Sounds like the transistor driving this gate is stuck open. The gate is driven by a TIP122 transistor and these can sometimes go bad and cause a coil to remain energized. When you open the coin door, all high power is cut (for safety) and thus the gate closes. You'll probably see that the gate is even open when the game is in attract mode (with the coin door closed).

First, find out which transistor is driving that gate. The manual should have a table for this, it is a Q followed by a number. Find that transistor in the backbox on the big board.

You're gonna have to check that transistor with a DMM. Set your multimeter to diode testing (beep mode) and then ...

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From pinrepair.com:
For the most part, the most common testing will be on "darlington" transistors (which means they are actually two transistors in one package) such as the TIP102, TIP122, TIP36 transistors. Also most testing is done "in circuit" (installed in the circuit board). For each of these have one lead of the DMM on the metal case (tab) of the transistor (which is usually the center leg of the transistor). Then the other lead of the DMM will test the outside two legs individually. A value of .4 to .6, or 1.0 to 1.2 should be seen, depending on the exact transistor, and which lead (red of black) is on the metal tab. The biggest indicator of a bad transistor would be a value less than .2 (probably a short). Look to the specific pinball repair guides for more exacting details of this. Also remember, a transistor can ocassionally test as "good", but in fact be bad.
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You'll probably find it's shorted and you're gonna have to replace it. Don't stop there, but also check to see if the gate's coil is not burned. If it was stuck on for too long it may have melted inside and need replacing too.

Hope this helps!

Haha, don't worry there is plenty of people here willing to help.

A DMM is a digital multi meter. You can buy one at an electronics store or online.

When you buy one, make sure it has a "diode test" setting, you'll need it plenty when doing pinball repair. In this photo it's the setting above the 10A setting. I think 99% of DMM's have this setting.

DMM-12-M.jpg

Hehhhehe.

One month before I feel the same, like you now.
Ever since I bought a DMM, a soldering machine, and a lot small things.
If you read this thread, you can see my story. And you can laugh on it.

http://pinside.com/pinball/forum/topic/1984-bally-tilt-problem

But believe me, a great feeling, if you repair your own pinball...

Sorry for my slow response.
Tip 102 = Tip 122 , They're interchangeable

You don't need to check them all - just the one associated with the gate.

Look at page 6 of the Operator's Handbook:
http://mirror2.ipdb.org/files/3780/Williams_1995_Congo_Operators_Handbook.pdf

From the photo that should be the right gate - so Q29.

That seems like the right one, let's measure it and see if it's stuck open!

Hey hassanchop it's pretty important you give this a try could save you a lot of wasted time. After reading this I realized that my gate was not working correctly either (it was opened all the time). The issue on mine at least turned out to be mechanical not electrical. Not sure this will fix your issue but it may so I would look into it before doing more complicated diagnostics.

There is a spring attached to a mini coil under the playfield the other end of the spring is attached to the gate mechanism. The problem was the spring where attached to the gate was moving all around preventing the gate from going down consistently. My easy solution to this problem was to use a tiny bit of duct tape to tape the end of the spring to the gate mechanism at the elbow (where the gate mech is bent up to prevent spring from falling off). This allowed the spring to be kept in a spot that would allow gravity to close it and the coil to open it when the appropriate time in the game.

I guess this shows to always start with the easy things first as we trouble shoot. Hope this info is of some use to you and others that own a Congo. If you need pics of what I am talking about let me know and I will do my best to get them posted as quick as I can.

Had the same problem with my transporter the rescue. Replacing the transistor fixed the problem.

Put your meter dial on the position to the right of 6 o'clock....The little speaker icon.

Put red lead in the right hole of your meter. Black lead in the center.

With power OFF the machine, touch your red lead on the top of the transistor where the little hole is. Touch your black lead on GND strap in the backbox or find the GND test point on your board. If the meter beeps or shows 0, bad transistor. If the meter doesn't beep and shows something like O.L. then probably good.

