question about voltage regulators

[jbshocks]

Ok,  This is again on my CEI slot machine.  I will explain my problem first then ask the question.  Coin comparitor, reel knocker and handle lockout solenoid all run 24 volts.  When I first got the machine to life I had 24 volts on the coin comparitor  and knocker and solenoid.  AS I have gone on playing most of the time I would hit the spin button and not the handle but the handle seemed to stick.  I wasn't to concerned just seemed slow from old grease. I also started to reject some coins  out of the comparitor.  This was a little annoying but I adjusted the pot blew air through the board thought maybe bad comp.  Then I propped open the diverter in the comp which would allow any coin to go to the hopper (this is cc-40 with built in optics)  now it would take all coins.  I kept playing on coins much longer than typical and it stopped counting coins.  I took a meter reading at the comp and got 15.5 volts I also tested knocker and handle with same result.  This was after the game was on several hours.  I unplug the machine and let it cool several hours and I get 17.5 volts and everything works but handle release is a little slow.  After about 5 minutes it is down to 16.35 volts but still counting coins and playing.  Once it hits 16.3 volts 30+ minutes it won't count coins.   Turning the machine off for 5 minutes  and it is back to 16.8 volts.

Now to the question.  My gut feeling is a bad voltage regulator dropping voltage out as it heats up.   Will a dying voltage regulator start to drop voltage off as temp increases?  There are 5 voltage regulators on this machine 2 are fixed 5 volts and clearly not for this.  The other 3 are variable voltage one LM350t and 2 LM317t.  I suspect the lm350t would be the bad one since it has the highest amp rating and I would think solenoids would have the largest draw.  I will try to follow traces later and see if I can pin the source to this voltage regulator.  (fyi I pick up no ac voltage)

I am just looking for a little validation.  Am I on the right path or barking up the wrong tree?   

[cowboygames]

I think your best bet would be to set the machine up so you can access the regulators while the machine is acting up and use a can of freeze spray, or a can of air duster upside down, and chill differant componants individually to see when the problem goes away and replace that componant. I'd more likely suspect a cap going bad as it heats up.

[stayouttadabunker]

I think your best bet would be to set the machine up so you can access the regulators while the machine is acting up and use a can of freeze spray, or a can of air duster upside down, and chill differant componants individually to see when the problem goes away and replace that componant. I'd more likely suspect a cap going bad as it heats up.

On the power supply board?

[jbshocks]

Thanks for the response.  I was thinking more than a degradation from heat because it is already starting low.  Still think a cap would bring it down from the start and drop over time with heat?  I see 3 caps in this circuit 2 small 47 uf 35 v caps that I think are filters and one really big 4700 uf 25v

[jbshocks]

I think your best bet would be to set the machine up so you can access the regulators while the machine is acting up and use a can of freeze spray, or a can of air duster upside down, and chill differant componants individually to see when the problem goes away and replace that componant. I'd more likely suspect a cap going bad as it heats up.

On the power supply board?

Power supply is built into the main board. only a transformer off the board.

[cowboygames]

Caps can absolutely go bad that way, but if he doesn't have any then probably not in his case. I'm definately not familiar with CEI power supplies. If they're using an adjustable voltage regulator then the problem could be in the connections on the adjustment mechanism. Show me a picture of it

[jbshocks]

I will try to post a close up of the circuit area.     When I say adjustable I don't mean that they are intended to be end user adjustable just that based on the setup it can produce output voltages of 1.2-33 volts.

[jbshocks]

I was setting up to do the cold test and before ever spraying the can the voltage started to drop much lower and the voltage regulator in question started to get very hot.  I turned it off and ordered caps and a voltage regulator.  I didn't want to risk leaving it on any longer so I will shotgun the caps and regulator and retest.

[stayouttadabunker]

Too bad we can't see the burning out inferno inside that IC component...
Something's gone awry...

[jbshocks]

I just hope the damage is contained in the IC

[cowboygames]

More than likely, voltage regs and horiz outputs tend to run pretty warm because of the voltage drop across them. ThatMs why they're generally accompanied by heat sinks. Let us know how the replacement does

[jbshocks]

   My digi key order showed up today.  I changed out the smoked IC the 4 big caps on the board and 3 others that clearly controlled the voltage regulator.  I am please to say it is back to life.  The voltage is still a little lower then I would expect but it is working perfectly.  I plan to change the rest of the caps on the board later and see if the voltage comes up.  The IC does not feel warm at all but the heat sink sure feels warm so I am also wondering it the heat transfer connection was not good and contributed to the failure.

