Bally 2518-17 Strobe Signals stay High

Hello Pin-Gurus

I'm new to the forum.

My name is Andreas. I'm 49 years old and from Stuttgart / Germany.

After reading a while and learning many things about pins and their electronics I decided to subscribe to the forum.

Thanks for your valuable input!

A few weeks ago I startet my first pinball project.

I'm trying to bring a Power Play (MPU 2518-17) back to life. After it's many years of hibernation I'm trying to restore the pin. The MPU board had the expected problems with oxidation so i changed all headers and sockets with new ICs (U8, U9, U10, U11) after cleaning the board carefully.

It boots fine but there seems to be a bigger problem with the switch matrix. After I got several wrong (and differend) results on switch testing, I isolated the MPU from the playfield and connected only J4. Then I measured the Strobes and Inputs on J2 with a scope from PIA up to the header pins.

I got readings of very nice and crisp signals up to the anode of the Diodes. In case of ST0 the diode CR43. On the kathode side of the diodes the signals goes bad. I looks like the signal can't "discharge" fast enough. Or some other signal or potential is crosstalking and keeps the strobes on "High". Sometimes after powering up the signals on the strobes are good. But only for a few minutes the they stay high again.

I'm staring at the schematics for hours and disconect caps and resistors along the trace. But no difference.

Any ideas what can cause the signals to stay high?

ST0_error (resized).jpg

#2 5 years ago

PIP

Quench

Pinside member

Thanks for reposting here @sinus.

Can you go into more details about the switch issues you are having?
Are some switches not responding?
Are some switches activating other switches within the switch matrix?

What happens if you connect the anode leg of a spare 1N4148 diode to the anode of CR43 and measure the floating unconnected cathode leg? Do you get the same reading on your oscilloscope?

Can you post some clear high resolution pictures of your MPU board so we can see how much battery corrosion it suffered?

#3 5 years ago

SIN

sinus

Inactive member

Thank you Quench for taking up the thread.

I will come up with some HighRes pics from the board and a detailed switch matrix table with listed switch numbers showing during the test as soon as I am home from work.

So much in advance:

When I'm doing a switch matrix test even without playfield the disaplay shows me switch "1" as closed after booting up. Somtimes it shows "3".
And sometimes "0" is blinking. When this is the case I do the I/O tests by wire jumping Rows and Colums from J2 and read the Numbers from the Display.
Nealy every new test shows a different result than the test before.
One time some switches are missing completely, next time Input-Row[#1] shows same numbers as Input-Row[#0] tested before.
I can not recognize a pattern to encircle the problem at one specific Strobe or Input. The only common is that the signals stay neraly at high level so there is no correct strobing...but only from the katheode side of the diodes (as in the printout).

#4 5 years ago

PIP

Quench

Pinside member

https://pinside.com/pinball/forum/topic/flash-gordon-target-causes-tilt#post-3220692

The capacitive effect you're getting might be normal. See the second picture on this post:

OP
Quoted from sinus:
When I'm doing a switch matrix test even without playfield the disaplay shows me switch "1" as closed after booting up. Somtimes it shows "3".

It sounds like you might still have some resistive corrosion on the MPU board to deal with. It can get underneath the dip switches which can be difficult to see. The dip switches are also a part of the switch matrix.
So use your multi-meter to check it. The resistance of all the switch strobe lines and switch return lines at the J2 pin header should measure about 57k ohms with respect to ground. If you get any resistance readings that are much lower then this is likely your problem.

#5 5 years ago

WOT

Atari_Daze

Spd

Houston, TX

7y 141K 10,053 7

to the OP, Quench is an invaluable resource, heed his advise!

Check out this post when time permits, then scroll back to the beginning...

https://pinside.com/pinball/forum/topic/future-spa-father-and-sons-second-restoration/page/13#post-4655044

I'm FAR FAR less experienced but was thinking the same as Quench about corrosion thus I will second his suggestion.

#6 5 years ago

SIN

sinus

Inactive member

Atari_Daze I sure will
I'm very grateful that so skilled people in this forum like Quench are pushing me into the right direction.
I already read many of his comments helping people to get their pins running. Especially in hopeless cases.
Quench : Thanks for taking care!

Find attached some pictures from the MPU and some results of the last few days from the switch matrix testing (without playfiled, jumper wired only)
Faulty readings are marked red.

And here the readings from strobes and returns to ground as you recommended.
First measuring from ST0 arranged me to change my meter 3 times! Didn't get any better...

ST0 --> GND 1 MOhm (!)
ST1 --> GND 49 kOhm
ST2 --> GND 43 kOhm
ST3 --> GND 43 kOhm
ST4 --> GND 50 kOhm

I0 --> GND 48 kOhm
I1 --> GND 48 kOhm
I2 --> GND 39 kOhm
I3 --> GND 25 kOhm
I4 --> GND 27 kOhm
I5 --> GND 36 kOhm
I6 --> GND 40 kOhm
I7 --> GND 43 kOhm

Measured with dip swiches in ON and OFF postion with same readings.

hires_front.jpg

hires_back.jpg

South_front.jpg

hires matrix.jpg

hires matrix_back.jpg

20190412_230652 (resized).jpg

20190412_230658 (resized).jpg

20190412_230706 (resized).jpg

20190412_230711 (resized).jpg

#7 5 years ago

???

jj44114

Pinside member

Your PIA's don't look new. Try known working ones.

