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(Topic ID: 279320)

DE Relay controlled coil mystery (2R doesn't work, 2L does)

By jaybeedee

48 days ago

Topic Stats

  • 2 posts
  • 1 Pinsider participating
  • Latest reply 46 days ago by jaybeedee
  • No one calls this topic a favorite


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#1 48 days ago

On my Time Machine. the ball trough eject (Coil 2R) is not working but the Chime-1 (Coil 2L ) does.

The facts:
1)The L-R relay operates correctly and voltage at coil
2) If I ground the tab on the Q45 transistor on the CPU board the ball trough eject fires properly (wiring OK, coil OK)
3) All other coils on the R side of the PPB multiplexing relay work correctly.
4) The chime works in test mode so the Q45 transistor seems to operate correctly, and the logic chip and pre-driver transistor seem to be behaving as expected.

The background.
*The pin hasn't been used for a while (alpha numeric display failed and just been replaced, machine moved and head disconnected and all connectors disconnected/replaced).
* Initially the klacker (1L) and Outhole (1R) coils weren't working either. I replaced the Q46 TIP122 and pre driver and these two coils now work. I didn't replace the Q45 transistor because I assumed it was good, seeing as the chime was working, and I wanted to minimise soldering on the CPU board.

Any ideas or debugging suggestions welcome. I don't know enough about transistors to know if it's possible the Q46 works well enough for the lesser load of the chime, but fails with the higher current of the eject coil ?


#2 46 days ago

So just to close this out, for anyone coming back from the future with a similar problem, replacing the TIP122 transistor solved thge problem.

So it seems the transistor was failing, but working well enough to operate the chime on the L side but not the (higher current?) coil on the R side when the PPB relay was energised.

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