Shield post not working on Medusa (Bally 1981)

Om Medusa, the Shield Post (“Shield of the Gods”) is controlled by the extra button next to the right flipper button.

When I press this button, the shield display counts down as it should (from five to zero for every button push). However, the shield post doesn’t move, because the coil doesn’t show any signs of activity.

I have measured the resistance of the coil (AN-26-1200) and it is 11.0 ohms (it should be 12.5 ohms according to a table I found). I have also cleaned the contact points of the blade switches.

The switch looks a bit weird. Is there a blade missing at “A”? See images below.

Any suggestions what to do?

#2 6 years ago

CRD

chad

Game Guy

11y 140K 15,202 9 4

if you took an alligator jumper from ground to tab of coresponding transistor , does the coil fire??

#3 6 years ago

PIP

Quench

Pinside member

OP
Quoted from nibre:
When I press this button, the shield display counts down as it should

This is telling you the switch is working. Your problem is elsewhere.

OP
Quoted from nibre:
I have measured the resistance of the coil (AN-26-1200) and it is 11.0 ohms

11 ohms is fine.

Quoted from chad:
if you took an alligator jumper from ground to tab of coresponding transistor , does the coil fire??

Yes, try this. Very briefly jumper a wire from ground to the metal tab of transistor Q4 on the Solenoid Driver Board. This transistor drives the Shield of Gods Post solenoid.

#4 6 years ago

NIB

nibre

Pinside member

I jumpered a wire briefly from the Q4 metal tab to ground and... nothing!

As a test, I tried the same thing with Q12 and then the left slingshot coil was activated.

I also resoldered the shield post coil connectors because they looked bad, but that didn't help.

I measured the resistance between one of the coil connectors (grey/white cable) and J1/5, and it was 0 ohms.

----------

Does this mean that the coil needs to be replaced? Despite the fact that it showed 11 ohms?

Or could it be the Q4 transistor? Or someting else?

#5 6 years ago

MSA

Majdi

Inactive member

Check the other side of the coil, and it's path to solenoid power.

#6 6 years ago

BIL

dothedoo

Pinside member

12y 106K 7,265

Coil should be fine. As Majdi suggested, do you read 43V at the coil lugs?

If so, run a jumper from the cabinet ground braid to the grey/white wire on the coil, it should fire.

If that works, you have a connection issue between the coil and J1 pin 5 on the solenoid driver board.

#7 6 years ago

NIB

nibre

Pinside member

I briefly grounded the grey/white wire on the coil and it fired!

Then I measured the resistance between the Q4 transistor collector and J1/5 and it was 546 ohms (should be zero).

After that I measured the resistance between the Q4 transistor collector and C4 and it was also 546 ohms (should be zero). So, I guess there's a problem between Q4 and C4. They are right next to each other on the board.

What next? Do I have to remove the entire board? Haven't done something like that before.

Advice greatly appreciated!

#8 6 years ago

PIP

Quench

Pinside member

If you re-measure the resistance of the Q4 collector tab to J1/5 and wiggle Q4, does the reading fluctuate? What about if you wiggle J1?

OP
Quoted from nibre:
Do I have to remove the entire board?

You probably have a fractured/burnt solder joint on the back of the board where the Q4 collector pin is soldered meaning you'll need to remove the board to access it so you can inspect/repair/resolder it.

#9 6 years ago

NIB

nibre

Pinside member

I flipped the board and what I found was more terrrifying than a scary movie! Nasty repairs... See images below.

I found the reason for for the resistance between Q4/collector and J1/5 (see image below).

I attached/soldered a cable between Q4/collector and C4 but it didn't help.

After that, I measured the resistance between the collector and the emitter of Q4 and it was 0,4 ohms (I made sure that there was no connection on the board). That means that Q4 is broken, right?

I also measured the resistance between the collector and the emitter of Q1 - Q19. Is it possible to say if any other transistors are broken from these values?

