Quoted from curban:
I hadn't done anything to the machine but play it for quite a while before F106 blew the first time.
I'm afraid I worsened things when I first attempted to measure the voltage by doing this: "Touched one lead to right side of fuse holder and other lead to ground.".
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.