#8 5 years ago

???

jj44114

Pinside member

Yours look bad, date code on U 11.
And U 10 has almost no marking, Usually a sign of counterfeits.

#9 5 years ago

AMS

barakandl

nvram.weebly.com

12y 132K 10,418

infinity resistance (open) pull down resistor @ R132? In one of your picture it looks like it could be physically damaged.

Untitled (resized).png

Untitled2 (resized).png

#10 5 years ago

GPE

G-P-E

GPE

Omaha, NE

13y 76,800 2,778 4

Both Quench and BarakandI hit onto this one.
When combined with your measurement:
"ST0 --> GND 1 MOhm (!)"

Resistor R132 is open yet C79 is still good. You are seeing the small value of C79 affecting the signal waveform as seen in your first post picture.

Replace R132.

#11 5 years ago

PIP

Quench

Pinside member

Quoted from jj44114:
Your PIA's don't look new.

Quoted from jj44114:
Yours look bad, date code on U 11.
And U 10 has almost no marking, Usually a sign of counterfeits.

Those PIAs are indeed remarks from China. I've used a number of them without issue.

OP
Quoted from sinus:
ST0 -->; GND 1 MOhm (!)
ST1 -->; GND 49 kOhm
ST2 -->; GND 43 kOhm
ST3 -->; GND 43 kOhm
ST4 -->; GND 50 kOhm

I0 -->; GND 48 kOhm
I1 -->; GND 48 kOhm
I2 -->; GND 39 kOhm
I3 -->; GND 25 kOhm
I4 -->; GND 27 kOhm
I5 -->; GND 36 kOhm
I6 -->; GND 40 kOhm
I7 -->; GND 43 kOhm

Also, the low resistance readings at the adjacent signals I3 and I4 indicate they are shorted to each other, infact all those resistance readings besides ST0 are too low. It looks to me like you may have resistive corrosion under the pin headers at J2 and J3. It doesn't look like there's any corrosion under the dip switches.

If you measure the resistance across the I3 and I4 signals at the J2 header which is pins 11 and 12, you should measure about 114k ohms. All the adjacent pin signals should measure around 114k ohms across them.

U12 also has bad corrosion - when you get some time remove and clean up that area.

PowerPlay_MPU_J2_CorrosionA.jpg
PowerPlay_MPU_U12_CorrosionA.jpg

#12 5 years ago

SIN

sinus

Inactive member

Gentleman, you all were so damn right...

@barakandl ; @G-P-E :

R132 was dead. As you predicted. I soldered it out a few days ago because it was in path with ST0 I'm having trouble with. I measured it with one leg out of the bord. It read OK. And resoldered it. May be it didn't survive my soldering skills...
Took it out today. Dead resistor!
Soldered in a new one.

@quench :
One shot one dead!
Days ago I replaced the header pins on J2 as recomended in every pinball tech channel concerning Bally MPU.
I took care on removing corrosion as good as i could. But I focused only on the backside of the MPU because there were the traces to the next components...
I didn't take care too much on the front side.

As you assumed...
Today I took out the header pins from J2 again.... after measuring the pins continuity with your predicted values of shorted header pins between them... chapeau man !!!
There was realy a big amount of....greasy dusty corrosive schmuh under it....
I overhauld the J2 section. And worked on both sides against corrosion. Could it be that my first attempt of renewing header pins worsed it? I used ab bit more flux to burn the oxides away...Are the residues of flux conductive???

New readings with new resistors:

ST0 --> GND 56 kOhm
ST1 --> GND 56 kOhm
ST2 --> GND 56 kOhm
ST3 --> GND 56 kOhm
ST4 --> GND 59 kOhm

I0 --> GND 56 kOhm
I1 --> GND 56 kOhm
I2 --> GND 56 kOhm
I3 --> GND 56 kOhm
I4 --> GND 57 kOhm
I5 --> GND 57 kOhm
I6 --> GND 56 kOhm
I7 --> GND 56 kOhm

Time was running out so could not reassemble the MPU into the backbox to test it...

For now...

I'm taking my hat off! Thank you!

unsoldered_1 (resized).jpg

unsoldered_2 (resized).jpg

overhaul (resized).jpg

#13 5 years ago

PIP

Quench

Pinside member

OP
Quoted from sinus:
ST0 -->; GND 56 kOhm
ST1 -->; GND 56 kOhm
ST2 -->; GND 56 kOhm
ST3 -->; GND 56 kOhm
ST4 -->; GND 59 kOhm

I0 -->; GND 56 kOhm
I1 -->; GND 56 kOhm
I2 -->; GND 56 kOhm
I3 -->; GND 56 kOhm
I4 -->; GND 57 kOhm
I5 -->; GND 57 kOhm
I6 -->; GND 56 kOhm
I7 -->; GND 56 kOhm

Those are excellent readings now
Good luck when you plug the MPU board back into the machine and let us know how it goes.

