Hi all,

I am having a problem with my T2 in that the drop target will not reset for me (this includes both in-game and in test). As such, I have two questions, one pretty simple (bordering on "you should know this already), and the other, well, the other is the real question.

The first question falls into the "ask a question and look like an idiot for five minutes; don't ask and be an idiot for the rest of your life." With a standard two lug coil (pop bumper, what have you), you're going to have two wires coming into the coil. Does it particularly matter which lug a certain wire goes onto? Looking at my pop bumpers, two are wired in one fashion and one in another, so my knee-jerk reaction is no, but this feels like something I should know, and also know why. Obviously, when a diode gets in there, there's a right and wrong way, and the same holds true of flipper coils with three lugs. If someone could point me in the right direction (theory-wise, example-wise, what have you), I'd really appreciate it.

The second question is, I'm a little confused as to why my drop target won't reset. I checked in the manual, and it appears I'm supposed to have continuity on the violet-orange wire to J107-2, the blue-yellow wire to J122-4, and on the violet-orange tieback diode to J122-9. I tested all of them, and they're continuous. I also popped out fuse F103 and tested that for good measure, and it's good. I will admit I don't exactly understand what a tieback diode is supposed to do, but get the impression continuity is a good thing?

I guess the overarching question I have is, what would be the next logical thing to check in regard to this? I'm a bit confused on this one. Thanks in advance to anyone who can offer assistance; it's greatly appreciated!

Luke

Hey Chris,

Thank you for the reply. After my post, I did some spelunking. The coil doesn't reset during test, which led me to the continuity tests, which eventually led me to (drumroll please) the TIP-102 transistor at Q20. And it was shot.

I replaced it, as well as the 1N4004 at position D5 (someone had done a rather poor job of replacing it prior to this). Now when I fire up the game, the coil locks on. Normally if this happened, I'd say, "hey, check the transistor," so I checked it out. One side reads .63 volts, the other .53, and the middle reads open. In my opinion, that's roughly in spec (please correct me if I'm wrong). As such, I'm at a bit of loss on this one. Any further advice for things I should check? Thank you again; I really do appreciate the time.

Luke

Hey,

Just so I can say I'm doing my homework, I'm currently looking through http://pinside.com/pinball/forum/topic/congo-top-gate-is-always-open, and will see what I can see.

Luke

Thanks again, Chris. I'll dig into that. And yes, it's facing the same way as before. As an aside, when someone solders wires directly to a board, it makes pulling the board and doing repairs more difficult than a fellow might think. Just floating that out there...

Luke

Hey,

I'm having a bit of trouble testing the pre-driver transistor. I bet you can figure out why...

image.jpg

Yep, time to go grab another one from the garage. Thanks for the help!

Luke

Hi again,

Alright, well, I guess I'm going around in circles here. The drop target now locks on. I replaced the TIP-102 and the previously non-existent 2N5401. The thing still locks on. From looking at the schematic, this is controlled by chip U2. Is there some way to test chip U2 without turning the game on i.e. using a logic probe, because the coil is going to fry if I do? Also, out of curiosity, would I be correct in thinking that pulling U2 should cause this locking to stop, as there would be nothing controlling the coil? Thanks again.

Luke

Hey,

Well, I repinned J115, as someone had taken the liberty of soldering directly onto the board, so I was doing all that board work with the board still in the game (don't do that; it's not fun).

Someone put in a 68K ohm resistor at position R25 instead of a 68 ohm resistor. I'm guessing this will be the next thing to repair... :-/

Luke

Hey,

Really appreciate the advice! This is the first time I've really had to do board work above and beyond the "replace J120/lJ121" thing, or throw in a new TIP-102. So, I have the solder station and have done that sort of work before. I have the standard Hakko "purple" solder station; can't think of the model offhand. I guess you could say I know enough to be dangerous?

The only question lingering is what exactly you mean by VCC? I now have the board out of the machine, so testing shouldn't exactly be an issue, but then again, I've never done it before, either. If nothing else, I'll know how to do it for next time!

The blue wire is a jumper that was in place before. It replaces a burnt trace. I could detach it, but I guessing I'd lose continuity along that path. And I'm betting at least part of this is that one WAY off resistor. I plan to grab the parts in the next couple of days and do the rework. I'll let people know how it goes!

Luke

Awesome! I'll look into that. I'll post a separate thread, but since I'm probably doing a DigiKey order anyhow, are there any other things you'd recommend to have kicking around (ULN2803A chips, specific resistors, that sort of thing)? Thanks!

Luke

Hey,

One more question, if you'd be so kind. Looking at the schematic, I can identify chip U2 as the IC feeding this. When I look at the pin out, I see this: http://www.embeddedlinks.com/chipdir/pin/74374.txt. However, when I look at the schematic, I see this:

image.jpg

Long story short, I'm having a bit of trouble with the schematic in regard to understanding the smaller numbers feeding into each side of U2. For example, on the schematic, it says Q3 feeds R22. That makes sense to me. However, it also has the number 16 next to it. The only way I can interpret that is as "Q3 is at position 16 on the chip", and according to the pin out, that's incorrect (the chip, and corresponding pin out, is for an SN74LS374N). Any thoughts? Thanks again!

Luke

Hey,

I must be an idiot, but I can't figure this one out. The chip that's in place is an SN74LS374N. So, if I copy and paste the pinout I found:

+---\/---+
1 -| /OE Vcc |- 20
2 -| Q0 Q7 |- 19
3 -| D0 D7 |- 18
4 -| D1 D6 |- 17
5 -| Q1 Q6 |- 16
6 -| Q2 Q5 |- 15
7 -| D2 D5 |- 14
8 -| D3 D4 |- 13
9 -| Q3 Q4 |- 12
10 -| gnd CP |- 11
+--------+

If I test my chip, I get slightly different voltages between the pins marked Dn, where n is some number, versus Qn, making me think I have the right chip relative to the pinout above. So, by the schematic, I read "Q3 is at position 16". By the pinout above, I read "Q3 is at position 9". I feel like I'm missing something completely obvious here.

With that said, I tested everything, and the big black eye is definitely the 67.8 kiloohm resistor at position R25 instead of a 68 ohm resistor. Also, R24 is supposed to be a 2.7 kiloohm resistor, and tests at 1.99. However, other corresponding resistors (R28, R32) test around 1.9, which confuses me a bit. Should I be replacing see, or saying, "yeah, works fine, play on"? The resistors appear to be correct based upon their bands.

As I say, thanks again for the help. I'm guessing the one resistor that's way off will be the culprit, but have to place a parts order tonight.

Luke

Hey all,

To close the loop on this: in addition to the pre-driver transistor being out, the 68 ohm resistor at R25 had been replaced with a 68,000 ohm resistor. I replaced everything from U2 onward, and now just have a couple of switches that are out. I'll poke around with those sometime over the weekend. Thanks all for the advice and assistance.

Luke