Haha! Testing transistors should be a sticky in the blue section,Don't you think it should be Robert?

lol...agreed.

That will work fine, if it's on the same board as the transistor in question. All the boards should have the same ground and it should NOT matter, but I always like to leave chance out of the equation (like a broken ground between boards).

Those 'bigger' transistors are PNP Tip36....Can't test those like that. If nothing happened on Q29 then that transistor is probably ok.

Odd it would test differently than the rest in that quad....The next step is to test the pre-driver transistor. It might be locked on, turning the larger Q29 transistor on. Could also be why you read differently on that one.

Here's a guide from Clay's pin repair on further testing Q29 (what we did was a quick test). Note, this time turn your meter dial to DIODE...That's the position immediately left of 6 oclock:

TIP102: Put the black lead of the DMM on the metal tab of the transistor. Put the red lead of the DMM on each of the two outside legs of the transistor one at a time. A reading of .4 to .6 volts should be seen. Put the red lead on the center transistor leg (collector), and a zero reading should be seen. Any other value, and the transistor is bad and will need to be replaced.

If that passes the full test, follow the trace up to the smaller transistor (no metal tab) for Q29 and test it:

2N5401, MPSD52, 2N4403 (pre-drivers): Put the black lead of the DMM on the center leg of the transistor (note this transistor doesn't have a metal tab). Put the red lead of the DMM on each of the two outside legs of the transistor one at a time. A reading of .4 to .6 volts should be seen. Any other value, and the transistor is bad and will need to be replaced.

If the transistor is a Tip102 or Tip122 and you don't get a beep when measuring like RobertMee said then the transistor is not bad. That would be pretty strange as from what you told us it almost seems 99% clear that the Q29 transistor is stuck open.

I think the above test does not always work. Could you try measuring it slightly different? Set your DMM to the diode/continuous/beep mode and try the following: put the black lead on the metal tab of the transistor and put the red lead on the left leg (you should get between .4 and .6) and then on the right leg (again, you should see a value between 0.4 and 0.6). If you get a beep on either of the two legs, the transistor needs replacing.

Hehe seems Robert was a bit faster than me with posting

Is there an echo in here

It would help to also know what type of meter the OP is using.

He posted pictures of it about 10 or so posts up....they didn't show up in the window, but you can click on the links.

It's asking to be downloaded.

Yeah, download it and open it in your favorite picture viewer....I used the picture to tell him where to set the dial on the meter.

Good Deal

You must have saved your post twice or something like a double post, I have corrected it and the images of your DMM are now showing.

Sorry title of this post indicated yours was 'always open' as well so I thought it may be a similar issue. I should have read your comments more thoroughly. Either way, it is very easy to check it out by pulling up the playfield and definitely the first thing I would do. Check the coil to make sure nothing is lose (wire or connection) and test it out with the playfield up to make sure it is functioning okay mechanically. Adjusting the spring fixed my problem so it works 100% now. I was hoping yours may be that simple as well.

When the coil is "on" or engaged it opens the gate when it is off via gravity the gate closes that is why it closes with the door is opened (due to coil going inactive). I would still inspect the spring to ensure it is allowing the gate to open and shut as it should. Also, run a test in the menu to see if the coil engages and disengages. Sounds like you got a lot of help here so you will get down to the issue sooner or later. Good luck!

_{Post edited by The_Dude_Abides : Got mixed up here sorry.}

So, Q29 is okay.

To find the small one to test, follow the center leg trace of the big one up...it will go to one of the outside legs of the small one (it might traverse through a resistor first). If you have trouble getting your leads on the small one's legs, get a paper clip and wrap it around your meter lead. Then touch the paper clip to the transistor legs.

Have you done a switch test yet? There may be a stuck switch that could be causing this. Just a guess as I have never owned a Congo. Besides, it couldn't hurt as it is just in the tests menu.

Any updates hassanchop? I'm in the process of troubleshooting the SAME thing but on a different game :/