SOLVED - I THINK - Stern Switch Fault

James

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Dec 29, 2017
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#1
Long story short - changed optos - had it working, put it back in, stopped working on WPT , there is a surface mounted 4148 diode, but the stern manual doesn't list MA or V on the schematic...

I imagine you can remove the SMT and just put anode and cathode of pin through in replacement, won't be pretty, but cheaper than a £80+ board.

Any ideas?
 

Homepin

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Mar 5, 2013
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#2
Have you determined the 4148 diode is faulty? Is it in fact a 4148 diode or some other part? Many SMT parts have very different numbers from the part you might expect it to be.

If it is a 4148 and it is faulty, a through hole part with leads will certainly replace it if you have the physical space.

1N4148 and 1N914 are identical parts
 
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James

James

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#3
Hey @Homepin - I have done a bit of reading on the issues and the two issues it seems to be are either the opto or the diode that can go (although I am probably wrong...)


Screen Shot 2018-11-17 at 09.30.36.png

I switched the opto and it was still intermittent. It was fine in test, I switched the game on, triple reset on all banks again, put it back in test and that opto closed all the time again.

I haven't yet switched the banks to see if it is a wiring issue, but will do that before ordering the part up.
 
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James

James

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#5
So.... there were two switch issues with this when I got it, the right ramp made opto's and the king resetting, looking into the switch matrix...


Screen Shot 2018-11-17 at 20.50.37.png

So.. they all sit on the 04 return - now as switch 20 and 36 all work absolutely fine, so I am hoping this isn't a board issue or they would play up...

Seems to be the little board at the back (520-5239-01) - which is causing the problem, if I switch the opto's on the right ramp made pair, it recognises the switch (as a different switch obviously) being made.

A6E2810A-0F8F-4B86-9A14-C5F7B98A34ED.jpeg

@pinballmania no longer seems to have them in stock - @philpalmer I don't see them on the website... anyone else know if this sounds like the part being at fault and where to source from the UK?
 

DRD

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Oct 26, 2014
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#14
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James

James

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#15
So... thanks @PinballDaze for getting this out to me so quickly - turns out it wasn't the board at all, in fact it was a diode on the trough switch (this wasn't working either I found out), I have changed that, had it up in switch test mode, all switches working - lovely old job, start the game up - problem is back...

There is an associated TIP120 on the board for this row, but I never get any issues on the first wired switch - it is always after the trough switch... could a bad switch itself cause the diode short on that and then upstream issues? I imagine taking it out of the circuit would resolve?
 
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James

James

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#16
Here it gets better - I focused on the trough issue and can get it working randomly - but when the left bank is closed the trough opens, when the left opto is opened, the trough switch closes, I have put my meter in continuity all over the board and can find nothing so far...


HELP!
 

DRD

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Oct 26, 2014
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#17
I feel your pain. I have been down this road. No-one on here will likely buy this game now. Folk seem terrified of SAM games with opto issues. Very few people are willing to do board repairs on Sterns. Fear is blowing the main board which is 400 or 500 I think.

See if the left bank of drop targets' reset bar is rubbing on the wiring loom and shorting something. This was the epicentre of my trouble. Seeing how Stern make games, compared to Wpc, system 11 and Bally ss put me right off stern.

My solution:

1. Take it to Phil or Andy Netherwood, to get it going. That way you won't unnecessarily blow opto boards
2. Dump the b1tch on Gumtree
3. Think hard before buying another Stern
 
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James

James

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#18
Hi @DRD - I don't think this is an opto issue - the boards are working fine and the optos are working - it is a random switch matrix issue- not 100% sure why I am hoping that @philpalmer or @pinballmania may have an idea - I can get a work colleague to do SMT work if needed .

I understand your logic with the not loving Sterns - we have spoken at length on it - but I am a Stern fanboy with their issues, I really want to have this game for the medium haul, so I am dedicated to getting it going.

My thoughts are:

A short - somewhere on the return (white and yellow) - but I cannot blinking find it if there is - I am loathed to cut out all the wire and re-wire it though.

The control chip (74HCT273) could be pulsing incorrectly giving false open and closes across the matrix (it says Q1 Line 5?)?

A diode somewhere else in the matrix is causing this, I am not great at switch matrix logic - any ideas here?

As I say - HELP LOL
 
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James

James

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#20
It's getting weirder...

If I engage ANY switch on the lower left drop targets closed - the switches act completely normally (Open as per below)


Screenshot 2018-11-20 at 20.11.14.png

when ALL of the switches are open - these three switches act closed.

Screenshot 2018-11-20 at 20.08.36.png
 
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Oct 27, 2015
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brockenhurst hampshire
#22
Got any mods on it James.....if they are connected on the same supply line as any opto's it will cause all sorts of ghost switching....they are real current sensitive. Particularly on the sam system. (Cannot imagine anyone bothering with mods on a wpt ...but never say never..!?)...seen it cause problems many times....the last cause was an illuminated instructions card joined in on one of the power lines to an opto control pcb!...eeekk! With bandage tape:D
 
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James

James

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#23
No visible mods I can see apart from LED backbox front right power supply - I can take that off though

To confirm can I run a jumper switch matrix test from drive to return and make sure there is no ghost switches? Do I need to put a diode on the wire?

Thanks for the help all.
 
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James

James

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#24
Progress - of sorts...

Jumper switch tested the board by jumpering the switch matrix - good as gold.

I then thought - hey lets jumper the rows back to the board. All golden but row 6. So I thought lets move row six around the pins, all it is doing is throwing out the drive voltage and getting a return, and hey ho, the closed switches moved around the matrix. This has to be a wiring issue - I have moved the opto boards around and it follows still, so as I say - must be that.

Is the only way to tell the actual path the wiring takes by physically following the wire around the playfield?

I couldn't see a block connecting the drive and returns for the switch matrix connecting to the backbox wiring, my thought was to jumper the drive connections between the block, then jumper the return to different connectors on the playfield, when it shows up, just go over that bit of wire with a fine tooth comb.
 
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James

James

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#25
Early indications are I have solved it - I managed to trace this back to the opto bank in question and although all four were behaving normally, when disconnected the closing of all other switches stopped when the bank was removed. I changed that opto that was in the line of the others and hey ho! No resets on startup. Out for a curry and a few beers, hopefully sorted tomorrow still as have a fun 12 player tourney tomorrow :)