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Scared Stiff crate sensor registering false hits

R

Roger

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10 Years
Joined
Jul 21, 2011
Messages
23
Hi all,
I have had this problem for a long time and finally decided to try and fix it. The problem is intermittent rather than constant, but it does happen very regularly.
When playing Scared Stiff the hits on the crate door are recorded by an eddy sensor under the playfield, just in front of the crate. Very often, after playing for a few games, the sensor will begin to record hits when the ball is nowhere near.
It will keep recording hits continually, just a few seconds apart, and switching it off and on will cure it for a while.
I have used both the original eddy sensor board (and adjusted it) and an auto-adjusting one from Martin at Pinbits, but I presume this board is not the problem as it persists with either one.
It is such a specific problem that I cannot find it covered in any of the repair guides.
Can anyone help me with ideas on diagnosis, even if it means trying a new board in there somewhere?
Thanks,
Roger.
 
Not 100 per cent sure of myself here but ...

My guess is that heat is playing a part. As metal gets hot, its resistance increases. This causes voltages to drop.

I would suggest cleaning pins and connectors on that crate board, as well has those on the power supply that feeds it. Very fine emery paper, followed by ipa for the pins. Reflow solder to them. For the connectors a squirt of switch cleaner and possibly a gentle round (tiny) file.

As above I would try to use the original board and consider changing the adjustment potentiometer if cleaning does not work
 
Thank you for those replies, I will carry out the advice and update on here as to how I get on.
Really struggling to find a replacement pot for the board though. I can only get 150mW rather then 250mW in the correct physical size and 10K rating. Anyway, I can give it a go and hope it was over-specced.
Or maybe I could get a 15mm pot (should be 10mm) and make some legs for it to fit.
 
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.
 
My scared stiff eddy sensor has been faultless for years. The damned thing started playing up over the weekend !!!!!

Luckily it was the adjustment pot, I would think that the warmer temperatures were behind it.
 
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