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jebem · 01-17-2019, 08:29 PM

(01-17-2019 12:08 AM)albertofenini Wrote: Thanks Hewlpac
we know that solution,
however PSU must be working, and also anode and cathode driver must be working,
so we need help in making PSU generating good Vss, Vgg and Vdisp, than we could think
of installing this.
Thanks again Alberto

These C machines are easily damaged by overvoltage coming from the charger. A bad contact between the batery pack and thr pcb and the ram chips can be destroyed, even with the machine in powered off state.
Not to mention the other chips when in power on state.

So the first thing to do is to not use the charger at this stage. And do not use the vattery pack at all for now.

If you do not have a lab power supply, use a battery holder with 2 x 1.5V AA battery cells. This is a cheap and safe way to test and troubleshoot. Use two wires and solder them to the machine battery terminals.

Next, you need a current meter inserted in series with one of the battery holder leads and the machine , so now you can measure the current consumption.

As the power supply voltages are low, and assuming that the 3volt AA batteries voltage is above 2.5 volts under load, a fault exists either in the power supply or at least one chip is shorted, or both conditions can be true.

You need a oscilloscope for proper troubleshooting as well.

Several things to do besides what other fellow members said above:
- Measure the resistance between each output power supply and ground. A lowish value means a short in that line.
- cut the copper traces for the 3 power supply lines and connect one 1kohm resistor between each output and ground to load a litle the powet supply., and check the voltages.

- If you do not want to cannibalize the pcb as described above, and you are skilled using a desoldering iron, then remove all the chips at once. Take carevto not overheat the chips, meaning that you need a powerful iron able to maintain high temperature to ket you remove the solder in the shortest amount of time.
This is an opportunity to do a proper full cleaning using IPA. I had similar symptoms in several machines whete the battery electrolytes were creating shorts everywhere.