On 05/06/2010 12:29 PM, Arthur Dent wrote:
"But now here is the finding..... The monitor board has the 7805 SMD version and
I was feeding from +12Volt and after a while the SMD voltage regulator
overheated
and started to drop the voltage.... and it was the reason to receive/display
garbled
msg.....the display is built into the same box as the gpsdo..... the temp of
the gpsdo
was around 45 Celsius, so inside the box the temp also was elevated so no wonder
why the SMD voltage reg overheated...."
Ernie,
Glad to hear you were able to find the problem. Quite often you can use a can
of spray
coolant to identify thermal problems like this one. The regulator is rated 0.5A
but the
amount of power it was asked to dissipate caused the thermal shutdown. It was
working
just the way it was designed.
One suggestion I would make is to epoxy a small heatsink onto the chip to make
sure
this doesn't happen again. The 75 ohm resistor you're using will probably take
care of
the problem permanently but even a small heatsink cut and formed from a soda can
wouldn't hurt.
-Arthur
My fluke.l monitor stopped working today after one overnight session.
LH is connected at the same time and is reporting good data from the tbolt.
I currently think that it's perhaps a clock speed issue, not a voltage
issue, because I'm getting 5V out of the regulator right now and it's
not working.
Here's how I got here:
The monitor is a recent model and has the regulator. I left it on
overnight, in its original case and out in the open, hooked to a 13.5V
supply. I had it on a ammeter the whole time, and it never draws more
than 0.02A. The backlight is fine and the display works.
It says "No Message" and occasionally gives garbled displays of other data.
Once it said "No Message / PowerSupply Fail" but not again.
Turning it off for an hour didn't help.
I tried it at a lower voltage (8V) and it works some, alternating
between "No Message" and some data or otehr every few minutes, but the
data doesn't appear to be accurate (claiming 2D/3D mode when it's not,
including question marks in numeric fields, etc).
With 12.2V-13.5V in, I get 4.99-5.01V from the square via on the left of
the board to the 3 round vias next to it, yet I still get "No message"
or garbled data.
Leigh/WA5ZNU
_______________________________________________
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.
