(Topic ID: 244053)

Evel Knievel: Bally rectifier board, bad TP3


By Brewchap

50 days ago



Topic Stats

  • 43 posts
  • 5 Pinsiders participating
  • Latest reply 16 days ago by Quench
  • Topic is favorited by 4 Pinsiders

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#1 50 days ago

I am working on a new to me Evel Knievel that I was able to power up and run a coil test with no problem. However I have ran in to a problem getting the MPU to boot. I believe that I traced down the problem to the rectifier board, test point 3, which only has 6 DC volts and needs to be 11.5 DC volts. All other voltages are correct. If I am correct, then this is my 5 volt input, and without this, the MPU will not boot.

Would anyone care to confirm if I am thinking in the right direction?

#2 50 days ago
Quoted from Brewchap:

test point 3, which only has 6 DC volts and needs to be 11.5 DC volts

Half voltage usually indicates a faulty bridge rectifier with one of it's internal diodes going open circuit. It's bridge rectifier BR2 in this case so you're on the right track.

With the machine off, disconnect the J3 connector from the rectifier board and do a diode check on that BR2 which basically has four internal diodes.
If the board is in very toasty condition you might need to resolder the bridge.

#3 49 days ago

Thanks Quench. The diode test showed an open circuit. I got some on order.

#4 43 days ago

I replaced all 3 bridge rectifier and nothing changed. I thought for sure that this would fix the problem.
Still have 6 DC volts on TP3.

#5 43 days ago

What's a diode test with your multi-meter saying about the replacement bridge?
What are you measuring at TP3 when the J3 connector (backbox harness) is disconnected from the rectifier board?

#6 43 days ago

Going by the picture

1. No reading
2. 0.475
3. 0.475
4. No reading

651px-TestingABridgeRectifierFourSteps (resized).jpg
#7 43 days ago
Quoted from Brewchap:

Going by the picture

Nice pic, you have another dud bridge rectifier. Two open circuit internal diodes, both on the same cycle.

#8 43 days ago

Test Point 3 is supposed to be 5VDC....................Not 11.5. Test point 1 should read the same as TP 3. Test point 5 is the input to the 5V regulator circuit and should read 11.5 or thereabouts.

A mod to these driver boards is to tie TP1 and 3 on the wiring side together with a jumper to improve reliability --not relying upon the connector.

What does test point 1 and 5 read on your meter?

#9 43 days ago
Quoted from minnesota13:

Test Point 3 is supposed to be 5VDC....................Not 11.5. Test point 1 should read the same as TP 3. Test point 5 is the input to the 5V regulator circuit and should read 11.5 or thereabouts.

We're talking about the rectifier board, not the solenoid driver board.

When J3 (backbox harness) is NOT connected to the rectifier board, TP3 on the rectifier board should measure around 11.9 volts.
When J3 is connected to the rectifier board, TP3 on the rectifier board will now measure between 14.5 volts and 16.5 volts thanks to the large capacitor at C23 on the solenoid driver board.

#10 43 days ago

Sorry my mix up.

#11 42 days ago

I found the picture on Pinwiki web site. Credit goes to Chris Hibler.

I measured and tested my last bridge rectifier. It tested good like it should. I installed it and powered it up. The MPU still will not boot. So I tested the BR2 again and it's bad again. Something must be shorting it out. It reads the same as in post #6

#12 42 days ago
Quoted from Brewchap:

I found the picture on Pinwiki web site. Credit goes to Chris Hibler.
I measured and tested my last bridge rectifier. It tested good like it should. I installed it and powered it up. The MPU still will not boot. So I tested the BR2 again and it's bad again. Something must be shorting it out. It reads the same as in post #6

The bridge shouldn't go bad like that and I would be surprised if two failed the same way. Bridges normally fail short circuit and blow the fuse. They can fail open circuit too... but i think they usually fail short first then burn open.

How are you testing the bridge? For testing bridge DMM on diode test. Red DMM lead to negative bridge terminal then probe to both AC ~ pins and you should see a normal 0.4-0.6v voltage drop. Then do the opposite on the other side. Black DMM lead to the positive bridge terminal and probe both AC ~ pins and you should see the voltage drop.

How about a bad driver board C23 filter cap dragging down the 12v? Can you try with the top right connector on driver board removed and see if the voltage comes up?

#13 40 days ago

Installed another MPU and the pin booted up. Thanks for the help and info!

2 weeks later
#14 24 days ago

I just replaced Fuse F4 after I found it blown, and it blow again telling me that BR2 is bad again. Is there anything that I should look for that would continue to mess with BR2 casing it to go bad? This pin has been running 24/7 for the last two weeks. Now, right before I found the fuse blown, I did find that the power cord going to the on/off switch in the cabinet, had broken its solder connection removing power from the pin. I soldered that back on and found the fuse blown.

#15 24 days ago
Quoted from Brewchap:

I just replaced Fuse F4 after I found it blown, and it blow again telling me that BR2 is bad again.

Are you actually measuring any short circuits across any BR2 pins?

Does rectifier board test point TP5 measure a dead short to ground? If yes the problem might be downstream from the bridge. Check the coin lockout coil on the coin door and make sure the green wire isn't also touching the coin door frame.

#16 24 days ago

No I'm not measuring any short across the BR2 pins like I thought that I would. I checked TP5 and didn't find a dead short, but I did measure some resistance.
I also checked the coin door and made sure that the green wire was not touching. What ever is causing the problem makes a loud hum in the speaker before the fuse blows.

