Board testing and repair services

[Roger]

Hi all,
Looking into my Scared Stiff problem of false crate hits (or possibly crate entries) I have tried different eddy sensor boards directly under the front of the crate and different boards with the adjustable pot that this links to.
No combination of these cures the fault so I presume these boards are not the cause.
I have also cleaned and reseated the relevant connections in the backbox and reseated all ribbon cables, and pressed home all chips including the Asic.
So my most likely culprit is the 16-opto under-playfield board A-16998. I have seen threads where LM-339 chips fail on these, amongst other things. However, testing this board and the components is beyond my scope - is there anyone who could test (and repair if necessary) this board?
I could buy a new board for about £80 but then there would be import duty etc. and it seems an expensive way to test for a fault.
Thanks,
Roger.

 

[AlanJ]

it’s gonna cost as much to fix the existing board. £30-50 an hour labour rates, parts and postage both ways. buy a new one

 

[Roger]

Yeah I plan to change the LM339's and socket them, then if no joy it'll be a new board. I'll test the diodes etc too.

 

[Moonraker]

I doubt it's the 339 more likely a failing/leaking capacitor on the 16 opto board. 339s are on or off normally not intermittent.

 

[Pick Holder]

@Roger - you are barking up the wrong tree.

The crate sensor is an eddy switch. This is not linked to the opto board at all. The crate switch goes straight onto the row/column and has diodes on the board.

These eddy switch boards are not always interchangeable - on ToM for example, two types exist. One for the trunk and another type do the two outlanes.

What I personally do with these is the wire that comes from the crate sensor to the eddy sensor board (two core) - solder it directly to the board. Those connectors go flaky.

 

[Roger]

@Roger - you are barking up the wrong tree.

The crate sensor is an eddy switch. This is not linked to the opto board at all. The crate switch goes straight onto the row/column and has diodes on the board.

These eddy switch boards are not always interchangeable - on ToM for example, two types exist. One for the trunk and another type do the two outlanes.

What I personally do with these is the wire that comes from the crate sensor to the eddy sensor board (two core) - solder it directly to the board. Those connectors go flaky.

Agreed for the eddy switch, but I think it might be registering crate entry rather than hits, which is the opto inside the crate. However I will solder those wires as you suggest, and if it persists I will change the caps on the opto board, then LM339's if it still hasn't gone away. Then if not cured I'm uncertain what I will do, perhaps have a beer.

 

[Roger]

I doubt it's the 339 more likely a failing/leaking capacitor on the 16 opto board. 339s are on or off normally not intermittent.

Thanks, I'll get some caps as they are only a few pence.

 

[Roger]

I would like to say thank you to the people that responded to my two posts about this, and I am updating both threads with the same information to let you know how I got on.

I initially thought I had a problem with the crate hit eddy sensor (my first post) as crate hits were being registered when they were not happening. I later realised that this could also be the crate entry opto sensor, as this would also register a false crate hit.

Having tried two different eddy sensors and two different PCB’s that the eddy sensor connects to I was reluctant to believe that the 2-pin plug-on connector between the two was the problem, although I do realise that both boards could have gone faulty in the same way at the same time.

I was also, as a later development, getting the crate kickout firing. Sometimes this appeared random, though it would always do it after a coffin lock entry or after two loops of the Bony Beast ramp (always after two, never after one). Therefore, this made me think the problem was more likely the 16-opto board under the playfield. (Switch edge tests revealed no short or false firing of one sensor when another was triggered).

So, as one suggestion, I changed the five ceramic capacitors and the one electrolytic capacitor on the 16-opto board. I reckoned this was cheap enough for parts and worth a try, but it didn’t fix it.

I had read reports from others, in the USA, that a LM339 chip on the same board had caused similar problems. There are five on the board so I removed all these, put sockets on and installed five new LM339 chips. (I had delayed doing this as it involved desoldering and installing 70 connections).
The good news (so far) is that everything seems fixed. No false crate hits, no firing of the crate kickout. I am aware that false hope can arise, and then the problem resurfaces immediately after declaring a successful solution. So I will update this post if that happens, when sober.

Cheers for the advice everyone.