Williams Power Supply Question...

Robran68

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I was considering rebuilding my Defender power supply instead of using a switcher but I've heard that the Defender version does not have overload protection. Is there a way to make it bullet proof and not possibly fry my boards? Also, I recently picked up a Stargate that had the Defender type power supply which I heard came in the early production Stagates. On the main connection for the harness was a card installed between the power supply and the harness and I'm not sure what it is. Can somebody tell me what the heck this is for??
 

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It's got SCRs on it to crowbar and shunt current away if the voltage gets too high... that circuity was added to the later wms power boards.
 
Congratulations, you have a collectors item. It's the overvoltage circuit that was added to the later power supply boards. They were put on the Defender power supplies after field reports of power supplied failing "hot" (i.e. higher than spec voltages being supplied). Most of the time operators didn't know what they were and just threw them away. I think they may have thought they were like the Galaga filter boards, which were useless and very prone to failure and just pitched them.

They began to appear on the Defender style power supplies in MakeTrax machines and the early to mid production run of Stargates. Some late production run Stargates and Moon Patrols came with Robotron style PS boards that incorporated the overvoltage circuit.

Using that circuit board with a Defender style ps board is the equivalent of having one of the later power supply boards.

ken
 
Congratulations, you have a collectors item. It's the overvoltage circuit that was added to the later power supply boards. They were put on the Defender power supplies after field reports of power supplied failing "hot" (i.e. higher than spec voltages being supplied). Most of the time operators didn't know what they were and just threw them away. I think they may have thought they were like the Galaga filter boards, which were useless and very prone to failure and just pitched them.

They began to appear on the Defender style power supplies in MakeTrax machines and the early to mid production run of Stargates. Some late production run Stargates and Moon Patrols came with Robotron style PS boards that incorporated the overvoltage circuit.

Using that circuit board with a Defender style ps board is the equivalent of having one of the later power supply boards.

ken

Wow cool!

Well I guess I'll just keep it installed in the Stargate and call it done. As for my Defender do you guys just repair the stock power supplies and use them as is? ....I guess my question is should my Defender boards be ok in a HUO environment using a rebuilt Defender PS or should I have some kind of over load protection power supply like Robotrons have??
 
IMO, most of the Defender style power supply failures are caused by the crappy IDC connectors failing. It has been my experience, that if you replace the headers and connectors (with new molex connectors) during your rebuild rarely ever will the power supply fail again.
 
Wow cool!

Well I guess I'll just keep it installed in the Stargate and call it done. As for my Defender do you guys just repair the stock power supplies and use them as is? ....I guess my question is should my Defender boards be ok in a HUO environment using a rebuilt Defender PS or should I have some kind of over load protection power supply like Robotrons have??


The one Defender power supply I have seen that failed hot did so because one diode in the bridge rectifier failed. Normally bridges fail by having the diodes fail causing a catastrophic short circuit, which blows one or more fuse. This is typically caused by running a machine 24x7 in a hot arcade type environment where there was insufficient cooling and the bridge just plain burned up.

If you rebuild a Defender power supply correctly, it should give years of service in a HUO environment. Most of them lasted 20+ years in a less than optimal environment.

ken
 
The one Defender power supply I have seen that failed hot did so because one diode in the bridge rectifier failed. Normally bridges fail by having the diodes fail causing a catastrophic short circuit, which blows one or more fuse. This is typically caused by running a machine 24x7 in a hot arcade type environment where there was insufficient cooling and the bridge just plain burned up.

If you rebuild a Defender power supply correctly, it should give years of service in a HUO environment. Most of them lasted 20+ years in a less than optimal environment.

ken

Thanx Ken for the advice, I might just rebuild the original power supply then. If the bridge recs are good should Bob's $12 kit be fine or should I get the $35 OEM deluxe??
 
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