Hello. I had the same problem with my pin. This is what I did unplug every thing from power board except the the molex plug below the 5v fuse. This molex goes to the transformer and there is a small 2 pin ground next to it leave this one pluged in also. Put in 5v fuse and power on if it blows you know it's the power board.
My problem was the 4 black rectifier diodes to the right of the 5v fuse and to the right of bridge. I use radio shack part
Model:276-1661 | Catalog #: 276-1661 6a 50v rectifier diode. Replaced all 4 'but you can google how to test them. Fired it if again with just the 2 molex plugged and see if it blows. Mine didn't so I plugged all the rest in and
And it started right up.
The pic show resistor r5 a little burnt looking and your missing fuse.
Good luck.

Very nice!
You can test those diodes with your DMM.
--
Chris Hibler - CARGPB #31
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Looks like R5 is 22K 1/2 watt 5%. 1N4004 for the four diodes.

Testing diodes is pretty simple, but you really need to unsolder one end to get an accurate reading. Think of diodes as a one-way gate for electrical signal. The power will flow one way, but not the other.

Set DMM to diode setting. Put the black lead on the side of the diode that has the band on it, and the red lead on the other side. The DMM should give you some numerical reading. When you switch the leads, the DMM should say OL.

If you get a reading both ways, the diode is bad. However, if you can find them locally I normally just replace them. The 1N4004s are usually cheap, and you've already unsoldered one end any way.

Those diodes and that resistor is in the HV section. When that resistor burns, it usually means the HV transistors are shorted.

Check the 12v bridge. I think it is the four larger diodes near the top middle.

I would bet that the four larger diodes are not a Radio Shack item. If you have to order them and the resistor, go ahead and order the two large capacitors too.

They are coming up on 30 years old and can dry up and fail. If I am not mistaken, one of them is the filter cap for the 5 volts, at least it is on the earlier version of this board. Just change them out and never have to worry about them again.

You need to do diode tests on all of them. You can test the HV transistors too.

I wouldn't blindly replace diodes or transistors unless there is evidence they have gotten extremely warm.

My advice was based solely on the 1N4004 diodes. They are cheap and you're going to have to remove one end from the circuit to test properly. Most soldering novices, and I include myself, can find it easier to simply replace those since the leads might be cut really short. However, if you can resolder them, go for it.

Transistors will normally test just fine in circuit, but I don't see any on this board.

There is three transistors for the HV section. Burnt resistors are a tell tale sign they went short. Typically all three go out at the same time.

Bridge rectifier diodes can be safely tested in circuit even though capacitors may stay charging from the dmm leads. You are basically just looking for a shorted diode (which blows the fuse) . Open diodes always visually look wasted.

You could have fooled anyone. Tres bien! And that is where my French starts and ends, despite two years of it in school and multiple trips to France.

You can also use 1n4007s in this case. Actually, you can use 1n4007s ANYWHERE that a 1n400x would go. The tolerances and specs/leakage of them are all identical these days, and the 1n4007's have the advantage of a higher voltage rating that can used in just about any application. I buy them exclusively. All you need are 1n4007's and 2n914/2n4148's for about 95% of all the diodes in a pinball machine.

Transistors can be easily checked with a digital multi-meter, without being removed from the circuit board. If you don't have one already, buy one. This will not be your last repair.

Watch a YouTube video on how to test transistors with a DMM on diode test.

Same goes for testing diodes (the four big ones top middle for 5v) with DMM.

That's cheating!

For transistors, you just need to know if they are NPN or PNP type and where the Emitter, Base, and Collector are located, unless it is a BJT transistor, then it is Gate, Source and Drain. In this diagram, the arrow indicates the direct of the flow. It acts like a diode, so you set your meter to Diode test, and check continuity in both directions. You should get readings similar to a diode in the arrow directions, and INF in the opposite direction. If you get 0 or INF on your meter in both directions, the transistor is faulty.

transistor-symbols.png

mos3.png

It's hard to tell from the online manual, but it looks like J6 is the power output to the backbox GI and some other lamps.

http://mirror2.ipdb.org/files/2272/Bally_1986_Special_Force_Manual.pdf

Check C1, the huge 10,000uf Cap for shorts. Also, your +5v regulator, U1, may be shorted out, explaining the reason you keep blowing fuses. The 4 diodes you replaced were for the high-voltage section for your displays, so that isn't going to help you with the game booting. The diodes you need to check are D1-D4. They are labeled as "MR751x4". I don't know what the equivalent or cross-reference for those parts are, but it is possible that 1n4007's would work there if there is a short. That is the most likely scenario here that there is a bad diode in that section.

On the power supply, pull all the fuses EXCEPT the +5v (Fuse #3 - 6amp). Also disconnect all the power cables going to the MPU and other various boards. All you want are the AC connections going to the PSU board. If the +5v fuse still blows, then you have an issue with those parts I mentioned. If it does not blow, and you can test +5v at the test point on the board, then the issue is a short on the MPU or somewhere else that uses that +5v logic power.

