Splitting power supply causing issues with Pinball Dreams on a 6128 Plus

Started by Cwiiis, 17:20, 20 August 21

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I have a Y-splitter for the power going into my 6128 plus to use my external Gotek - I've got a 3rd party power adapter, as well as the original coming from the CM14 monitor. It seems, however, Pinball Dreams locks up fairly quickly using any combination that isn't just the power supply going straight into the machine, unsplit. Has anyone encountered this? And does anyone know any work-arounds? I suppose this must be messing up interrupts somehow, or just perhaps the draw of both disk drives and the machine going at full pelt is too much(?) (if that's the case, does anyone have any supply recommendations that can handle this?)


I suppose to answer my own question somewhat, yes, the power supply wasn't beefy enough. Even using it alone, if I use the C4CPC at the same time, Pinball Dreams is unstable - this is fine using the power supply from the CM14 monitor, so I suppose even 3A isn't enough to power the Plus and flash cart when at maximum load. Currently I have a separate 2A adapter powering my OSSC and HDMI splitter, then the 3A adapter on the Amstrad and I'm using the stock cart for now... I suppose a 5A adapter might be good enough to power everything? Would that be an ill-advised thing to do?


There are two ways you can have problems with the power supply, and both are actually inherently a voltage drop. When the voltage is too low going into the ICs, you get glitches and crashes.

Insufficient current capacity is the first cause, but what actually happens is when the load exceeds the capacity the voltage coming out of the supply drops. (It's really a power limit, volts*amps, which stays constant - when amps is high volts has to drop.)

The other one is the voltage drops across the resistances in the circuit, in the wires and especially across the connectors. These drops are always present, and go *up* as current goes up. Even if you have a 5V power supply that can supply 100A, as the system draws more current the voltage drops get greater until the IC's aren't getting enough voltage, even though you still have 95A spare capacity in the supply and it's putting out a rock steady 5.0V. Therefore adding a supply with more current won't help. You have to either reduce the voltage drops in the circuit (clean connectors, improve solder joints, use thicker wire) *or* you use a power supply with a greater starting voltage so that after the voltage drops the IC's still see nearly 5V. You are probably running right at the edge of stability when connected directly to the CM14, and the splitter cable introduces just enough extra resistance to push you over the edge.

The Raspberry Pi has had these problems for years, and actually started selling 5.1V supplies to address it, before switching to a usb-c and buck-boost regulator in the Pi 4. For the CPC, I actually opened up my CTM644 and adjusted the 5v output to be 5.3V, which solved all my stability issues even when I'm running a full stack of peripherals. Inside the CPC the voltage still isn't quite 5V, but it's no longer dropping to 4.5v.

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