(Topic ID: 306537)

Stern Tron, no coils, DC on all test points, F10 fuse OK, but led off

By paladin-ng

5 months ago

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  • Latest reply 4 months ago by paladin-ng
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#1 5 months ago

Hello, I'm pretty good with digital electronics and repairing video game logic boards, but I'm not good with analog/power and haven't fixed pins, and the logic of this issue has got me confused esp without much knowledge of these systems.

Anyway my Stern Tron stopped working probably a year ago, haven't had time to look at it till now.
The game "boots" and I get lights etc., but no coils at all. The LED under F10 on the power driver board is not lit (though the LED itself works/lights if I touch my multimeter to the ends in ohmmeter mode). I do have AC power at the inputs on the molex that feeds the bridge recitifer. The F10 fuse is also fine and all the test points on the power board are OK.. kind of

on the bottom left voltage test points
18, and 20 are good, but 50 is actually at 70V

on the right/center +5, +12 and whatever the other was (-12 or -5 I forget) are OK

ALL the green power LEDs on the bottom/center of the board are lit!

if I open the coin door it will say "20/50" disabled, however that message only comes once I open the door, and does NOT go away after I close it.

Does anyone have any ideas? I contacted stern a few days ago but no response yet (not that I am complaining... it is the holidays and there's a pandemic

pics of the board powered on at

pics of the board after being powered off at

any pointers/ideas/help appreciated.

#3 5 months ago
Quoted from LTG:

Usually high not under load.

Then it's not getting power.

As in pulled and checked with a meter ?
LTG : )

Thanks for the info about the +70V, in terms of the fuse, yes pulled and checked with an ohmeter, and swapped another just for completeness sake.

So if it was not getting power though, why would I still see +20VDC? that's what's really confusing me. I figured maybe the bridge recitifer was bad, since I have AC at the the molex terminals that feed the BR, and and I do have continuity from the molex terminals to the BR terminals. I cannot test the DC power coming out of it (the BR) as physically I cannot get my meter into the terminals when it's in the box, but I figured that's what the test points would validate?

2 weeks later
#4 4 months ago

Well I figured this one out.

Found the schematics for the driver board.
After probing around I found that some the of smt solderwork was "bad".
Connection from the pin 2 of BRDG2 to D46 was questionable and had a ton of resistance, same between cathode of D46 and R7, Megaohms of resistance. The joints looked completely different than the others on the board too. (not much solder relatively, not clean and shiny)

I just did tiny jumper wires myself between the connections and it's working again. Fun thing again +20DC was actually fine it was just that LED circuit
but the schematics that LED circuit actually need to work as the output of the LED is the input of INTRLK20 and was causing the system to think the interlock was open.

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