[time-nuts] fluke.l monitor for Thunderbolt

Steve steve65 at suddenlink.net
Sun Jun 5 23:34:20 UTC 2011

Thanks everyone for the advice, both on and off list.

I do see voltage transitions on P0.5 of the C8051F330D, which is pin 19 
on the DIP version of the microprocessor. So it appears that the serial 
data pulses are making it from the Thunderbird to the input to the 

However, voltage as measured from the microprocessor VDD to GND (pins 6 
to 5) is 4.94VDC. The C8051F330D manufacturer's spec for VDD is 4.2VDC 
"Absolute Maximum Rating." Didier's speculation seems on point . . . 
overvoltage on the microprocessor has likely damaged it.

There is a caveat: The way the iCruze is constructed has the C8051F330D 
sandwiched between two PCB's and not readily visible. So I am assuming 
that the microprocessor is a C8051F330D, but that is not verified (at 
least not by me). Getting at the microprocessor requires desoldering the 
16-pin header which connects its PCB to the display PCB.

Not sure where to go from here . . . trash can?


On 6/5/2011 4:25 PM, shalimr9 at gmail.com wrote:
> Check that the serial data is going to the processor. The schematic is on my web site www.ko4bb.com look for GPS Monitor
> You should see the inverted serial data on the processor pin that is driven by the NPN transistor used as an inverter and level converter. I forgot the pin number and I am not in range of a computer.
> While you are at it, check that the processor is powered from 3V. Some units sold by fluke.l applied 5V to the processor. If you see 5V, the processor is probably toast.
> Didier KO4BB
> Sent from my BlackBerry Wireless thingy while I do other things...
> -----Original Message-----
> From: Steve<steve65 at suddenlink.net>
> Sender: time-nuts-bounces at febo.com
> Date: Sun, 05 Jun 2011 15:23:55
> To: Discussion of precise time and frequency measurement<time-nuts at febo.com>
> Reply-To: Discussion of precise time and frequency measurement
> 	<time-nuts at febo.com>
> Subject: Re: [time-nuts] fluke.l monitor for Thunderbolt
> David,
> Thanks for the suggestions. There is continuity to the PCB in the iCruze.
> Not sure what to make of the voltage levels on pin 2 of the DB9. Using
> just a scope connected to the Thunderbolt, the voltage switches from -10
> to +10. With the laptop connected, it switches from -9 to +9. With the
> iCruze connected, it switches from -6 to +6.
> I don't know if the -6 to +6 is normal, but it seems low to me for RS-232.
> Taking the troubleshooting to the next level on the iCruze involves
> desoldering a 16-pin header. I dunno . . . .
> Steve
> On 6/5/2011 4:56 AM, David Bobbett wrote:
>> Steve,
>> The two lines of text are what the iCruze will display when it thinks
>> it doesn't have any data. The RS232 input on my system can be
>> unplugged and that is exactly what is shown on the display in those
>> circumstances.
>> Personally, I would start with the simple stuff, just continuity check
>> the '232 lines from the iCruze plug all the way back to the PCB.
>> If that doesn't work, there's a circuit diagram of the device on
>> Didier's web site.
>> 73 de David, G4IRQ
>> On 04/06/2011 22:17, Steve wrote:
>>> About a year ago I installed one of the iCruze monitors from fluke.l
>>> on a Thunderbolt GPS receiver. I paralleled the iCruze with the
>>> serial port on my laptop PC. Sometimes the PC was connected,
>>> sometimes not. The iCruze worked OK either way.
>>> Last week I noticed the iCruze was no longer functioning as before.
>>> It now alternates between two lines of text: "Trimble LED Monitor"
>>> and "Waiting for GPS". Whether the laptop is connected or not does
>>> not make a difference. The laptop running tboltmon works ok with or
>>> without the iCruze paralleled across the serial data line.
>>> I substituted another Thunderbolt and saw the same results.
>>> The iCruze has about 10VDC on its power input.
>>> I not particularly competent at serial communications or
>>> oscilloscopes, but on the DB9 feeding the iCruze I can see the
>>> transition of voltage from about -6VDC to about +6VDC. I didn't look
>>> at those voltage levels when I installed the iCruze last year so I
>>> don't know if that's what it has always been or not.
>>> I have rebooted the iCruze several times as well as the Thunderbolt
>>> and laptop, no change in iCruze behavior.
>>> Any advice as to where to go from here?
>>> Thanks.
>>> Steve
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