NASA Navtex repair

[bonny]

I too have a Navtex which has suffered from a leaking battery, I have repaired a couple of tracks, replaced the battery and a number of components.

But there is obviously something I have missed as the screen is illuminated without the menu and the 78L06 6V REG get blistering hot.

Can anyone suggest which component(s) could be the causing this!

The 78L06 should not get hot, hardly even warm! This would tend to indicate that it is supplying too much current to something.
Can you measure how much current the unit is drawing from your 12V supply, I would guess about 50mA with the display light off and 100mA with the light on, anything more than double these figures would concern me and I would power off immediately.

Which components did you replace?

You say the display is illuminated, can you see anything on it, (even jibberish)?
Is the display all black dots or all white?
Do you get a thin horizontal line when you press all four buttons together?


Can you measure any voltages with a multimeter - be very careful not to short anything.
Try measuring battery voltage, output of 6V regulator to ground, voltage across the 10uF capacitor at the bottom corner (near the display connector).

[bonny]

I sold my boat in 2021 and the navtex with it. Consequently I don't really look at this forum these days.
I just found your post in my junk mail.
So glad it was of help to you.
In my case the 39k resistor was physically broken and as such was supplying a -ve voltage to the pic (pin 2) and consequently damaged that input to the Pic. I was able to get a replacement Pic direct from NASA, the guy who designed it. I think he's a one man band, but was very helpful.