Dreaded acid corrosion - Some success?????

[Retropin]

Thank you for the JK operation info... armed with this valuable information i dived back into her. Chip in question is a 74ls161 NOT a 156 as i incorrectly stated earlier. I looked up the operation for this chip ( my problem was lack of output pin15 ).
The schematics for Zac games are very confusing.. you cant read them like you would a normal schematic. On the diagram, pin 1 input has a bubble on it indicating that input should be a LO... which i have so all is OK yes??

Not quite.... data operation states that Reset Input ( pin1) MUST be high for normal operation.... if its LO then ALL outputs are set to Lo.

 

You can see why working on these machines hurts your head.

So i check my IC.... input pin1 is LO.. all outputs including my pin15 are Lo.

Now the signal coming for this is from IC19, shown as a NOR gate..... looks like 2 highs in to a LO out.... WRONG... gotta read these daigrams as a logic gate schematic NOT what the signals are.

So i start to think that maybve i shouldnt worry about whats going in too much other than both signals should be the same.
RUN comes in as a LO... but i have a HIGH.. other input is a LO.... i go through RUN cct and start testing IC11 where it originates from...

Suddenly my CPU LED burst into life... IC11 is just off where my corrosion went to.. everything here looks good, but obvioulsy its not.

OK - CPU is now booting again.... not sure how long it will last as i must have a bad connection/ chip around IC11.
While the LED is lit i test the inputs to my 74LS161 and what do you know... have oscillation at pin15 as i should and input pin 1 should be HIGH!!!

RUN is now LO.

Bloody hell, its a bit rough when you cant trust a bubble   


I take my leads off the CPU ( im bench testing) and boot her again... seems she boots straight away with no first flash.

I plug her into the game and once again all solenoids are resetting. bang.. bang.. bang.

I disconnect POWER FAILURE wire from power supply and she still boots... this is wrong

I check power failure cct on CPU and i have the capacitor C5 discharging and charging... with each discharge the solenoids fire.. also each comma section on displays flash with each discharge... but these also strobe to each comma on whole display... no numbers are displayed.

So here i am..... back to 2 weeks ago or so... but i now know why the solenoids are firing at 2hz!

[ajlaird]

Well, at least you have learnt something in the interim!

Good luck with this one, sounds like you are going to need it.

[Strangeways]

I have a feeling this thread will be as long as Rob's Pro football !

Keep at it Gav, the more you dig, the more you will find !

[ajlaird]

I have a feeling this thread will be as long as Rob's Pro football !

For Gav's sake, I certainly hope not!!

[Retropin]

Well now boys,

 I did have a cunning plan.

I did some trade off business with a pinball fellow for a completely working Zaccaria CPU board that i was going to rejumper and slot right in to get my game working.
Deal was struck... board to be posted.

Board has never arrived and im now having trouble getting any reply to my messages.

If i have to fix up the one i have, this thread will go on for bloody ever! I want to nip it in the bud with the new board... problem is that i need the board!

[Retropin]

Pro Football thread this aint!

Update on this... I eventually sourced another board guaranteed 100% working. Well the CPU booted but the board itself was not 100% working.
I have several problems with this machine.

Flipper relay does not pull in and so ground is lost.. i can activate flippers by bypassing the relay at the power board connectors...
I also have several solenoids that do not fire.. they have power to coils and work in test mode but not in game mode. Is a bit hard to determine whether this is a CPU or Driver problem... if its a driver fault then i have all three 4724 IC's failed.. this is very unlikely and so the CPU gets tested.

I downloaded a test Eprom from Flipperfan here....http://www.flipper-pinball-fan.be/

I find that this site has quite a bit of usefull stuff on it that cant be found anywhere else.. also includes an ATARI repair guide .. something that is pretty hard to come by.

Anyway, Beaky burnt me the test Eprom ( many thanks mate )... in fact twice!

