(Topic ID: 130530)

Gottlieb System 80 Ground Mod Confusion - Board to board vs. Connector

By davebart5

6 years ago


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  • 42 posts
  • 17 Pinsiders participating
  • Latest reply 6 years ago by Pinterest
  • Topic is favorited by 28 Pinsiders

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#1 6 years ago

Hello fellow Pinsiders. When it comes to the Sys-80 ground mod, I've seen some confusing info out there regarding what route is the right way to handle the grounding issues in these Gottliebs. I'm about to begin bringing a Haunted House back from the dead and want to start mapping out my restoration game-plan.

One method is to install ground connections from board to board and finally to a grounding plate as in this video here.

But then I see professional restoration videos like TNT Amusements where Todd says your wasting your time wiring board to board and all you need is the additional wire in the connector from the MPU to the Driver Board and that's that... His video is here.

TNT has to have restored hundreds of Sys-80 games and this seems to be their method of handling it, which seems to work. I have yet to come across info online saying this method has failed. Has anyone installed just the extra wire in the connector with major issues down the road?

Any thoughts?

Thanks!

Dave

#2 6 years ago

Good ground is a tying a heavy ground completely from source to end and using ring terminals as often as possible (some places not possible - soldered instead).

Regardless of what Todd says -- the ground still goes through the edge connectors on the CPU's J1 connector and these will cause just as many headaches as the CPU/Driver board interconnect (I know first hand). Can also repin J1 but best to add a heavy connection that does not rely on plugs. Add to the fact that Todd also says to use a *used* wire from a scrap connector - one that has already gone through who knows how many installation/removal cycles.

First video you link to does his 'star' connection at the ground straps at the bottom of the head. Doesn't matter where the star connection is as long as everybody is tied together somewhere.

I run a heavy 16AWG black ground from bridge to cap, from cap to a 'star' connection at the screw in the middle of the CPU board. Star goes off to power supply board (mine has a screw terminal on the board specifically for grounds), to the driver board and also to the sound board. I also run a few red 16AWG wires - heavy power from bridge to cap, from cap to power supply input (mine has a lug terminal on the board) and from power supply to CPU board. This task is made far easier when you use a power supply with screw terminals for +V input, +V output and ground.

Also fix the ground 'mess' of 0.093 connectors at the transformer assembly *if* it used the bunch of ground connections through the 093 plugs (not all did).

Ed

#3 6 years ago

Todd is just wrong about his version of the ground mods.

The whole problem is that Gottlieb used a daisy chain of connectors to bring ground from the power supply, to the CPU, to the driver board. By the time ground gets to the driver board, if the connectors aren't perfect, ground could actually not be "0 volts". Due to the resistance of the connectors, it could be slightly higher.

The problem with this is due to digital logic... it doesn't do well when things aren't perfect "0" or "+5" volts (which translates to "0" or "1" in it's digital mind.) What if the voltage is slight above 0 volts? Is that a "1" or a "0"? It gets confused, and wacky stuff happens (like locked on coils.)

To make things obvious to the digital circuit, it's best to not rely on connectors, which with time, can gain resistance. That's why you've seen the ground modifications to the power supply, CPU board, and driver board on system80 games. To be frank, the rest of the boards don't really matter in regards to ground. But if you want to tie hard grounds to them too, it certainly isn't going to hurt anything. (the sound or light chaser boards sometimes need better grounds, but nothing smokes and burns if that doesn't happen.)

So bottom line, on sys80 and sys80a games....

0. If there's an orange 12 volt filter cap on the bottom board, replace it with a new 10,000 mfd 20 volt cap. Time: 2 minutes.

1. Take the main green ground wire that attaches to the lock in the backbox, and bolt it to the power supply frame. This involves undoing two screws. Note this wire goes down to the bottom board's brass metal "ground central", where all the green wires connect together. Time: 10 seconds.

2. Modify the power supply supply with a 3" piece of wire. Run it from the power supply negative lead of cap C1 to the metal power supply ground frame. Time: 1 minute.

3. Run a 6" piece of wire from the CPU board negative lead of cap C1 to the metal frame of the power supply. Time: 1 minute.

4. Run a 18" piece of wire from the ground plane of the driver board to the metal frame of the power supply. Time: 1 minute. Check out a picture to make sure you do this step right. It's a bit tricky to find the right trace.

5. Optional: Double up the +5 and ground lines on the double sided connector going from the CPU to driver board. Note this is the modification Todd does. Frankly it's helpful but not mandatory if steps 1-4 were done above. But go ahead and do it, as what the heck, it's 6" of wire and four connector pins. Time: 2 minutes

6. Don't listen to Todd anymore in regards to Gottlieb grounds.

So in 10 minutes you can do the job RIGHT. I hope this helps.

