What not to do during a board repair

Archived from groups: rec.games.pinball (More info?)

I am finally tackling my Space Shuttle project. It is a little early
for me to take on such a large project at my skill level but I wanted
to give it a try. It is plagued with many problems including the High
Voltage section of the power board. I decided to start with the display
first to see if I could get it to work. I bought a rebuild kit from
Great Plains Electronics and proceeded with the install.

Well everything went fine during the rebuilt. I put the board back in
the game and nothing happened. I took the board back out to see if I
could identify any bard solider joints and checked all the traces. I
had a bad fuse at F1. Replaced it and put the board back in. When I
applied power to the game the seconded time, that little puff of smoke
escaped again from the F1 fuse again. I took the board back out and
measured all the readings again rechecked the schematics and noticed
that I installed all 4 transistors all in the wrong positions. I
incorrectly swapped the position of Q1and Q3 transistor on the power
board. I also did the same thing with the Q2 and Q4 transistors. They
did all look the same at 1:00am in the morning. During the install I
didn't even bother to check to see if the parts were different. And
the worst part is that if I would have followed the instructions that
came with parts I wouldn't have had a problem. It was late at night
and I wanted to finish up before I went to bed, lesson learned.

Would I be correct in assuming, from the readings below, that MJE15031
transistor is the only one bad? I am going to just replace all of them.
I put in a reorder with Ed the other night. I won't get them until
July he went on vacation. Have fun Ed, I'll wait until you return.

MJE15031 is now reading .001 and .502. In circuit

MJE15030 is now reading .512 and .822. In circuit

2N5401 is reading .647 and .657 In circuit

2N5551 is reading 1.818 and 1.975 In circuit

Jeff www.jeffpinball.com
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More about what board repair
  1. Archived from groups: rec.games.pinball (More info?)

    Looking at the schematics, mixing up these transistors creates circuits
    where current should not go, You may also have damaged Z2. On the plus
    side, the failed transistor may have protected your other parts.

    1) Clip the MJE15031 - it's dead anyway.
    2) Replace the fuse - if it does not blow, check for -100V at R6. If
    you find it, or something very close, then Q3 and Q4 are looking good.
    3) Check for 100V at Z2 - if it is there, the MJE1501 may be your only
    bad part. If not, you may have some more diodes to replace.
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