Guess what… CORVETTE

[Spandangler]

I am quite literally at the end of my rope with this game.
I literally just metaphorically put the cherry on the top by fixing the pop bumper lamps and installing a switch which was missing to finish (apart from the gate coil) this four year project which has fought me at every turn.

So the start up procedure on this game everytime is. LT5 motor test. Moves side to to side and finds its self.

Then, the racetrack test. Blue car up to the top, red car up to the top, both cars return home.
Thats it booted and ready to go.

This time, the LT5 only did half its test and the racetrack motors kicked in but the cars didn’t move so I assume it was the reverse motors, then it stopped.

Now’s here’s the strange thing.
If I go into test and test each mech individually, they both work perfectly and pass test. As soon as I come out of test and shut the coin door, it goes nuts.
Sometimes the kites spin up to a really quick rpm, way faster than normal.
Sometimes the racetrack test overlaps with the LT5 test. It’s all over the place.

If I unplug the motor board under the playfield it boots normally with the LT5 test.

Then just now, with it all plugged it in, it booted normally with both mechs passing test.

No acid damage on the cpu board.

It has to be logic cpu based right? Or could it be the little motor board underneath?
Ribbon cables!! I dunno. What I do know, is I’m about to pour petrol over it

 

[Moonraker]

Replace the cap on the 12 way opto.

 

[Moonraker]

And repair any damaged tracks.

 

[Spandangler]

The opto board you say!!!
It’s a ten opto board on this, if it makes any odds

Now. Far be it from me to challenge a man of your calibre on such matters,
But my brain can’t fathom how they’re connected.

I have no switch errors and everything works in test fine.

It boots fine on switch on but any subsequent reboot, like exiting the test menu it fails and goes silly.

I did however make a hash of repinning the top ribbon header pins on the slave board in the backbox and lifted a track then. I did repair it but could that be an issue?

 

[Moonraker]

I'd cut down on number of potential causes of switch issues, opto or not.

Other suggestion is to leave it sitting in switch test for 15+ minutes to see if anything is happening to the switch matrix. Then try thumping the playfield to see if vibrations are activating any switches....

Also check active switch match those listed in the manual.

 

[Spandangler]

I don’t have any switch issues mate. I’m confused sorry . Doesn’t take a lot

Granted I’ve posted a few threads lately on corvette with switch issues but they’re all resolved now.

 

[Spandangler]

Video showing the issues. They differ each time. It’s all over the place

 

[Moonraker]

The problems you are talking about sound very much like potential switch problems to me.... LT5 only half working and race track motors kicking in/out at random or at the wrong time.

 

[Spandangler]

The switches in the motor and racetrack aren’t powered by the 10 opto board. They’re all fine. And it works in test, it’s just on reboot. So strange. And it just started doing it all of a sudden .

 

[drhex]

Might be the motor board, there is quite a bit of logic on it. Are the cables from CPU to motorboard and to the slave board ok? Check your repair and repinning. Follow @Moonraker advice on thumping the playfield and seeing if any switches or motors activate otherwise. The new switch you put in is cabled correctly and not inadvertently closing on vibration?

 

[Spandangler]

if I unplug the motor board the LT5 still fails test on boot up.
Is the master board in the back box used for both the motor and the racetrack? Or is it purely for the LT5? It was that board which I replaced the top ribbon header pins and lifted a trace on.

The switch I was fiddling with before it happened to start this behaviour was a ramp micro switch. It was missing so I just installed it.

I’ll do as advised and report back
Thanks

 

[Spandangler]

Just a quick test while I had two mins.
Powered on with dmm on 12v test point.
Immediately went to 11.90v and no drop at all during startup.

Switch test. Banged and rattled the playfield and cabinet. No activations.

Unplugged LT5 then powered on. Racetrack still misbehaving.

Both mechs work in test.
It’s is quite literally only happening during a reboot and start up test.

 

[Ragnar1057]

I'm not familiar with this machine so apologies if I'm way off the mark - but I've seen similar issues on other machines if the start position of something 'movable' isn't correct. It will pass test when the moveable object goes through its range of movement - but fail during power on self test if the moveable object is not in the correct position initially.
I found this addendum on ipdb.org - https://www.ipdb.org/files/570/Bally_1994_Corvette_Manual_Amendment_16_9890.pdf
It details a setup/adjustment procedure for the centring potentiometer for LT5 that may be relevant to your problem. Again, apologies if I'm barking up the wrong tree.
Good luck

 

[Spandangler]

Thanks mate. I’ve read through that pinwiki.
It could be that!! I’m going to try another driver board from my wh20 to see if it changes anything

 

[Wayne J]

I'm not able to offer any specific advice, BUT.

If the problems only started once you fixed/added the missing switch, try disconnecting removing it and seeing if the problem still exist.

If nothing else it will mean you can be assured that the issue isn't related to that switch in any way, as bizarre as it may seem.

 

[Spandangler]

It occasionally muddles through its start up test sequence (completely out of sequence and drawn out) and when it does you can play a game flawlessly. The engine revs and shakes like it should, the cars move along the track as they should.

It’s funny, it throws a credit dot immediately when it’s going to fail, like it preempts it.

 

[Ragnar1057]

Do you have another RAM chip for the MPU board (in case of a faulty location) or a different game ROM to try?

