Knocker Coil Locked On

[Slash]

Ive got an issue with the knocker coil on my Gottlieb Buck Rogers.

At first I just thought it was a bad coil as when I disconnected the coil the game booted up and worked fine, except of course when you beat the high score and got a free game, the game locks up because there is no knocker.

But, I had a new coil arrive today and I installed it.  As soon as I did I got the old message "danger coil locked on" and the game won't boot.  I disconnect it again and the game works.

It's clearly not the coil or diode on the coil since both are brand new, any suggestions please?

[Boots]

You've got the power to the banded side of the diode right?

[Slash]

I do, I even tried it the other way too just in case 

[Homepin]

I do, I even tried it the other way too just in case 

You can't just "try it the other way in case" - if you have done that then you have damaged the driver transistor and possibly other things with almost 100% certainty.

Please excercise great caution with electronics as massive damage can be caused very quickly.

"Bad coils" NEVER - repeat - NEVER just lock on by themselves, it is something driving them that causes this.

[Slash]

The game works fine after I disconnected it again.

With the pascal board it disables all the coils from the outset I think when it detects one locked on. Which is what it has been doing whenever the coil is attached.

[Brunswick Brawler]

I don't know much about modern games and their diagnostics, but the error message seems to indicate a short circuit on the wires feeding the coil.

Does the coil 'knock' when connected?  If there is a short on the feeding wires, it would not, or at best the knock would be weak.  Check the wiring all the way back from the coil to the board.  But more likely an issue with the whatever powers the coil.  If its a faulty transistor driver (presuming that is how it works), disconnecting it could fix it.

[Slash]

No the coil doesn't knock when connected.  The board simply detects that the coil is locked on so it shuts all the coils down. 

According to the manual for the Pascal board this is the process for the coil test on startup (and what I believe is happening on my game):

Moreover, the PI-1 X4 board makes an electrical test of the current that flows thru coils #6, 7, 8, ‘OUTHOLE’ and 'KNOCKER', to make sure that each coil and its associated driver transistor are working well. At power-up, the name of each tested coil is briefly displayed. In case of trouble, the coil protection relay shuts all coils down, the relay status LED is unlit, and an error message is displayed along with the problem source.

So it sounds like it could be a driver transistor on the board?  Maybe the driver transistor was stuffed from the outset since I was always getting that message from the very first time I ever booted the game up (even before I swapped the wires to the coil  ).

[Pintoxicated]

Sounds like a dud transistor.  Have you contacted Pascal for his thoughts?  His customer service and knowledge has always been top notch.

Have you identified and tested the transistor driving that coil?

[Slash]

Sounds like a dud transistor.  Have you contacted Pascal for his thoughts?  His customer service and knowledge has always been top notch.

Have you identified and tested the transistor driving that coil?

Yeah I just emailed him then to see if I can get some input from him.  I have a spare transistor that he ships with the board if that's the case.  But I will need him to tell me which transistor it is so I can test it, since I have NFI.  Kinda sums up my electronics knowledge 

[The pinballist formally known as Dean Morgan]

Is it a Pascal all in one board? Or are u using the original driver board ?

[Slash]

It's the all in one board.

I spoke with Pascal about it and he suspects the original knocker coil was defective so it damaged the driver transistor Q1.

He said to turn the game off and disconnect A3J2 & A3J4 to test the transistor.

My problem is when I have googled how to test transistors whilst they are still on the board I seem to find numerous different ways of how to do it, many of the tests dependent on the type of transistor. The transistor in question is a BDW93C, but I cannot see this relating to any of the commonly referred to pinball transistors in any repair guides etc, so I don't really know how to test that particular type of transistor.  It also doesn't help that I know "F" about this $hit!

Pascal also said to check the diode just below the transistor too.

Fortunately there is a spare diode and transistor that came with the board, but I don't want to unnecessarily replace stuff on the board if its not needed, particularly when my soldering work won't be anywhere near as neat as the original.

[Slash]

Ok so from what I can tell the BDW93C transistor is an NPN with the left leg as base.  So I put the DMM onto the diode setting (is this right?), put the red probe on the base and the black onto the middle then right leg.  I got readings of 853 and 995.  When I reverse the probes with black onto the base I get infinity for each leg.

I have NFI what scale that reading is?  I have seen some sites saying to use the Ohm settings and others the diode setting, and it says I should be getting a reading in the range of 0.3 - 0.9.

So do those readings I am getting sound right?  Is it suggesting that the transistor is ok?

If I am also going to test the diode that Pascal suggested do I need to disconnect one end from the circuit board to test it?

[Mr Pinbologist]

Those readings seem ok but checking transistors with a multimeter sometimes doesn't tell the whole story.
I've seen transistors many times where they check ok on a meter but are still bad, ie they break down under operating conditions in circuit. Diodes can also fail in this way.

Another test is to check across the collector and emitter with the meter set on ohms, you should get infinity reading.

 

[Slash]

Those readings seem ok but checking transistors with a multimeter sometimes doesn't tell the whole story.
I've seen transistors many times where they check ok on a meter but are still bad, ie they break down under operating conditions in circuit. Diodes can also fail in this way.

Another test is to check across the collector and emitter with the meter set on ohms, you should get infinity reading.

 

I put red on the collector and black on emitter and got infinity.  When I switched it around I got 28.4 (I was on the 200K Ohms setting).  Should that reverse setting actually read 0.00 if it was ok?

[Mr Pinbologist]

I just had a look at at data sheet for that transistor, it has an internal diode across the collector/emitter so that reading for collector/emitter sounds like it could be normal, check again on diode check.. you should see about 0.6v one way and infinity when the leads are reversed.

If you get anywhere near zero reading on any transistor on any two of its three pins its fried!!

If in doubt replace i always say.. As i said before multimeter reading can't always be trusted!