#17 24 days ago

I did measure a dead short on BR3.

#18 24 days ago

Yeah sorry, BR3 is the solenoid bridge that's fused by F4.

What bridges are you using?

Are you by any chance overheating them for too long when soldering them?

#19 24 days ago

From memory, 200volt 10amp. Its possible that I'm over heating them. I did have a hard time getting the solder to flow around the pins. I got a hotter iron that I use on the playfield that I can try. Flow the solder faster might be the trick.

#20 24 days ago

Not sure if it helps, but I always solder the bridge after screwing the bridge to the rectifier board/plate, and also wait at least 5 minutes between soldering each leg.

#21 23 days ago

Good idea. I'll do that also.

#22 18 days ago

Well, I replaced BR3 (also replaced knocker and chime coils that were bad) and now all of my solenoids are locking on when I turn the pin on. What is going on now?

#23 18 days ago

I went ahead and disconnected the newly install coils, but that didn't help.

#24 18 days ago

Does it happen if you disconnect J4 from the SDB (Solenoid Driver Board)?

#25 18 days ago

I found it.....I had some transistors backwards.

#26 18 days ago

I thought that I fixed this, but it is happening again.

Quoted from Quench:

Does it happen if you disconnect J4 from the SDB (Solenoid Driver Board)?

All solenoids lock on

#27 18 days ago

I have to pull J1 and J5 from the SDB to keep the solenoids from locking on.

#28 18 days ago

No it's working again. I don't understand this. On top of this, the new coils for the chime and knocker are not working.

#29 18 days ago

Q3 and Q7 I think is for the chime and knocker

#30 17 days ago

I keep shorting out Q3 and Q7 for some reason.

#31 17 days ago
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#32 17 days ago

Please do not take this the wrong way, but the soldering is not the greatest. It's making connection, but be careful with strands sticking out like some photos show.

I always tin my wires after they are stripped by applying some solder. I also tin the coil lug the same way. When you insert your wire to the lug, just a bit of heat and extra solder and you're done.

#33 17 days ago
Quoted from Brewchap:

I have to pull J1 and J5 from the SDB to keep the solenoids from locking on.

With these two connectors removed:

* What voltage are you measuring at TP3 on the SDB?
* what voltage are you measuring at pin 24 of the U2 chip on the SDB
* Is the flipper enable relay clicking on at powerup? i.e. do the flippers always flip when you press the flipper buttons regardless of being in game over mode?

#34 17 days ago
Quoted from Quench:

With these two connectors removed:
* What voltage are you measuring at TP3 on the SDB?
* what voltage are you measuring at pin 24 of the U2 chip on the SDB
* Is the flipper enable relay clicking on at powerup? i.e. do the flippers always flip when you press the flipper buttons regardless of being in game over mode?

TP3 is 5.25 Dc volts

Pin 24 is 5.23 Dc volts. When I first touched pin 24, all of the solenoids fired at one time. Of course I jumped and lost connection. The second time I was able to get a reading from the DMM

No the flippers do not work in game over mode.

#35 17 days ago

Sorry, I just re-read your posts and you mentioned it's all working properly again. So those three diagnostic questions I asked are only relevant when the game is locking on the coils at powerup.

The only way all coils can lock on at powerup is a failure of some sort with the 74L154 chip at U2 on the SDB. I would carefully inspect the solder joints of pins 12 and 24 on that chip which is ground and 5V power respectively. Follow the connection between pin 24 to TP3 since it goes through some jumper links and carefully inspect their soldering too.

#36 17 days ago

Could that cause failure of the Q3 and Q7 transistors? I believe that is for the knocker and chime since they dont work. It seems like they fail as soon as I turn the power on.

#37 17 days ago
Quoted from Brewchap:

Could that cause failure of the Q3 and Q7 transistors? I believe that is for the knocker and chime since they dont work. It seems like they fail as soon as I turn the power on.

When do those transistors fail? At first poweron after replacement, or first activation during attract/game mode?

#38 17 days ago

At first activation upon boot up at this point. I changed to another SDB that fixed the Q3 failing, but the Q7 (chime) is still popping the transistor. Also so far no coils locking on at power up with this board.

#39 17 days ago

Is this wired right? I'll clean up the solder job in a bit.

20190701_163906 (resized).jpg
#40 17 days ago
Quoted from Brewchap:

Is this wired right? I'll clean up the solder job in a bit.

Yes, the green wires go to the coil lug where the banded side of the diode is.

If the transistor driving that coil keeps blowing, the coil diode might be shorted. Before you solder that white wire on the other coil lug, measure the resistance across the coil - should measure around 53 ohms. If you measure a dead short circuit, replace the diode on that coil. Also check that the diode is properly soldered because if one leg isn't, the transistor will always blow on first activation of that coil.

You might just want to replace the diode on that coil anyway.

#41 17 days ago

Ok I found that I had .3 ohms on the coil. I replaced the diode and measured again and had 53 ohms. I then replaced Q7 on the SDB board. At power up, the Q7 blew.

#42 16 days ago

I replaced the diode again and now it's working!

#43 16 days ago

Hmm, if you still have the diodes that were removed from the coil, measure if those diodes are shorted. The problem might actually be an intermittent short in the coil winding..

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