BK2K Pinball tripping house fuse box - NTC needed?

[ffollim]

Hi everyone,
I’ve got a Black Knight 2000 system 11 machine that keeps tripping the house breaker when turned on (fortunately just the garage one or it would be annoying for my wife!)

Sometimes it powers on fine particularly if it’s a second attempt. I have disconnected all circuit boards from the transformer to try and isolate the cause (PSU, aux PSU, alpha numeric display, MPU/CPU board, interconnect board, 18v lamp power on CPU board) but it still trips with everything disconnected.

I’ve read the article linked below about system 11 pinballs being notorious for tripping breakers and using an NTC, but is this likely to be something else like a short circuit or bad transformer? Any ideas on how to diagnose this would be greatly appreciated.

Flippers.be - Main breaker of your house trips when turning on a pinball machine

Main breaker of your house trips when switching on a pinball machine

www.flippers.be

Thanks,
Matt

 

[s000m]

That'll be your inrush current.

I had the exact same issue on a CFTBL.

When you power on the machine, the transformer can draw a large surge of current (inrush current), especially if there’s no inrush current limiter (NTC thermistor).

This alone can trip a sensitive house breaker, particularly newer AFCI or GFCI types, or ones rated too closely to the machine’s draw.

Check the Line Filter

• Unplug the machine.
• Use a multimeter to test for continuity (ohms) across the line filter input and output.
• You should not see a dead short (0 ohms). If you do, the line filter may be internally shorted.

Inspect and Test the Power Cord

• Look for frayed insulation, melted spots, or brittle areas.
• Measure resistance from hot to neutral, hot to ground, and neutral to ground with the power switch on and everything disconnected past the transformer.

Add or replace the inrush current limiter

• Add an NTC inrush current limiter NTC Thermistor on the AC line input, especially on the hot wire before the transformer.
• This slows the initial surge and often solves nuisance tripping.
• This slows the initial surge and often solves nuisance tripping.

Flippers.be - Main breaker of your house trips when turning on a pinball machine

Main breaker of your house trips when switching on a pinball machine

www.flippers.be

 

[ffollim]

That'll be your inrush current.

I had the exact same issue on a CFTBL.

When you power on the machine, the transformer can draw a large surge of current (inrush current), especially if there’s no inrush current limiter (NTC thermistor).

This alone can trip a sensitive house breaker, particularly newer AFCI or GFCI types, or ones rated too closely to the machine’s draw.

Check the Line Filter

• Unplug the machine.
• Use a multimeter to test for continuity (ohms) across the line filter input and output.
• You should not see a dead short (0 ohms). If you do, the line filter may be internally shorted.

Inspect and Test the Power Cord

• Look for frayed insulation, melted spots, or brittle areas.
• Measure resistance from hot to neutral, hot to ground, and neutral to ground with the power switch on and everything disconnected past the transformer.

Add or replace the inrush current limiter

• Add an NTC inrush current limiter NTC Thermistor on the AC line input, especially on the hot wire before the transformer.
• This slows the initial surge and often solves nuisance tripping.
• This slows the initial surge and often solves nuisance tripping.

Flippers.be - Main breaker of your house trips when turning on a pinball machine

Main breaker of your house trips when switching on a pinball machine

www.flippers.be

Many thanks for this, that’s very useful and I will check all of those things.
One question - if I have disconnected all the boards and lamps, and it still trips, I assume the draw will be a lot less and shouldn’t trip the breaker? If that is the case is it more likely to be a short somewhere?

 

[s000m]

Many thanks for this, that’s very useful and I will check all of those things.
One question - if I have disconnected all the boards and lamps, and it still trips, I assume the draw will be a lot less and shouldn’t trip the breaker? If that is the case is it more likely to be a short somewhere?

Depends if the inrush current thermistor is just plain out failed see my diagnostic step about the testing the continuity

 

[cooldan]

Also try attaching to a multiplug

 

[Fubar]

Unplug the game and open up the line filter box (in front of the cab on the right). I've seen many games where the thermistor was blown and just replaced with a straight wire. Post a photo if you're not sure.

 

[Paul]

possibly need a "type-c" breaker to handle the current inrush when you fire it up.

 

[Jay Walker]

One question - if I have disconnected all the boards and lamps, and it still trips, I assume the draw will be a lot less and shouldn’t trip the breaker? If that is the case is it more likely to be a short somewhere?