Exactly.

Like I said above, one of those large capacitors, filters the 5 volts for the logic on the MPU board. After verifying the transistors and diodes are good and have replaced the bad resistor, check those capacitors.

Bottom line, if that 5 volt filter cap isn't working correctly, the MPU will not boot up. Worst case, it totally fails and fries all the chips on the MPU board.

J6 is not used on "Special Force".

derp

what does the LED on the MPU do?

you need to figure out if your power board is making +5vdc. check the regulator input and output. input 12v output 5v

From Pinwiki: http://www.pinwiki.com/wiki/index.php?title=Bally_6803

TP1 - 5VDC
TP2 - 190VDC, adjustable via the trim pot
TP3 - 230VDC, unregulated
TP4 - 43VDC
TP5 - 14VDC, unregulated
TP6 - 11VAC
TP7 - 11VAC
TP8 - 6.3VAC
TP9 - 6.3VAC
TP10 - Ground

The regulator is the silver oval part that is mounted in the center of the large black metal heat sinks.

TP 1 is where you should be checking for your 5 volts.

I am going to try and make this straightforward.

Disconnect the power input plugs on the MPU, sound board, and display. Just have the power board connected.

Check TP5. for +12vdc or more

Is there 12vdc or more? If so go to check Check TP1

If there is less than 12vdc. Measure for 0.25VAC or less across the 11,000uF filter cap right above the regulator. If there is more than a 0.25VAC on this cap, replace it with a value 12,000 to 18,000.

If there no 12vdc on TP5 or very low. Check fuse. If the fuse is blown. Check the 4 diodes to the right of TP4. Power off and use diode test looking for one shorted in both directions. From the picture, the top right diode of the 4 looks burnt. Use 6 amp diodes here if they are shorted. If one is bad, replace all 4.

If the fuse is good, check the wiring coming from the transformer and through the input plug.

If all that looks good....

Check TP1 for +5vdc.

If +5vdc is low or missing. Check the 11,000uF filter cap as described above and replace as needed.
If the filter cap is good, TP5 is correct, and TP1 is low or missing, replace the regulator LM323K.

If you start blowing fuses or having low voltage when the sound board, mpu, display is connected then deal that later. Get your power board working first.

If you want to go the shotgun route. Just replace the diodes, filter cap, and regulator. Resolder any suspect header pins too while you have the board out..

You should be measuring AC voltage on that cap. It should be reading 0.3 VAC, or less.

If it reads higher, and I am betting it does, replace it before you do anything else.

Another quote from Clay (aka Shaggy).

From the section entitled, "Before Turning the Game On: Ok, So You Didn't Do the Above. You BETTER do This!"

Check the AC Ripple on the Solenoid Driver Board's C23 Capacitor.
Before connecting the J4 connector on the MPU board, check for AC ripple on the solenoid driver board's big C23 capacitor. This capacitor takes +5 volts DC from the rectifier board, and makes it smooth. If this cap is bad, it will not be giving the MPU board good voltage. To test this, try this:

Remove connector J4 form the MPU board.
Turn the game on.
Put the DMM on AC volts.
Put the DMM leads on the solenoid driver board's C23 capacitor.
An AC voltage of less than .3 volts should be seen. Any more than that, and C23 is not doing its job, and needs to be replaced. Do this BEFORE you put power to the MPU board!

Oh..........yes.

You can always go up in both voltage and capacitance, but never down. Actually, going up, is a good thing.

Personally, I would try to find one, with the same type of terminals, that is at least the same specs, at the best price. Sometimes it means getting a new one that is slightly larger but that's fine, as long as it will fit onto the board.

Are you setting your meter to volts AC? (not DC) when testing this cap?

ebay.com link: Nichicon LQ Series Snap in Electrolytic Capacitors 12 000uf 50v

Replace this cap if it reads more than 0.3VAC. Otherwise I would suspect the voltage regulator LM323K is bad.

I assumed he did, but replacing it is always a good idea.

If it indeed reads 19+VAC, the chips on the MPU are most likely toast.

Yeah... i don't think it is possible to have that much AC across the cap.

If the fuse is blowing it still could be that cap. The fact he has something on the 12v rail and NOTHING on the 5v rail makes me think the regulator could be bad.

That is DC. The AC setting has a squiggly line.

If you have 19vdc for unreg and 0vdc for the +5v, id say the regulator is bad (the cap very well could be bad too, it is rated for 20v and 19v is pretty damn close to the ceiling).

Yes, AC voltage should have a symbol similar to this ~

I'm not sure what meter you have but some have separate settings for AC and DC voltage. Others have a push button, that selects between the two.

Looks like the capacitor you linked to is in the correct range. However, it is what's called a "snap cap", because of the type solder leads it has.

In my experience, this type is best used where you are soldering the capacitor onto a circuit board. Those leads "snap" into the holes in the board, and hold it into place while you solder it in.

I would look for one that has the same type of leads, called "lugs", as the capacitor you are replacing.