Opening it up and checking the supply voltages around the PCB revealed nothing surprising. Everything looked OK. The processor on the main PCB is a BGA packaged part. Taking a well educated guess I repowered the 'scope while pressing down on the processor, it worked :) so after applying foil around the chip and heating it with a hot air gun I had a working 'scope.
When I found the thing it was wet through which hadn't done the LiPo battery any good and it looked a bit 'puffy'. I have plenty of NiMh cells lying around so I thought I would make up a battery pack from these to replace the LiPo battery. First I checked the PSU to see what kind of provision had been made for charging the batteries....
The output stage of the PSU looks like this...
The battery is just connected across the output via the main switch.
The 'scope draws...
360mA, 8.4V, LCD Backlight.
380mA, 8.4V, Main board.
80mA, -8.4V, Main board.
After trying out a NiMh pack and realising it was stupid, I decided to dump the entire power supply and have the thing powered externally by a ready made 19 volt or so ( old laptop psu ) brick. Clearing out the power supply left lots of space. I can get lead acid batteries for free and there is room for a small one plus its charging psu plus all the other power stuff I am going to need.
While I'm modding this thing I might as well swap out that LCD backlight for an LED one, that will save 200mA !!!
This was easy to do :)
The replacement power supply is fed with 19V and provides 13.8V for charging the lead acid battery, this stage is followed by a further regulator which outputs +/-8.4V.
The backlight is powered from the 8.4V via two 47R paralleled resistors which gives it 20 to 30mA, which is plenty bright enough.
No comments:
Post a Comment