(Topic ID: 335797)

Flash system 6 mpu blanking signal

By dmartin244

11 months ago


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  • 36 posts
  • 9 Pinsiders participating
  • Latest reply 10 months ago by joetechbob
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#1 11 months ago

Hello all,

Working on restoring a Williams Flash with a system 6 mpu.

Here's what I've done and/or checked:

1. Power supply voltages all check out fine. Large cap replaced.
2. 40 pin interconnect has been replaced
3. New green rom set and new sockets for each
4. mpu led's flash when game is turned on and then the led's turn off

GI works but I have NO feature lamps or displays. The blanking signal voltage at TP4 is 114 volts!!! I've checked pin 37 of the interconnect and it's also 114 volts. I've replaced IC23 thinking that might be the culprit but no change, voltage remains the same at 114 volts.

Any ideas on what might be causing this? I know it's supposed to be 5 volts and I'm guessing that the high voltage is the reason I'm not getting displays or feature lamps.

Thanks in advance for any help...

Dave

#2 11 months ago

If the onboard dual LEDs come on and then go off at power on, then the 6802 is operating. If it were being subjected to 114VDC, it would have been roasted in the blink of an eye.

The board doesn’t receive that kind of voltage and it can’t be made on the board.

Measure again.
Let’s see a pic of the meter and reading.

Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
Thank you for checking out the PinWiki - http://www.PinWiki.com/

#3 11 months ago
Quoted from ChrisHibler:

If it were being subjected to 114VDC, it would have been roasted in the blink of an eye.
The board doesn’t receive that kind of voltage and it can’t be made on the board.

Thanks Chris. Exactly my thoughts hence why I’m so confused. I’ll post a video this evening to show the meter reading.

Dave

#4 11 months ago

Keep in mind blanking being low is almost always a symptom of a locked up MPU, not the cause of it being locked it.

Blanking is a protection that keeps things turned off it the computer is not running properly.

#5 11 months ago

ChrisHibler So here is the picture of the meter reading. I’ve measured this ten times now and am doing it the same way as the incoming voltages on the mpu which all measure good.

Any thoughts?

Thanks again

Dave

IMG_4165 (resized).jpegIMG_4165 (resized).jpeg
#6 11 months ago
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#7 11 months ago

Those are millivolts. The mv symbol gives it away.

#8 11 months ago

Doh! I see that now. Well don’t I feel dumb. I guess that’s what happens when the reading is too low. At least now I know what direction to head with the repairs. Thanks!

Dave

#9 11 months ago
Quoted from dmartin244:

Doh! I see that now. Well don’t I feel dumb.

Don't. We all start somewhere. I guarantee you're better equipped now having had this experience.
As barakandl mentioned above, lack of blanking is almost never caused by a failed blanking circuit.
The blanking circuit is doing it's job buy preventing the software from driving the hardware into a possibly damaging condition.

The blanking circuit that Williams used (and DE too) remained unchanged from System 3 all the way to System 11.
A 555 timer is configured as a "missing pulse detector", with a specific "time out".
I've added info about the blanking circuit into the PinWiki Data East section. You can find it here to use as a reference:
https://www.pinwiki.com/wiki/index.php/Data_East/Sega#Blanking_Signal_Stuck_Low_or_Pulsing

For your System 6 MPU, the "reset" pulse to the 555 timer originates at IC18, pin 4.
IC18 is the PIA that is in the display section.
If that PIA isn't being updated so that it pulses pin 4 within the "timeout period" of the 555 timer, then blanking will be pulled low.

It's a virtual certainty that the microprocessor isn't running.
Why? There are numerous reasons. We always start with the basics first.

1. ROM images correct
2. Power correct
3. Reset signal (s/b low, and then high a split second later, sometimes hard to see with a logic probe)
4. Clock signal (the input at pins 38/39 to the 6802 can't be seen with a logic probe. But, the output clock, pin 37, can. Assume the clock is good if pin 37 is pulsing)
5. The "8T" bus buffers at IC3, 4, 8, 9, and 10 are working. These are easy to test with a logic probe. What goes comes out of the output side should always match what comes into the input side.
6. Any craptastic "scanbe" sockets replaced. This goes for any socket that doesn't tightly grip the chip legs.

