Williams driver board q

[FirePower]

I have a problem with my Williams driver board. As background I am an engineer who works in the automation field and am ok with methodical testing and fault finding techniques, I can read schematics, logic and software are no problem. I have limited skills in component level electronics, but a basic understanding. My fault finding has led me to believe I have a blown final solenoid drive TIP122 transistor (Q6). The background is that solenoid fuse (F2) blows on startup. Observation lead me to believe a bumper was staying energised. Disconnecting the special solenoid connector 2J12 from the drive board allows the fuse to survive. An examination of the bumper in question shows the coil resistance (4 ohm) and associated switching (special input and matrix) to be good. A 0V drive signal is present on the solenoid drive pin (2J12-3) at all times and this is providing a path to ground, permanently energising the bumper. The logic on the ttl gates IC6 and IC8 driving the 2N4401 pre switch transistor appear to be functioning.  The final straw that leads me to believe the solenoid drive transistor is blow is that the collector to solenoid ground resistance is about 1 ohm. The other functioning final drive transistors read a typical resistance for this collector to ground path of about 6 MegOhm.  (One other measures 800 kOhm and I plan to replace it as well)

So, I have to pull out the drive card and attack it with a soldering iron - this is doable but makes me a bit nervous, so I'd like to do the sensible thing and replace any other components whilst I have the card out and on the bench. So, as a newbie, my questions are;
 - Is it normal to replace both the pre driver 2N4401 and driver TIP122  of the questionable soleniod drive at the same time?
 - are there any other parts that would / should be routinely replaced with the board out?

If my questions are too detailed or inappropriate for this forum please let me know and I'll pull my head in :)

Thanks for any pointers or suggestions offered,

David.

[MartyJ]

Not sure if you have seen these guides for repairs?

http://www.pinrepair.com/sys37/index.htm

This is always my first area to look when trouble shooting!

[ddstoys]

Firstly id remove a wire from the suspect coil and try turning it on if it still blows the fuse then you can rule out the coil being the issue.

[ajlaird]

Pretty sure I have heard of people having to replace TIP222 before today, so no surprises there.

If the board has electrolytic capacitors on it I would certainly consider replacing them while you have the board out. They tend to go leaky over time.

[ddstoys]

Doing well andrew we will make a pinball tech out of you yet

[ajlaird]

Doing well andrew we will make a pinball tech out of you yet

Heh, heh, I do have a few years of hobbyist electronics under my belt, plus experience of dodgy capacitors on computer motherboards.

I have yet to have had to touch any boards in my machines, touch wood!

[Strangeways]

David - You post was spot on - I'd be replacing the TIP122, you can replace the pre driver while the board is out. The interconnect between the CPU and Driver boards are the source of most issues on the System 4-6 machines, and as a general rule of thumb, I replace them on all Williams machines I restore.

Look for any connectors that look fatigued or tarnished, and cold solder joints.

[ddstoys]

Ill second that Nino while the boards out replace the interconnectors big job but well worth it.

[goodolddays]

Also suggest checking the diode on that bumper coil .. something caused the transistor to blow in the 1st place