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?

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.

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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?

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!

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

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?

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.

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

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".

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...)

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?

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

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

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...

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.

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

Thanks again for great advice!

Here's a picture of the different types of fuses.

Fuses (resized).jpg