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> Newb Working On A Pinball Macine, transistor and capacitor questions
esj001
Posted: May 06, 2012 07:26 pm
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Hello--i hope i am barking up the right tree by posting this here but no one at the pinball forums seem to be able to help.

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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CWB
Posted: May 06, 2012 09:49 pm
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yep ... wrong section , welcome to the forums . laugh.gif

pinball machine ... hmmm ... a combination of digital and analog (the ball rolling around and the slingshots and bumpers) .
pick one of the two sections .

the length of the post is ok ... it contains pertinent information .
do you have a schematic that you can post a link to so that it can be downloaded ?


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Nothing40
Posted: May 07, 2012 01:04 am
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For testing caps,it's best to pull one leg at least,and test that way. Otherwise 'stray' capacitance,or other components on the board might upset the readings.
Same with the transistor (pull 2 legs,or just completely remove it)

Where does the signal go after that transistor?

Kinda hard to say without a schematic.


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Jimthecopierwrench
Posted: May 07, 2012 04:01 am
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QUOTE
...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...
possibly not relevant. In the stuff I work on for example the service codes are prioritized - that is there may be multiple faults but the one displayed is the one that was 'checked' first by the firmware. Only after clearing one will the next display (if present).

QUOTE
Can a transistor test good but still be bad?
When used as a digital switch - fully on or off, or what we refer to saturation or cutoff respectively, it's not likely.

Presuming the transistor is connected 'common emitter' mode with the emitter grounded, a voltage greater than ~.7V on the base should bring the collector low - to near ground. Also presuming a small signal transistor, the collector when low should then be able to sink current to power a small load - like an LED. if it does, the transistor is almost certainly good. That said, common transistors are a dime if you're considering one suspect.

As mentioned, a schematic would help - but I'm guessing the mfgr only publishes 'wiring' diagrams as opposed to full functional schematics, in which case you're pretty well stuck with producing your own the long way, or a few good quality snaps of the board section with a photobucket, etc. link.

QUOTE
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.
As mentioned, are you testing them in circuit? Still, I wouldn't tend to give the hairy eyeball to a ceramic cap in such a low voltage low frequency configuration for a hard fault.


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tekwiz
Posted: May 07, 2012 06:19 pm
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In circuit testing of components isn't accurate. To use an LCR meter, the component must be disconnected at one end, or other circuit elements will skew the reading.
The best way to test biploar transistors is to measure the voltage on the various legs when the circuit is powered up. If the voltage on the base changes & the voltage between emitter & collector does not, the transistor is bad.
Also, testing transistors with external testers is the same as other components...it cannot be done accurately in circuit.


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esj001
Posted: May 07, 2012 09:44 pm
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thank you all very much for the good info--it has helped me a lot---i will scan the wiring print when i can and post it on here so i can understand further----my friend that owns the machine has a guy coming by to to take a look at it.

He trusts this guy and is pretty sure that he will at least be able to tell him if it is in the board or not---if he says its in the board,, i think we will remove the transistor and the capacitor from circuit and test them or change them or send the board out

I will find out later today what the verdict is--thanks so much for all the replies and also where in the forum should i be posting these kinds of questions exactly and should i try to move this thread over to that section??

EDIT: I see that a mod has moved it to the appropriate section thanks guys

This post has been edited by esj001 on May 07, 2012 09:51 pm
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esj001
Posted: May 08, 2012 09:40 pm
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Hey guys ---how do i attach a few pdf's of the wiring schematics on here?----do i need to convert them to a URL somehow?--if so how?

thanks and sorry for the ignorance in this matter
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kellys_eye
Posted: May 08, 2012 10:04 pm
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Upload the schemmy to photobucket (or similar) and post the relevant link that it produces in your next message here.



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tekwiz
Posted: May 09, 2012 06:00 pm
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QUOTE (kellys_eye @ May 08, 2012 01:04 pm)
Upload the schemmy to photobucket (or similar) and post the relevant link that it produces in your next message here.

Yes, & photobucket generates direct IMG links, & these are the ones you use to get the picture to show up in your post.
Note, however, that very large images will be converted into links by our mod team. We ask that you restrict direct images to those that fit easily into a single screen.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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esj001
Posted: May 09, 2012 10:01 pm
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ok guys i think i got my links to wiring prints all set up

just to recap----the 2 lower mag accelerators wont fire and are controlled by the opto switches 37 35 and 34

the switches test fine and the voltages at the opto amp boards seem fine as well as the voltages at the mag accelerator board---(but the mag accelerator board also controls another magnet accelerator that is working)

have tried swapping the opto amp board with a known working one to no avail

the only thing that seems in common with these 3 optos is the Q5 transistor coming from pin 6 on the top right of the CPU board scheme and the C225 capacitor

could this capacitor being suspect cause pc board not to see opto switch function and thus cause mag accelerators not to fire off????