That should get you started.
Press on soldier.
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#10 11 months ago

I see that the scanbe sockets have been replaced. Good.
I also see an AMI 6810 memory chip. AMI chips are always to be suspected.
You can test 6810 with the NeoLock SRAM tester, try it in a known working board, simply replace it, or use Leon's ROM which has the ability to test memory.
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#11 11 months ago
Quoted from dmartin244:

Doh! I see that now. Well don’t I feel dumb. I guess that’s what happens when the reading is too low. At least now I know what direction to head with the repairs. Thanks!
Dave

You can press the RANGE button on your multimeter to take it out of millivolt range. FYI

#12 11 months ago

ChrisHibler thanks for the encouragement. Pressing on! Here's what I've found working on the board today:

1. ROM images correct ** bought some new green roms. I'll have to pull a working sys6 mpu from my gorgar to check to make sure the roms are working correctly. I don't really have another way of testing the roms
2. Power correct ** all power inputs are good coming in to the mpu
3. Reset signal (s/b low, and then high a split second later, sometimes hard to see with a logic probe) ** not sure where or how to check this exactly but if at TP8 with a logic probe it starts low when game is turned on and then goes high a split second later.
4. Clock signal (the input at pins 38/39 to the 6802 can't be seen with a logic probe. But, the output clock, pin 37, can. Assume the clock is good if pin 37 is pulsing) ** pin 37 is pulsing "low"
5. The "8T" bus buffers at IC3, 4, 8, 9, and 10 are working. These are easy to test with a logic probe. What goes comes out of the output side should always match what comes into the input side. ** these were checked with logic probe and all appear to be correct

Also to note, I've tried 4 different 6821 at IC18 and get the same results every time. Someone else installed a new socket there at one time so this makes swapping out much easier.

-Dave

#13 11 months ago

It also appears that the Roms are correct. Put them in my working Gorgar mpu and all so good. The flash booted right up and I could play a game

-Dave

#14 11 months ago

You can attempt to run the built in memory test by opening the coin door and pushing the diag button on the MPU. Both red MPU LEDs should blink twice if no error is detected. If one or both come on solid and error has been detected.

That test has a bad reputation because when the cpu is totally locked up it can give random results, but it is pretty reliable as long as it boots up enough to get to the test program. So run it a few times and see if it reports the same error. Compare to your working sys6 game if you are unsure about the behavior of the LEDs. Coin door must be open it will report the 5101 is bad.

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#15 11 months ago

Performed the test. The LED’s blink twice and then stay off. According to the chart it’s passing the test. Does thi

#16 11 months ago

I performed the test. The leds blink twice, and then both of them stayed off. I assume this means it passed the test and there’s something wrong with the blinking signal circuit itself?

#17 11 months ago
Quoted from dmartin244:

there’s something wrong with the blinking signal circuit itself?

Quoted from barakandl:

Keep in mind blanking being low is almost always a symptom of a locked up MPU, not the cause of it being locked it.

Quoted from ChrisHibler:

As barakandl mentioned above, lack of blanking is almost never caused by a failed blanking circuit.
The blanking circuit is doing it's job buy preventing the software from driving the hardware into a possibly damaging condition.
The blanking circuit that Williams used (and DE too) remained unchanged from System 3 all the way to System 11.
A 555 timer is configured as a "missing pulse detector", with a specific "time out".
I've added info about the blanking circuit into the PinWiki Data East section. You can find it here to use as a reference:
https://www.pinwiki.com/wiki/index.php/Data_East/Sega#Blanking_Signal_Stuck_Low_or_Pulsing
For your System 6 MPU, the "reset" pulse to the 555 timer originates at IC18, pin 4.
IC18 is the PIA that is in the display section.
If that PIA isn't being updated so that it pulses pin 4 within the "timeout period" of the 555 timer, then blanking will be pulled low.
It's a virtual certainty that the microprocessor isn't running.

#18 11 months ago

I'm obviously missing something "obvious" here. So if not the blanking circuit and everything else is checking out, where to look next?

So if the diagnostic LED test passes and the board seems to be booting as it should (LED's blink at power up and then turn off), what is failing?

Checks out so far:
Driver board
ROMS
diagnostic led test
proper input voltages
reset working

I should note that pin 4 on IC18 does not "pulse" with a logic probe when the game is turned on. I don't know if this tells me anything but thought it was worth noting because of one of the earlier comments.

Thanks for all the help so far. I feel like I'm at least getting closer.

-Dave

#19 11 months ago
Quoted from dmartin244:

I should note that pin 4 on IC18 does not "pulse" with a logic probe when the game is turned on.

The 555 timer will time out and blanking will be pulled low if pin 4 doesn't pulse before the timeout period.
Make sure that IC18 is both connected correctly to the data lines AND it is receiving the chip enable signals at pin 22, 23, and 24
Pin 21 is read/write
pin 34 is reset and should follow the reset signal present at the 6802
The clock signal should be pulsing at pin 25
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball
http://www.PinWiki.com - The Place to go for Pinball Repair Info

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#20 11 months ago
Quoted from dmartin244:

I'm obviously missing something "obvious" here. So if not the blanking circuit and everything else is checking out, where to look next?

