(Topic ID: 8066)

tip122 testing

By Larry212

11 years ago

Topic Heartbeat

Topic Stats

  • 13 posts
  • 6 Pinsiders participating
  • Latest reply 9 years ago by TomGWI
  • Topic is favorited by 1 Pinsider


Linked Games

#1 11 years ago

Hi all. Quick question on testing the tip122 transistors. On testing these transistors on my system 11 Board. Touching the top of the transistor with one lead and to the ground strap with other lead, if I get a reading or buzz of continuity does that mean that transistor is shorted? What is the proper way to check? Thanks to all.


#2 11 years ago

Yes,transistor is shorted.Do you have a coil locked on when you turn the game on?

#3 11 years ago

The proper way to test is to set your dmm to diode test (usually 2k setting on the ohm scale). Transistors have three legs; an emitter, a base, and a collector. If you look very closely at the transistor, right above the legs on the black plastic you'll probably see the letters e b c. Determine which leg is the base. Put the black lead on the base leg (middle leg, I think) and then touch the red lead to the other two legs, if either one reads zero the transistor is bad.

#4 11 years ago

Here's what I have going on. It all started with the jet bumpers and sling bumpers not working
During play. Switch wise and solenoid wise all check out. All the solenoids will fire OK during the system 11 self test. I have read a few troubleshooting articals on this and read that if solenoids fire durning test but not play their are a few things to check on of which are the tip122 transistors. I checked them all. The test I was advised to do was to place my meter on the top of transistor and other side to the grounding strap. If I get a reading on any of them it's shorted. The problem is I get a reading or beep on 5 of them. I wasn't sure if that was an accurate test. Everything else in the game is working just fine except these (special solenoids). Their are a couple of other things
It could be that I am looking for.

1) 4.7k pull up resistor

2) 7408 chip

If you know where these are located and a test I would appreciate it. Any information on this ongoing issue would be welcome.

Thanks ,


#5 11 years ago

If you search old posts for capacitor testing you'll find a thread I posted. In that thread someone posted a link to a website that tells you how to test a bunch of different components. It's very helpful. As for location, i have no idea. If you have the schematics they should help.

#6 11 years ago
Quoted from Larry212:

Touching the top of the transistor with one lead and to the ground strap with other lead

I believe the top (connected to the middle lead) is ground. You need to, *I believe*, on diode setting put the red to the top, and check the readings of the outside legs with the black. check the readings against the other tip122s, and if one reads out of spec from the others, it is bad.

I doubt that is it though, if one is bad it's either open (never works) or closed/shorted (coil locks on) How did you test the sling switches? When you are in test, can you hit the sling switches and the coil fires? If no, and the coil test cycling the coils is the only thing the fires the coils, I would suspect your sling switch connections. It is likely a broken wire that needs to be resoldered.

#7 11 years ago

Atomic boy, all the slings and jets fire under testing mode. None of them react during play. Would one broken wire on one of those switches shut them all down?


#8 11 years ago

Fire as in cycling through the coils, or as in activating the switch and making them fire? Can you activate a sling or pop bumper switch in testing and fire the coil, or only in cycling through the coils?

Which game is it?

#9 11 years ago

Ok game is high speed. The coils for the sling and jet bumpers only fire through system testing.
Once the game is in play none of them react, even when I touch them.

#10 11 years ago

I had to check my pinpot to confirm how the switches are wired. They are independent of each other, thus it can’t be a single switch, resistor or cap IMO.

In reading clay’s description, the PIA pulls the 7408 low to operate the coils in test mode. That works. The PF switches also pull the 7408 low on other inputs for this IC, which then go to the 7402 and pre-driver and driver transistors (tip122s). Clay states though that if the either trigger (pia or PF switch) operates the coils, everything from the 7402 and after (pre driver and driver) must be ok, however I question the 7402 myself.

The reason is that I find it hard to believe that all PIA inputs for the 7408 would be fine, but all inputs for the same chip would be shorted for the PF switches, as none work in game mode. I would test the 7402 on diode settings against another 7402 known to be good.

We do know that the driver’s and pre driver work, and the PIA must be fine, so it likely lies within the 7402 and possibly the 7408. I would test them myself, but they are dirt cheap and replacing both should cost $1, and be easy enough to do.

Hope that helps, maybe someone else can chime in.

#11 11 years ago

Here is the link for the site I mentioned earlier. http://www.pinrepair.com/begin/index.htm#howdmm . I hope it helps you, good luck.

2 years later
#12 9 years ago

Post edited by woofer768: posted by mistake

#13 9 years ago
Quoted from Larry212:

Ok game is High Speed. The coils for the sling and jet bumpers only fire through system testing.
Once the game is in play none of them react, even when I touch them.

If the coils fire in test, they are fine. You likely have switch problems. If a ground wire fell off a switch it can make the other switches none responsive. Go into switch test and see if you get the switches to respond.
If wiring is fine and switches don't work, you may have a row or column out of switches.

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