[time-nuts] Fluke monitor

ernieperes at aol.com ernieperes at aol.com
Fri Jun 4 10:42:21 UTC 2010

Hi Gents,

Just received a few hours ago my new Fluke monitor and just right now making  the mods... I used 2SMD diode and the voltage on the CPU is 3,6 Volt..... hopefully will work properly......

Will report later on any problem.

Rgds Ernie.

-----Original Message-----
From: GandalfG8 at aol.com
To: time-nuts at febo.com
Sent: Fri, Jun 4, 2010 11:57 am
Subject: Re: [time-nuts] Fluke monitor

In a message dated 04/06/2010 05:47:32 GMT Daylight Time, Leigh at WA5ZNU.org  
fixed my  fluke.l monitor.
This evening I got mail today from Bob  Mokia:
The problem is too much volts on CPU  (8051F330D).
ust have  diodes 1n4148 etc at D1 and D2.  Drop cpu  volts to 3.6volts.
aximum  volts from data sheet is 4.2  volts.
D1, D2, and D3 are zero-ohm SMT resistors in series from the 5V  
egulator output.  They are visible from the CPU board edge.   Without 
emoving the CPU board from the display, I was able to remove D1  and 
ack a pair of 1N4148's in series from the D1 plus pad to D2, both  right 
t the board edge.  I left D2 and D3 in place.  I made the  leads as 
hort as possible, but still had to bend the parts up a bit to  fit it in 
he case.
As soon as I plugged it in, it worked.   It's been on about 15 minutes 
ow with no problems.

i Leigh

ongratulations on getting your monitor fixed.
hat's great news and very interesting, many thanks for sharing  it.

ine are still packed away but I'm getting closer to being up and  running 
gain so will check them over when I can and adjust as  necessary.

arking the component positions D1, D2, D3 presumably  implies that the 
esigner of the PCB allowed for this from the start  so raises the question," 
hy wasn't it implemented as  such?"

easurements I made following the initial confusion over supply  
equirements did confirm that the display module will still function at 3.6  
olts but 
 would have expected the contrast to require adjustment if the supply  to 
hat had also been dropped so perhaps the regulator output splits  before 
he diodes.
hat might also explain also why the option to fit the diodes was  given in 
he first place, instead of just using a lower output  regulator.

erhaps the design of the original iCruze processor board was rather  
lindly copied, with variation where necessary to accomodate the different  
ackage and/or pin out of the 8051, but otherwise left the same and without  due 
consideration given to the voltage requirements of the replacement  

lso of concern is the fact that your unit, and it appears some  others 
oo, did work as expected for quite a while before  showing the symptoms you 
reviously described.
hose symptoms then being consistent, at least without  dropping the supply 
oltage, suggests the possibility of some form  of irreversible change, so 
 wonder if something in the processor  itself, perhaps a protection device, 
ight have been permanently  damaged?



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