Sorry. I generally try to nudge people in the correct direction rather than being explicit about it. It is much more rewarding when you figure it out for yourself (with or without a nudge) than to be pointed directly. Some people don't care for it and prefer to be given the fish rather than learn how to fish. I can never tell but always default to thinking that people would rather learn how to fish. If you didn't want to learn then you should just pay a repair technician to fix the board.

Quoted from dmartin244:

So if the diagnostic LED test passes and the board seems to be booting as it should (LED's blink at power up and then turn off), what is failing?

Plenty of things could be failing. That's the diagnostic challenge. Finding where the failure is. If you expect someone to say "I've seen this before and it's obviously this" then you should send the board out for repair. Think of a non-functioning board like presenting to your physician with "I have a headache". If your physician says "I've seen headache before and it must be a migraine" then go find another physician. There are a myriad of causes for headache from simple stress to metastases. It needs to be investigated.

Quoted from dmartin244:

I should note that pin 4 on IC18 does not "pulse" with a logic probe when the game is turned on. I don't know if this tells me anything but thought it was worth noting because of one of the earlier comments.

The pin will only start pulsing if the software is updating the display. I believe this happens during the ISR. PA2 of the display PIA is part of the 4-bit number for the digit strobe. The software has to strobe all 16 digits to produce the correct result on the display. It must strobe then CONSTANTLY. Hence, the software must be executing.

Your board falls into the category of "no boot" at this stage. You might think it has started as the LEDs blink. That's true. It does execute software. It just doesn't execute the main loop of the software. The processor works. It is either reading the wrong code to execute or the code is reading the wrong data and executing incorrectly due to the invalid input. Unless you put a hardware debugger on the processor, you won't be able to find out what the software is doing. It actually doesn't matter. Your board does not work properly.

Somewhat related, the thread @ https://pinside.com/pinball/forum/topic/i-fried-my-system-11-cpu-board-now-what describes a diagnostic and methodical way to process these boards. The cause for the circumstances are different but the net result is the same. Your board doesn't work.

My suggestion for the next step is to use the Leon to ensure that all the PIA ports are operating correctly. Make sure that you test the input port of the switch PIA as well. Right now, you don't know if the PIA is behaving incorrectly and causing the software to "crash" which results in the enabling of the blanking circuit.

#21 11 months ago

Thanks for the more thorough explanation(s). I’ve been fixing pinballs for over 20 years but one thing I’ve never been great at is understanding circuit boards and processors. I can desolder/solder with the best but the circuitry isn’t my strong suit. I’d rather “fish” so I can learn so I do appreciate where you’re coming from.

I’ll take what’s been given here and do some more probing, etc. I do believe the problem lies somewhere around IC18

Thanks again

-Dave

#22 11 months ago
Quoted from dmartin244:

I’ll take what’s been given here and do some more probing, etc. I do believe the problem lies somewhere around IC18

When dealing with boards, always suspect prior work. Even your own. In your image above, it looks like someone has done some work with IC11 - the switch matrix PIA.

If you want better advice, post a well illuminated and in-focus image of the boards. Both boards. Both sides.

Otherwise, start probing around. Use the schematics as a guide as to what should be connected to where.

#23 11 months ago

At Chris’ advice above I did probe all the data lines and the chip enable signals. All connected as they should be, buzzing from pin to pin. I’ve got matching signals at the resets. The clock signal is pulsing at pin 25. Next step tomorrow is to take a closer look at prior work, that’s good advice. I’m also grabbing Leon’s test rom from a local friend to start working with that.

Thanks

Dave

#24 11 months ago

Leon's test ROM should be illuminating.
It has a memory test also. It is said that it isn't a comprehensive memory test, but it's probably good enough.
Pin 4 of IC18, with a properly working MPU, will pulse with Leon's test ROM.
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#25 11 months ago

Leon's ROM only tests one (or a few addresses) depending on version, so it is more of a chip select and bus test but sure good enough, since most RAM failures are chip-wide and very seldom in just a single bit.

#26 11 months ago

It passed the memory test if both leds blink. At this point likely to be a PIA issue or maybe interconnect issue. Leon test rom would be helpful to see if the PIAs toggle. I wouldn't be surprised if you find one PIA not doing anything during Leon test.

As someone mentioned before, always suspect and double check previous rework. AMI PIAs are pretty notorious for going bad on this this system if you have any.

1 week later
#27 10 months ago

Well I finally got the Leon’s test rom and had some time to work with it. Here’s what I found. I am testing with cpu in game with only the power input connector installed and relevant fuses pulled from power supply. Power on and LEDs flash like they are supposed to on/off. IC18 Pins 2 thru 17 are alternating high and low with logic probe. Pin 19 pulses low only (no alternating to high). Pin 39 is also alternating high/low.

