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b.w.d Mini-Lab Model 603B, includes  function generator, regulated power supply and voltage/operational amplifier

Power Supply
The Power Supply of the BWD is fully working. I measured the 200V DC, the 15V split rail and 6.3V AC power supplies, and all are measuring within 10% of nominal voltages.

Amplifier

I did find some issues with the amplifier section as it wasn't delivering the correct output.  This is a minor issue with the Op-Amps which are easily to replace. I did insert a new one into a slot, and it seemed to work, however I didn't fully test this after that to confirm.

Function Generator

The function generator has had some significant changes done to it.  The ramp generator was working and this fed into the 1st stage to produce the base Triangle wave to feed the three function outputs (ie. Square, Triangle and Sine waves).


The function generator is able to produce a square wave, however it doesn't produce the Triangle or Sine wave. 

Analysis of the circuit shows that several components are missing:

  • U100 - possibly an LM3046 to produce the sinewave
  • U101 - possibly an MC1445L - used for the Amplitude Modulation (AM)
  • R18 - Unknown Value

 

Changes to the board:

  • U5 - FET has been replaced with a likely equivalent, and plugged into the IC socket.
  • S102 - Looks to be rewired - unknown reason why as this selects between the three waveforms.
  • Several circuit board tracks have been cut (drilled/knife). I suspect this is done to change the circuit board to produce the square wave only.
  • Additional resistors are soldered off the board. 

Square Wave - Works

 

Triangle Wave - not working

Looks to be missing the buffer stage between Stage 1 to the amplifier, alternatively R18 goes directly into the amplifier, which I don't think would work without the buffer impedance change.  I copied the buffer design from the Issue 21 of the BWD 603B on a breadboard, and was able to produce the triangle wave output via the Function Generators amplifier.

Possible solution: Add an extra board and tap into the Stage 1 triangle output and input it into the Function Generator amplifier output

 

Sine Wave - not working

U100 and other components are missing. The board looks to have had some changes to it to accommodate a square wave output only.  I couldn't get a sine wave output. Without the schematic I decided it would be easier to build the circuit on a separate board and then tap it into the amplifier output section.
Possible solution: Add an extra board and tap into the Stage 1 triangle output and input it into the Function Generator amplifier output

 

Amplitude Modulation (AM Input) - Not working

 

FM input - Not tested



Call Tim with any questions 0419 363 992 or email me on tim_marshman@blackboxproductions.com.au This item may be inspected by appointment at our office 76 Orsmond St, Hindmarsh Adelaide. Please check out my store, we have a large inventory of high quality industrial automation and process equipment and we are constantly adding new stock. If you would like to be notified of new arrivals you have the option of signing up for my store newsletter.