What probably happened is that your meter wasn't set to the correct measurement mode when you touched the fuse holder and the ground. It might have been set to measure resistance / continuity and then when you placed the probes, the meter kinda shorted the power lines through the resistance measuring circuit , hence the weird effect of maxing out the volume. It is unlikely that you damaged the board this way. There were more chances of actually breaking your DMM or the main fuse of the transformer than your boards.

If you post a picture of your multimeter we can guide you as to how you set the meter before taking a measurement. There are 4 types of measurement you need to understand.

AC voltage (wavy line on your meter, VAC)
DC voltage (One straight and one dotted one, VDC)
resistance / continuity (measured in ohms, the omega symbol, continuity often has a speaker symbol and beeps when it measures a low resistance)
diode test (often is the 2nd function of the continuity test its symbol is a line with an arrow inside)

If you mix AC and DC on you meter while trying to measure voltage you will simply measure nothing. So if you are unsure that you are supposed to be measuring AC or DC, trying measuring both types of voltage.

Continuity/resistance is used to measure shorts and coils. It is on the same function as diode. A continuity test will give you a value in ohms while the diode test will give you a value in volts. A short circuit in diode test will give you 0v. A typical diode will read .3 to .7 volts depending on its type. Polarity just be observed on a diode and the black probe must match the side with the band.

The circuit is actually very simple and you should be able to pinpoint the problem fast enough.

The very first test is to place your DMM on AC volts (wavy line), pull out F106 , measure the voltage between J129 pins 6 or 7 and 4 or 5. It should be around 16 VAC. This is probably still normal , but it is the first thing to check.

Removing the diodes to test them should not have been necessary, not in this circuit, especially if F106 is out.

On the picture below, you can measure each diode, in circuit using the diode test on your DMM (line with an arrow inside) by applying the probes to :

D12 -> Red : A (Ground) Black : B (One side of the fuse holder)
D11 -> Red : A (Ground) Black : D (Pins 4 or 5 of J129)
D14 -> Red : B (One side of the fuse holder) Black : C (TP102)
D13 -> Red : D (Pins 4 or 5 of J129) Black : C (TP102)

You say the diodes tested good when pulled, but all showed flow when tested in circuit. Was this with a good F106 fuse ? Most probably. If they all showed flow, this means TP102 and ground are shorted together.

Place the meter in continuity and measure between TP102 and ground this should NOT give you 0 ohms. If this is indeed short (most likely) and the diodes tested good (.3 to .7 volts typically), then either C12 , C11 , R6 + LED102 , C7, Q2 (3 pin 12 volt regulator LM7812),C5 or C40 are shorted. Out of all these , the most likely culprit would be the LM7812. There should not be any continuity between any of the 3 pins of the regulator. (pins 1-2, 2-3, 1-3). It can be easily pulled out but there should not be any shorts in both cases, in or out of the circuit.

This circuit is the reason why you are missing both the 18v and 12v from TP102 and TP100. Did F101 burn ? Is this fuse the correct value ? The manual says it's a 0.63A fuse. Unless this fuse is the wrong one and it much higher in value , I don't think the problem is beyond that fuse.

PIN1.png

Your D11 results are normal , on one side it measures 482 millivolts , or 0.482 V, and on the other infinity (1). The diode should not conduct in reverse and especially not read 0 which is a short circuit, and it doesn't when you try to reverse the probes.

Don't compare with D8 , because you are actually reversing the probes when it measures 1.276 Volts. If you look at the circuit , you can see that you actually end up measuring a lot more that just that single diode in reverse when you reverse the probes on D8.

The important thing when measuring a diode is to measure the voltage drop on it , by respecting the probe orientation (the .3 to .7) and that you don't measure a short or open circuit (nothing at all when respecting the orientation). When you see weird results like your reverse D8, the absolute test is to remove it. If you have access to the schematic then you can look and try and figure out why you have those results.

(In your D8 case , by reversing the probes you placed the negative on the ground of the whole board and since the return path for the measurement will always be the shortest path , if the diode was shorted , you'd measure a short, but you won't if it isn't and the current flows through other parts to return to your meter (through other diodes , resistors and maybe even op-amp as in the picture, which ever is the shortest path for the current).

PIN2.png

Oops, it seemed obvious.. You are measuring for AC, on the board, with the connector disconnected.. But we are interested to know if the connector you removed, brings the correct voltage to the board. You're supposed to measure the connector itself, not the pins on the board when you are checking if the 16v comes in.

You want to measure those 2 blue wires.

Screenshot_20210615-123943_Firefox.jpg

Did you measure 1.3 ohm with the lamp connectors disconnected from the board? Either way, 1.3 ohm is way too low. You should NEVER measure resistance/continuity in a circuit while power is on, you risk damaging your meter and the board. Aynways , 18v in 1.3 ohms would equal over 13 amps.. 1.3 amps in your case is probably the probe resistance and / or the connections you made while probing. The real result is probably even less , making the current even more.

There is an issue here for sure. Go back to my first picture and measure continuity between H (one side of F101) and ground. Is this side shorted as well ? Can you remove Q2 and measure continuity again on TP102 and ground ?

That part is fine. 14.4 VAC is about 20.3 VDC and with the rectification of the voltage , it comes even closer to 18 VDC.

Just to confirm, you did desolder all 4 diodes , tried the diode test on them and they all tested fine, correct ? You should check the regulator next. Keep J121-126 disconnected for now. With everything disconnected , resistance between TP102 and ground really shouldn't be 1.3 ohms. Time to test the regulator (LM7812).

Ok, this should indicate that the short isn't after the LM7812. Looks like Pins 1 and 2 are shorted , but not 2 and 3.

Do you have any tools at all for desoldering? You're not supposed to remove any components without first removing the board from the cabinet. How did you pull out the diodes? Did you just heat them up and pull on them from the component side? With the proper tool, a desoldering pump, you can get that part out in under a minute when the board is removed and you are working on the solder side..

If you pulled on the diode without being careful, you might have damaged the "via". That's the connection between both sides of the board that every hole has. It is easy to damage when you do just that, pull on a leg of a component.

You shouldn't learn to work on boards with an iron, in a board that is precious and has value. If you don't have the skills yet and you really want / like to learn, find some scrap boards and remove components and solder them back to get used to it and not damage the traces and the solder pads/vias.

There aren't really any other steps. If the diodes are good and the lamps aren't connected and tp102 and ground give you 1.3 ohm, you can only test Q2. Testing it out of circuit will easily confirm it was the first (and hopefully) only issue which caused f106 to blow.

OK, then we are getting closer. So without j122, you get no continuity, which is what we need. I looked up j122 and it does connect to the lamp matrix, and brings column 8 to the coin door board. It is connected to the start button lamp. In your first post you mentionned disconnecting j125 and j121, but we missed that j122 is also in the circuit.

With j122 disconnected, does the fuse still blow? It probably won't.

Check around the start button lamp, anything touching the casing anywhere?

Yes, definitely the lockbar is grounded by the chassis of the machine otherwise it would present a danger for shock if something shorts inside. Glad for you it was an easy fix.