To test the Homepin 24" opto board VERY easily follow this:

(1) Remove board from machine
(2) Connect the two left pins of J1 & J2 with a jumper wire, short them together (see pic)
(3) Apply 12V to J3 (+ and GND are clearly marked on the board next to the connector)
(4) The green "Beam Test" LED should be ON
(5) If the green LED is NOT on, adjust the trim pot (centre of the board) about 10 degrees either way until the green LED DOES come on

If the above doesn't work the board is possibly faulty (rare but anything is possible).

If the board works as it should with the above test, you probably have faulty TX or RX opto devices, broken wires between them and the board, or faulty connectors in those wires.

It isn't easy to look at the TX LED glowing using a phone or camera as this circuit does not work in the usual manner. The TX LED is switched at approx 50% duty cycle and at about 40Khz (see pic) so the TX LED will be much dimmer than a standard opto TX/RX circuit.

Some might be wondering why the additional "Beam Test" green LED is mounted at an angle on this PCB - When the board is installed in a BSD, you are able to see this green LED through the open door and easily test the beam without even removing the glass (see pic).

This board is designed to be "stand alone" meaning it can easily be tested fully on its own and does not need any of the machines diagnostics to fault find.

Another point often misunderstood is this 24" beam uses standard opto TX and RX LEDs as used everywhere else in the machine. They ARE NOT special types at all, it is the way in which they are used by this circuit that makes the operation of the circuit different but the TX and RX parts are exactly the same so please don't go looking for "special optos" for replacements, they are just common types.

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*that's 10 degrees either side of THE FACTORY SET POSITION*

Did you try the adjustment I mentioned in my previous post?

A fuse needs to at least have one end free of the clips to measure with a meter.

Forget about measuring in circuit and also forget about "it LOOKS good" - that doesn't mean a thing, you HAVE to measure it with a meter set to resistance and it should come in well under 1 ohm - virtually a short circuit.

The band end of a diode across a coil ALWAYS faces the 'hot' side. That is the side with the 50V supply voltage which is (in your example) the thick purple/yellow wire.

The diode hanging there on your coil is connected the correct way around without one end connected of course.

You should measure it first to make sure it isn't shorted. Leaving it off can (and probably will) damage the driver transistor. If you have a new one just replace it - they are very common and cost pennies each. 1N4007 is what you want if you don't have one but a 1N4004 is as good if you have that.

Technically that's correct but there is no harm, and arguably some good, that can come from adding a diode right at the source of the high back EMF.

I saved a picture from a post somewhere in the distant past (below).

You can test the opto board for go/nogo simply by unplugging the two opto connectors and adding a shorting link across the two pins as shown.

Doing this will tell you if you have an opto fault or a problem on the board.

Picture shows a Homepin board BUT I can't see any reason why it wouldn't work exactly the same way for an original board.

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Sure, but the pic I posted is a "quick & dirty" way of getting a go/nogo without any fuss and without even removing the board from the machine.

Absolutely no problem whatsoever to fit a higher rated part over the original. in fact, the machine (in the USA) uses an 8A mains fuse and that tells me straight away that the filter originally fitted (5A) is UNDERSIZED for the job and a 10A should have been used originally.

https://www.pinballlife.com/24-opto-replacement-board-a-15646.html

$89.95

This one will work perfectly and it's only AU$22

https://www.pinballspareparts.com.au/knr-001.html

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I found this somewhere;

"Short these two pins together to test this Homepin replacement BSD opto board. The green LED should light and the adjustment pot on the board can be fine tuned to ensure the green LED is solid."

It looks to me like this takes the optos out of the picture and allows you to set the board sensitivity or something like that without unknown or flaky optos or opto wiring and plugs causing possible problems?

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Why? The difference will be negligible to NONE!