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Dr Who Outhole Kicker - Locked On & Smoking

X

Xephlon

Registered
Joined
Aug 7, 2018
Messages
38
Location
Redditch, England
Hey,

I have been stumped by this magic outhole that always seems to lock on whenever the game has power. When the game is turned on, the coil will immediately energise and start smoking after just a short period. This already melted one coil and completely blew up the driver transistor.

I have already replaced all the driver components (Q45, Q46 + passive components) that were near the exploded TIP102. After connecting a new coil, the same symptoms preside. I'm reading ~75V between the two connectors (VIOLET-ORANGE, J107-2 & WHITE-VIOLET, J127-8). To try and diagnose if there was a power driver board fault, I disconnected J127, but the coil is still locking on. Does this mean it is not on the power driver board?

I'd appreciate some pointers from someone with more WPC experience than me. I've run out of ideas for what to look for.

Thanks
 
Where does the signal come from, have you checked what state this is in? Could that be stuck on?
 
Does it have a big tip36 which controls a coil and a flasher? Had a similar thing on my space station where the short showed on the tip102 which was actually fine and was being ghosted by a component further up the chain.
That’s obviously an old system 11 so may very well be different.
Just a though though.
 
Is the new coil definitely ok, does it have diodes? Take a reading between the 2 lugs, you're looking for >4 ohms preferably (>3 is ok) but if knackered, will normally show as a dead short

Check any diodes in the chain

If you've replaced the transistors, check them again to make sure they are still ok, also check the continuity is good for any part you replaced

If all of the above is good, it can only really be upstream so it will be the logic chip (74LS374 I think)
 
If you are disconnecting j127 and that’s it’s trigger and it still locks on then it must be shorted to ground somewhere in the wiring harness de solder the small trigger wire from the coil turn it back on and see if it locks on my guess is it wont
 
Did you replace everything (eg. new transistors, new coils, etc) all together at the same time before switching on? if not, then one will cause the other to fail and you can be going round in circles trying to correct it...

You could try disconnecting the ribbon cable between the MPU and driver board. Then switch on and put the game in to switch test, then check the switch matrix to see if anything is on that is not supposed to be.
 
russdx1 said:
Where does the signal come from, have you checked what state this is in? Could that be stuck on?
Click to expand...
The LS374 is the controller for the solenoid driver. I never bothered to replace it since every troubleshooting guide said it was invulnerable.
mufcmufc said:
Is the new coil definitely ok, does it have diodes? Take a reading between the 2 lugs, you're looking for >4 ohms preferably (>3 is ok) but if knackered, will normally show as a dead short

Check any diodes in the chain

If you've replaced the transistors, check them again to make sure they are still ok, also check the continuity is good for any part you replaced

If all of the above is good, it can only really be upstream so it will be the logic chip (74LS374 I think)
Click to expand...
The new coil is definitely ok and tested working. It doesn't have diodes, but neither did the original outhole kicker solenoid, and I think that is factory spec. The coil definitely works, since it energises and 'kicks' when the circuit is live. I have checked the 1N4004 for the 50V line in the solenoid driver just now, and it has the same reading as all neighbouring 1N4004's. With the diode out of the circuit, I connected the kicker solenoid and it still energises, so I wonder if it is getting its power from somewhere else? The transistors definitely don't look burnt like the ones I replaced, but I can't believe they are the root cause of this problem. If they were the cause, the fresh transistors would have fixed the issue. I want to test the LS374 as it is still OEM, but I don't have a logic analyser and can't find any way to test the output.
Spandangler said:
Does it have a big tip36 which controls a coil and a flasher? Had a similar thing on my space station where the short showed on the tip102 which was actually fine and was being ghosted by a component further up the chain.
That’s obviously an old system 11 so may very well be different.
Just a though though.
Click to expand...
There is a small TO-92 package transistor just before the big TIP102, but it has been replaced (and I think it was working before replacement anyway) so it shouldn't cause the issue. Definitely a good thing to have checked though.
CHRIS B PINBALLS said:
If you are disconnecting j127 and that’s it’s trigger and it still locks on then it must be shorted to ground somewhere in the wiring harness de solder the small trigger wire from the coil turn it back on and see if it locks on my guess is it wont
Click to expand...
I am getting quite confused since I had it disconnected J127 for more testing, and then the coil wouldn't energise when connected. I must have been forgetting whether J127 was connected or not when I jumped the coil. I'm relieved to know there are no stray shorts in the harness and can rely on it being in the power driver board's area.
CHRIS B PINBALLS said:
Can’t believe it hasn’t blown the fuse either
Click to expand...
I wish it had... would have saved me buying a fresh one... Guess the slow blows don't blow fast enough?
Moonraker said:
Did you replace everything (eg. new transistors, new coils, etc) all together at the same time before switching on? if not, then one will cause the other to fail and you can be going round in circles trying to correct it...

You could try disconnecting the ribbon cable between the MPU and driver board. Then switch on and put the game in to switch test, then check the switch matrix to see if anything is on that is not supposed to be.
Click to expand...
I replaced all of the transistors and passives simultaneously, but I can't remember if I connected the old coil as well. I was likely hoping that it was still working, but testing has shown it to be 100% dead. If the shorted coil had killed all of my fresh components, what would be the culprits? Everything still looks shiny, but I can replace any one of them with all of the spares I ordered. As for the switch test, outhole switch was normally open and was closing good. Nothing seemed to be out of the ordinary.



