Greetings,

I’ve already posted this on RGP but we haven’t had much luck pinpointing the issue. So I thought I’d expand over to here in hopes another set of eyes will be able to help out.

Issue:
Black Knight (System 7) Blanking Circuit Signal will not go between the 4v-5v requirement to play. It actually measures just a little above 3v. If I jumper the blanking test point with 5v, the game plays just fine.

Parts Replaced on MPU:
IC23 (and also put in a socket since it did not have one)
IC7 (and also put in a socket since it did not have one)
Q1
Q5
C84
C31
C27

Voltage Measurements:
Test Bench Power Supply = 4.91v and 12.02v
TP1 = 12.02v
TP2 = 3.89v
TP3 = 72.5mv
TP4 = 3.4v
TP5 = 4.64v
TP6 = 2.37v
TP7 = 4.69v
TP8 = 4.73v
TP9 = 4.81v
Header Pin 37 = 3.4v
1J3 Pin4 = 3.4v
IC23 Pin 8 = 4.84

Continuity Testing from IC23:
(All test near zero)
Pin 1 to ground test point (TP10)
Pin 2 to the junction of R21, R22 and Q21 base
Pin 3 to
-TP4
Pin 4 to
-IC36 Pin 34
-R29
-R30
-Q2
-TP8
Pin 5 to
-C17
Pin 6 to
-C31
-R23
Pin 7 to
-Pin 3 of IC23
-TP4
-Header pin 37
Pin 8 to
-C63

Any other suggestions what to test / check?

Thanks much!

Additional info:

On bench with game ROMS, 7 segment flashes "0" and the 2 LED's also flashes once at the same time as the "0". I believe it means it passed the initial test.

With Leon Test Rom, all diagnostics pass.

Went over the repair guide again (http://pinball.flippers.info/system6repairpart4.asp).

From the guide: "To use the test LED, connect the negative end to ground and then touch the positive end to each output on the PIA (pins 2 through 17)... If you don't get a flash on one of the pins, or one of the pins gives you a continuous signal, then you will need to replace the PIA."

On IC36, pin 9 appears to be dead. I'll try and get a replacement soon. If I'm understanding this correclty, the other PIA (IC18) would affect the blanking and not IC36.

Also noticed that on both PIA's, pins 2-9 were more dim than 10-17.

From the guide: "The crystal is connected between pins 38 and 39 on IC1. You should see a waveform if using your scope probe on these pins or approx. +3 volts if using your DMM."

I'm getting around 1.4v for each pin. Not sure if this is an issue or related to blanking.

Again from the guide: "If your game seems to be booting properly with the Game ROMs however you're not getting a plus on pin 4 of IC18 (the PIA that drives the blanking signal), check the outputs of IC25 (a 4020). If the interrupt signal is not being generated at the correct speed, then IC18 will not generate the required "pulse"."

Not sure what is meant by "a plus on pin 4 of IC18" Does that mean any voltage or perhaps around 5v? When I test mine, it shows 2.4v.

Thanks

I believe I did but will double check. I failed to mention that I had already replace the interboard 40 header pins and 40 pin receiver.

I measured after the interconnect on the driver board and the voltage is the same.

I do have a Wittig OsziFox. Suggestion as to how to wield it to pin point the lower than average voltage issue?

I just swapped IC36 and pin 9 is the same. I'm going to assume this is ok for now unless someone with a Sys7 can validate this is not normal.

A new crystal quarts is on it's way to eliminate a "weak" crystal.

What specifically should I be seeing on my Wittig OsziFox scope? Haven't really used scopes that much.

Thanks

Interesting I'll check that out when I can. I do have an IR temp gauge, now I can finally put it to use.

Yeah, I've been following the part about blanking circuit on that page but haven't looked too closely at the scope examples. Can't seem to carve out time on my short evenings lately to wrap this up.

A couple things about this from the guide. It doesn't specify what are the outputs of IC25. Do I check all the pins? What is the correct speed that it mentions? How does the correct speed look on a scope? Should IC25 be another replacement candidate?

If I'm understanding Blanking...it should either be ~5vdc or ~0vdc. 5v meaning everything is ok and move on to play. But in my case, it acts like all is well but somewhere along the line, the voltage is getting pulled down a little too much.

I have acquired another MPU and Driver board from a buddy of mine to maybe help in troubleshooting. I'll need to look more closely at them to see what kind of state they are in. They have been loose in his inventory for a while. I was thinking to first put in a different Driver board to definitively eliminate the Driver board.

Thanks

Got distracted with other squirrels but managed to carve out a little time tonight.

Changed out the crystal (boy are the new ones tiny compared to the old ones), no change.

I was able to borrow another driver board from a friend. Mated the MPU and the loaned driver board, BINGO! I now have 4.72v compared to the 3.3v. The issue must be with my driver board. As mentioned before, the interboard connectors have been replaced. I re-inspected the soldering and they all appear nice, shiny and solid.

Now that we know that something is pulling my driver board down ~1.5v, suggestions what to interrogate first?

