Thanks for your quick reply,

Unfortunately these suggestions are not the solution yet.
- MCLR has only 33k resistor to +5V as in your blink-a-led circuit. During
the first attempt it gets 12.5 V and stays 12.5 V until removal of the main
+5 V supply
 
- RB6 and RB7 are only connected with the blue and green wires of the
programmer. Measuring the resistance between the programmer and the PIC pins
doesn't show any abnormalities.

- the white LVP wire is connected to pin 36 and stays low

- measuring resistance between all pins used and the parts connected to
shows nothing abnormal so connections in the breadboard seems to be OK

- +5 V supply is 4.96 V. even rebuilding the supply with several other power
transformers did not help. Several capacitors are added: 0.10, 0.15, 400
microF.

Any other suggestions?

Thanks Jos

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