i also linked the 2 I/O schemes as they seem connected to the mag accelerators but i get bogged down trying to figure it all out

i am hesitant to desolder anything from these big boards untill I know that i am on the right path in my thinking--my soldering skills arent the greatest but i will attempt after some practice on junk board---i just really want to know if im on the right track and whether or not this transistor and capacitor can be tested and proven bad in circuit somehow

thanks again for all the help thus far


https://www.box.com/s/068a1869505493ce99bf
is scheme for OPTO switches 37 and 35

https://www.box.com/s/4a307165a12a1aa5b3b3
is scheme for OPTO sw 34

https://www.box.com/s/9496b02100f8b1d70243
is scheme for magnet accelerators and board

https://www.box.com/s/d82778f89084ffeea47f
is scheme for CPU board CN5 connector

https://www.box.com/s/a01166cc1efeab7bc440
is scheme for IO board J10

https://www.box.com/s/a20e2adc1feed20f026b
is for scheme for IO board J6 and J7

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CWB
Posted: May 10, 2012 02:17 am
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a leaky cap on Q5 could cause the fet to not "turn on" as would happen if the fet was "leaky" as well .
pulling these components and replacing them is the best quick method .

yes , you can check some components in circuit ... but not always .
i have seen components that passed the "in circuit" test and were actually bad .
in some cases , due to the associated components an accurate indication was/is not possible .

an in circuit test method :
if you have a logic probe or a 'scope (a dmm will work too) ...
place the machine in the diagnostic mode and step to the test that toggles Q5 .
check on both sides of the associated 22K resistor ...
there should be very little change in voltage between one side and the other .
this will verify that the fet is getting the correct drive .

performing a similar toggle test on a working fet and associated resistor will provide you baseline voltages to compare with/to .

there should also be a list of "nominal test voltages" for select components (and states) *somewhere* in the manual .
i always scribbled notes on or kept a note folder with the shop schematic(s) .

ps ... if you are not up to it ... have someone else remove and replace the suspect parts .
this is easier than trying to repair torn traces , etc .


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esj001
Posted: May 10, 2012 02:40 am
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thank you CWB for the test method of the transistor--

i will do this and see what voltage it gives if i can figure out how to toggle the transistors in the diagnostic mode

i dont remember any nominal test voltages in the manual but will look for it

also what about the transistor Q26 connected to pin 2 on J6 connector that seems to go to both lower mag accelerators????

below the J6 connector it says flash lamp drivers===does that mean those transistors are for lamps only???

once again thanks very much for the knowledge and no i wont mess up the traces with any unskilled hacking--we will send the board to someone if we can be pretty sure its in the board
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tekwiz
Posted: May 10, 2012 06:50 pm
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You have checked the electromagnets themselves for voltage during operation? What about the triple driver board?


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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esj001
Posted: May 10, 2012 11:13 pm
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QUOTE (tekwiz @ May 10, 2012 12:50 pm)
You have checked the electromagnets themselves for voltage during operation? What about the triple driver board?

yes that is what is so confusing about it

the electromagnets and the triple driver board connectors all seem to be getting the correct voltage
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tekwiz
Posted: May 11, 2012 06:44 pm
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QUOTE (esj001 @ May 10, 2012 02:13 pm)
QUOTE (tekwiz @ May 10, 2012 12:50 pm)
You have checked the electromagnets themselves for voltage during operation? What about the triple driver board?

yes that is what is so confusing about it

the electromagnets and the triple driver board connectors all seem to be getting the correct voltage

If the electromagnets are getting the correct voltage & they still don't operate, then the magnets themselves must be at fault, by deduction.
Thre are basically only two things that can go wrong with an electromagnet...either they go open circuiit, or they develope shorted turns.
They are basically nothing but coils of fine wire.
Shorted turns would affect other things by drawing far too much power. Only an open circuit would show no performance when receiving the right voltage.
This can be confirmed by measuring the electromagnets themselves with an ohm meter. They should show a fairly low resistance, no more than a couple of hundred ohms max, most likely much less.


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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CWB
Posted: May 12, 2012 01:48 am
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many of those solenoid coils have a dual winding .
one was very low resistance to provide a healthy amount of "pull in" .
once the armature/plunger was "sucked in" it triggered a leaf switch that opened the low resistance winding to keep it from burning up .
the higher resistance coil was used to "hold" the armature/plunger at the "in" position .

PWM circuits/drive have done away with the "dual coils" in many cases .
using a single winding and modulating the power applied has lowered the number of arcing/burnt contacts and parts count (mechanical and electrical) .


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