Thanks

OK, I think I may have FINALLY found something of interesting. One of the first things I did a long time ago when upgrading the components of my driver board was to install a blanking signal LED. This was advised on Clay's guide by taking an LED along with a 1/4w 150ohm resistor and placing it between interconnect pin 37 and ground. (Even has a nice pic as to where he soldered his.) The thought is when there is a blanking signal one can easily, at a glance, see if it is up. One evening I had a thought and decided to see what would happen if I de-solder the blanking LED. Metered out the signal, wow! It's actually super close to 5v now!

I took the same LED and soldered it onto my buddy's driver board. Same exact symptom. The blanking signal was pulled down to a hair above 3v. I metered out the resistor and it is almost spot on 150ohm. I then snagged a different LED, even a different color, the same exact symptom. Down to around 3v.

I guess I could live without the blanking LED but now I'm more curious as to why this simple mod advised by Clay's guide would do this. The LED does light up and as far as I know, resistors are not polarized.

Thoughts?

Thanks!

I just tried a 3rd totally different LED (larger orange) along with a different 150ohm resistor (brown-green-black-black-brown), same issue. LED's do have polarity and wouldn't light up if installed backwards.

Those of you who have this mod installed, can you do a quick test on TP4 and see what voltage is showing up? If the voltage still holds strong near 5v, perhaps there is something a bit weak on the board's power supply circuit?

Thanks

Most likely the power circuit is ok since I do get an equal voltage on TP9 to that of what my bench power supply puts out (~4.82v). I did a little poking around the blanking circuit and not sure if what I found helps in troubleshooting. IC23 (LM555 Timer) does keep consistent voltage on pin 8, which is the +VCC (~4.82v), when I apply the LED. However pins 7 and 3, which both appear to go to TP4, do fluctuate between 4.78v down to the 3.3v when LED is applied.

I have already replaced the IC23 with a new part as well as installing a SIP socket.

Any other thoughts or places to look?

Thanks

Here is a pic of the blanking LED.

Blank LED.JPG

I checked the blanking signal with a scope and it appears to be just a solid line. The the only time I see it change is when I remove the LED, then the line jumps up a tad.

Thanks

photo(1).JPG

Here is a pic of the CPU board just in case there is something visually obvious that I'm missing.

Board.JPG

A buddy of mine did lend me a few boards. Were you referring to the CPU board? Unfortunately, the CPU board that he lent doesn't seem to power up at all. It appears to have gotten some water damage around a small part. The extra driver board does appear to work however.

Thanks

It's been a while and I have spare CPU and driver boards to play with. Unfortunately, I'm even more confused than before. Mated the 2 spare boards together, powered it up on the bench and measured header pin 37. Very close to 5v like my boards sans LED. Here is where it boggles my mind. I put on an LED (w/ 150ohm resistor) and took a measurement. I'm getting the same 3.4v that I'm getting on my boards as well?!?!

Could it be possible my spare boards have the exact same issue as mine? Barakandl stated above that he does this mod all the time and always shows 5v. It wouldn't have anything to do that these boards are on the bench and not in the back box (no plugs)?

Seeking advice....

Thanks!

<bump>

Yeah, it would appear it's the LED or combination of LED and resistor. I've also noted that the spare boards don't really boot up correctly on the bench too. The 7 segment LED has a zero and never goes out like it should. Just stays on. The boards are of unknown condition so not surprising. I have tried various sizes of LED's but don't know if they are different brands.

Anyways, I'm in agreement that I'll just have to leave the LED off and toss this into the unsolved mysteries bin, move on, and play some pinball.

Perhaps someone in a few years will have a similar issue and dig up this cold case....hopefully have better luck.

Thanks all!

Whoa! Glad I refreshed this tab before closing! I guess I never thought about using higher rated resistor. I'll see if I have some in my inventory and give that a try.

Thanks!

Only had a chance to look for a replacement resistor last night. The closest thing I have is 470 ohm or 2.2k ohm. Will give them a try when I get a chance. The timer IC I installed is a LM555CN. If I recall, this issue I'm having is the reason I had swapped it in the first place.

Stay tuned.....

Tried first with the 470 ohm. This time the blanking signal was maybe a .1v higher than before. Tried the 2.2k ohm, another .1 - .2v higher than the original 150 ohm. With the 2.2k, the LED is pretty dim.

I did manage to get the loaner boards to boot up now and tried the same thing with it's blanking signal. I'm getting the same results. IC23 on the loaner is NE555P. It's really looking like its my batch of LED's since I'm getting the same results on both boards. The LED's I'm using are from a Radio Shack assortment pack and it doesn't give any MA specs. The size I'm using is the same size as the 2 next to the 7 segment LED. (3mm perhaps). I do have a pack of 5mm reds that are not from Radio Shack and they are rated for 100ma. I'll poke around some more to see if I have any non-Radio Shack 3mm LED's laying around....

Thanks!

Found another LED from a buddy that is not RS and is even smaller than the one I had. Doesn't have the specs on the LED so the draw is unknown. Same thing.

Brought the boards over and installed in the machine. It plays as long as there is no LED on the blanking signal so I guess I'll just leave it off.

Unsolved Mystery.

Thanks!