Firepower
Williams, 19801980 Firepower
My "ball ramp thrower" (sol. 08) is not working during game mode or solenoid test mode, but the solenoid will fire when I ground Q29 driving that coil. I just replaced Q29 (visibly blown and tested open), but I suspect that the 2N4401 could be bad as well. One of the outer legs measured around 0.225 with my DDM on diode setting (granted, this was in circuit).
I don't have a 2N4401 in stock. Will a 2N4403 or a 2N5401 work as a substitute?
Thanks!
2n4403 and 2n5401 are PNP and will not work.
Is the middle leg reading shorted to ground? If so that is the one connected to the 7402/7408 (i forget now) and could be that TTL IC. Pull the transistor leg and see if it is still shorted.
I put the red lead on the middle leg, and the black leg on alternating outside legs.
I get 0.225 on one leg and 0.58 on the other leg. I'll go back and check if the middle leg of the 2N4401 is shorted to ground.
2N2222 is fairly close and really common. Not positive it will work as a pre-driver in this circuit, however.
Compare the readings from the suspect transistor to a know good one.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
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Quoted from ChrisHibler:Compare the readings from the suspect transistor to a know good one.
Chris, can this test be done in circuit? The transistor next to the "suspect" one reads about 0.45 and around 0.57 on the outer legs. I'm guessing these should be between 0.4-0.6? Keep in mind, this test was done with the transistors still in circuit on the board...if that matters.
Thanks for the replies
Yes. For this purpose, in circuit is fine.
The two transistors should measure near identically as they are connected identically.
I'd say you've identified a likely suspect.
--
Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The new place for pinball repair info
To test the TTL IC that turns on this transistor...
DIode test. Red lead on ground, black lead middle leg. If it reads shorted to ground the, it is likely the TTL IC it is connected to output is bad. You can pull the transistor leg to be sure. That is the only thing you can't test that with that transistor in circuit. Otherwise normal diode testing like chris mentions is good.
That transistor is a penny or so and the fact multiple readings are bad indicates it is likely bad. Just do it! hehe
Yup, Radio Shack sells that transistor in their stores:
http://www.radioshack.com/product/index.jsp?productId=2062615
I was able to catch an order from GPE before it shipped. Ed threw in a few for free. Love GPE. Will report back once replaced.
Quoted from barakandl:To test the TTL IC that turns on this transistor...
DIode test. Red lead on ground, black lead middle leg. If it reads shorted to ground the, it is likely the TTL IC it is connected to output is bad. You can pull the transistor leg to be sure. That is the only thing you can't test that with that transistor in circuit. Otherwise normal diode testing like chris mentions is good.
That transistor is a penny or so and the fact multiple readings are bad indicates it is likely bad. Just do it! hehe
The middle leg of the suspect 2N4401 is connected/shorted to ground, as I get a beep in continuity mode. Out of the game, the new transistor tests fine, but on the board, one side is down to around 0.25. I haven't dug into the TTL chip yet. It appears to be tied to IC2.
Quoted from midcoastsurf:The middle leg of the suspect 2N4401 is connected/shorted to ground, as I get a beep in continuity mode. Out of the game, the new transistor tests fine, but on the board, one side is down to around 0.25. I haven't dug into the TTL chip yet. It appears to be tied to IC2.
Yeah... that means the TTL chip is bad. When replacing transistors on this driver board i always do diode test red lead ground, black on middle leg of 2n4401. If it shorted to ground, the IC is probably bad. Do this test when you have the transistors out for replacement. That way you are for sure checking that TTL output pin and not the 2n4401 leg.
Honestly... a lot of times when the main driver sticks on hard... it blows out the TTL chip before the 2n4401.
do not use 74LS here. You need 74F
Good to know. I will put in a new socket and chip. Is the 74F, the same as N74F08N? (from GPE's website).
Thanks!
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Naperville, IL