In a message dated 04/06/2010 05:47:32 GMT Daylight Time, le...@wa5znu.org writes:
fixed my fluke.l monitor. This evening I got mail today from Bob Mokia: The problem is too much volts on CPU (8051F330D). Must have diodes 1n4148 etc at D1 and D2. Drop cpu volts to 3.6volts. Maximum volts from data sheet is 4.2 volts. D1, D2, and D3 are zero-ohm SMT resistors in series from the 5V regulator output. They are visible from the CPU board edge. Without removing the CPU board from the display, I was able to remove D1 and tack a pair of 1N4148's in series from the D1 plus pad to D2, both right at the board edge. I left D2 and D3 in place. I made the leads as short as possible, but still had to bend the parts up a bit to fit it in the case. As soon as I plugged it in, it worked. It's been on about 15 minutes now with no problems. --------------------------- Hi Leigh Congratulations on getting your monitor fixed. That's great news and very interesting, many thanks for sharing it. Mine are still packed away but I'm getting closer to being up and running again so will check them over when I can and adjust as necessary. Marking the component positions D1, D2, D3 presumably implies that the designer of the PCB allowed for this from the start so raises the question," why wasn't it implemented as such?" Measurements I made following the initial confusion over supply requirements did confirm that the display module will still function at 3.6 volts but I would have expected the contrast to require adjustment if the supply to that had also been dropped so perhaps the regulator output splits before the diodes. That might also explain also why the option to fit the diodes was given in the first place, instead of just using a lower output regulator. Perhaps the design of the original iCruze processor board was rather blindly copied, with variation where necessary to accomodate the different package and/or pin out of the 8051, but otherwise left the same and without due consideration given to the voltage requirements of the replacement processor.? Also of concern is the fact that your unit, and it appears some others too, did work as expected for quite a while before showing the symptoms you previously described. Those symptoms then being consistent, at least without dropping the supply voltage, suggests the possibility of some form of irreversible change, so I wonder if something in the processor itself, perhaps a protection device, might have been permanently damaged? regards Nigel GM8PZR _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
