Is it possible to test the transistor that goes with the forward/reverse relay on proto board P4 prior to installing it on the board? BB-0000054 is its p/n
Bruce
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Sure, it's a common PNP transistor, the 2N5087 Just use the diode function of your meter and ring between the base and emitter and base and collector. Then swap the polarity of the leads and do it again. You'll get a diode reading in one direction and open in the other direction. Any other reading and it's probably bad.
Here's a page with testing details: https://vetco.net/blog/test-a-...17-05-04-12-25-37-07
Those transistors are run close to their rated maximum on the pS-1 system. When I replace them, I often make a heat sink out of tin can stock and fasten it with heat transfer epoxy.
You can also use a heatsink that is made for the TO-92 package.
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Thanks, John
gunrunnerjohn posted:You can also use a heatsink that is made for the TO-92 package.
That's pretty much what my homemade ones look like. 
True Roy, but I spend about 3 cents for these, and they just slip on with a spot of thermal paste, takes me ten seconds. Cutting one out of a tin can is bound to take just a little longer. 
gunrunnerjohn posted:True Roy, but I spend about 3 cents for these, and they just slip on with a spot of thermal paste, takes me ten seconds. Cutting one out of a tin can is bound to take just a little longer.
My sincere thanks to you experts on this forum who willing share your wisdom. I have an irrational love for my MTH PCC streetcar (30-2505-1,Pittsburgh 64E. Pgh. Wilkinsburg route (PS1)) and recently it stopped running in forward. It only ran in reverse. With information from here I metered out the circuits and determined that the 2N5087 transistor that picks the forward relay was bad. The 2N5087 order from Mouser showed up today and I replaced the defective transistor and now all is well again. Many thanks and Happy New Year
Rick
I wonder if it is an overload problem or inductive spike from the relay coil. Good practice on circuit design is to install a diode across the relay coil to surpress the inductive spike when power is cut to a coil. The transistor can withstand it, but it's just a matter of time.
They do have protection diodes for the relay coil spike in the design. They are 30 years old. It is an occasional failure, but not common failure. G
