Atari Pinball repair.

StratDoc

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Oct 7, 2018
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So I am showing AC voltage coming off the transformer that all seem within range. For the blue blue wires which are for the logic bus I am reading 11 volts. Those 11 bolts should also be present at pin 1 j9 MPU connections but are not. There is continuity between the pin 1 j9 connection and the power supply. The fuse on the power supply is also good. I am also not showing volts at the auxiliary board. All rectifiers and capacitors on the power supply have been replaced.
 
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Pinballsurgery

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Jul 21, 2011
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Great news but please forget J9 pin 1 just for now. First you need to:

1. Unplug the table and check that you have continuity from one blue transformer wire to the CR2 Bridge rectifier and the other Blue wire and the F2 holder.

2. Check F2 is good - pull it out to do this never trust fuse tests in the holder, put it back

3. Then check the other side of the F2 fuse holder, violet / black wire which should also go to the CR2 bridge

4. Plug it in switch on and you should definitely find the 11v AC from the transformer across the CR2 bridge rectifier between the Blue and Violet/Black connections. So check the DC volts across the other two Orange/Blue (+) and Yellow/Black (-) wire connections to that bridge they should read ~16v give or take. If there is no DC voltage there then either the bridge is dead or its been replaced with the wires on the wrong pins.

5. Those wires go directly to either side of C1 the 4500uF Capacitor - there are a couple of big caps so you are looking for the one with the Orange/Blue (+) and Yellow/Black (-) wire connections again

6. Check for the same voltage again across the Orange/Blue (+) and Yellow/Black (-) wire connections on Pins 3 & 4 of J21

7. Check again that the voltage is coming out of the Orange/Blue (+) and Yellow/Black (-) wire connections on Pins 3 & 4 of P21 which should be plugged into J21

8. Now you have arrived at P9 :) so check the Orange/Blue (+) and Yellow/Black (-) wire connections on Pins 1 & 2 of P9 have 16v

Here's the diagram again, we are talking about the bit in green:-

upload_2017-5-15_22-23-20.png
 

StratDoc

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Oct 7, 2018
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I checked points 1, 2, 3 above and have continuity. Each connection buzzed the multimeter.

Point 4 showed less than 1 VAC and 2 or so DC volts. I double checked the wiring and it is correct on the rectifier. I even swapped the violet/black and blue connections - these are the only two that could be missed connected as the other two orange/blue and yellow black are clearly marked + and - on the rectifier. Still no change. I pulled the bridge rectifier and checked to see if it is good and it is. Multimeter set to ohms with black lead on positive and red lead on the other two adjacent terminals results in an reading of .447. Red on negative and black lead on the adjacent legs results in a reading of .444.
 
If you have 11v AC at the two blue wires from the transformer yet only 1v AC across the blue and violet/black bridge wires on the associated bridge and you are certain that the continuity up to the bridge from the transformer is good. Then something is dragging the output down so take the orange/blue connector off of the output + connection of the bridge and check again across its blue and violet/black AC inputs as you must then get 11v AC unless the bridge is faulty. If you still only see 1v AC then remove the Blue wire and check the voltage from that wire to the violet/black wire still on the bridge which will then have to be 11v AC.
 

Moonraker

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in other words - Just disconnect P21 and J21. Then check the voltages on Pins 3 and 4. If you are getting the correct voltages then the problem is in the game, if you are not getting the voltage then disconnect ORN/BLU or YEL/BLK from C1 then check voltages again. If the voltages are back then either C1 is faulty or there's a problem with kit A020317-02 assuming it is connected.
 
in other words - Just disconnect P21 and J21. Then check the voltages on Pins 3 and 4. If you are getting the correct voltages then the problem is in the game, if you are not getting the voltage then disconnect ORN/BLU or YEL/BLK from C1 then check voltages again. If the voltages are back then either C1 is faulty or there's a problem with kit A020317-02 assuming it is connected.[
Good plan and I should have restated that you still need to have the boards disconnected but this it still jumping ahead as you still don't know if that bridge is failing under load, or there is something silly in the wiring. So either check the bridge voltages first or, when you test with Moonrakers suggestion remember that if you still have no voltage after disconnecting C1 the bridge could still be an issue.
 

