One panel light out

[Toyguy]

So before I found out about the double-sided LEDs, I had put one behind the 25C graphic between the Coin Accepted and Insert Coin lights.  It didn't work, and a known-good regular bulb also doesn't work, using the known-good bulb holder.  I am suspicious that something on the MPU has gone but I can't figure out what pins or components drive that light.  The Coin Accepted and Insert Coin lights work fine, it's just the 25C light that's out, so I'm assuming it's not a fuse.  Anyone have a clue what I should be looking at for this?
I had the MPU out and saw no obvious signs of damage, nor was there ever any smell or smoke that I could tell.


On a related note, what number bulb are they for those three lights?  They're obviously larger than the #86 button bulbs.


10MHz MPU, early S+ RWB machine.

[rokgpsman]

Did the bulb behind the 25cent sticker work before you installed the LED? If not then the problem could be a few different things. But if the LED caused a problem typically there will be a board trace that has burned open on the board where the LED was installed, and hopefully not on the mpu board. You can take out the display board where you installed the LED and look it over on both sides of the board for any damage. Was the LED you installed one of the ones that has leads on both sides of the base?
 

[sixcardmark]

On a related note, what number bulb are they for those three lights?  They're obviously larger than the #86 button bulbs.


10MHz MPU, early S+ RWB machine.

#555 6.3v work well, or use T10 6.3v LED's

[Toyguy]

Yeah, it had the wraparound leads.  I put it in a couple days ago before hearing about that problem.  It did have a working bulb but it was dim, so I put an LED in from the seller.  Little did I know..


I didn't notice any signs of damage but it could be internal I suppose.  If I can work out the connector pins and/or transistor, I can test and replace as necessary.


A related question - is that 25c light a controlled lamp, i.e. does the game ever turn it on and off?  If not, it's probably not MPU related.

[rokgpsman]

Yeah, those LED's that cause the problem put a hard short on the lighting bus and something will burn open. Sometimes it is a thin board trace on the display board that fails first and they can be repaired with a jumper. Maybe someone here is familiar with that circuit and what to check. If I remember right from the past postings folks sometimes ended up replacing that display board, but I haven't read those threads in a while. If you don't have any spare parts or another similar machine so you can quickly find out what assembly is bad then you'll want to do an extra-good visual inspection and sniff test. Then break-out the drawings and find the circuit that provides power and ground connections to that 25 cent sticker bulb.

[sixcardmark]

A related question - is that 25c light a controlled lamp, i.e. does the game ever turn it on and off?  If not, it's probably not MPU related.

Denom light stays on even when door is open.

[Toyguy]

Thanks guys.  That probably means it just gets AC power directly and likely hasn't blown an MPU transistor.  I'm having a hard time tracking that light down on the schematic.  Have to do some more digging...

[Toyguy]

Well, may have found my problem 


Have to look and see if R3 is in the circuit for that lamp.  It's really the only sign of damage, and I have good continuity all the way to the motherboard plug, so it seems like a good bet.  Now the big question will be if I can source one locally.

[Toyguy]

Anyone have a schematic for an S+ motherboard?  None of the docs I've been able to download seem to have it.  10MHz MPU if that matters.

[rokgpsman]

You could try replacing R3 with another 180 ohm resistor and try it. I'm thinking that 180 ohms is a typical sized resistor used for LED circuits, like door optics, coin optic boards, hopper coin counter optic, etc? Other than the denom light problem is everything else ok?

[Toyguy]

I found a posting on the boards that gave the values of those 4 resistors as 180 ohms for three of them, and 3.9 ohms for the R3 that was burnt.  I desoldered it today and it was clearly open.  Of course, with the demise of Radio Shack, there is nowhere around to buy small quantity components so I ended up cannibalizing a couple old pinball boards.  I was able to find a 9 ohm, a 20 ohm and a 33 ohm which, bundled in parallel, came out to about 5.2 ohms or something like that.  I figured that would be close enough and it is.  The denomination light is back on and looks as bright as ever.


For future reference, R3 on the motherboard is indeed in the denomination light circuit.

[rokgpsman]

Thanks for the followup. In the past NLG postings you can probably find some good sources for LED's for your machine, that is a popular mod to do.