Racal RA1776 Help! - UK Vintage Radio Repair and Restoration Discussion Forum

Dipole · 28th Sep 2006, 11:28 pm

I have recently obtained an RA1776 which is works fine below 18MHz. When I select 18MHz and above, the "Out of Lock" LED illuminates and the radio goes deaf!

I've not even had the case off yet, any clues as to where I should start?

Any help would be appreciated

Sean Williams · 28th Sep 2006, 11:34 pm

First stop - get a manual - you will certainly need it!

Second, get real familiar with Phase locked Loop circuitry.

Then hope that the fault is supply rail related, and not in the custom ICs that Racal love so much!

Once you have some info come back to us, and we can have a go!

What level of experience do you hold - it will make a difference in the sort of replies you get!

Welcome to the Forum

Cheers
Sean

Dipole · 29th Sep 2006, 8:57 pm

I have the manual!
I have a reasonable radio based background with cough-cough years of fault finding, I just cannot get my head around the PLL circuitry! Racal had some great ideas but wow!, complex!

I need to get the case off and probe around. I have a gut feeling there are 3 oscillators and a changeover happens at 18 MHz!

Hopfully someone may have an idea!

28th Sep 2006, 11:28 pm	#1
Dipole Retired Dormant Member Join Date: Sep 2006 Location: Kent Posts: 3	Racal RA1776 Help! I have recently obtained an RA1776 which is works fine below 18MHz. When I select 18MHz and above, the "Out of Lock" LED illuminates and the radio goes deaf! I've not even had the case off yet, any clues as to where I should start? Any help would be appreciated

28th Sep 2006, 11:34 pm	#2
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	Re: Racal RA1776 Help! First stop - get a manual - you will certainly need it! Second, get real familiar with Phase locked Loop circuitry. Then hope that the fault is supply rail related, and not in the custom ICs that Racal love so much! Once you have some info come back to us, and we can have a go! What level of experience do you hold - it will make a difference in the sort of replies you get! Welcome to the Forum Cheers Sean __________________ Engineers make things work and have spare bits when finished

29th Sep 2006, 8:57 pm	#3
Dipole Retired Dormant Member Join Date: Sep 2006 Location: Kent Posts: 3	Re: Racal RA1776 Help! I have the manual! I have a reasonable radio based background with cough-cough years of fault finding, I just cannot get my head around the PLL circuitry! Racal had some great ideas but wow!, complex! I need to get the case off and probe around. I have a gut feeling there are 3 oscillators and a changeover happens at 18 MHz! Hopfully someone may have an idea!