Need some help identifying diode on Mr. & Mrs. Pacman

[kralleman]

Need some help identifying diode on Mr. & Mrs. Pacman

I recently acquired my first pin, a Mr. & Mrs. Pacman, and I have some problems with it. I knew it had problems when I bought it but thought it would be a good learning experience. And so far it has. The MPU board had a leaking battery that had damaged it quite bad so I replaced the board. And I also rebuilt and bullet-proofed the power supply section of the solenoid driver board.

Next, I replaced a burnt transistor (and its related diode and resistor) part of a solenoid circuit on the solenoid driver board. This burnt transistor+diode+resistor-circuit is for the left 4 drop targets. I powered the game up again, it played well for a minute or so and then there were some fireworks from the same transistor. So... That had to be replaced again and I looked at the corresponding coil underneath the drop target mechanism. It had a burnt diode. I'm not sure it was necessary but I ordered a replacement coil. Now, here's where I am stuck. The replacement coil has a diode wired as pictured in the link below. But the original coil from my game also has an additional diode wired between the left and middle connectors that seems to be the one that went bad (see attached picture). Now I'm wondering, what diode should be here? It was burnt badly and as I tried to get it loose, it just crumbled. I tried to read the value of the corresponding diode in some other coils but I just can't make it out. The schematics says "all coil diodes are 1n4004 but I'm not sure if this one is regarded as a coil diode.

http://www.pinball.center/en/shop/p...omponents/coils/2582/coil-nb-26-1900-dc-bally

Anyone knows what diode should go there?

 

[pacmandan]

Just use a 1004 diode on it..

 

[Cmndr Brain]

I don't think there is a real difference but that same schematic page says that coil diodes are 1n4004.

 

[kralleman]

Yeah I noticed that. I wasn't sure if the broken diode actually counted as a coil diode. I was thinking that the diode between the left and right connectors was the coil diode. Maybe they both are. So either a 1n1004 or a 1n4004. If the latter works, then that's good as I have a couple of ones laying around.

Thanks for the input!

 

[Cmndr Brain]

How was that original coil wired in? Although, I believe that coil you linked to would work, here is a link to an exact replacement.

http://www.actionpinball.com/parts.php?item=NB-26-1900

 

[kralleman]

Again, thanks for the reply

I see. Hmmm.. The original coil (the one with the broken diode) does not have any wiring from the actual coil to the middle lug. The wiring from the coil only goes to the two outer lugs and the wiring to the middle lug only comes from elsewhere on the playfield (sorry I have the pinball on a separate location so I can't take a photo of this right now).

If the coil itself is the same as the replacement that I ordered (which the label implies), the only difference seems to be the lack of a middle lug and a second diode going to it. To avoid confusion, I should've ordered the one you linked to but I will probably just try to put a diode in the one I have as suggested above.

 

[pacmandan]

If it uses a second diode and lug you have to wire it back exactly the way it was or you will get strange solenoid Behavior!!! Trust me...I learned this the hard way!

 

[Cmndr Brain]

Again, thanks for the reply

If the coil itself is the same as the replacement that I ordered (which the label implies), the only difference seems to be the lack of a middle lug and a second diode going to it. To avoid confusion, I should've ordered the one you linked to but I will probably just try to put a diode in the one I have as suggested above.

That's what I would do. I don't see any harm by doing so. Since the number on the coil paper match up (26-1900, that's 1900 turns of 26awg wire) the resistance should be within tolerance. I would add the second diode (1n4004) as per the manual. Make sure you position the diode correctly. Make a loop on the added diode leg and solder your playfield wires directly to that diode. Then solder the diode to the coil. Might want to consider using some heat shrink over the leg you solder your wires to as added protection because, if the diode leg/playfield wire are too long, you might bump it and short it out.

It looks to me that the diode across the wires of the coil is a flyback diode to prevent voltage spikes in the rest of the circuit. The other diode (that is missing in the coil you ordered) looks to be probably a steering diode, so the solenoid doesn't "fire" when it's not suppose to due to being on a matrix design.

Add the second diode and enjoy your game.

 

[kralleman]

Thanks a ton for the input! I won't have a chance to work with the game for at least two weeks but will report back here once I've replaced the coil+diode.

 

[MTPPC]

..
It looks to me that the diode across the wires of the coil is a flyback diode to prevent voltage spikes in the rest of the circuit. The other diode (that is missing in the coil you ordered) looks to be probably a steering diode, so the solenoid doesn't "fire" when it's not suppose to due to being on a matrix design.

Add the second diode and enjoy your game.

The one in parallel with the coil windings is the shunting diode that sinks the generated voltage on release to ground. The one before the coil prevents a ground feedback to neighboring coils that can make them buzz.

You know the funny thing about this post is that I had this game about a year ago and don't recall seeing 2 diodes on any of the coils. I thought the one before the coil on the schematic was on the SDB.

I must say for certain that I have never seen coils arranged on a matrix. I agree with you otherwise.

Usually when a transistor blows, I look for a weak connection on a shunting diode. Transistors do NOT like reverse voltage and when a coil releases, it can create a very high "reverse" voltage for a moment.