Racal RA1792

[bill knox]

HI

I have just managed to purchase one of the above receivers, and for the money that I paid I did not expect it to work.

I have several problems:-

1) I have no audio, though looking at the user manual I believe I have to have plugged into the back of the receiver a facilities/function plug, Marked J2, I think that the audio comes out of that socket, for remote operation and if the function plug is inserted, the audio goes back into the receiver for local use, if other members agree/disagree that I do require a "facilities/function plug" and would like to sell or tell me what make and type of plug it is can someone contact me, MODS correct me if that last piece of typing is not allowed.

2) I have one segment, on one digit missing, on the frequency display, I have yet to look at that.

3)In the right hand display I have the word FAULT permanently displayed, it does not matter what buttons I press, is there any way to read the display and find what the fault is.

4) Although the mode display all seems to function correctly, the display in the freq display stays at ZERO with all zero's displayed, i.e. no tuning.

I am adding some pictures to show what is happening and if anybody has answers it would be appreciated.

Bill

[frsimen]

Hello Bill,

You don’t normally need to plug anything in to the RA1792 other than the aerial and power.

The audio on the RA1792 is switched to various places by an analogue switch, which has to be set up by the CPU. From the photos you seem to have the triangle with an exclamation mark showing to the left of the frequency display. That indicates that the receiver is operating independent of the front panel. The remote indication isn’t lit, so it would appear that the REM button hasn’t been pressed.

I’m not sure if any or all of the buttons are working from your description. On the front panel memory board there are three switches, S1A, B and C. According to the manual, closing switch S1B alone will put the radio into self test mode, you could try that to see if it gives any more help.

The RA1792 will not respond properly to the controls unless all three of the switches are in the open position, so make sure you return S1B to the open position after you have tried the self test.

Check that the REF INT/EXT switch, S2, on the rear panel is set to INT.

Check that the battery on the CPU board hasn't leaked, you will be in for a lot of trouble if it has.

If that doesn’t bring success, check that the power supply rails are as they should be. Short circuit tantalum capacitors are quite common on the RA1792. Sometimes they burn out feed resistors and chokes, while appearing undamaged themselves.

The frequency display indicates what the CPU intends the receive frequency to be, rather than the actual frequency that the radio is tuned to.

The LCD segments on the frequency display are driven individually by CMOS 4056 latches. The missing segment could be due to the failure of its driver 4056 or a poor connection to the LCD itself.

If the above doesn’t help get the radio going, note if any of the controls work at all. A completely non responsive radio could be due to a faulty CPU board, if you are unlucky.

Paula

[Radio Wrangler]

THere was a large number of RA1792 variants for remote control, lacking the full front panel and displays which showed up on the surplus market. Telford electronics well known for manuals and surplus sales designed and manufactured a replacement panel so these could be converted to the full monty. The blue colour of the upper panel is a sure identifier of these sets. If any further confirmation is needed there can be few original racal panels left with good clear LCDs.

David