A DIY bench RF step attenuator with Arduino and Aeroflex-Weinschel step attenuators

A while ago I made a bargain purchasing a couple of Aeroflex-Weinschel step attenuators (models 150T/11 and 150T/70) for 20EUR each.

The idea was to implement a bench step attenuator for my lab.

Here is the project.

Those attenuators offer serial and parallel digital interface. I choose to use the parallel interface protocol.

Each attenuator is controlled by 4 bits (a nibble), so, with the help of the following map, I built an Arduino sketch to drive the attenuators by a rotary encoder:

The table on the left simply lists all the wires coming out of the attenuators with color and function.

My HP 6632 Power Supply has got crazy (SOLVED)

My 6632A s/n 3145A-06821

 

Symptoms:

• power on is ok; no self test errors on the display;
• VSETing from the front panel to values greater then 5/6 Volts triggers OVP.

Checks:

• with these symptoms always double check the sensing terminals (S+ and S-): they must not be left floating. Be sure they are directly connected to output terminals on the rear terminal strip or to a remote load. For testing purposes mine were connected to the terminal terminals on the rear output strip;
• checked OVP circuit as per SM: voltages at U110 are ok; both R158 and R155 checked ok.

Further investigation:
    • 0.1 Volts < VSETs < 4/5 Volts work but the readback (front panel) is out of, say, 15% and slightly unstable; the actual output is about 4x VSET and highly unstable: it jumps randomly up and down few volts.

NOTE: from now on I  connected my Arduino GPIB controller to the unit so that I can quickly issue commands to it without pushing the control panel buttons.
      
This is the result of “VSET 2” GPIB command:

The first spike is the direct consequence of VSET 2; the second is just pure random noise. Please note the rms voltage is more then 4 Volts instead of 2. The peak reached by the first spike was 20.4V, barely not enough to trigger OVP.

Graetz Joker-834 portable radio repair What a challenge!

 This radio is as old as me: born in 1959.

Initial conditions

Found it in very tough conditions: dirty, smelly, not working (dead).
Inside the PCB was dirty and strangely greasy in some area.
I have found the schematic in my personal old paper archive.
Here is the annotated version I used during the repair job (look at the end of the article for a high res pristine version):

Please note this rig uses PNP transistors so GND is positive.