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Coin lights flashing + sound pulsing?
bkenobi:
One of my MAME cabs has an issue all of a sudden. The coin lights flash and the speakers pulse (kinda thump) when I turn off the machine. The volume of the beat and the brightness of the lights dim over a couple minutes and eventually stop.
I initially thought this was a dying relay that I use to turn the thing on. I use the computer to control the power on for the rest of the machine kinda like a home made Smart Strip (there's a tutorial around here that I used to build it). I've used this same setup on my other cab and haven't had any issues.
Anyway, I replaced the relay and the issue is a little better, but not fixed (the lights still blink slightly). I'm wondering if this could be a sign of a dying PSU? I assume the pulsing is caused by the power being dissipated by the closing of the relay. Some power builds up, the relay opens, the power dissipates, the relay closes, repeat... If this continues, it will burn something up (probably the relay again).
I don't happen to have an extra PSU sitting around right now, so I can't just test it like I normally would. Any thoughts?
lilshawn:
--- Quote ---I'm wondering if this could be a sign of a dying PSU?
--- End quote ---
my first thought.
but as usual i have no idea what you have in your cabinet, or how you have anything hooked up.
if your running a standard arcade power supply:
sometimes if they don't have enough load on the 5V line they can get uppity, especially when they get old and crotchety. adding a 5 or 6 ohm 5 or 10 watt resistor to the 5V line and ground terminals often fixes the issues they have... of course you could always run a bunch of stuff off the supply to load it down properly.
bkenobi:
Sorry, you are correct that I was not very clear how I have things set up. I'm running a PC with a standard power supply and a 20" CRT PC monitor as the display. As for the relay setup, I used something similar to BobA (can't find the link I used, but this is pretty much identical).
http://forum.arcadecontrols.com/index.php?topic=69269.0
The PC power supply drives the relay with the 12v rail. When the PSU is on, it opens the relay and turns everything else on. When it's off, the relay closes and nothing should have power. I'm thinking that the PSU may be generating a small amount of power for some reason. Maybe I have a PSU somewhere I can test with...
lilshawn:
you probably need a diode on that relay. 1N4004 or 05 or 06. stripe end of the diode on your + and the other on your -
what i think is happening is a reverse voltage EMP or inductive kickback or back EMF... it's called all sorts of things..
when you cut power to a coil of wire such as a relay or solenoid, as the magnetic field collapses, it generates a reverse voltage (it can easily reach 200 volts peak). because it's attached to the power supply directly, it dumps into the capacitors of the power supply. charges them up a bit... and they dump back into the relay, clicking it back on for a second (repeats until the field is dissipated.)
the problem with this is the voltage regulators and MOSFETs in the power supply REALLY REALLY REALLY don't like this since they are being driven backwards. eventually they begin to fail.
the diode acts like a resistor when you dump voltage into it backwards and acts like it's not there frontwards. so when the EMP is generated by the coil the diode absorbs it. all that passes through the diode is about .5 volts, low enough for the power supply to dissipate.
if you do indeed have a diode on there, then it's likely blown and need to be replaced.
bkenobi:
I don't have a diode, but that was one thing I was considering. Of course, I'm no EE, so I didn't know if that would be effective or a good idea. Where do I put the diode though? In BobA's design, he puts it across the 12v to ground legs of the relay. That seems reasonable since that's the power that needs dissipating.
I just checked my parts box. I currently have 1N4001 and 1N4148T diodes. Will either of those work in lieu of the 1N4004? I can stop by Radio Shack tomorrow if that would be better.