Power Supply Problem

rted

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Jurassic Park Data East display went blank. Voltages at the DMD are as follows;
Pin 1 (-110) -111.5
Pin 2 (-98) -98
Pin 3
Pin 4
Pin 5
Pin 6 (+5) +4.9
Pin 7 (+12) 0
Pin 8 (+68) +68.5

I have no +12V on the DMD board and at the PS board. Swapped my DMD and it works fine, game sound, lights etc work fine. I know it's the 12 V portion of the power supply. I have inspected the PS board closely but didn't find anything obvious, see pics. What do I check next?

I have gone through the past threads but found nothing specific to +12 volts missing.
 

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Is fuse F4 good? If it was bad you'd not have lamps so I'm guessing it is okay.

Assuming F4 is good, do you have the tools and ability to unsolder and solder components from a PCB? If you look at the schematics, you'll see that +12v comes from a 7812 regulator on the power supply. It, and the two electrolytic capacitors around it are the most likely culprits. Radio Shack stocks the components you'd need to fix it.
 
Thanks for the quick reply. Yes F4 is good. I am good with a soldering gun and replacing the suggested parts ( see jpg ) are no problem. You certainly made the repair look easy.....thanks very much!!!
 

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That's where I'd start. Radio Shack does not stock the 0.1 uF 500v ceramic disc cap, and it is most likely fine so don't worry about it at this point. But if you are placing an online order for parts, throw in a few of those .01 uF 500v caps just in case. And while you are at it, check R16. You may have to unsloder one end and take a reading on it to get an accurate measurement.
 
Really appreciate your help. How can I test 7812 with a mulimeter to make sure it's defective? Resistor reading is not a problem and I will also remove pins and check the capacitors.

Many thanks.
 
I don't think there is an easy way to test the 7812 other than hook it to power and a load, and take measurements. Of course this is what was being done when you took measurements. The 7812 itself could be good and a cap is causing the problems, but for the cost associated you may as well get a new one and replace it.
 
Thanks again!

Understood, will order the parts and do the switch this weekend. Your help is greatly appreciated
 
Connector CN1 pin 1 reads 0 V. Is this upstream of the VR1 circuit?
 
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Correction;

Just checked the PS schematic further and note the connector CN5 pin 2 -98V, pin 3 -110V and pin 4 -68 V are supplying correct voltages. Connector CN4 pin 6 +16 V, is this supplying the voltage to the VR1 circuit? Should the connector CN1 pin 1 be 0 V if I am not getting 12 V at connector CN5 pin 5. So it must be the VR1.

Is this logic correct?
 
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The lamp matrix (CN4) is powered from CN1 pin 1, as well as the +12v from the display (CN5). This is why I asked if you had lamps and if F4 was good. If you don't have lamps as well as not having +12v, the problem is upstream as you said.

CN1 is the input, it then goes to CN4 for the lamps, then to the 7812 regulator to generate the +12v for the display board.

CN4 and CN5 are outputs. If you aren't measuring something there, your problem is back towards CN1, or before it.
 
I do have lamps and F4 was good so it must be the VR 1 not upstream. Just checked with my local electronic supply store and see they stock part # LM340T15 not the VR 1 7812 # LM340T12. Is it compatable?
 
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Once again thanks for the help and quick reply. I did have lamps and the F4 is good. Just checked my local electronics shop for VR1 7812 # LM340T12. This is not available can I use #LM340T15?
 

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Yes, you can use the LM340.

Edit: I mean the LM340T12, not the T15.
 
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Great and thank you very much for your help. Hope to have it up and running in the next few days thanks to you!!!!
 
Once again thanks for the help and quick reply. I did have lamps and the F4 is good. Just checked my local electronics shop for VR1 7812 # LM340T12. This is not available can I use #LM340T15?

--NO-- you cannot use an LM340T15. This is a 15V regulator. You can use an LM340T12 but not an LM340T15.

Ed
 
--NO-- you cannot use an LM340T15. This is a 15V regulator. You can use an LM340T12 but not an LM340T15.

Ed

Edit: I think the question about the LM340T15 was added after I responded. I seem to remember the datasheet being attached after I replied and it wasn't there on the original post. I was referring to the LM340T12. If not, then I missed the question the first time. Thanks, Ed!
 
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testing a regulator is pretty simple ....you have an input, in this case usually around 15vdc that is regulated to a 12vdc output....check to see if you have your input voltage and then see if it is producing the correct output....if you need to, you can desolder the output pin incase there is something pulling the output down.
 
Yesterday afternoon I was able to purchase the correct VR 7812, also replaced resistor R16 and the two cap. Installed them on the board last night, assembled the PS board and the problem still exists. No 12 V at CN 5 pin 5. All the other voltages are OK. To summerize I noted the following;
1. Turn on power - NO DISPLAY.
2. Music starts OK
3. T-Rex does the testing OK
4. Lights on game
5. Game plays OK but noted the pop bumper light don't.

Decided to take more voltage readings see attached jpg. Hope this helps!!!!
 

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The 7812 is shutting off the output voltage to protect itself from a short circuit on your 12v line.
Unplug the output connector and confirm your 12v is now present, then follow the 12v around your boards looking for possible culprits.
I don't have the schematics so cannot be specific, good luck.
 
Something is not adding up here. You can't have working insert lamps and 0v on Pin 6 of CN4. If you have no insert lamps and no voltage at the input of fuse F4, then the problem is either at CN1 Pin 1 or upstream of the power supply. You need to check fuse F2 for 13v AC in the backbox (above the big capacitor). If it is good, you then need to check the bridge rectifier (BR1).

If these check good, you need to look at connector CN1, Pin 1 and make sure it isn't burned.
 
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