#4 6 years ago

Here's a video from the PinballNinja.com blog that shows you how to do this stuff.

#5 6 years ago
Quoted from cfh:

1. Take the main green ground wire that attaches to the lock in the backbox, and bolt it to the power supply frame. This involves undoing two screws. Note this wire goes down to the bottom board's brass metal "ground central", where all the green wires connect together. Time: 10 seconds.

I would like to disagree here Using the power supply frame as a common point for GND introduces a new potential problem. What's the case......The power supply frame is only isolated from the incoming +12V at the case of the power transistor. This piece of material can be damaged after dismantling the power supply and the result can be +12V at the frame of the power supply. Normally this doesn't hurt but fuses don't like attaching a Ground wire now I did see this happening a few times already. The same counts for using the sys80B heatsink as a common point for GND.

As a common point for Grounding, I always use one of the yellow straps in later system 80A games, the lower hinge of the lamp panel in earlier sys80 games (circuitboards mounted at the lamp panel), or the screw left below in the backbox which holds the panel at which the circuitboards are mounted (Haunted House and later).

Just my 2 cents.....

Greetings from a technician from Holland

Marco

#6 6 years ago

Thanks guys, great information, especially the bulleted lists of what to do. I've seen the wiki sites and the pinrepair lists and all that, but it's always easier having it broken down into a concise list and amount of difficulty laid out. Sometimes less information is more when it comes to digesting all of it.

It seems to be the mindset here is better be safe than sorry, and the extra grounding procedure only helps and not hurts if done the right way.

I'm still shocked that TNT only uses the extra wire method and operates like that on a daily basis. You would think a pin repair shop would go out of business if they used faulty methods to issues as crucial as this. I'm local to them, and one day may have them overhaul a game, but might just request they go the extra mile to do the ground wires board to board to play it safe. I do like things looking nice and neat, even on the inside, but definitely want this thing to truly be bulletproofed and it seems the extra mile does that.

Dave

#7 6 years ago
Quoted from cfh:

6. Don't listen to Todd anymore in regards to Gottlieb grounds.

Haha noted, thanks cfh!!!!!!

#8 6 years ago

I'm working on a volcano currently myself. Previous owner installed a rottendog PS board. Just curious about +5v rating. I'm reading about 4.8-4.94 throughout the boards. Is this lower amount possibly a problem? Can it be turned up? Game seems to boot up fine, but ball isn't kicking out, and ground mods seem to all be done

#9 6 years ago

Maralb, I don't know. Never had that problem. Been doing it that way for over 20 years. And probably on hundreds of games. Not that this makes it right! Just never seen what you describe. Does that happen if the power supply's power transistor's mica fails ?

#10 6 years ago

COnsidering the strange issue I'm having with my Amazing Spider Man, seeing this info is good timing for things I'll go through and check. Thanks Ed and Clay for great information.

#11 6 years ago
Quoted from konghusker:

I'm working on a volcano currently myself. Previous owner installed a rottendog PS board. Just curious about +5v rating. I'm reading about 4.8-4.94 throughout the boards. Is this lower amount possibly a problem? Can it be turned up? Game seems to boot up fine, but ball isn't kicking out, and ground mods seem to all be done

That is a normal operating voltage for +5v with a load. You'll want to inspect that coil and make sure it has power, along with its associate transistor.

#12 6 years ago

Think of it this way,,,

Would you like it if the ground to the ABS unit in your car was connected to a module, that was grounded through a cable, to the CAN buss and then to the vehicle ground?

Or would you like it better if it was hard grounded at the ABS unit?

Adding that 2nd ground wire on the harness 'helps' if the other ground in said hardness got weak/tarnished, but it does not help if the MPU board has a bad connection through its small power connector.

Do all the grounds, be safe. If you do not do them you may be ok, you may be swapping coils every once in a while. And those old Gottlieb coils cost more every year. One other trick I do is add 2.5a SB fuses in holders at every larger coil under the PF (5 Bank Reset and VUK's love to eat coils).

#13 6 years ago

I agree on downsizing some fuses!

#14 6 years ago
Quoted from cfh:

Maralb, I don't know. Never had that problem. Been doing it that way for over 20 years. And probably on hundreds of games. Not that this makes it right! Just never seen what you describe. Does that happen if the power supply's power transistor's mica fails ?

