I bought it from the CrystalRadio forum. At first the price was $20 including shipping. But before it gets shipped out, the seller told me it suddenly stopped working. So he sold it to me for $15 finally.
After received it, I tested it immediately. Yes it is not working. No display at all. But if I enter BEEP and press enter, I can hear the beep. It means that at least it is running. There is possibly just some issues with the display.
I decided to test the plotter first. Plug in the power supply, the low battery light comes on. This should be normal. Turn on the power switch of plotter, the motor seems to do something. Set the online to ON (instead of LOCAL), press FEED to feed some paper. Type LRPINT “HELLO” on PB700, press enter, and yes, it is working!
Now it is time for some repair. I probed the resistors and capacitors first, they all seems to be good. The voltage on potentiometer is -14.5V, I guess that is also good. Then I tried to probe around the LCD board, however the -14.5V is not there. Finally I determined one via is bad, fly wire fix. Now it is working!