Looks like a shorted coil may have killed all my fresh components. This will be my next course of investigation to get to the bottom of this.

Thank you all so much for your detailed responses and for replying so quickly.
 
ok then it’s on the board. either power transistor or upstream. buy a cheap £15 logic probe. invaluable. i’ve saved myself a lot of hassle just with a cheap n nasty one
 
LS374's are not bullet proof, I've repaired a few in the past and have several in stock as minimum order was 25 pieces I think.
 
I'll definitely get myself a logic probe and have some LS374s ready to order. Hopefully, that is all the problem is. Thanks for the tips, guys. 👍
 
Xephlon said:
I'll definitely get myself a logic probe and have some LS374s ready to order. Hopefully, that is all the problem is. Thanks for the tips, guys. 👍
Click to expand...

Check all the other stuff first, don't just randomly change parts - you need to be methodical
 
How are your soldering skills? I know its a touchy question, but if you're not 100% at soldering, then you may have missed picking up a track. Remember that there are tracks on both sides of the board and you need to be absolutely sure all are connected. If there is any lack of continuity to the associated diode, then the drive transistor will blow on its first outing,
Can you post phots of your repair?
 
Also, you can easily test the driver transistors in circuit to see if they are toast.
Testing a TIP-102 transistor

  1. Set the DMM to diode check
  2. Place the black lead on the center leg
  3. Place the red lead on each of the flanking legs in turn
  4. A measurement between .5 and .7 should be displayed
  5. Readings outside of this range (generally dead shorts) indicate the part has failed.
Testing a TIP-36c transistor

  1. Set the DMM to diode check
  2. Place the red lead on the center leg
  3. Place the black lead on each of the flanking legs in turn
  4. A measurement between .5 and .7 should be displayed
From here: https://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Transistor_.22Quick_Check.22
 
The thing that concerns me about the original post is that you say you measured 75V across the coil. The power driver board shouldn't have 75V on it at all - the coils are driven by a 50V supply. Are you certain this is correct?
 
Ragnar1057 said:
The thing that concerns me about the original post is that you say you measured 75V across the coil. The power driver board shouldn't have 75V on it at all - the coils are driven by a 50V supply. Are you certain this is correct?
Click to expand...
75v is ok.
 
Ragnar1057 said:
Thanks.
Just curious, why do you say that 75V is OK?
Click to expand...
I have actually seen 100v but that was because the line voltage was set wrong so everything was overpowered.

Not my words:

The transformer is providing 50 volts AC RMS.
RMS means the Root Mean Square of the waveform, and can be interpreted
to mean the mathematical equivalent power if it was DC.
When you rectify a 50 VAC supply you will get a pulsating DC voltage
waveform with a peak voltage of 1.414 x the RMS AC value, so in your
case, 1.414 x 50 VAC = 70.7 VDC peak.
This is fundamental power supply design math.
This peak voltage is what you will see with no load.
 
Thanks for this. Your explanation of AC vs. DC is correct of course – but I really didn’t expect to measure 75VDC as it means that the WPC schematic diagrams are wrong.

As you correctly say, you can easily calculate a rectified DC voltage by multiplying the AC (RMS) voltage by 1.414 (and back again by multiplying the DC voltage by 0.7071).

I took some measurements on my TAF power driver board with my (true RMS) test meter and was surprised by the results. I measured an unrectified 55.5VAC and a rectified 74.9VDC for the coil supply (the calculated value is 78.5VDC without a load applied).

I looked again at the WPC schematic manual (and a PinLED replacement power driver manual I downloaded). The manuals both show a rectified supply of 50VDC. Both manuals are very specific and mention 50VDC in several places – despite it being 75VDC (or thereabouts).

This came as a bit of a shock to me because I’ve recently redesigned the electronics for my TAF machine based on my assumption that the coils used a 50VDC supply (even the flipper coils are labelled as being 50V devices). I’d planned to use a 48VDC supply instead of 50VDC as there was very little difference. Now that I know the coils use a 75VDC supply, I’m not sure if the coils will pull the plunger in quickly enough. I’m going to have to recalculate everything to make sure the coils will mechanically function as designed. Ho hum.

Anyway, none of this helps the with OP’s solenoid problem. The OP initially states that disconnecting J127 doesn’t help – meaning the solenoid still energises. However, I read a later post that suggests this may not be the case. I think it is important to be certain as will point us in the right direction.

  • If the solenoid energises with J127 disconnected, then my money is on a wiring fault – meaning the ‘low side’ of the coil is finding a low resistance path to ground.
  • If the solenoid does not energise with J127 disconnected, then the problem is the power driver board.
If we assume the problem is on the power driver board then we need to figure out which component(s) is causing the problem.

To make the solenoid energise, the CPU board tells the 74LS374 to drive the output low. This causes the 2N5401 PNP transistor to drive the base of the TIP102 power transistor high. This causes the TIP102 to conduct – causing the low side of the solenoid to drive to ground. This causes a potential difference between the high side of the solenoid (75VDC from J102) and the low side of the solenoid (from J127 down to ground). Current will flow and the solenoid will energise.

The explanation is the easy bit, the more challenging bit is going to be figuring out which component is causing the problem.

Let me know when you get your logic probe and I’d be happy to help more if you are struggling.
 
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