Hello Clay, I've seen it 2 times in 12 years I repair games. At 1 game, somebody left the mica insulator completely, and in another game, a tiny piece of metal became between the power transistor and heatsink which pierced the mica insulator. Well, if the insulator is okay there won't be any problems, but the heatsink is very very close to the incoming +12V which prevents me from using it as a common point for grounding..... Maybe it is a matter of taste or feeling but I prefer to take a different approach.

Marco

#15 6 years ago
Quoted from MarAlb:

The power supply frame is only isolated from the incoming +12V at the case of the power transistor. This piece of material can be damaged after dismantling the power supply and the result can be +12V at the frame of the power supply.

Good point. I'd be a liar if I said I didn't do a continuity check after a regulator replacement to make sure the isolating film was in place and not shorting to the heat sink. POOF!

#16 6 years ago

Wow never seen or heard of that happening. Very interesting.

#17 6 years ago

Todd mentions he's been doing it that way for nearly 30 years, since receiving a tech bulletin from Gottlieb to add the single extra ground wire in the 80s. I asked him about it in the video comments once and he said he'd never had a problem in all this time. He also mentions on several occasions that he knows other people put lots of grounds all over the game and that he believes it to just be overkill.

I remain unsure who I believe. Clay and Todd both have years of experience. Todd has seemingly sold and operated every solid state game in existence. But Clay has a lot of technical electrical understanding. Who wants to buy two identical System 80 games, put one ground in one and a ton in the other, then burn them in for weeks and see if the one wire version fails?

#18 6 years ago

Star grounds are a good practice though. Take a single point and run grounds from there to all of your boards. You do this in tube amp builds to eliminate noise from chaining, RF issues, as well as other issues.

#19 6 years ago

Me overkill, Todd under kill!

#20 6 years ago

I like to err on the side of caution. So extra grounds for me. Sure it's a few minutes extra work, but I feel it's worth it.

#21 6 years ago
Quoted from KenLayton:

I like to err on the side of caution. So extra grounds for me. Sure it's a few minutes extra work, but I feel it's worth it.

The way I see it, for the extra 10 minutes of work adding them and nearly zero cost, may as well do it, as long as you aren't introducing a ground loop (the other reason star grounds are good).

#22 6 years ago

Agreed. I'm going to do the extra wiring to ensure things are all good.

Now that places like radio shack are no longer in business. Where is the best place to get the wiring and parts needed to complete the full ground mod? I don't recall seeing it on PBR or Macro but maybe I overlooked it.

Thanks again for everyone's insight in this thread. Extremely helpful.

#23 6 years ago

Just a question, I've been having an issue with two pop bumpers. Sticking down after activation isn't a ground issue correct?

Only the coils that are main board activated are affected by the ground mods?

It had the issue so I did the main ground wire mod between the boads, and checked continuity between it, the other boards and thea in strip in the cab. All less than .5ohm.

Still acting up afterwards.

#24 6 years ago

System 80 pop bumpers are activated through the pop bumper driver boards. Check to see they have been updated and do not have any bad solder joints.

#25 6 years ago

All pins have been reflowed, and I've swapped the boards around. It stays with the pop.

#26 6 years ago
Quoted from Slim64:

All pins have been reflowed, and I've swapped the boards around. It stays with the pop.

Once down, do they stay down if you turn off the power? If so, its magnetism of either the plunger, stop, or both. I seem to recall some discussion way back about a bad run of plungers? This assumes the plungers have been inspected already and are not mushroomed out at the base.

#27 6 years ago
Quoted from Slim64:

Sticking down after activation isn't a ground issue correct

The coils may be partially baked and internally swollen from being over-held due to driver board issues. Once repaired, if you do not have the mods then do them as they may have contributed.

#28 6 years ago
Quoted from cfh:

Wow never seen or heard of that happening. Very interesting.

Was on an Oberheim OBX-a I think. Not an analog poly synth you want that to happen on. I think I had to replace like 20 logic IC after that.

EDIT: Nope, wait, it was on some shitty cheap-ass effect unit. It did kill some ICs unfortunately.

#29 6 years ago

Now that local places like radio shack are no longer in business. Where is the best place to buy the wiring and parts needed to complete the full ground mod? Is there a list out there in the community that will guide me on what to buy?

Thanks again to everyone for all of your help.

#30 6 years ago

you can get wire and other items form amazon, MCM, or other online places. If they are just ring connectors, you can probably get them at you local big box store. you can also see if you have a local industrial electronics store.

#31 6 years ago

Thats true, Amazon is super easy. I'll probably just go that route.

Is there a complete list of "ground mod items to buy" compiled out there on the web that anyone has ever seen?

