[hardtailer]

Thanks again for your replies.

I won't connect it to the car again until it's fixed.

Using my 20 MHz scope I measured the following on the pins of 8051, S700 on the NOK DME, powered on the bench:
Pin 5 4.85 V 33 Hz
Pin 18 0.8 V 33Hz
Pin 19 0.9 V 0 Hz
Pin 30 2.36- 2.40V, square wave at 33Hz
Pin 40 4.8 V
Pin 9 kept resetting at 33 Hz.

I left the working DME with the car, so no data using the 20MHz scope on that.
I take it that the 8051 is damaged and must be replaced?

(Edit: correct bandwidth of scope is 20MHz, added Pin 30 signal)