[poppo]

If one of the caps was bad, it would have caused the voltage regulator t work harder by trying to constantly compensate for the ripple that the caps should have filtered out.

[jbshocks]

So I swapped out the rest of the caps with the exception of one 16v 10uf (ordered 1 to few by mistake)  and then I noticed 4 50 v 2.2 uf and 1 35 v 10 uf.  It seems to be working fine now and really it was after the caps with the voltage regulator.  I am sort of torn between if its not broke don't fix it and it had some bad ones swap them all.  What do you guys think?

[poppo]

I am sort of torn between if its not broke don't fix it and it had some bad ones swap them all.  What do you guys think?

The parts are cheap or if I already had them on hand, I would go ahead and replace them.

[jbshocks]

Let me run another one by you guys.  Even though the machine is working I still think there are some things that are not right.  The voltage is only 17 volts at start up drops a bit after operation to maybe as low as 16.  The coin comp still works but is a 24 volt set up and the solenoids are 24v as well.  So I think the thing should be closer to 24 v.  When I first got the machine going I swear I saw something close to 24v at comp but who knows.      The cooked IC voltage regulator is fed by a bridge rectifier (model BP61). I have tested the rectifier with DVOM on diode and get no bidirectional readings.  Is that the be all end all test?  If not shorted or open it is good?  I tend to think that maybe one leg is out on the bridge rectifier  and it is not providing full voltage to the voltage regulator.  I have 2 other junk boards for this as well which are both earlier versions.  CEI changed the bridge on each version and one of them has clearly had the bridge rectifier changed in the field leading me to believe this is a problem area.  In my mind the low voltage could also have caused the IC to fail as the amp draw would have increased.

What do you guys think? 

[poppo]

One test would be to measure the AC voltage going into the bridge rectifier.

[jbshocks]

I set up a test stand to get some voltages and my son was not happy that his legos were being used in my slot machine.

My findings,  the questionable rectifier bridge has 30 volts ac coming into it.  On the output I am getting like 15.8 v DC.  If I switch to AC scale I get 31 volts ac on output.  Is this just seeing the ripple as AC since this is before it gets conditioned?   Souldn't I have gotten 28-29 v DC on the output of the bridge?

[poppo]

I set up a test stand to get some voltages and my son was not happy that his legos were being used in my slot machine.

My findings,  the questionable rectifier bridge has 30 volts ac coming into it.  On the output I am getting like 15.8 v DC.  If I switch to AC scale I get 31 volts ac on output.  Is this just seeing the ripple as AC since this is before it gets conditioned?   Souldn't I have gotten 28-29 v DC on the output of the bridge?

Yeah, you have a problem if you are reading that much AC on the output. Yes, the output should have been about 28VDC

[jbshocks]

You think replace the bridge and see what happens?

[poppo]

You think replace the bridge and see what happens?

Yep. Might look at replacing the cap on the output side again too. They don't like being fed AC like that.

[jbshocks]

ok,  Thanks for your help.  I ordered the bridge and a fresh cap. Should I replace the voltage regulator at the same time or see how it goes?

[poppo]

The regulator is probably ok. But if you already have another spare, it can't hurt.

[jbshocks]

Well guys here is the update.  I finally have 22.8 volts  I changed the bridge rectifier and the big filter cap and ended up with 18 volts  and no stray ac.  I started measuring the voltage straight at the VR.  My non functioning board would produce 24v.  I changed out the VR again and still 18v.  So then I start mapping out the schematic as best as I could and removing and testing resistors as that is how you control v out on the regulator.  All tested good.  Finally as a last ditch effort I remove a tiny cap between the V out and adjust circuit on the regulator.  There were no markings so I could not get a fresh one I had to pull from my parts board.  I  now have good voltage to all solenoids and coin comp.  I ran 450 quarters into with a single reject.  Thanks guys for letting me bounce ideas off you and your suggestions.  

Hopefully my final question on this topic.  how can I tell what this capacitor is with no markings?  I would kind of like to put a new on in rather than a 25 year old one.

[poppo]

Hopefully my final question on this topic.  how can I tell what this capacitor is with no markings?  I would kind of like to put a new on in rather than a 25 year old one.

Is this for the LM350T? If so, this generic schematic might help.