#32 6 years ago

John Roberston (John's Jukes in Vancouver) was the first to identify the grounding issue with Gottlieb games. Here's how he does it:

https://www.flippers.com/gottlieb_ground_cures.html#System80

and the original letter date Feb 1987 to Gottlieb describing the grounding issue and proposed fix.

https://www.flippers.com/premier_technology_GroundLetter.htm

Hopefully John will chime in with some more useful info. I bet he's probably fixed more Gottlieb SS games than anyone

#33 6 years ago

Thank you Woz! This is super helpful. Just when you think you've seen and collected all of the best resources on the web for this, out of nowhere more and more useful docs and information keep popping up.

Much appreciated.

#34 6 years ago

You can buy wire at Home Depot and Lowe's.

I buy the Stellar Labs stranded 18 gauge wire from MCM Electronics.

http://www.mcmelectronics.com/product/24-15065

I use # 8 sized red fork terminals (100 pack):

http://www.mcmelectronics.com/product/27-6452

#35 6 years ago

Perfect Ken! This is exactly what I'm looking for. This makes me feel better than I'm 100% buying the right wires and accessories.

I'm going to be picking up a Weller SP23 soldering iron and 60/40 solder from Kester's.

#36 6 years ago

I like the good quality of the Stellar Labs wire. I also buy the red and black stranded 18 gauge wire to use for adding the additional power wires to the System 80 cpu-to-driver board harness.

MCM Electronics has great prices on wire and crimp terminals.

#37 6 years ago

I don't use fork or ring connectors. It's another connector! All you need is wire. Strip it back 1/2" and tin it. That's all you need. It's cheap and easy and looks OK if you do a good job with the tinning.

#38 6 years ago

Fork connectors / ring connectors -- they are both good and give you a bit better looking connection. These don't suffer the same problem as other connectors such as push on type connectors because these are screwed down and don't come loose. I have never seen one of these go bad although I can see how the wire can break (but so can a tinned wire).
Fastons or spade type terminals - now that's a different story, those I do not recommend.

The 100 pack fork terminals Ken pointed to are fine. Also, having a good crimper for these makes a world of difference. Watch ebay for WT145C crimpers -- you can sometimes pick one up for about $20.

1 month later
#39 6 years ago
Quoted from cfh:

0. If there's an orange 12 volt filter cap on the bottom board, replace it with a new 10,000 mfd 20 volt cap. Time: 2 minutes.
1. Take the main green ground wire that attaches to the lock in the backbox, and bolt it to the power supply frame. This involves undoing two screws. Note this wire goes down to the bottom board's brass metal "ground central", where all the green wires connect together. Time: 10 seconds.
2. Modify the power supply supply with a 3" piece of wire. Run it from the power supply negative lead of cap C1 to the metal power supply ground frame. Time: 1 minute.
3. Run a 6" piece of wire from the CPU board negative lead of cap C1 to the metal frame of the power supply. Time: 1 minute.
4. Run a 18" piece of wire from the ground plane of the driver board to the metal frame of the power supply. Time: 1 minute. Check out a picture to make sure you do this step right. It's a bit tricky to find the right trace.
5. Optional: Double up the +5 and ground lines on the double sided connector going from the CPU to driver board. Note this is the modification Todd does. Frankly it's helpful but not mandatory if steps 1-4 were done above. But go ahead and do it, as what the heck, it's 6" of wire and four connector pins. Time: 2 minutes
6. Don't listen to Todd anymore in regards to Gottlieb grounds.

edit: got the location off the pinwiki!

I'm doing the ground mods on a Sys 80b right now, using John Robertson's images here: http://www.papinball.com/tips/sys80b_Ground_mods.html?sa=X&ved=0CBwQ9QEwA2oVChMI1NeUzIrwxgIVRqWICh3FkwTK

Most of this makes sense to me when using cfh's list, but can someone clarify where the ground attaches on the 80b power supply? Looks like it comes out the bottom in the pictures, but I can't tell where it's attached. John also uses a different location on the MPU.

#40 6 years ago

As long as you tie into the yellow coated ground strap in the head, you'll be OK. It's tied to the bottom board panel.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info

1 month later
#41 6 years ago
Quoted from davebart5:

Now that local places like radio shack are no longer in business. Where is the best place to buy the wiring and parts needed to complete the full ground mod? Is there a list out there in the community that will guide me on what to buy?
Thanks again to everyone for all of your help.

NAPA is a great place to pickup stranded ignition wire - cheap, good, and you can get any gauge and color you want.

#42 6 years ago

Hey there! Got a moment?

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