Q1: 770 kohms.
Q2: 80 kohms.
Q3: 5 Mohms.
Q4: 0,4 ohms.
Q5: 582 kohms.
Q6: 630 kohms.
Q7: 756 kohms.
Q8: 771 kohms.
Q9: 22 ohms.
Q10: 22 ohms.
Q11: 22 ohms.
Q12: 22 ohms.
Q13: 22 ohms.
Q14: 22 ohms.
Q15: 2,9 kohms.
Q16: 22 ohms.
Q17:4,8 Mohms.
Q18: 780 kohms.
Q19: 1,2 Mohms.

DSC_4180 (resized).JPG

DSC_4179 (resized).JPG

#10 6 years ago

PIP

Quench

Pinside member

OP
Quoted from nibre:
After that, I measured the resistance between the collector and the emitter of Q4 and it was 0,4 ohms (I made sure that there was no connection on the board). That means that Q4 is broken, right?

Yes it looks like transistor Q4 is internally shorted and needs to be replaced. Do it again with connector J1 disconnected from the Solenoid Driver Board (SDB) to make sure the short isn't downstream on the playfield.

Regarding the transistors with 22 ohms across C-E pins, you are probably measuring the resistance across the solenoids downstream on the playfield. Try testing these transistors again if you want but disconnect connector J5 from the SDB first to isolate the solenoids away from the transistors.
Replace faulty driver transistors with TIP102 transistors. Q17 and Q18 appear to be unused in case you don't have spare transistors.

Have a read here:
http://www.pinwiki.com/wiki/index.php?title=Bally/Stern#Solenoid_Driver_Board_Issues

Another thing you need to check/replace is the diode across the Shield of Gods Post solenoid lugs. If this diode is open or short circuit, you will blow transistor Q4 again.

By the way, check the fuse under the playfield next to the the right flipper mechanism and make sure it's a 1 amp slow blow fuse. Somebody in the past has probably installed a higher value fuse that's contributed to the damaged traces on the SDB when things have gone wrong with playfield solenoids.

#11 6 years ago

NIB

nibre

Pinside member

You were right about the fuse. It was 5A. I only had 2.5A and .75A at home so I changed it to 2.5A (will buy a 1A later).

I removed Q4 and replaced it with a similar transistor from position Q18 (not used).

I desoldered the diode across the Shield of Gods post solenoid lugs (so that it would be possible to test it) and it was fine according to my diode tester.

After resoldering the diode, I started the machine and now the Shield of Gods post solenoid acitvates as soon as I start the machine and the solenoid stays up/on. I dare not keep the machine on for long because I fear that the solenoid or Q4 will break (with the solenoid "on").

Any advice?

#12 6 years ago

PIP

Quench

Pinside member

OP
Quoted from nibre:
You were right about the fuse. It was 5A.

Grr..

OP
Quoted from nibre:
I desoldered the diode across the Shield of Gods post solenoid lugs (so that it would be possible to test it) and it was fine according to my diode tester.

Do you remember what diode readings you got both ways? Did you install it back in the correct orientation (the banded side of the diode must be connected to the solenoid lug where the double yellow wires are).

OP
Quoted from nibre:
After resoldering the diode, I started the machine and now the Shield of Gods post solenoid acitvates as soon as I start the machine and the solenoid stays up/on.

Damn, that means the replacement Q4 is probably blown now too.
Did this happen immediately on the very first power-up, or after you powered up and started a game and then activated the solenoid for the first time via the button?
This will help determine why the transistor failed.

Can you check the resistance across the Q4 Collector - Emitter pins again? (do it both with connector J1 connected and then again with it disconnected)

#13 6 years ago

NIB

nibre

Pinside member

I used the diode test function and it showed .501 V in one direction (red on anode) and 0L in the other direction (red on cathode). I only desoldered one of the diode legs before the test in order not to mix up the direction (cathode to the double yellow wires).

With the double yellow wires and the diode disconnected from the solenoid, I measured the resistance between the other solenoid lug (grey/white cable) and ground and it was 1.9 Mohms. Because a connection between grey/white and ground could have been an explanation for the solenoid fireing right at startup. There is no such connection.