 

[Spandangler]

That’s my next step. I’ve got an old Rom but I mangled the legs when I extracted it last time. I’ve straightened everything out. Just waiting for some friends to leave and I’m trying it straight away

 

[Ragnar1057]

Another thought comes to mind. Given the random nature of the problem, have you had a good look at the 5V supply?

I know there is a test point on the power driver board - but I think I'd be checking it out on the MPU board directly.

I believe the MPU supervisor circuit (MC34064) is designed to kick in somewhere around 4.5-4.7V - and TTL logic has a supply range specification of 4.75-5.25V.
It is just possible that the 30 something year old MPU board logic could be misbehaving if the 5V is around (or beneath) the low end of this range - even if it isn't yet low enough for the supervisor circuit to kick in and trigger a game reset.

 

[Spandangler]

Thanks mate

So, I put the old Rom back in. No change.

I put the driver board from wh20 in corvette. First boot it misbehaved as normal but did its random thing of doing tests out of sequence and eventually passed allowing it to boot without error.

The next few times I’ve power cycled the game it’s behaved.

I’ll continue to test and leave it to soak for a while.

If it behaves then I think we can assume it’s the driver board.

A suggestion from Sir Squires is if BR5 is failing it could cause issues with the 12v line.

So I will replace that anyway whilst the board is out.


Thanks for all the suggestions. Keep em coming just in case


Edit: spoke to soon. No change no change ffs

 

[Ragnar1057]

12V was a reasonable thing to check out as the 12V is used by the switch logic on the MPU board.
I'm just curious, how are the old power driver board power supplies (12V/5V) looking when you measure them?

I've worked on a few power driver boards lately where problems were caused by an aging capacitor (C4). I don't know if you have an LCR meter handy to check it out - but many of the ones I've replaced lately were actually reading about 20-30uF instead of the rated 100uF - and their resistance was pretty horrible too.

 

[Spandangler]

I’ve booted it on with the dmm attached at the 12v and 5v test points and the voltage is bang on straight away.

Just now I started a game after a seemingly incomplete test check on the LT5. It certainly wasn’t correct but it passed test and I started a game.
It went nuts. Spat 2 balls out. Engine revving wildly, dmd displaying all sorts, tilts the lot.

I power cycled the machine and it booted fine and tested fine.

I starting to suspect ribbon cables. But which ones!!!
I have a spare set but Corvette has two extra ribbons. An extra long one between the motor master and slave (brand new), and one between the cpu and the motor master board. I don’t have spares of this

 

[Ragnar1057]

I can get you spare ribbon cables if you need them - but I won't be able to post them until Monday I'm afraid.
If you have another machine - you could always loot a set just for testing purposes.

Another problem I had recently with a power driver board was a tarnished ribbon cable connector (J113). This is the short cable that links the power board to the MPU board. The symptoms were similarly strange. The weird thing was that it was unreliable when fitted to one of my pinball machines (as well as in the customer's pinball machine) - but worked perfectly on my bench testing setup.
Finally, I realised that these tarnished pins were not making reliable connections to the old ribbon cable in my machine - but were making good connections with the new ribbon cable on my bench test setup. I changed J113 and the problem went away - with both new and old ribbon cables.

I'm not suggesting that J113 is bad in your case, but I now make a point of inspecting all ribbon cable PCB connectors for tarnished surfaces - and replacing those that look suspect. It might be worth looking at.

 

[Spandangler]

Thanks mate. I have spare ribbon sets but the longer one for the mpu to motor Master is one I don’t have spare.
The pins look nice and shiney.
I have a spare cpu winging its way in the post. But I’ll need to swap the asic chip into it, which I’m not keen on doing!

If the new cpu doesn’t work I’ll be putting the machine in the car and driving over to @Jmac to try the motor boards and slave boards from his. He doesn’t know that yet though

 

[Ragnar1057]

I've sent you a direct message.
Be careful with those ASICs - they can be tricky without the right tools.

 

[Jmac]

Thanks mate. I have spare ribbon sets but the longer one for the mpu to motor Master is one I don’t have spare.
The pins look nice and shiney.
I have a spare cpu winging its way in the post. But I’ll need to swap the asic chip into it, which I’m not keen on doing!

If the new cpu doesn’t work I’ll be putting the machine in the car and driving over to @Jmac to try the motor boards and slave boards from his. He doesn’t know that yet though

Gaz if you have room for it I can just send the pin to you for a while until you get your gremlins resolved. Drop me a text and we can do whatever suits you

 

[Spandangler]

Gaz if you have room for it I can just send the pin to you for a while until you get your gremlins resolved. Drop me a text and we can do whatever suits you

You’re a legend Jon. I’ll see how I go after swapping the cpu.
If i do take it, I’ll drive over and swap over Mousin or something

 

[David_Vi]

I was going to suggest pushing on or reseating the ASIC. I had weird issues with WCS occasionally and it was the ASIC.

If you try my old mpu you'll have to put an ASIC in it, I believe Thomas has sent an ASIC puller with it.

 

[Spandangler]

I was going to suggest pushing on or reseating the ASIC. I had weird issues with WCS occasionally and it was the ASIC.

If you try my old mpu you'll have to put an ASIC in it, I believe Thomas has sent an ASIC puller with it.

I’ve done that mate.
I’m so excited by the prospect of removing the asic, I’m not sure I’ll sleep

 

[David_Vi]

I found it less stressful than removing a rom. With the right tool it's ok!