(Topic ID: 205684)

Testing Williams HV Display Board D-11610

By ajfclark

6 years ago



Topic Stats

  • 4 posts
  • 2 Pinsiders participating
  • Latest reply 6 years ago by G-P-E
  • Topic is favorited by 2 Pinsiders

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#1 6 years ago

The Space Station I have currently has an LED display installed that works.

The HV display was included (originally from a Big Guns), but had been replaced with the LED. The previous owner says "one day I turned it on and it just wasn't working. My tech guy replaced it with the LED one".

So I have no idea what the actual state of the HV display is.

I started off looking at the HV side of the power supply. The fuse blew immediately even with no load. I pulled one leg of each passive comment and found Q1 and Q3 were faulty and ZR2 and ZR4 have strange readings. (Details https://www.aussiearcade.com/showthread.php?t=91312 )

I replaced every component on the HV side of the power supply and it now starts without blowing the fuse and I see 100v and -100v on pins 4 and 3 as expected.

Now, before I plug in the HV display board, is there anything I should check?

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Visually this jumped out at me:
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#2 6 years ago

Feeling brave/stupid I plugged it in. The was some arching in the legs of the P3 display and F1 blew.

Spent some time hoping around the board with the DMM.

In diode mode, these 4 pins gave different readings to similar chips in the circuit:
U13 pin 11 .718, pin 8 .031
U16 pin 11 .043, pin 8 .032

I also checked all the 1Mohm resistors.
R27,28,30,31,32,33,35 are all within 5% of 1Mohm. R34 never gives a stable reading but fluctuates between 800 and 900kohm.

There's pitting in the board between the HV pads of R33 and R34. The gap between the traces there is very small.

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I'm wondering if R34 being out of spec allowed to much voltage to flow which allowing an arc between those two pads? Shorting the two 100v lines together.

The IC readings above need further investigation, but that'll do for today.

1 month later
#3 6 years ago

When I removed display 3, R34 read as in spec. This make me think the p3 display is shorted, right?

Tested the 6118s and 3 of the 4 read bad. Removed the other 3 displays and they still read bad.

Couldn't get UDN6118A-1, but found some UDN6118As. As they are rated for a lower voltage, I swapped out the 100v zeners on the power supply for 91v ones. Popped in some sockets, installed the chips and tested.

So it turns out the arcing wasn't between the legs on p3... It is directly between the two points mentioned above.

How can I stop the arcing between R33 and R34?

#4 6 years ago

Contaminant on the board such as carbon is possible.
First thing to do is give it a good cleaning so you can see what is really in there. Hit it with a soft bristle brush and alcohol to clean the old crap off.

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