I measured the resistance across the Q4 collector-emitter pins and it was 546 ohms with J1 connected and 1.7 Mohms with J1 disconnected. I guess this means that Q4 might still be working.

I did not notice if the solenoid was acitvated right at startup the first time but that is very likely. It was not when I pressed the shield post button for the first time (I would have heard it). The only happening at the first button push was that the shield display counted down.

I think that it i very strange that the solenoid is activated when the machine is started. It should happen when a game is started (with a push at the coin door button). Is the solenoid driver board really active before a game start? For example, you can't activate the flippers before a game start.

#14 6 years ago

PIP

Quench

Pinside member

Ok, so something on the Solenoid Driver Board (SDB) is causing transistor Q4 to be activated all the time so we'll need to take some measurements to find out why.

With your multimeter set to diode mode, check diode CR4 which is directly above transistor Q4. Test it in circuit first and if it measures an obvious short circuit, then replace it. If it doesn't measure as shorted, then unsolder one leg to disconnect it and measure it isolated from circuit.

If it seems ok, install the SDB in the machine, however leave connector J1 disconnected (we don't want that solenoid locking on and burning out).

Set your multimeter to DC voltage and hookup the black lead of the meter to a ground point (there is a "GND" test point on the SDB).

Power on the machine and measure the voltages with the red meter lead at the following points on the SDB:

1) Metal tab of transistor Q4
2) Lower leg of diode CR4
3) Upper leg of diode CR4
4) Pin 7 of U1
5) Pin 8 of U1
6) Pin 7 of U2

Report back with your readings.

#15 6 years ago

NIB

nibre

Pinside member

I removed J1, J2 and J5.

Tested diode CR4 (and CR13 for reference) without desoldering them (tested red on anode / and the other way around):

CR4: Diode test .29V /.29V ; Resistance 515 ohms / 515 ohms
CR13: Diode test .29V /.29V ; Resistance 520 ohms / 520 ohms

Turned machine on and did some tests:

1) Metal tab of transistor Q4: .555 V
2) Lower leg of diode CR4: 1.307 V
3) Upper leg of diode CR4: 2.023 V
4) Pin 7 of U1: 2.020 V
5) Pin 8 of U1: 2.352 V
6) Pin 7 of U2: 3.518 V

#16 6 years ago

PIP

Quench

Pinside member

Looks like U1 is faulty. It's a CA3081 transistor array.
The voltage measured on pin 8 of U1 is excessively high (most likely because pin 8 is internally open circuit). This is causing U1 pin 7 to be high which is activating the Q4 transistor.
When the solenoid is not being selected to activate, pin 8 will normally sit around 0.8 volts and pin 7 should be near zero volts which leaves transistor Q4 switched off.

For your reference if you want to check voltages at another location for comparison below: The voltage chain of events starts at 6) and ends at 1)

1) Metal tab of transistor Q10
2) Lower leg of diode CR10
3) Upper leg of diode CR10
4) Pin 7 of U3 (other CA3081 chip)
5) Pin 8 of U3 (other CA3081 chip)
6) Pin 13 of U2

#17 6 years ago

NIB

nibre

Pinside member

1) Metal tab of transistor Q10 0 V
2) Lower leg of diode CR10 0 V
3) Upper leg of diode CR10 0.4 V
4) Pin 7 of U3 (other CA3081 chip) 0.4 V
5) Pin 8 of U3 (other CA3081 chip) 0.9 V
6) Pin 13 of U2 0.9 V

I guess this means that I will have to replace U1, right? Which is the best way? Cutting off all legs before delodering? And then delsolder the legs? And then put a socket in place before the IC? I suppose I will need a desoldering pump in this process.

By the way, is U1 hard to find? It is marked "CA3081 RCA806".

#18 6 years ago

PIP

Quench

Pinside member

Great Plains has CA3081 ICs or you can simply find them on ebay.
https://www.greatplainselectronics.com/proddetail.asp?prod=CA3081N

While you're getting parts, grab some 1N4007 diodes, replacement TIP102 driver transistors for the SDB, plus some fuses too.

