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midibob

Tales from Midibobs workshop, Sys80

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I thought it was about time to cut my teeth on Sys80.

Quite an interesting tech which I need to get my head round. All in good time.

First a couple of 8K CPU boards that had work done previously due to battery vapours. The first one would fire up but only if the board was flexed near the RAM area. It didn't seem to matter how much or little it was flexed as it didn't always start. As luck would have it I noticed a tiny nick in a track just under the negative battery terminal.


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You couldn't really see it with the naked eye, certainly not with my eyesight! Holding the board up to the light made it a bit easier to see.

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Once patched out it started everytime.:)

The next one was purely a visual check as I've not powered it up for testing yet.

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Look at the track next to the green patch wire! After a clean up, a bit of careful adjustment, resoldering and a bit of green mask we end up with this...

1723800957_P1030845(Custom).jpeg.cb0fa131fa756044f70cf20f07b771b8.jpeg

Another issue I've come across which I'm sure the Sys80 boys are aware of is there are two types of 8K CPU cards. I was looking at doing a RAM adaptor for testing being as I don't hold any 5514 RAM chips. This is the Heath Robinson version ...

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This was all very well until I tried to plug it in to the second CPU board and noticed the RAM sockets were further apart, by another pin space! Any thoughts of making a proper PCB means there would have to be two types. I'm sure others must have hit this one before.

Another thing I've noticed was the PSU connector. Quite a few of the Molex crimps connectors had lost their tension and weren't mating too well. I'm sure this is well known by the Sys80 sage's but once retensioned made a noticable difference to the supply voltages.

So it's all good fun for the moment and reading other folks repair reports there's going to be a lot of horror stories to come.
Wish me luck.:headache:

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Best of luck with this tech bob im sure it will be a learning curve one way or another!great games and a true  classic era for fruities just like mpu3.  

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Another board was showing weird voltages all around the RAM and ROM chips. Didn't take much looking to realise why.

895651577_P1030848(Custom).jpeg.3bd62fd32197fadb4f2e34d3e1da9c78.jpeg

The top ground pad on the battery had been ripped off and this provides continuity to the ground plane from the bottom pad to the RAM and ROM chips.

So it's out with the copper garden labels again and a rivet.

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Fix the rivet and new pad in place and solder up.

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Finally a bit of the old green mask and we're done. Good as new.:)

1578268006_P1030851(Custom).jpeg.4acb8d7de471916706abca164a2967d0.jpeg

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I was pleased to see it said you can cut tracks from copper sheet although I'm wondering how much those bits of pre cut track would actually cost? Probably pricey I expect. My bag of garden labels will probably see me out!:lol:

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lovely  work bob  and  a  top class  repair  .do  like  the  alternative  andrew has  illustrated  as well .

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1 hour ago, midibob said:

I was pleased to see it said you can cut tracks from copper sheet although I'm wondering how much those bits of pre cut track would actually cost? Probably pricey I expect. My bag of garden labels will probably see me out!:lol:

I think you are right! stick with the copper sheet! I have no idea how much the replacement pads and tracks actually are with the glue on them! like you say not cheap I bet! I will still stick to the wire I use soldering it onto the tracks for repair, It does the job and is fine for fruit machine boards! there seems to be nothing in the board repair specification for battery eaten tracks!! maybe I should ask them for there guidance!! not repairable I bet they would say!!!

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Well the saga continues trying to get a working system.

At present I have two I/O boards, an early one and a version 3. I'm not 100% convinced these are OK even though I have found faults on them with bad chips. For now though they appear to behave exactly the same albiet the difference in I/O enabling of course.

I also have 4 CPU boards, one 12K and 3 x 8K. The 12K is fitted with Top streak with 3 ROMs and the 8k's have been tried with Steppa nudge, Double up deluxe (only 1 Rom) and Mystery spin.

The 12K board appears to be the nearest to running in that the watchdog pulses are present after a reset, from IC15, but disappear affter a few seconds. During this time there is a 2.4KHz o/p from IC15 which makes it's way to the interrupt on the CPU (pin25). The reels then power up (don't spin) and then the watchdog kicks in and a reset follows. Disabling the watchdog obvioulsy stops it resetting the system but the watchdog pulses never return although the 2.4KHz stays active. 

The odd thing is none of the 8K boards let IC15 on the I/O board send out a 2.4KHz signal although they do let it generate the watchdog but again it dies after a few seconds.

