(Topic ID: 282566)

LED flash locked on... another one (heavy sigh/eye roll)

By dtrimberger

3 years ago



Topic Stats

  • 3 posts
  • 3 Pinsiders participating
  • Latest reply 3 years ago by barakandl
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You

Linked Games

  • Stars Stern Electronics, 1978

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#1 3 years ago

It’s been a minute since someone posted a LED locked on post so I thought I’d get it going again since everyone was likely anxiously waiting on one.

I’m working on a Stern Stars and have a Alltek board ready for it. I am still redoing play field and cabinet components so while I tinker with those I decided to try to get the original board fixed because I’d really like to use the board for Stern Stars 2020 (check out that forum, its pretty impressive). It also seemed like a great way to learn more about something I was aware of but haven’t ever tried on my own.

My soldering experience was limited prior to pinball but its coming along nicely and I figured this was a good way to get better, I also won’t be heartbroken if it doesn’t work out.

There was a lot of battery corrosion (someone had removed the battery at some point thankfully) and I used a Gerberdesigns kit to change out the reset zone. I lost one trace at U8 pin 8, and my tinning was a little suspect so I jumpered the 5V trace on the back to improve it.

I also made test bench using a arcade power supply which allows me to adjust the voltages.

Of course, first time on with power supplied at TP 5, 2 and ground the LED went solid red.

I’ve gone through the Clay’s guide but need some help with a few things.

1. With the arcade power supply on and reading 12 and 5 Volts at its supply posts if I check TP 2 and TP 5 I get 11.53 V and 4.42 V. I’ve tried looking in Clays and other forum posts how to track where this voltage drop is coming from but it’s never really mentioned anywhere. I’m guessing it has something to do with the traces or other components. What’s an acceptable level of variance at these points?

I can turn up the power supply to get these voltages up to proper levels but it doesn’t seem to do anything to get the LED to flash and it wouldn’t matter anyway when I get the board in the machine.

2. Testing U9 pin 40 I get low voltage then 4.74

3. U9 pin 2 I get 4.4

4. shorting R1r3 drops pin 40 to 6 mV

5. U9 pin 3 2.21V

6. U9 pin 36 2.59 V

7. U9 pin 5 31 mV. Cycling on and off never changes this. I don’t have a logic probe (yet) but this pin is off from what I can see. I dabbled in following that part of the circuit but decided to come here first for some help before going checking further as none of the numbers I was finding were correct.

I changed out the sockets for U8 (in the kit) and U11 (had some corrosion at pin 1 and 2)

I also have new chips for U6, U9, and U11 installed currently (I haven’t changed 2 because I didn’t realize its importance until after I ordered the other chips). I have sockets for U9 and U11 but haven’t installed them, again thought I’d better ask before heading down that route.

The voltage drop at TP5 seems to be reflected in lower than expected voltages throughout the other pins. I don’t think it explains pin 5.

Where should I go next? Thanks ahead of time, I’m new to this but teachable sensei

Dan

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