Transformer, Bridge Rectifier and Voltage regulator question

[jbshocks]

I have this CEI hot slot that I got running about a year and a half ago.  Well it started to intermittently stop working and now won't run at all.   It started to have issues similiar to to when I got it so I investigated the 24v region of the mother board and swaped the bridge rectifier and the LM350.  The machine still has the same issue so I measured the voltage coming out of the BR at 37.7v  The LM350 is getting burning hot and putting out about 34 volts.   Specs for the LM350 say it is only good for input up to 35v.  Now a little more to the story.   The 4700 uF ripple cap was rated at 25 volts from the factory. When I got it running it had 30v coming out of the BR and puffed the new 25v cap I installed.  I replaced it with a 35v and everything seemed fine.  I thought maybe that caps used to be better and CEI cheaped out and put a 25v cap in a 30v circuit figuring it would last long enough.  Now that the voltage has climbed higher I am guessing that the secondary winding in the transformer is breaking down and causing the voltage to climb.  Is this correct thinking? 

Now what can I do about this?  Disconnect the 24v line from the transformer and hook a separate 24v transformer up directly?  Should I only use an AC transformer?  Can I use a DC one and still run through the bridge rectifier?  Replacing the transformer is probably not a good option since these machines are so scarce. 

Any other ideas?

[CommTech]

Lets look at this one step at a time... The Original problem is that the machine would intermittently stop working.  Can you elaborate on this? Does the machine loose all power or does something else happen?

You said that you swapped the bridge rectifier and the LM350.  Why did you do this?  What was the voltage output before you swapped them out?  38 Volts DC seems a bit high for a 24 volt circuit.  Are you sure it is suppose to be a 24 Volt circuit?

Is the Secondary winding center tapped?  What  AC voltages are you seeing across the secondary windings of the Transformer?

The LM350 may get hot under load, depending on the current draw from the circuit it is feeding.  The Output voltage of the LM350 is set by a resistor off one of the legs (regulator resistor may be open?).

Do you have a schematic for your machine?  

You say that the machine won't run at all now.  Does that mean No power at all?  Please elaborate.

As far as Electrolytic capacitors go ... The ratings are their break down voltage.  You should always use a voltage rating HIGHER than the DC voltage that is present in the circuit.

As for the Transformer ... Chances are, there is nothing wrong with the transformer.  Also, there is no such thing as a DC transformer.  

[jbshocks]

I do realize transformers are AC.  I should have said power supply.  For clarity the machine starts and runs but will not spin the reels.  The led display shows a code for reel controller failure.  The reel controller and the coin comparitor share the 24 volts.  I do not have a schematic for the machine and it is unlikely that I could find one.  I only have the operators manual.  The transformer has multiple taps but no documentation as to what they should be.  I did not do a  voltage check before changing the bridge and vr.  I did check them with a dvom on diode check and they failed.  They now pass.  I also checked the control resistor and it checks OK. 

The only reason I know 24 v is right is because the motors and coin mech.  Also when the machine worked fine I had 22 v after the regulator.  I never really got a full 24v. 

[CommTech]

Not having a schematic makes it very difficult to troubleshoot.

To answer your previous question about adding your own 24 volt supply ... Yes you can do that, but I am doubtful that simply decreasing the voltage to 24 volts will completely correct your problem.
That said, you would just need to purchase a 24 volt DC supply with sufficient current capabilities (I would suggest something like this 8.4 Amp one ($40 shipped) Ebay # 251374606864), and install the output AFTER the Regulator circuit.
Remove the regulator to isolate the old circuit.  That way you will have well regulated 24 Volts DC to the rest of you machine. 
8 amps is probably overkill, but unless you know for sure what kind of current that circuit requires, it is better to error on the high side.

Best of luck to you. 
 

[jbshocks]

With an lm350 being rated at 3 amps shouldn't I be good with a 3 amp power supply?

[CommTech]

With an lm350 being rated at 3 amps shouldn't I be good with a 3 amp power supply?

Yes.  That makes sense. A 3 amp should do the trick nicely!