RCBS Chargemaster Combo

I know your response was not asking for more info..... But this might help you find the problem.

Scale has a thingy that when bent changes a voltage. That voltage is very small and gets amplifed( the change) and sent to a microcontroller ( a tiny PC). The PC has logic inputs, 1&0 type, and also analog input (the scale thingy voltage).

You set a charge weight, machine starts dumping powder mechanically. The uC (PC) watches for the voltage from the gauge in the scale to reflect the correct change equaling the weight you chose. uC then says STOP to the motor dumping the powder.

So if the gauge is messed up then he scale will be off. You don't have that. If the signal from gauge (voltage) is not amplified correct the uC doesn't stop motor in time to get correct weight.

If uC gets it all correct, since it's a weeny part with no power handling ability typically, it needs to signal a relay to do the motor control work. Or it sends a go/stop signal to a stepper motor, a motor that moves incrementally with pulses from a controller. Pulses stop, motor stops, pulses continue, motor continues.

If it's a relay then the relay can get sluggish and take many milliseconds to switch and that would continue to dump powder when it should have stopped. If it's a stepper then the stepper motor may be crapping out, if it gets 10 pulses, it only moves 5 times, your 5 intervals short. But it's a feedback loop. The control keeps the motor running until the scale hits the right weight. So the issue must be with the feedback circuit from scale to dispenser. The scale “stop” signal is not being acknowledged in time to arrive at the right weight.

That's a layman a term breakdown of closed loop controls.

If the scale weighs correct then the scale is not typically at fault since there should only be one strain gauge for the scale and it's readout is fed by the same gauge that the dispenser gets signal from. If the scale readout is what is programmed for a charge weight, then the relay sending power to the dispenser may be stuck on or sluggish, making timely starts and stops impossible. He scale thinks all is well, dispenser just does what it's told. Neither can call back granules so it'sade a mistake that it can't take back.

As you look at the devices, maybe the control loop description will help isolate the error. If rcbs will offer a schematic, I'd like to see it, it will direct the very narrow few pints that could cause the error. Since they don't do repairs, it's all electrical and if component level then can be fixed. If it's a one off proprietary ASIC (application specific integrated circuit) uC they developed, then the chip doing all this is difficult or impossible to obtain. But usually it's NOT a chip, it's a supporting device like a transistor or relay or even a simple pull down resistor that stops the works!

Just remember it's unlikely that rcbs developed this, it's Chinese and Chinese use cheap sundry ICs wherever possible to keep coat down. ASIC are very expensive to build and payback on an asic needs many millions in production usually. I don't know how many of these scales have been sold. I doubt “many millions".

The tweaker ( not the meth head) in me is desirous of a repair! For the sake of the tweak! Sent by phone, forgive typos