Womble
Well-known member
Answers above cover 1 and 2
Depends on the degree of voltage drop, if it drops to zero or close to zero you have a dead short on the board due to a faulty component somewhere, or a PSU that cannot drive any load (rare).
Voltage drop that doesn't go to zero is usually a result of wiring that is too thin, or as mentioned above, a single wire used when the board has 2, 4 or 6 pins dedicated to a single power rail. The amount of copper in the conductor determines how much current a wire can deliver, the result of a board trying to pull too much current through wiring that is too thin to support it is heat and voltage sag. Its why you often find boards with burnt up edge connectors, the contact got dirty and oxidised, the contact failed and the board pulled current through a smaller surface contact area. This causes runaway heating.
In general older boards and physically larger boards take more current than more modern smaller boards. A modern 15-in-1 board will draw a fraction of the current that an original 1980s/90s would draw, even though both need 5 volts. As such modern harnesses you buy on ebay are designed for modern boards. Their power wires are puny, even if they look fatter than the signal wires they are usually mostly insulation. Put a thirsty board on one end of one of those, and an arcade PSU at the other and you will find 5V at the PSU leads to 4.x volts at the PCB.
Replace the 5volt and the ground wires with thicker wire, or more parallel runs of thing wire and the voltage drop should vanish. Don't skimp on the ground wires either, that's the return path.
PCB power questions.
3.) So I have a two board set that is not working, at the very least, because of a 5V voltage drop. How does one tell if the voltage drop is due to components on the boards or due to a power supply issue? In other words, is it possible for the power supply to be putting out proper +5V, +12V, etc... to the edge connector, but fail to deliver that voltage once connected? What if the voltage drop is due to crummy edge connectors themselves? What is the correct process to diagnose the source of the problem?
Depends on the degree of voltage drop, if it drops to zero or close to zero you have a dead short on the board due to a faulty component somewhere, or a PSU that cannot drive any load (rare).
Voltage drop that doesn't go to zero is usually a result of wiring that is too thin, or as mentioned above, a single wire used when the board has 2, 4 or 6 pins dedicated to a single power rail. The amount of copper in the conductor determines how much current a wire can deliver, the result of a board trying to pull too much current through wiring that is too thin to support it is heat and voltage sag. Its why you often find boards with burnt up edge connectors, the contact got dirty and oxidised, the contact failed and the board pulled current through a smaller surface contact area. This causes runaway heating.
In general older boards and physically larger boards take more current than more modern smaller boards. A modern 15-in-1 board will draw a fraction of the current that an original 1980s/90s would draw, even though both need 5 volts. As such modern harnesses you buy on ebay are designed for modern boards. Their power wires are puny, even if they look fatter than the signal wires they are usually mostly insulation. Put a thirsty board on one end of one of those, and an arcade PSU at the other and you will find 5V at the PSU leads to 4.x volts at the PCB.
Replace the 5volt and the ground wires with thicker wire, or more parallel runs of thing wire and the voltage drop should vanish. Don't skimp on the ground wires either, that's the return path.
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