CPU's and RAM have been swapped across between both types of board and there's no difference. This is certainly turning out to be a head scratcher and reminds me of the trials and tribulations with BFM Sys85 and Scorp1. Luckily no custom chips with this one.:)

As I'm still much of a novice on this tech all I have at present is the reel deck with an I/O and CPU card and nothing else. There's no looms or anything else plugged in although I don't think I'm missing anything crucial that would stop it starting, unless anyone knows different of course.

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.

 

Would you like me to send you a fully working cpu and io board so you know you wont be going around in circles

Edited by sulzerned

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44 minutes ago, midibob said:

There's no looms or anything else plugged in although I don't think I'm missing anything crucial that would stop it starting, unless anyone knows different of course.

Yes you normally have to ground input port 5 ( staring from 0 ), most of the sys80 games in MFME need that to run.

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Hmm, interesting. I did see that in the game manual and tried it to no avail. Wouldn't it be awful if that input line was buggered! I'll persevere on that front. Thanks for the tip.

Thanks for the offer of extra bits Nick but the one thing about having all the faulty bits is I'm going to know this inside out by the time I've got it working. (even if it does mean jumping in the Thames.:lol:) If I get desperate then I'll let you know.

Onwards and upwards.

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Yep that's the johnny.

Fresh head tomorrow and we'll see what happens although I did try it earlier this afternoon.

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If the code reads that port as high, it will stick in a tight loop writing a 1 to IC15 pin 7 and therefore disabling all the Outputs and effectively stopping it stone dead.

This is the code in Top Streak:

 

Capture.JPG

Edited by Wizard

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Oh didn't see this thread. I'm also working on a daughter board for 6116 ram on Sys80... much like the original MPU3 one

 

Here is the proof of concept and it's foing on stripboard tonight

 

 

Where did you find the double ended pins? I tried 1mm header but it don't fit on the ram socket.

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I was going to say that it won't boot without the Input plug connected as it has a lockout. On the roms I've used the IO board will boot with no reels and output plugs connected,... but it's hard to see it's booted witnout 1 reel plugged in.

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On 10/2/2018 at 4:19 PM, midibob said:

Another board was showing weird voltages all around the RAM and ROM chips. Didn't take much looking to realise why.

895651577_P1030848(Custom).jpeg.3bd62fd32197fadb4f2e34d3e1da9c78.jpeg

The top ground pad on the battery had been ripped off and this provides continuity to the ground plane from the bottom pad to the RAM and ROM chips.

 

yep very common for those pad to get ripped off!

I have one here just the same!

IMG_2750.jpg.97965cca27034c00b8c22d3240e5765e.jpg

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31 minutes ago, Louie Bee said:

Oh didn't see this thread. I'm also working on a daughter board for 6116 ram on Sys80... much like the original MPU3 one

 

Here is the proof of concept and it's foing on stripboard tonight

 

 

Where did you find the double ended pins? I tried 1mm header but it don't fit on the ram socket.

 

I've used these before:

https://www.rapidonline.com/truconnect-turned-pin-sil-header-32-way-22-1705

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28 minutes ago, Louie Bee said:

I was going to say that it won't boot without the Input plug connected as it has a lockout. On the roms I've used the IO board will boot with no reels and output plugs connected,... but it's hard to see it's booted witnout 1 reel plugged in.

Yes I mentioned that above

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Tomorrow could be a eureka moment then. I won't sleep tonight.:lol:

Don't forget the different socket spacings on the 8K boards! I don't know how many variants there are or which is the most common. I can't remember where I bought my pin headers, probably the same as Wizards but I may have got them from RS, I'll see if I still have the invoice.

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27 minutes ago, Wizard said:

Yes I mentioned that above

Yer you beat me to it.

Had a quick look in fortune trail to see if it were the only lockout as there seemed to be a couple more on ic1  pins 2 & 14 also linking to the same -ve voltage on the loom as ic4 pin 14. But the Io board don't care about these, just need to tie R118 to -ve and will boot...

 

Sorry it's a black wire...

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Thanks for the heads up on the 8k. I'd not noticed with my flexible hookup and was about to make the same mistake lol.

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Well, what a start to the morning.

Connected the input port to ground, as I did yesterday, and of course nothing. Then I remembered it's got to be to the -12v, not ground. :clown:

So what happened next. What can I say, all the CPU boards that I'd fixed blind all worked as did both the I/O boards. One point of note is the 12K board did actually get the 2.4KHz interrupt out to the CPU even without the link whereas the 8K's did nothing so that's solved that conundrum.

Next step is to get some sort of test rig together to check all the I/P's and O/P's. That's the easy bit.:D

Thanks to all for getting me off the bottom rung and Wizard with that snippet of code. So obvious when you know.:clap:

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