StratDoc

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Oct 7, 2018
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This is great advice.

Progress, I think. I didn't have everything unplugged from the boards. I unplugged everything and now have 11vac on the blue and violet/black wires. I have no DC volts on the orange/blue or yellow/black connections. I pulled the rectifier again and it tests good - same as in post above.

An aside question, there is no ground braid in this pin so I am using the metal at the front of the cabinet for ground to test for DC volts. It doesn't look like there was every a ground braid. Is this typical of atari pins?
 
That indicates that in all probability one of the boards is dragging the 5v rail down. Follow Moonrakers suggestion now and pull P21 from J21 and check the dc across pins 3 & 4 etc. etc. my money is on the 5v circuit on the main CPU board its Zener or LM323. You should not need to use an earth for measuring just now, its the voltage across the points we mentioned that's important.

Atari pins are pretty untypical. We used to chuck away the large CPU board shields as they slowed up repairs in the arcade, pretty stupid really as then the screws and nuts which inevitably fell of the playfield dropped onto the board and shorted it out. Still we didn't care as the tables were scrapped after a couple of years. It was not the worst though as Hyperball only lasted two months as it spent more time off than on, it was lobbed off the side of the pier into a skip parked on the beach at low tide below the arcade as no one could be bothered to carry it back over the turnstiles.

The best story I know about these pins came to me from Gary Flower, he recounted entering an arcade with windows running around the room where the operator had hung the Atari back boxes about two feet above their associated tables (for the record there is no electronics in an Atari backbox, just a bulb) and run the power to the back boxes from the roof. You could play and look out of the window......
 
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StratDoc

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Oct 7, 2018
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The atari do not get any respect but I find them very interesting. For some reason I am drawn to them - was looking for a good project for a while before landing the space riders. My collection of 18 pins are all early SS 1978-1984 except for one EM and a Stargate DMD. Really like restoring part of pinball history. Thanks for the schematic as well. I had pulled it off of the internet pinball database.

Pulling P21 from J21 results in 11vac across the blue and violet/black wires. Still no DC volts on orange/blue or yellow black. I dropped in another new bridge rectifier and have the same results - ugh.:mad:
 
Right then it has to be the C1 capacitor there is nothing left as the kit mentioned previously (A020317-02) is not used in Airborne Avengers. So disconnect one side of C1 then check for DC voltage on the output of the bridge again.
 

StratDoc

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Oct 7, 2018
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The C1 is a brand new capacitor on the power supply. I replaced both of those capacitors, but will check again by removing one of the connections on the capacitor.

Any chance it is a ground issue?
 
Only if one of the wires has been misconnected :) There's only the Capacitor and the bridge after the transformer, if AC is going into the bridge from the transformer and the P21 plug is out then the bridge and the cap is all there is and as you've replaced them the only thing left is a problem with the dc side of your multimeter…
 

StratDoc

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Oct 7, 2018
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I was travelling the past 10 days so just now getting back to working on the pin. I purchased a working Atari power supply on ebay and dropped it in. Lights are still flashing and displays still flashing. Still not showing 5 volts on the MPU. What the heck.

Is it possible I am not grounding properly to check vdc? Since the atari does not have a ground braid I am connecting ground to the metal around the coin door and pf glass latch. Is there someone else I should be connecting for ground? I don't see any ground "loops" on any of the boards.



Robert
 
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StratDoc

New Member
Oct 7, 2018
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I decided to check DVC on the the two prom chips top left of the PCB. I am measuring 4.95 vdc there so I am doing something wrong measuring vdc off the power supply. I am not showing any volts on the main MPU chip that is left center of the board.

Robert
 
The voltage entering the MPU board is passed though a 5v power supply circuit which outputs across the capacitor at C34. The negative side of this capacitor is the rail for your black lead, then try measuring the voltages on those chips again.

Watch the large resistor it does get stupidly hot, especially if the board is locked up. If everything is flashing in time when it's powered up I.e all of the coils (except flippers) pulsing, lights flashing and the score displays flashing up random digits you have a reset issue with the MPU. This is good news as thanks to Leon you can get a test chip blown for a few dollars and follow this guide:
http://pinwiki.com/wiki/index.php?title=Leon_Borre_Atari_First_Generation_Repair