badly. I did make some of these daughter boards a few years back but I don't know if I've still got them. That could save a lot of hard work. Further investigations showed no 5v coming out the regulator so more faulting tomorrow to see what is going on.
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