MSP430 not starting in MS6816

[goaty]

Hi all,

I´ve got a cable tester Mastech MS6816, where the receiver part does not power on.
I found out that the Texas Instruments microcontroller MSP430F135 has a 4MHz clock which oscillates,
but there is initially no activity whatsoever on it´s outputs, specifically to the display.

When I stop the clock by shorting the crystal, it comes alive for two seconds and the display is initialized and the device beeps,
but then freezes again.

I tried another crystal and also added some 15pF caps to it, but that did nothing.

Display shows some plausible stuff, but it does not react to keypresses and also not to the reset pin of the microcontroller.

I have not yet tried JTAG, but wanted to ask the community if there is any hint in what this bahaviour of the micro could cause.

Is it more likely dead chip or is the firmware corrupt ? What could it be that it does not react to the RST pin ?

The sender works fine and there the same processor is used and the RST pin just works fine.

Thanks for any hints.
Thomas

[Psi]

They might be using the RST pin as GPIO, would explain why you don't get a reset when you trigger it.

Other thing that might cause RST pin to be ignored is a low voltage triggering brown out to hold RST active.

Could also be a GPIO line which is in an odd state due to a fault and is locking up the startup sequence.