Quoted from MydknyteStyrm:I pulled the board out and I found some real worrisome things. There’s a discoloration over the area, some green foil is gone, and there is evident damage at Q49. ... It also has the most visible scorch.
Not cleaning the flux makes it hard to make a full assessment but I suspect that scorching at Q49 is from someone using a soldering iron that was probably too hot. I've seen a fair amount of this when someone uses a "Radio Shack" soldering iron to do work on a board.
Quoted from MydknyteStyrm:I mentioned in previous post that there was a lot of heat coming off of the ceramic from R82 to R89, enough to cause the hotglue holding the alphanumeric top left to come off.
When using the OEM lamp column circuit this is normal. The Darlington 2N6427 is used for orders of magnitude current gain to drive the TIP42 hard. The current driving the base goes through those resistors and is dissipated as heat. LOTS of heat.
The issues with your switch matrix is not related to the lamp columns and almost certainly not related to any dissipated heat from the lamp column circuitry. There has been prior work done in your switch matrix circuit on that board. It's not a nice thing to say but I always suspect prior work. In the majority of the cases I have looked at it ... it is the prior work that is/was the problem.
Quoted from slochar:I don't know if anyone has come up with the mosfet swap for system 11 to get rid of the hot lamp resistors, but them being hot is normal for the darlingtons that are stock.
The MOSFET modification works in all System 3-11 games. The lamp column circuit is essentially the same. The PIA controls the 2N6427 that controls the TIP42.
Quoted from slochar:I haven't done any tests but I've often wondered if the resistors will still get hot with LEDs in the game.
Makes no difference if you use LEDs or incandescents in the controlled lamps. The current dissipated through the 27 Ohm resistors is driving the base of the TIP42 and is not passing through the collector/emitter of the TIP42. That's my understanding of the circuit. I am fairly sure that you already know this.
I have LEDs in my System 11 games and for the boards I have not done the MOSFET modification those resistor get hot to the touch within 30 seconds of powering on the machine.
Pulaski, PA
