WMS System 6 power supply board - getting 12vdc where 5vdc should be

Bullwinkle

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WMS System 6 power supply board - getting 12vdc where 5vdc should be

I'm working on rebuilding a system 6 power supply board. I've completed replacing pretty close to everything on the board. I power it up and on J6, pin 6 gives me 13.75vdc (which I expect, that's the 12vdc unregulated pin). Pins 7,8,9,10 all give me 12.52vdc. this is bad as those pins should be +5vdc. I have replaced the two large diodes in the 5v section. I'm assuming at this point I need to look at the voltage regulator on the big heat sink, I'm just sort of curious as to why I'd get 12.5volts. If it were failing, I'd think it'd be lower.

Does this sound right or is there possibly another explanation to this?

thanks

-tom
 
Also look very closely on the board for any spots that might have solder bridges causing a short somewhere or some other mechanical contact being made where it shouldn't be.

-Hans
 
the schematic from firepowerpinball calls it a 5A-9049. Marco Specialties has it cross referenced on their site to part #LM323K. Their cross referenced number shows up on mouser for a few dollars less and I already had an order submitted today..so I'm just going to add it to the order.

Thanks Ken
 
I'm pretty sure that the LM323K is what I've used in the past as well.

-Hans

When in doubt check the datasheets.

I learned this when I ordered 50 DS1811 in a surface mount package when I wanted through hole. The package was actually listed incorrectly on Mouser's site and they offered to take them back but I just modified my designs to use both and kept them. If I would have checked the datasheet I would have noticed their error.
 
The regulator transistor was indeed the issue. I removed the old one and noticed there was no mylar spacer or the rings that protect the legs from shorting. Thought that was odd. Put the new one in and everything works perfectly. First time I've ever seen exactly 5.0v coming across the +5v pins :)
 
The regulator transistor was indeed the issue. I removed the old one and noticed there was no mylar spacer or the rings that protect the legs from shorting. Thought that was odd. Put the new one in and everything works perfectly. First time I've ever seen exactly 5.0v coming across the +5v pins :)

You did remember the thermal paste too, correct?

-Hans
 
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