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(Topic ID: 207823)

Back to the Future Help :(

By the_watcher87

2 years ago

Topic Stats

  • 8 posts
  • 4 Pinsiders participating
  • Latest reply 2 years ago by the_watcher87
  • Topic is favorited by 1 Pinsider


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#1 2 years ago

Hi, hope you will be able to help me.

Bought a BTTF Data East pin back in October and I had a couple of things to sort on it. Namely new drop targets and I wanted to install an NVRAM chip. I had just been using AA batteries since I bought it.

This week the machine stopped on Monday, it would just light up but no startup sound or no way to start a game. I took the batteries out and it fired up so I assumed just flat batteries. I fitted the NVRAM chip and again fired up ok.

Today I decided to replace the drop targets, I got them fitted no problem but upon starting the machine up the pop bumpers and slingshots will not work. I had a play around inside but can't see anything out of ordinary. Then the machines went back to no startup sound? So far I have removed 3 boards from behind the backglass for a visual inspection and no burn marks or anything. After and hour of fiddling around basically plugging stuff in and out it'll boot now again but pop bumpers and slingshots aren't working.

I have checked all fuses etc and all look fine, I have read the manual and to be honest I'm a total newbie with pins so don't really know what I'm doing. I have been searching google and this is the only thing I am coming across on this site.

Flippers don't work, and Neither do the Special Coils.
The flippers do not work during game play, and all or some of the special coils (pop bumpers, slingshots) do not work either. If the fuses are Ok, check the chips at locations 12B and 12A (7402). Often the chip at 12B will fail, causing the flippers and the special coils to not work. The chip at 12B is also used to enable "blanking". If this chip has failed, often the CPU will not even boot properely.

Can anyone tell me where this 12B chip is? I am at a total loss.

Thankful for any help

#2 2 years ago
Quoted from the_watcher87:

I have checked all fuses

Does this mean you actually tested them with an ohmmeter? If not, you should.

Then is best to start with testing the voltages at the top right of the (original) power supply, 5v, 12v, -12v. This really is an important step since without them, game will not boot up if it does not have the proper voltages.

#3 2 years ago

I just visually inspected them, I can't currently find my multimeter so I'll have to go buy one tomorrow. If they do indeed all check out as well as those voltages whereabouts is that chip they talk about on that page?

#4 2 years ago
Quoted from the_watcher87:

check the chips at locations 12B and 12A (7402).

Stated there. 12B is an IC 7402. Make sure it is not 74LS02 nor 74HC02.

I actually would suggest replacing the capacitors on the power supply if it is an original DE power supply. Highly likely, you are having 5 volts issues due to capacitor failing and may even be leaking.

Also, remove CN1 and inspect for any burnt pins.

#5 2 years ago

12 B refers to the grid layout of the CPU. Numbered rows and letter columns printed on the circuit board. You will find the 7402 chip located where row 12 and column B intersect on the board.

#6 2 years ago

Found the chips, thanks guys. By the looks of things they are indeed 7402. The chips look fine front and back, I had that board out last night seeing if I could see any marks anywhere.

I've ordered a multimeter from Amazon, should be here tomorrow. Is there a way to test the chips to see if they're functioning correctly?

The power supply is the original DE one, the caps look ok but as we know that doesn't necessarily mean that they are fine. Again what's the best way to test that?

Sorry for all the questions, feel like I've been thrown in at the deep end here.

20180120_110130 (resized).jpg

#7 2 years ago

You can't check chips by "looking at them" - sorry.

You machine has simply stopped - don't overthink things and start ripping everything apart, you will make it worse.

Use your meter as suggested to measure the fuses AFTER you lift one end - don't measure them in circuit.

#8 2 years ago

I agree I am just overthinking it and dreading worst case scenario. Can't do much until the multimeter arrives really, one query though.

In that quote it says about flippers not working. Mine are?

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