System 7 Power Supply

Shocker Shocker, a System 7 power supply with a fried GI section.   To be quite honest, this is probably the most poorly designed section of a pinball machine fully of poorly designed sections.  If you ever find a System 7 machine that doesn't have this area roasted to a crisp.... nevermind that thought, they are ALL like this.  From System 7 all the way through the end of WPC-95 production,  Williams constantly had issues with overloading their GI lighting circuits,  System 7 just happened to be the worst.

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The problem is under-rating of the connectors.   My Black Knight, for example, has 65 GI lights.  With the original #44's, at .25A each, that's 16.25 amps JUST for the bulbs.  That doesn't include additional amperage draw created by the sockets, connectors and wiring.  The input connector is only rated for 12A.  So that's why the input side always fails. 

 The output side though, the one that's the worst in this case, fails for a variety of different reasons.  Technically, the connectors here SHOULD be up to the task.  They're rated at 7A per pin, and average 4A per pin of power.  However, that's assuming perfect conditions.  Throw in the notoriously cracked solder connections, some oxidation, heat, and humidity,  and the actual rating starts to drop pretty fast.  This is made worse by the small contact area of the IDC connectors that the wire attaches to, then the flat connector onto a round pin.  This is, of course, assuming they used the phosphor-bronze connectors, not the plain brass which is only good for 5A when new.

As you can see here,  a poor attempt to re-solder the header pins was already tried.  But it's a useless piece of work, as the pins themselves have already been compromised.  Tarnished, burned up and oxidized pins like those on this machine need to be replaced.  A common fix is to bypass them by soldering the wire directly to the big trace on the board, but that's a poor hackjob repair.  The fuse clip also has to go, as that's been compromised too. 

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Now, once everything is off, we see more of the issue here.  The fuse clip and connector have been overheating so badly, that it's delaminated the trace from the board on both sides. This is probably worse than most others that I have repaired,  but it IS repairable.   It's just a matter of getting down to good clean metal, re-establishing the thru-board continuity, and getting better quality parts on there.

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Now, I'm going to do my best on this one.  Of course, this needs eyelets,  as so many of these burned up traces tend to need. As you can see, I'm getting much better with them as I get more experience using them.  I don't know how I did all these repairs without them. The front side of that fuse clip doesn't look as nice as I would like, after soldering between the eyelet and the trace,  but you must do that before installing the components to maintain good continuity.  Otherwise you're just going to end up repeating the repair eventually. The backside will get soldered together when I install the fuse clip. I also needed one in the input connector too, which came out very nice, eh?

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Now I can go ahead and put in new fuse clips and new connectors.  I always replace the fuse clips in pairs, as you can see.  The .156 header is a square pin, which maintains much better surface area, and thus maintains the 7A amperage rating much nicer.  If you use the newer molex high current connector, with the box style crimp connector, these can be good for up to 13A per pin!   At the very least though, use trifurcon pins here.  They have the same amperage rating, but again have increased surface area to maintain that rating over a wider range of conditions.

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The power input connector will be supplied with new pieces for the wiring side too,  to make sure all new and clean metal is in there.  Another option is to convert to a System 11 style pigtail, but in this case it was requested to keep it with the original style.  Not an issue if you can reduce the amperage,  but if you insist on running all #44 bulbs this connector will fail again eventually. The owner said he is planning on swapping all new #47 bulbs into the machine, which add up to a 9.75A draw, and thus within specs for the connector.  LED's are even better for this, as it gives a massive buffer of available capacity. 

As a historical note, Williams eventually abandoned this whole area of the board in later designs, and many early System 11 machines still used this basic power supply.  System 9 saw remote fuse cards introduced,  early System 11 saw the pinput connector remoted to a pigtail,  and the last versions of System 11 even remoted the relay.... using one each for the playfield and the backbox.

WPC-89 saw the GI lighting controls moved back onto the power-driver board,  but a drastically redesigned system that could dim the individual sections of GI lighting via a pulsewidth modulated control system.  Yet they STILL had output connectors burning up all the way to the end by putting too many bulbs per pin on the connectors.