Hi guys!

I am a Black Hole export version owner from Oslo, Norway. I am some months down the road of my from "rock bottom to tip top"-restoration of my BH, and yesterday I did my first power up. It ended with a bit more magic smoke than I had hoped for.

I have gone the Pascal route with the boards, and I have checked every coil and diode - and renewed some. One of the newly installed coils is (was?) the infamous tube ball lift kicker coil A-4893. So, when I switched on I instantly smelled burning and switched off again. The smoke came from said coil.

During the process of restoration I tested the under playfield transistors to be good. I did not take them out of circuit, but they ticked all the boxes on http://pinwiki.com/wiki/index.php?title=Gottlieb_System_80#Remote_Mounted_Transistors. Reading up on all the issues with the ball lift kicker, though, it seems to be a rather common problem that these remote transistors go bad.

I have the following questions:

- Even though they test as good, are these transistors - or more specifically the 2N5875 that is connected to the A-4893 - likely to be the culprit? The circuit is rather simple, so except for the mentioned transistor, I can't really see any other explanation except for a wire short somewhere. The all-in-one-Pascal board is right out of the box. The fuse (which I understand has a too high value, but still...) is good. The resistor tests as good as well I think.

- When testing the coil, it seems to be ok. The resistance of the A-4893 is supposed to be 2,1 ohms and it is spot on. It looks ok as well. There was, however, quite a lot of smoke and heat. Do you think the coil is good for another round, or should I replace it?

- My under playfield transistors are all 2N3791, except for the 2N5875 which I think has been inserted at a later stage. I see that the suggested replacement for the latter is MJ2955. Can I replace all remote transistors with the MJ2955? Given what you see in the attached pictures, will I have to start replacing/introducing resistors? This is where I am really green, so any detailed suggestions are welcome.

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IMG_0550 (resized).JPG

I'll clean them up as you suggest, LTG. Continuity tested ok though. I have not installed any resistors. The ones that are there already are in the picture in the first post.

Thanks, zacaj. I checked the colour bands on the resistors now, and they seem to be the recommended 4.7k ohms 5%. The way I read the pinwiki article is that this is the upgrade, so I guess the 2N3791's are interchangeable with the MJ2955 (which are the recommended substitutes for the 2N5875/2N5879.

And yes, there is a wire going from the transistor to the resistor (red and white wire in both pictures). I found some further reading which made me a bit wiser by the way: http://www.pinwiki.com/wiki/index.php?title=Black_Hole#Pull_Up_Resistors_Added_to_Remote_Transistors_.28Centrally_Located.29_on_Lower_Playfield

So for troubleshooting, basically what you are saying is: disconnect the driver board wire - switch on - if the coil locks on the transistor is shorted. Sounds good!

By the way, should I consider the previously smoking hot coil as fried, or can I still use it when it checks out fine in the resistance test?

After some more testing following zacaj's instructions, I landed on the conclusion that the under playfield transistor was indeed the culprit. I swapped all transistors both on the upper and the lower playfield for new MJ2955's, as these seem to be the suggested replacements for the 2N5875's listed in the schematics. Thus, I choose to disregard the fact that most of the under playfield transistors are actually 2N3791's (with 4.7k ohm resistors) and hope for the best. So for now the upkicker works! Some problems remain with the game, but I will try to sort these myself and come back with a new thread if I don't. Thanks to everyone here who got involved!

After two weeks of gameplay, I can confirm that the MJ2955's do the job just fine.
I was not aware of Critical Mass. Checking out the TNT video now. Thanks for the tip!