Homebrew RF generator & DFM

[ed731pdh]

This one is an interesting one out the box.  Found 3 cooked AA cells and a rotted PP3 clip that needed replacement. Power up and now the fun starts.

There are no markings on the dials. The one closest the BNC is power and selects either RF generator or RF gen and DFM.  The slide switch I have yet to work out.  The DFM is an Ambit module with an LCD display.  layout is simple, the DFM takes a large chunk of the board, the top corner houses a module made up of two vero circuit boards fitted with Toko coils etc to produce the signal.  The yellow terminal is not connected.

Now the issues and one I'm struggling on as it appears there may or may not be a wiring issue on the second switch.  Put the scope on the red and blue terminals and the output from the switch positions is as follows.

1)  No signal
2)  314 - 409 khz
3)  498 - 798 khz
4)  1.11mhz - 1.8 mhz
5)  No signal
6)  No signal

From the BNC we get...

1)  No signal
2)  342 - 478 khz
3)  568 - 1.126mhz
4)  1.256mhz - 2.839mhz
5)  No signal
6)  No signal

The DFM stage tracks the frequency from the BNC, not the red and blue terminals.  The DFM freewheels when the no signal positions are selected.

Now, positions 1,5 and 6 give no output and this is confirmed as they are not wired on the first half of the rotary switch.  But and a big but, three wires from the RF board go to the second side of the rotary switch but there is no wire from the corresponding rotor. I can't help thinking there is something *missing* from the board, why fit a 6 way rotary switch when you are only going to use three positions, and only half of the switch at that.  Not having a circuit diag for the RF stage is a pain, compounded by there being no legend at all for all of the switch settings on the front panel.

Any suggestions gratefully received.  Nice unit, but perplexing.

[ed731pdh]

Bit extra to this, quick sketch of the rear of the three vero mounted Toko coils and how they connect to the 2P6W rotary switch.  Pole B is not connected to anything. 

For clarity, the bottom rows of pins on the Toko are not shown as earthed as per the vero mounted examples.

[AlanBeckett]

You've certainly jumped in at the deep end there.
Perhaps this is the one that didn't get finished.

Alan

[ed731pdh]

I hope not. Build date says 1980, I don't think the original builder would have marked if up if it was not completed but.....!

[ed731pdh]

Function of the DPDT slide switch has been sussed. The DFM module has an extra function that switches the display between decimal and non- decimal mode. I might have a frequency output of 4.567kHz shown with the switch in the first position, or just plain 4 in the second. Freewheeling of the DFM has been cured, tracked down to the aforementioned DPDT switch that needed a good clean up.

I'm wondering if the switch arrangement was due to whatever the constructor had in the parts bin and not a design feature that was not taken further. What I will try later is move the green wire from one switch pole to the other and see if a different set of frequencies come out. If so, a c/o switch in place of the unused yellow plug point will expand the range.