[Premium-Rx] HRB Systems - HW1390 LF Demodulator

[GandalfG8 at aol.com]

Hi All
 
I have an HRB Systems HW1390A LF tunable demodulator, around 1992  vintage, 
that has developed a fault and I'm looking for any information and  
particularly a schematic.
If anyone can help I'd be very grateful.
 
This was working fine but then the manual tuning for both frequency and BFO  
suddenly stopped working. They share a common rotary encoder via a switch but, 
 as far as I can tell, both encoder and switch are working ok.
A lot of the logic on the CPU board is 74 series, and I've checked  most of 
that out, but there are also several house labelled ICs, possibly PROMS,  and 
some are in the path of the encoder signals.
The unit functions fine under computer control, so the microcontroller and  
DDS are working OK, but tracing signal flow around the unidentified ICs is  
proving difficult without knowing their function.
 
There's no specific computer control software for this, I've just deduced  
what I think is a complete command set by trial and error, and use this via  
Windows Hyperterminal.
If anybody else has one of these and wants to try computer control I can  
provide information on the commands and COM port settings etc.
 
regards
 
Nigel
GM8PZR
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