Hi people.

I have a Police Force (Williams System 11B) with several problems.

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----> The first one and more visible is the displays. The top line is always lit / on.

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Probing around I found that touching with my logic probe in one UDN7180A pins the entire line / segments went off.

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But during the process I damaged one UDN7180A and now I have two bad UDN7180A if I'm not mistaken.

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To test the UDN7180A I have used this method:

Put the DMM on the *diode* setting.
Connect the red DMM lead to ground.
Put the black DMM lead on each UDN pin 2 to pin 8.
A reading of .5 to .7 should be seen.
Put the black DMM lead on each UDN pin 11 to 17.
a NULL (no) reading should be seen!

So now I have to search / buy some sockets and some UDN7180A chips to replace these.

----> The second problem is the sound, the music to be more precise. The machine have no music but have some sounds.

The 4 beep sound´s in the boot indicated a U19 problem If I´m not mistaken. So I have tested the rom´s and only the U21 was slightly different to the one in IPDB.

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Erased and reprogrammed the U21 and now all roms are equal at the ones in IPDB.

This not solved the sound problem.

After some research I decided to swap the audio driver board with one from a Cyclone to verify if the problem are CPU board related or audio driver board related. With the Cyclone audio driver board (with the Police Force rom´s) all the sounds and music seems to work, so the problem are only in the audio driver board.

After some testing and probing to encounter the problem the Cyclone audio driver board stop playing music to. This was made with the board out of the machine and powered with a computer PSU.

To add a extra problem, now in the Police Force (not in Cyclone machine) I have a "tik tik" noise in speakers.

This "tik tik" after some time gets louder and after a little its stop. Probing U23 (YM2151) I have pulse at the rhythm of the "tik tik", and when the sound stop the pulse stop to.

With this kind of problem I assumed there is something wrong with the crystal or the oscillator. I swap the oscillator with one laying around (not sure if its okay) and nothing changed. Buy some new crystal´s and after changed it nothing as changed to.

I decided to make some measurements and probing to compare with a Earthshaker audio driver board (similar) to see if I can find the problem.

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The 1 means High, the 0 means Low, the P means Pulse, and the 10P or the 01P means that I have a 1 and 0 and a Pulse in my probe. The X means I have nothing.

The components are the ones who make part of the crystal circuit. The R1 do not make part but I have a pulse in it when the "tik tik" sound exist so I decided to include it.

All the readings have been taken with a DMM and a Chinese component tester (probably not very accurate or trustworthy) in circuit in their appropriate machine.

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I have just purchased a Chinese capacitance meter (M6013) and a ESR meter (MESR-100 V2) to help in the future with the capacitor, and a Portuguese ESR meter (EVB SBR) but right now I have to work with the tools I have.

So if someone can give me a little I really appreciated.

----> I have a third problem that I´ll address after repairing the audio drivers board and after receiving a ESR meter. The machine sometimes reset after activating something and other times plays fine.

Sometimes launching the ball and hitting the "spinning target" in the shooting lane it is enough to cause a reset.

The voltages in power supply board are good (when I verified them a time ago) but I do not have make any more research on this for now.

Thanks in advance.

Sorry ForceFlow but the post wasn´t complete and I have submit it by mistake.

The problem in display are related to the UDN7180A so yes I have to change the damaged ones.

The part I really need some enlightenment is with the sound / music.

Just to add to some of my testing, yesterday I have checked the CR1 oscillator pulse in the U16 and out of it and it seems working normally.

Tested C2 - C34 - R2 and R3 out of circuit and all are good.

I was trying to find the cause of the resets occur and basically if I unplug the speaker inside the cabinet the reset stop´s. I swaped the speakers with another (the one in the machine is in bad shape) and the problem persist.

At first I was thinking that maybe the problem was related to the coil´s because sometimes when I turn the machine on one (or more) coil fire up an I hear the "pak" sound similar to the credit sound coil. I can almost swear that if this "pak" occur then I do not have reset´s even with the both two speakers.
I turned on the machine with no power to the coil´s (in auxiliary board) but rolling the spinning target in shooting lane the reset happens, so I dismiss a problem with the coil´s.
Attention that the reset do not only happens with the spinning target, if I press the other targets the reset happens too. I only use the spinning target because is more pratical.
I have also disconnected the power to the interconnect board the problem happens to.
I have only reached the sound part in last hope and began to reveal some things when I unplug the J1 plug (Interface to CPU) or the J2 plug (Volume Control), but only when I unplugged the J5 (channel + output) the reset´s definitely stops. After that I unplugged the speaker of the backbox but the resets continues and after unplugged the speaker inside the cabinet (the speaker in the backbox plugged in) the resets definitely stopped.

Anyone know why this happens?

The last day I make some measurements, but I really don't know if they mean something useful.

I have connected my DMM in the +5 VDC and +12 VDC test points in the power supply and start some games to see if they have fluctuations that can explain the reboots.

In the + 5VDC I don't see any fluctuations and I presume all is good here.

In the + 12VDC... it´s another story. It seems that the voltage is a little low and we see a lot´s of fluctuation´s.

Now the question... this fluctuations are normals or not? During the reset we cant see any major fluctuation (greater than the other we see), but probably is due to the DMM not being capable to refresh in time.

Looking at this:

<B>Low +5 volts from the Power Supply board.</B>
A low +5 volts coming from the power supply can often be attributed to the 47 mfd 50 volt capacitor at C8. If this cap fails (opens up), a low +5 volts will result. A low +5 volts can cause your game to reset randomly. Also a bad capacitor at C10 (18,000 mfd 20 volts) can cause a low +5 volts. This cap is the main +5 volt filter cap. [I][U]To test this cap, turn the game on and put your DMM on AC volts. Put the leads of your meter on the positive and negative leads of the C10 capacitor. If you get more than .5 AC volts, replace this capacitor.[/U][/I] Filter caps don't last forever. Expect about 10 years life from them (which means most system 11 games should have their C10 capacitor replaced!). But when in doubt, just replace C10 as it's probably due to be replaced anyway.

I measured the capacitor C8 and C10 in circuit and out of it. I used the ESR Meter and Capacitance Meter I have received and both are good. With the measurement in the +5 VDC and no sign of fluctuations I think the problem are not here.
But after doing the test indicated in the underlined text I have measured something like +0.65 VAC (I´m not sure now), so maybe I have to change this capacitor.

[B]Low +12 volts from the Power Supply board.[/B]
If your +12 volts is low (below 10.5 volts), check/replace the large power transistor 2N6057 on the power supply board. Sometimes the socket used to connect this transistor is corroded or simply not making good contact.

In regards of this... after see what looks to me a low +12 VDC, I think it´s probably better to change this transistor. Maybe the value rise a little and the fluctuation go away at the same time.

If this is the cause of the reboot I really don´t know.

So the other day I decided to work again on my Police Force and terminate the display repair.

In the end I have to change five CD4049 (U8 to U12) and three UDN7180a (U15, U16 and U20). Everything was socketed and now the display is working again except the small display (jackpot). I have to verify first if the information is send to this display or the display is dead.

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About the sound problem...

When I was working on this machine, after some search in the board I assumed the problem maybe in the U15 (74LS138) and swapped it. Nothing as changed and stop to work on this machine.

Now I have resumed the work and verifying my notes I realized that the problem can be in U15 or U14 (74LS139). So I checked the U14 (only removed an tested with my IC Tester because I have one now lol) and it was good.

Now I think I have to start from the beginning and start to search elsewhere in the board.

Thanks Hawk007 and GRUMPY, next week I´ll try to work a little more in this.