OP
Quoted from nibre:
I will have to replace U1, right? Which is the best way? Cutting off all legs before delodering? And then delsolder the legs? And then put a socket in place before the IC?

Yes, cut the chip out and then desolder the legs to make life easier.
Try not to put too much pressure on the solder joints with your soldering iron and don't let the iron linger too long on the joints - you want to avoid damaging the circuit board solder pads. Add fresh solder if you're having trouble melting the original soldered joints.

OP
Quoted from nibre:
6) Pin 13 of U2 0.9 V

I presume this is a typo? You should have got a reading around 3.5V or higher at pin 13 of U2 (just like you got on pin 7 of U2 - the big chip). The 0.9 volts downstream at pin 8 of U3 is correct.

The other voltages from the secondary tests are what you should expect after replacing U1 (CA3081).

OP
Quoted from nibre:
1) Metal tab of transistor Q10 0 V

For future reference, this will measure 43 volts (via the solenoid) once you reconnect the playfield connectors back onto the Solenoid Driver Board.

#19 6 years ago

NIB

nibre

Pinside member

Yeah, Pin 13 of U2 was actually 3.6 V (confusing schematis with double numbering for U2).

I will order the components asap.

Thanks a lot for superb advice!

(2 out of 3 issues fixed, now on to the next one in another thread...)

1 month later

#20 6 years ago

NIB

nibre

Pinside member

This is what happened:

I replaced U1 and I replaced the fuse (under the playfield next to the the right flipper mechanism) with a T1A.

After that everything worked as it should for approximately 20 games!

And then, all of a sudden, the shield post stopped working again. Furthermore, the coil that kicks the ball into the launching position also stopped working!

Depression!

The explanation turned out to be that the T1A fuse had blown. I replaced it, and now everything seems to work again.

However, it is likely that it will happen again. It is probably the reason someone had put a 5A fuse there earlier.

My amateur theory is that I might have pushed the shield post button at the same time that the ball was kicked into the launching position so that those two coils (shield post and kick-to-launch-position coil) were active at the same time and this made the fuse blow.

Any better theories?

#21 6 years ago

MSA

Majdi

Inactive member

Stupid question, did you use a fast or slow blow fuse?

#22 6 years ago

NIB

nibre

Pinside member

The "T" in T1A stands for slow (actually "Time delay").

#23 6 years ago

PIP

Quench

Pinside member

OP
Quoted from nibre:
I might have pushed the shield post button at the same time that the ball was kicked into the launching position so that those two coils were active at the same time and this made the fuse blow.

These Ballys can only activate one momentary solenoid at any time and during game, the time is about 33 milliseconds per activation.

Did the fuse blow violently (i.e. glass all black inside)?

You might have to be patient with this one. Install a replacement fuse, but disable the Shield of God solenoid (put some tape between the switch). Play a heap of games. If you're happy all is ok, then re-enable the Shield of God function and see what happens. The point is to isolate whether it's the Shield of God solenoid causing the fuse to blow or something else.

Just out of interest, which one of the below did your T1A fuse look like?

Fuse_SBx3.jpg

#24 6 years ago

NIB

nibre

Pinside member

It wasn't very violent (the glass is slightly black, hardley noticeable). Here's a picture of the blown fuse (left) and an unused one (right).

DSC_4301 (resized).JPG

#25 6 years ago

PIP

Quench

Pinside member

Have a look at the post here showing fuses like yours:
https://electronics.stackexchange.com/questions/25055/slow-blow-vs-fast-acting-fuse/59865#59865

The guy mentions near the end of his post:
"A problem with this type of fuse is that occasional currents just above the rated value may cause some unwanted diffusion to occur, altering the fuse characteristics without visible change."

The surge currents when activating solenoids could be contributing to this. Might be worth getting/trying a more traditional slow blow fuse.

#26 6 years ago

NIB

nibre

Pinside member

I disabled the Shield of God solenoid by putting some tape between the switch blades. After a few games, the fuse blew! This means that it can't be the Shield of God solenoid causing the problem, right?

