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(Topic ID: 274571)

Williams Pinbot - loud constant hum


By debaser

79 days ago



Topic Stats

  • 8 posts
  • 5 Pinsiders participating
  • Latest reply 78 days ago by frunch
  • Topic is favorited by 2 Pinsiders

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#1 79 days ago

I've got a Williams Pinbot that has loud hum that I can hear on the other side of the room. It's not the normal hum that changes in tone with the CPU lamps. This is a constant hum that doesn't change at all, even when adjusting the volume control. All the boards are securely attached to the backbox. I pulled the sound board and went thru all the caps with my ESR meter and replaced all the ones that were bad. No change. I did the same with the MPU board. All the 100uf caps had either high ESR or their uF's were way off. I replaced all those and no change.

This pin had a Kohout Enterprises System 7-11a power supply in it when I got it. Not sure if that power supply is causing the hum or not. Unfortunately I don't have an original System 11 power supply right now to swap it and see.

Anyone else have experience using the Kohout System 7-11a power supply and if so did you get any loud hum?

#2 79 days ago

You’ve checked to make sure all the ground connections are good? (Including the screws that hold the boards to the head.)

#3 79 days ago

I have a Taxi that can sometimes have a pretty loud hum when I first turn it on but it goes away pretty quickly I’m not certain what’s causing my issues but it sounds like probably the capacitors are worn out on mine

#4 79 days ago
Quoted from debaser:

This pin had a Kohout Enterprises System 7-11a power supply in it when I got it. Not sure if that power supply is causing the hum or not. Unfortunately I don't have an original System 11 power supply right now to swap it and see.
Anyone else have experience using the Kohout System 7-11a power supply and if so did you get any loud hum?

I just put a Kohout 11C power supply in my Earthshaker and noticed a hum in audio too...after installing it on my Earthshaker... so I'm following. My old PS was bad and MPU was having issues so I can't test it either.

#5 79 days ago

If you still have the original you should try rebuilding it. It’s about $20 in parts for all 7 capacitors and it works great for another 25+ years

#6 79 days ago
Quoted from Matthew2000tx:

I just put a Kohout 11C power supply in my Earthshaker and noticed a hum in audio too...after installing it on my Earthshaker... so I'm following. My old PS was bad and MPU was having issues so I can't test it either.

Ok in decided to Hook Up my old power supply and not the 100v which had the issue: I can say that the was a audio hum with old power supply too! So I don’t think it’s the power supply with my Earthshaker. Ok 3:48am now I can sleep! LOL I was sitting in bed wondering if I had the hum before the new power supply. Apparently I did (it’s a new to me project pin)

I plan to rebuild my original ps as a backup but I like the Kahout upgrades and build in volt meter

#7 79 days ago

If it’s not the power supply causing it try using Nylon screws on the MPU and Sound board to help reduce the ground loop and reduce noise. Alternatively you can pull all of the boards. Sand the areas where the screws go and clean the metal parts up and that could also help

#8 78 days ago

Not sure if this will fix your problem, but ferrite beads installed in the right areas may help. Here's a thread covering the topic:

https://pinside.com/pinball/forum/topic/jokerz-hum-solved#post-5780250

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