[time-nuts] Fluke Thunderbolt Monitor Revisited
GandalfG8 at aol.com
GandalfG8 at aol.com
Sat Jun 5 11:04:25 EDT 2010
Further to earlier comments I have now traced the full schematic of the
8051 replacement processor board in the iCruze display.
The schematic is so close to Didier's original that I don't think it's
necessary to provide a copy but could do so if required.
Differences are described below and most of the detail is clearly visible
anyway in Brooke's excellent photo....
Other than D1 to D3 being fitted as zero ohm links, rather than diodes as
they should be, the other differences are as follows....
1...The addition of the 78D05 regulator onboard. This is a conventional
circuit with an SMD electrolytic capacitor in parallel with an SMD ceramic
capacitor on the input and two of the same electrolytics and another ceramic
in parallel on the output.
The electrolytics are marked E105, which indicates 16 or 25 volt rating
depending on which tables you read, and also seems to indicate they're only
1uF which seems low to me but the marking might again be manufacturer
There are spaces for a through hole or wired LED with SMD series resistor
directly across the supply input but these are unused.
2...Several more SMD ceramic capacitors have been added to the board for
additional supply decoupling.
3...The series input and base to ground resistors on the RS232 interface
are both 180 ohms, rather than 10K and 3K3 respectively as in Didier's
4...Didier's 10 pin JTAG interface connector has been replaced with a 5
pin single row connector.
Both end pins are ground and the others match Didier's three connections to
On the rear of the PCB, the side normally visible, these pins are marked 1,
7, 4, indicating their relationship to the original circuit.
5...Although marked as R3 on the PCB the 3k3 resistor that Didier shows on
the JTAG connector has been replaced with a ceramic capacitor.
I though this might be a one off error at first but Brooke's photo also
shows a capacitor.
Just to be sure I did attempt to measure it and it indicates as open
circuit on my DMM.
Although all the ceramic capacitors look to be identical none show any
My LCR meter wasn't happy trying to measure them in circuit but
"fortunately" the two adjacent to the contrast adjustment pot were only soldered at
one end so easy to remove.
These I measured as 100nF, or 0.1uF depending on which flavour you
So there you have it, nothing significantly different from the original
other than the lack of diodes and they really do need to be fitted if it's
going to be run with the 5 volt regulator doing it's job.
This one I've dismantled did run for at least a couple of months with the
processor at 5 volts before being taken "off air" so even though the
specified "absolute" maximum is 4.2 volts there's obviously some tolerance on that
but I certainly wouldn't want to push my luck and run it now without the
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