Hello, Matt,

It's still the transformer, though. As I understand it, a transformer produces a 'dynamic' or working resistance once it's powered up, but until that builds up there's this 'inrush current' which is the usual cause of tripping circuit breakers. Some games seem to be affected more than others; one of works' Fire games was always knocking out the circuit breaker at a boozer, to the extent that the landlord expected it. Williams began using a thermistor/Ntc at some point during the wpc era, but there's no reason one couldn't be used on your Black Knight 2000.

 

[ffollim]

Hello, Matt,

It's still the transformer, though. As I understand it, a transformer produces a 'dynamic' or working resistance once it's powered up, but until that builds up there's this 'inrush current' which is the usual cause of tripping circuit breakers. Some games seem to be affected more than others; one of works' Fire games was always knocking out the circuit breaker at a boozer, to the extent that the landlord expected it. Williams began using a thermistor/Ntc at some point during the wpc era, but there's no reason one couldn't be used on your Black Knight 2000.

Ok thanks. I’ve ordered a thermister to put in the machine to see if that resolves it

 

[Bobbdobalina]

Yeah, I don’t believe the transformer needs any load on it as it more to do with the physics of the transformer.

 

[ffollim]

That'll be your inrush current.

I had the exact same issue on a CFTBL.

When you power on the machine, the transformer can draw a large surge of current (inrush current), especially if there’s no inrush current limiter (NTC thermistor).

This alone can trip a sensitive house breaker, particularly newer AFCI or GFCI types, or ones rated too closely to the machine’s draw.

Check the Line Filter

• Unplug the machine.
• Use a multimeter to test for continuity (ohms) across the line filter input and output.
• You should not see a dead short (0 ohms). If you do, the line filter may be internally shorted.

Inspect and Test the Power Cord

• Look for frayed insulation, melted spots, or brittle areas.
• Measure resistance from hot to neutral, hot to ground, and neutral to ground with the power switch on and everything disconnected past the transformer.

Add or replace the inrush current limiter

• Add an NTC inrush current limiter NTC Thermistor on the AC line input, especially on the hot wire before the transformer.
• This slows the initial surge and often solves nuisance tripping.
• This slows the initial surge and often solves nuisance tripping.

Flippers.be - Main breaker of your house trips when turning on a pinball machine

Main breaker of your house trips when switching on a pinball machine

www.flippers.be

Hi, so this is the box on my pinball. Do I need to replace the orange wire with the NTC limiter?
Also which terminals are the input and output on the line filter? From load to line?
Thanks Matt

 

[Fubar]

Hi, so this is the box on my pinball. Do I need to replace the orange wire with the NTC limiter?
Also which terminals are the input and output on the line filter? From load to line?
Thanks Matt

Correct - you can get one here:

8A Thermistor Inrush Current Limiter

Mains Input Thermistor. Goes inline on the live input to the mains filter. Has high initial resistance but quickly reduces to nothing which prevents current in-rush, and can help prevent your mains tripping out on switch on. An ageing Thermistor can cause random resets.

pinparts.co.uk

Here is the schematic btw:

 

[ffollim]

Correct - you can get one here:

8A Thermistor Inrush Current Limiter

Mains Input Thermistor. Goes inline on the live input to the mains filter. Has high initial resistance but quickly reduces to nothing which prevents current in-rush, and can help prevent your mains tripping out on switch on. An ageing Thermistor can cause random resets.

pinparts.co.uk

Here is the schematic btw:

View attachment 280747

Ok not the prettiest as used black heat shrink but here you go,

 

[ffollim]

Ok not the prettiest as used black heat shrink but here you go,

00.5 ohms from input to output

 

[ffollim]

00.5 ohms from input to output

 

[ffollim]

Correct - you can get one here:

8A Thermistor Inrush Current Limiter

Mains Input Thermistor. Goes inline on the live input to the mains filter. Has high initial resistance but quickly reduces to nothing which prevents current in-rush, and can help prevent your mains tripping out on switch on. An ageing Thermistor can cause random resets.

pinparts.co.uk

Here is the schematic btw:

View attachment 280747

Ok problem solved! It’s no longer tripping the breaker! Thanks for your help

 

[s000m]

Ok problem solved! It’s no longer tripping the breaker! Thanks for your help

Good, good