[time-nuts] Fluke Thunderbolt Monitor Revisited

Richard W. Solomon w1ksz at earthlink.net
Fri Jun 4 15:47:31 UTC 2010

Does anyone have a picture of the Board showing where these diodes go ?

Thanks, Dick, W1KSZ

-----Original Message-----
>From: GandalfG8 at aol.com
>Sent: Jun 4, 2010 7:14 AM
>To: time-nuts at febo.com
>Subject: [time-nuts] Fluke Thunderbolt Monitor Revisited
>Hi All
>As there still seemed to be unanswered questions regarding the circuitry of 
> these I've separated the two PCBs from one of mine to determine exactly 
>what is  going on.
>Whether or not the regulator circuit is based in any way on the iCruze  
>original processor board I don't know but it's now quite clear that the  
>processor circuitry itself is an amost exact copy of Didier's version  using the 
>20 pin DIP C8051F330 processor.
>The only differences I've found so far are the values of the resistor  in 
>the programming interface and those on the RS232 input but  the layout itself 
>looks to be identical.
>I'll go over it more thoroughly later and produce a complete  schematic.
>Didier's original schematic, which includes the three series diodes for use 
> with a 5 volt supply, can be found here .....
>As commented by Leigh earlier, all the diode positions on the PCB are  
>occupied by zero ohm links so I think it's reasonable to assume this is probably 
> universal and ALL monitors are likely to need modifying to keep the 
>processor  supply voltage at a safe level.
>The absolute maximum rated supply voltage is 4.2 volts,  IO port  and RST 
>pins are indicated as tolerating up to 5 volts, but the  specified operating 
>supply voltage range is 2.7 to 3.6 volts so I would  recommend fitting all 
>three diodes as per Didier's original circuit rather than  just two.
>The supply to the display is taken directly from the output of the  
>regulator and not via the diodes.
>For anyone wanting to avoid hardware modification another option would be  
>to run the unit from an external 5 volt supply, as was originally  
>suggested, and let the onboard regulator just act as a dropper.
>With a 5 volt supply the output voltage from the regulator is 3.6  volts 
>but of course it isn't regulating and the supply to the display is  also 
>I have found that my display at least will run ok at 3.6 volts  but the 
>contrast pot may need adjusting.
>However, if this route is followed there's little room for error and it's  
>important to make sure the external supply is kept below 5.6 volts otherwise 
>the  processor supply will again exceed 4.2 volts.
>Fitting the diodes is a once and for all solution and is certainly the  
>preferred option.
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