#14 5 years ago

SIN

sinus

Inactive member

I reinstalled the board today and expected a nice starting up.
The MPU was booting correct and lights went on...but no sound from the chimes and none of the other coiles were firing...
All diaplays show static zeros on all digits.
And the board doesn't change into diagnostic mode when the test switch pin is shorted to ground.
I only had J4 and J1 connected.

Then I ozilloscoped the new J2 headers with their Strobes and Inputs.
The signal quality is so much better now.
But I wonder why the signals on all Strobes are the same pattern. Is that normal?
I expected a different pattern on each strobe.
I have no idea what could have caused this problem.
Even with the faulty signals an semi shorted header pins on J2 the the game started up an got into reday mode.

new_signals (resized).jpg

#15 5 years ago

???

jj44114

Pinside member

Maybe those “remarked” PIA’s aren’t so good.

#16 5 years ago

???

jj44114

Pinside member

I was taught step 1 in MPU repair is make sure you have known good IC's at U2 through U11, Before getting the soldering iron out. So now you have the same issues as when you started. Swap in good know PIA's. May not be the problem, but easy to eliminate those. As far as remarks go, I have gone through quite a few from China. With PIA's I found 10% DOA, about 20% die young, and about 70 good. The MPU will boot with about 90% of them.

#17 5 years ago

PIP

Quench

Pinside member

OP
Quoted from sinus:
The MPU was booting correct and lights went on...

Which lights went on? Was it just the general illumination lamps or also the feature lamps? If the feature lamps came on, were any flashing? Were they all stuck on or just some of them?

Does the LED on the MPU board flash seven times on power up to indicate the MPU board has passed self diagnostics?

If all the switch strobe signals show exactly the same waveforms then it's indicating that game execution is getting caught in a tight loop.

Sounds a little like you may have an interrupt problem possibly the display interrupt generator is running too fast.
What frequency do you measure for the display generator at pin 40 of U11? Should be around 320Hz
What frequency do you measure for the zero crossing detector at pin 18 of U10? Should be around 100Hz

The switch strobe signals (U10 PA0-PA7) are also used to address lamps and the displays. What happens if you disconnect J4 from the lamp driver board to isolate it from the U10 PAx signals?

Have you re-terminated the wire connectors that plug onto the MPU board?

#18 5 years ago

AMR

BigAl56

Pinside+ Frequent

Palatine, IL

7y 64,800 1,658

Looking at the photos of the board I see there are brown Palmer IC sockets. Those should be replaced.
I also see the PIA chip U11 does not have a socket?

If you are doing this as a hobby project, keep up and good luck. Otherwise this board is toast and I would not waste time on it.
Keep in mind the board will never run reliably with the brown sockets.

#19 5 years ago

SIN

sinus

Inactive member

@quench : The GI is going live and a bit of the feature lamps

The MPU is passing it's self-diagnostics and flashes 7 times on power up.
So I went for the signals on U11 and U10.
Pin 40 of U11 ist static at 5V. Pin 18 of U10 is static at 0V.
I overhauld header J4 because of the experiences on J2. But with minor success at this time.
Then i wanted to look for the signal from U12 and when I touched pin 7 with the probe the machine startet it's game ready tune and fired coiles and chimes...and scared the .... out of me!
You already pionted out U12. I put in a new one in today.

@bigal56 : The PIAs are in sockets. Maybe it's the perspective of the picture. The new sockets for the RAM are one the way and will be replaced.
It's a hobby project. I'm just getting in touch with pinballs and solid state electronics.

#20 5 years ago

SIN

sinus

Inactive member

A new U12 is soldered in. Everthing is O.K. now.
MPU is booting fine. Coils are all triggered one after another, chimes are playing and the strobe signals look much better know.
Tomorrow i will report a new switch matrix test. I hope for better results...

Under the culprit... And strobe signals after changing U12

ne555out (resized).jpg

new strobes (resized).jpg

#21 5 years ago

PIP

Quench

Pinside member

OP
Quoted from sinus:
Then i wanted to look for the signal from U12 and when I touched pin 7 with the probe the machine startet it's game ready tune and fired coiles and chimes...and scared the .... out of me!

OP
Quoted from sinus:
A new U12 is soldered in. Everthing is O.K. now.

Great to hear - the display interrupt generator (U12) was suspicious of causing that lockup issue.
.

OP
Quoted from sinus:
It's a hobby project. I'm just getting in touch with pinballs and solid state electronics.

Glad to see you are diving in and learning

#22 5 years ago

SIN

sinus

Inactive member