I’m looking into pin 19 next as I assume there is an issue there as my research tells me that should also be alternating high/low

Thanks

Dave

#28 10 months ago
Quoted from dmartin244:

Well I finally got the Leon’s test rom and had some time to work with it. Here’s what I found. I am testing with cpu in game with only the power input connector installed and relevant fuses pulled from power supply. Power on and LEDs flash like they are supposed to on/off. IC18 Pins 2 thru 17 are alternating high and low with logic probe. Pin 19 pulses low only (no alternating to high). Pin 39 is also alternating high/low.
I’m looking into pin 19 next as I assume there is an issue there as my research tells me that should also be alternating high/low
Thanks
Dave

IIRC 2-17 are the only pins you need to check

#29 10 months ago
Quoted from dmartin244:

Well I finally got the Leon’s test rom and had some time to work with it. Here’s what I found. I am testing with cpu in game with only the power input connector installed and relevant fuses pulled from power supply. Power on and LEDs flash like they are supposed to on/off. IC18 Pins 2 thru 17 are alternating high and low with logic probe. Pin 19 pulses low only (no alternating to high). Pin 39 is also alternating high/low.
I’m looking into pin 19 next as I assume there is an issue there as my research tells me that should also be alternating high/low
Thanks
Dave

Hi! But what about LEDs once the diagnostic pushbutton is pressed? LEDs indicate possible failures at memory chips.
Good to know that output pin 2-17 of PIA are pulsing H/L as per manual, but remind that the test program will be executed even if the PIA has problems so your problem is elsewhere. Follow the Leon's test rom guide to check signal with probe or multimeter

#30 10 months ago
Quoted from dmartin244:

Power on and LEDs flash like they are supposed to on/off. IC18 Pins 2 thru 17 are alternating high and low with logic probe.

This shows that IC18 (PIA ports A and B) are functioning.

Quoted from Theonlylilo:

Good to know that output pin 2-17 of PIA are pulsing H/L as per manual, but remind that the test program will be executed even if the PIA has problems so your problem is elsewhere.

Yep. The problem is not IC18.

OP: Here's a suggestion that seems to have been overlooked.

Quoted from DumbAss:

When dealing with boards, always suspect prior work. Even your own. In your image above, it looks like someone has done some work with IC11 - the switch matrix PIA.
If you want better advice, post a well illuminated and in-focus image of the boards. Both boards. Both sides.

#31 10 months ago

Thanks everyone. I should note that when Leon’s test rom is installed the memory test passes (when diagnostic button is pressed). I’ll post some detailed pictures tonight of both sides of the mpu. The driver board works just fine in two other machines so I do not suspect any issues with the driver board.

Thanks

Dave

1 week later
#32 10 months ago

Finally had some time to jump back on this board tonight. Here are some pictures. I’m not seeing anything obvious at first look probing around and under the microscope.

Anybody find any issues or anything suspect?

Thanks

Dave

IMG_4284 (resized).jpegIMG_4284 (resized).jpegIMG_4285 (resized).jpegIMG_4285 (resized).jpegIMG_4286 (resized).jpegIMG_4286 (resized).jpegIMG_4287 (resized).jpegIMG_4287 (resized).jpeg
#33 10 months ago

At the first look it seems all fine. Just one thing, check my picture. I see spurs in the red circles...
Did you follow the complete Leon's guide? Or just the memory test..
There are some other test to verify the ICs.
What can I suggest you is:
* Did you check continuity from pin to pin for every new socket installed?
* Did you perform Leon memory test with game roms installed? Maybe a fault rom could block the running program..
* Why not try a new 5101? Brand apart (AMI is known as unreliable), I had cases with good ram in test but bad in the game..
You can also use a lamp under the PCB to see any accidental solder bridge or interrupted paths

Cattura (resized).PNGCattura (resized).PNG
#34 10 months ago

@Theonlylilo
Good eye!
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
https://www.youtube.com/c/ChrisHiblerPinball - My YT Channel
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#35 10 months ago

Theonlylilo thanks for your help. I did check for continuity between all new socket pins. Nothing. Double checked the ones you pointed out also (which for some reason don’t look as bad in person as they do in the picture). Nothing there.

I’ll look at the 5101 and possibly replace it. I have to go back in my notes to see how far I went in the Leon’s test. Some of the info out there on how to perform these tests is a bit above my skill level but I’m learning, slowly. I do not have an oscilloscope but do have a logic probe. Ill also try the lamp under the board trick and see if that reveals anything.

Thank you

Dave

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