I had posted a separate thread for my Black Hole repair, but figured I'd try here as well. I fixed a dead MPU with a new CPU, a bad RIOT, and a also corrected a couple output 74LS chips with a dead pin. Added NVRAM at 5101. Board passed all of the Pinitech diagnostic adapter's tests as well as the Marco extended test ROM. It boots and mostly plays a game, but I wanted to tackle the main issue I'm seeing. Displays 3 and 4 ("B" bank) have no a-g segments. The vertical 'h' segment works. Displays are good via swap to displays 1/2.

Z21, which controls the a-g segment output to the B bank, has its output pins stuck low despite pulsing input. Both it and Z20 have been socked and replaced with no change (in fact I tried a couple chips just in case. even though they're new and from a known good source). That said the pulsing input on Z21 (and output of Z20) sounds "noisy" as compared to Z18/Z19 with the A display bank. The only thing not in common between Z18 and Z20 is the CK at pin 9. Both of these trace back to RIOT chip U5, and they definitely sound "different" although pulsing (and I'm guessing should not since all 0s should be displayed on the displays after boot). Pin 13 on U5, which controls that CK signal on Z20 pin9 is labeled PA5.

Like I said, that RIOT chip passed all of its diagnostic steps and I've even tried a couple other RIOTs at U5 and all have the same result.

What am I missing here? I'm guessing Z21's output stuck low is because its input, while pulsing, is probably floating somewhere to not really have a high or low??

I know what you mean. I have a decent Elenco which has red/green lights for HI/LO but also a separate LED for pulse. I do not have an oscilloscope but I can just tell that something isn't right with the U5/13 -> Z20/9 clock pin signal given the audible sound on the logic probe (even though it's pulsing).

Everything else on Z20 is tied with Z18 back to Z16, so I know it's not that since the A displays work fine.

What's I'm trying to understand is how U5 tests OK, and yet if PA5 (U5/13 = Z20/9) is bad, where else is that signal coming from. Attaching schematic...

20180402_093031 (resized).jpg

There is no explanation other than the 74LS48 chips I purchased from Marco are either counterfeit or defective.

1.) There is no short between any of the pins. The 4 input pins to Z20 are tied to the 4 input pins of Z18.
2.) All of the pins tied to Vcc on Z20/Z21 are reading 4.99V and all the ground pins are 0V.
3.) Continuity checks pass on all pins of both Z20/Z21 with no connectivity anywhere else on the board.
4.) Z21's A,B,C,D input signals are pulsing. There should be no circumstance under which Z21 3,4,5,16 are hi, 8 is lo, and the inputs are pulsing and that the outputs are stuck low.
5.) Z20s input and flopped output signals appear "correct" in comparison to Z18 and Z22.
6.) Voltage across C27 is 4.99V (as is C26 and C28), and the powered pins are reading correctly.

I'm going to use an Arduino later today to power the 74LS48 chips on a breadboard and pass it the correct decoder signals to output the a-g segments to prove my case. Marco is looking into the chips right now and comparing it to their stock. They are not known for electronics parts, but since they had them stocked along with a bunch of other pinball repair stuff I needed, I went with them.

Yes, 74LS48 is an appropriate chip here. The stuck low pins for the Z21 a-g output pins also occurs on the bench, so I know it's not a connector or harness. This wouldn't make any sense anyways since the display connector is a one-way street.

Marco is sending me several more from a different lot today. In the meantime, since the 7 BCD decoder truth table is pretty straight forward, I'm going to use an Arduino and a breadboard to build a simple test circuit for this chip out of the game. If the output pins are still stuck low, then we know the chips are bogus.

Thanks for your help.

Yep, bogus chips. Was fun writing the code to test this though! Marco is sending me new chips from another source.

20180403_173313 (resized).jpg

Yeh it has a Texas Instruments logo, followed by 45H12LD and then E4 with a line under those two characters.
Next line is SN74LS48N.

PinballAir, actually this was a rogue issue. When I bought it the game wouldn't boot, due to a failed CPU and 1 RIOT chip. No corrosion issues, but I did the NVRAM mod anyways. In testing all of the 74LS series chips on the board, I found 3 with dead pins (one lamp, one switch, and then Z21 had one bad display pin). So I socketed and replaced those 3, and despite this chip passing the diode test, I still had no displays, which led me down the path above to the found discovery of the replacement 7448 chips I bought from Marco were junk. Can a huge outfit like them test every chip? Heck no. Would I have bought these from Ed @ G-P-E? Absolutely, but he's been out for a while. Marco said they have no more from this lot, and a few replacements are in route, free of charge. Can't ask for better customer service. Hopefully they test good and issue resolved.

So good news. First, MAJOR MAJOR kudos to Steve at Marco who fast-shipped me replacement chips, no questions asked. Both of them tested good in my Arduino rig above, slapped them in the game, and I have working displays! Can't believe how long I spent down an issue stemming from replaced a bad original chip with 2 NEW bad (counterfeit?) chips.

Now onto the rest of the game. A couple bulbs out but I think the rest of this should hopefully go smoothly.

Evan

I swear this Black Hole is going to be the death of me. Now that I have (hopefully?) resolved the display issue, I replaced some bad lamps (actually LED'd all of the inserts) and fired up a few games.

Immediately I'm noticed the following behavior as soon as a ball hits the shooter lane:
1.) I'm getting a ton of 10 point registers on the LOWER playfield display anytime a coil fires (flippers, ball into the shooter lane, etc.). It seemed that when I lifted the upper playfield into the vertical position that this stopped (need to do more testing). I looked at all of the switches on the lower PF and none of them appear closed or within vibration distance of closed.
2.) The tilt tilt tilt tilt tilt... sound track plays repeatedly when the points are registering, along with other audio. However the game doesn't actually tilt? (flippers flip, points registered, etc.). This is by far the oddest behavior!
3.) F22 fuse blows on the center top pop-bumper on the lower playfield.

I've been fighting this Black Hole back from the dead for a while, and finally picked it back up tonight. It's 99% of the way there...

The odd behavior I'm seeing is that 50% of the time when a ball gets kicked into the shooter lane, it's fine. There's an interesting light sequence, audio effects followed by the music of the game play.

The other 50% of the time, I see what I've uploaded below. The audio effects are replaced by the Tilt...tilt...tilt...tilt...tilt...tillllllllt sound effect, except the game is not tilted. You can proceed to play the ball normally, but there is no background music.

I've done all of the ground mods here: https://www.flippers.com/gottlieb_ground_cures.html

How can I resolve this?