opto problem on Stern Nascar and other questions from a newb
First of all sorry for the very long post but i just want to be detailed about what I have tried
My friend has about a dozen pinballs and can repair minor things but cannot read wiring prints very well
I am an airplane mechanic and have had a few electricity classes and can read wiring prints pretty well.
I have access to all kinds of tools and test equipment.
We were are trying to troubleshoot a Stern Nascar pinball
Basically he has 3 opto switches that are not testing in test mode----he replaced these and still no go----- the new ones seem to test fine when you probe the back of them and interrupt the light the voltage changes like it should.
I got into the wiring print and discovered that these 3 swithes go to two different opto amplifier boards and then the row or column signal (cant remember which) for all 3 go through one NPN transistor up on the main power board
Ok------ so we figure it has to be that transistor----but in circuit (we have not removed it) it tests fine and gives similar readings to all the others of the same value------which brings me to my questions
Can a transistor test good but still be bad?? Is there a way I can rule this out and make sure its good or bad without removing it from the board???
Also in the wiring print there seems to be a capacitor and a resistor connected to this transistor
Resistor ohms out fine
But the capacitor seems to give a different reading than the others of the same value ( it is still in circuit as well) It is a .01 microfarad capacitor
I tested it with LCR meter for testing capacitors and set it to 1khz
I got a reading of 88 nanofards for the suspected bad one, and a reading of 66 nanofarads for the 8 other ones of the same rating.
Could this mean that the one capacitor that is different is bad?
Can I test this little capacitor like that or should I remove one leg from the board to test properly??
It seems like if they are .01 micro then they should be reading 10 nano, not 66 or 88---or am I way off in my thinking.
Sorry for the long winded post but I am very interested in getting into pinball repair and want to do it right---I am ok at soldering but need some practice before doing anything to a big main power board---my buddy has a board repair guy that he sends stuff to and would be happy to do that if we knew that the problem was defiantly in the board but this one has us scratching our heads---
the optos all glow red and seem to work according to the book---that is, they show 1.2V until the beam is interuupted and then they show 0V when tested on the back side of the recieving opto, on this nascar pin there is a test mode for the optos that fire the magnet accelerators-----
when the ball goes through the first two optos and the 1 mag accelerator fires it shows up on the dot matrix as a little flashing square for each opto------
then the ball comes around to the next 3 optos on the track and none of those flash on the screen indicator and the 2 magnet accelertors hence dont fire either---it also throws a code saying L2 missing which is the last opto switch in line, the others are L0 and L1 but it doesnt mention them----the only thing in common with those 3 is that transistor and that capacitor ( or so it seems to me).
we tried tonight to switch the one of the opto amp boards with the known good one and it didnt change a thing-- the first two still indicate but the last 3 dont
Any help would be much appreciated
Thanks in advance and once again sorry for the long winded post
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