Today whilst both young kids were asleep i quickly tested the board... flipperfan's instructions can be a bit scratchy, but you can work out whats meant to be going on.He tells you to test only 3 outputs to IC38.. but there are 8 on this chip and all are used so i tested them all. Glad i did cos at pin 9 CN10 i have no output signal.

This goes back to IC38 pin9 where signal is present.

This chip has been replaced on this board and a socket installed also. Zac games can be tricky to work on as the tracks lift with too much heat, plus i find that the joins between the solder pads and traces are very easy to break... too much heat and this will give way... too little and it snaps.

For this reason ALL repairs MUST be buzzed out before being installed back into the game again. The output of this IC ( my dreaded 3081 transistor arrays) cannot be tested as they are open collector and so current must pass for the output to be tested. Without a test Eprom, all you can do is replace this chip in the hope that it will rectify your fault... if it doesnt, its easy to assume that all is OK here.
The Eprom identifies a signal missing.
A quick check on schematics reveals that this output is ROW 7 for solenoid contacts... Ok is looking promising!

But then the kids ( well one of them) woke up and so my work stops there.
When i get the chance, ill fix the broken trace and install the board.. may well have the solenoids firing.... maybe flippers too?

Im getting closer to having this sucker nailed!

[63wizz]

Good work mate, my Time Machine has decided to stop working, it keeps resetting, most likely acid damage on the CPU, i have taken the CPU board out and treated it with Vinegar and am waiting for it to dry and will re install it to see what happens.
I hope i dont have to start an epic thread like this to resolve my problem

Ian 

[Retropin]

Good work mate, my Time Machine has decided to stop working, it keeps resetting, most likely acid damage on the CPU, i have taken the CPU board out and treated it with Vinegar and am waiting for it to dry and will re install it to see what happens.
I hope i dont have to start an epic thread like this to resolve my problem

Ian 

Im getting a feel for these boards now and the logic is starting to gel a bit.

My find with these is that they are prone to the same problems that GTB system 1 and 80 is... ground sucks on these!

To get ground, the boards rely in the pads at the back of the mounting screws... get these dirty or a loose board and ground will keep dropping in and out.. this will cause resetting.
Ive soldered a grounding strap to the trace on the CPU... the other end of this has an earth mounting lug on it that goes to grounding strap mount at bottom of header... ive done the same to driver etc... all now go to "true" ground.
Also a resetting MAY be the power failure cct playing up... does the game boot OK? Or does it take a couple of switch ons to get her going?

If so - look at the capacitor C5, diode D3 and resistor R34... this is the delay cct at start up and allows the voltages to settle before CPU boots. One of these components goes out of spec and it will interfere with the 5V logic to CPU.

If game keeps resetting then CPU is booting... with battery corrosion the prime symptom would be lack of CPU running

[dj10555]

Hi Gavin,

the 3081 can be tested with a meter on diode test.Hope this helps.


From Pinrepair.com
Now we need to test the chip that drives the diode and driver transistor. This chip is a CA3081 (NTE916) transistor array. Basically it's several transistors packaged in a chip format. This is known as the "pre-driver transistor pack". You can test this too:
Turn the game off.
Remove the Solenoid driver board from the game.
Put your DMM on diode setting.
On the component side of the board, put the black lead of your DMM on the GND test point just to the left of the U1 chip.
Put the red lead of your DMM on the two pins of the pre-driver chip (one at a time) that you noted above.
For the pin that connects to the 1N4004 CR diode, you should get a reading of .1 to .2 volts.
For the other pin, you should get a reading of .7 to .8 volts.
Reverse the DMM leads (red lead now on GND). You will get the same .1 to .2 volt reading for the pin that connects to the CR diode. The other pin will read 1.1 to 1.3 volts. Note this test is far less conclusive than the first test with the black lead on GND.
If you get any other meter readings, replace the pre-driver CA3081 (NTE916) chip.

regards Derek