Is the fuse only for two solenoids ("Shield of God" and "kickout to shooter lane")? if so, the problem ought to be with the latter...

#27 6 years ago

MSA

Majdi

Inactive member

Quoted from Quench:
Have a look at the post here showing fuses like yours:
https://electronics.stackexchange.com/questions/25055/slow-blow-vs-fast-acting-fuse/59865#59865
The guy mentions near the end of his post:
"A problem with this type of fuse is that occasional currents just above the rated value may cause some unwanted diffusion to occur, altering the fuse characteristics without visible change."
The surge currents when activating solenoids could be contributing to this. Might be worth getting/trying a more traditional slow blow fuse.

My experience with those is they do get kind of melty and may have a lower effective value as a result.

OP, can you acquire some Bussman MDL-1s where you are? I'd like to see this with a known good fuse.

#28 6 years ago

PIP

Quench

Pinside member

OP
Quoted from nibre:
Is the fuse only for two solenoids ("Shield of God" and "kickout to shooter lane")? if so, the problem ought to be with the latter...

No, that fuse is for *all* playfield solenoids *except* the flippers.

As Majdi and I suspect, it could be those fuses you're using. We are curious to know if it is the case.

In the mean time, install another one of those fuses you have and put the game in solenoid test mode for a few minutes and take notice of the last solenoid that activates before the fuse blows again. Note, solenoid test mode activates solenoids for a longer period of time (approx 116ms - 140ms) so should stress the fuse a bit more.

#29 6 years ago

NIB

nibre

Pinside member

I ran the solenoid test (according to the manual, the flipper buttons are supposed to be held 'in' during the test but that wasn't necessary). It went through seven cycles without the fuse blowing and after that I ended the test.

1 week later

#30 6 years ago

NIB

nibre

Pinside member

I finally got a hold of some other types of fuses (see image). The two at the top blew pretty fast (usually happens during the first three games).

However, the one at the bottom ("spiral" model) did NOT blow! I played ten 5-ball games without any problems! A pretty expensive fuse but it was worth it! (By the way, my highest score during these ten games was 649,230.)

I wonder if cheap fuses were the explanation for the original problem. My guess is that this 1A fuse kept blowing and that someone replaced it with 5A. Could this have destroyed U1, which led to the shield post giving up?

Säkring av hög kvalitet (nederst) (resized).jpg

#31 6 years ago

PIP

Quench

Pinside member

Excellent - thanks for confirming the fuse.

Can you post a picture of the box showing the brand details of the original T1A fuse that was blowing so people know not to use them for the playfield solenoid fuse? They might work fine for other slow-blow applications but being repeatedly hit with solenoid high current surges indicates they are not up to the job for this scenario.
.

OP
Quoted from nibre:
I finally got a hold of some other types of fuses (see image). The two at the top blew pretty fast (usually happens during the first three games).

Are these both fast blow fuses? the glass one top right looks like it.

OP
Quoted from nibre:
My guess is that this 1A fuse kept blowing and that someone replaced it with 5A. Could this have destroyed U1, which led to the shield post giving up?

Yeah, there could have been a solenoid issue to begin with that was blowing the fuse and ultimately U1 when the 5A fuse was installed. Conversely U1 might have been the very first item to fail in this episode and then caused solenoids to lock on and blow the fuse.

#32 6 years ago

MSA

Majdi

Inactive member

Since the actual solenoid output is buffered, I suspect U1 failed first, the solenoid was stuck on, this eventually killed the transistor, which was poorly replaced...and from there, fuses started to blow, someone eventually "fixed" that with the 5A, and that's how this machine arrived at that state.

OR:

The transistor failed first, it was incorrectly replaced (causing static damage, or asking too much drive current of U1, or whatever), which killed U1, and then the fuse bit.

Apologies for the expensive fuse -- not sure what's available where you are, but I tend to stick to Cooper/Bussman or Littelfuse fuses. They're definitely not the cheapest but I've seen some bad cheap fuses over the years.

#33 6 years ago

NIB

nibre

Pinside member