“Ensure that there's not simply a problem with Q2 or the LED itself (i.e. the board isn't actually booting up anyway, just with the LED locked on). A logic probe on pin 18 of the U11 6821 PIA will tell you if the LED signal is changing.”

I put a logic probe on pin 18 of the U11. The probe showed LOW – No pulse. To me, that shows the signal is not changing.

Then I checked a working MPU and got the same reading, LOW – No pulse.

What should the logic probe be showing on pin 18?

Thanks

Bob

#2 3 years ago

ZAC

zacaj

RPC

Rochester, NY

11y 158K 10,388 85 122 1

The led is connected to pin 39, not 18.

#3 3 years ago

AMS

barakandl

nvram.weebly.com

12y 132K 10,420

That is a typo / mis read of the schematic.

Lamp interrupt (mpu200 speech busy) is U11 P18.

Lamp strobe 2 (u11 p39) doubles as the diag LED. When the signal is HIGH it turns on the base of Q2 which lights up the LED. When signal is LOW the LED is off. In attract mode most games (sans like F2K and maybe a few others stern talkers) the signal will be pulsing and the LED is dimly lit. Probably pulses at 120hz with each zero X cycle.

#4 3 years ago

RAP

oldschoolbob

Pinside member

Collinsville, IL

10y 111K 1,778 2

Is this a typo also?

OP
Quoted from oldschoolbob:
the board isn't actually booting up anyway

Should that read IS actually booting up?

#5 3 years ago

ZAC

zacaj

RPC

Rochester, NY

11y 158K 10,388 85 122 1

I think that should read "the board is actually booting, just with the led locked on"

#6 3 years ago

RAP

oldschoolbob

Pinside member

Collinsville, IL

10y 111K 1,778 2

Can this be fixed? It's fine for you guys that know your way around the MPU but for dummies like me that go to PinWiki for answers it's really a problem. I put all my trust in PinWiki.

BTW I tried U11 Pin 39 and the probe goes low / high with the flash of the LED. Thanks for the lesson.

Bob

#7 3 years ago

PIP

Quench

Pinside member

8y 114K 8,041

OP
Quoted from oldschoolbob:
Can this be fixed?

Calling ChrisHibler

#8 3 years ago

237

slochar

Pinside member

7y 86,550 6,915

If the board boots but the LED stays on it's usually Q2 being bad.

#9 3 years ago

TOX

ChrisHibler

Chris' Pinball Repair

Chesterfield, MO

12y 120K 9,997 46

Thanks for the page @quench.
And thanks for pointing out the typo @oldschoolbob.
I think that error was probably the result of trying to read the craptastic Bally schematics.
Pin number correction made, and wording improved substantially.
Thanks all.

"Ensure that Q2 and the LED itself are working properly (i.e. the board may be booting but the LED provides no indication). Pin 39 of the 6821 PIA at U11 drives the LED. Probing pin 39 and finding it pulsing indicates that the MPU is booting (or at least partially booting) and that R28 (8.2K), R29 (470), Q2 (2n3904), or the LED itself has failed."

--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact ... for board repairs
http://www.PinWiki.com - The Place to go for Pinball Repair Info

#10 3 years ago

RAP

oldschoolbob

Pinside member

Collinsville, IL

10y 111K 1,778 2

Thank you Chris for correcting the PinWiki. That website is such an important place for anything pinball and you do a very important service for all us. I would be lost without it.

And thanks to Quench for contacting you.

Bob

#11 3 years ago

TOX

ChrisHibler

Chris' Pinball Repair

Chesterfield, MO

12y 120K 9,997 46

My fellow authors and I humbly thank you. I’m glad that folks find it useful.
—
Chris Hibler - CARGPB #31
Http://chrishiblerpinball.com/contact
http://www.PinWiki.com/ - The new place for pinball repair info

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