[Premium-Rx] WJ 8718A help

[L D Ritta]

Hello Les
I had this crazy idea since I know the basics of pcb design and I have took 
a pcb design course at college.
I would replicate the pcbs used in the preselector and make any mods for 
parts no longer available, since
I have not seen any preselectors for sale. The chip is U3 and is used in the 
796002 decode/GPIB Extension
board. The preselector has a motherboard which 5 filter board and digital 
control board, I can only guess that the
decode /GPIB Extension is pluged into a motherboard on the chassis. Perhaps 
this not possible to build.
BTW I am using Altium winter 09.

73 Lee
----- Original Message ----- 
From: <lrlayton at cox.net>
To: "L D Ritta" <ufp at optusnet.com.au>
Cc: <premium-rx at mailman.qth.net>
Sent: Friday, January 16, 2009 1:58 PM
Subject: Re: [Premium-Rx] WJ 8718A help


> Lee,
>
> I am looking at the preselector on my WJ8716 and don't see a chip with 
> that number. I am assuming the preselector for the WJ8716 and 8718A are 
> similar but I could be wrong. My preselector is part no. 796012 and the 
> only chips I see are on the A6 board and they are common SN74LS42N and 
> SN754538P types.
>
> I don't have any data on the pre-selector option, but have been looking 
> for a schematic and alignment info.
>
> I recently read some posts about the WJ8718 MPF version having clicks 
> every 10 kHz and thought I would see if my receiver had this problem as I 
> didn't recall anything like that. The only clicks I heard were at wide 
> spaced intervals that I believe are switching points in the preselector. 
> But I did discover a problem with higher background noise only between 800 
> and 1200 kHz than anywhere in the rest of the tuning range. This problem 
> disappears when the A1preselector board is pulled, so I'm thinking the 
> problem lies there. Maybe a switching diode or tantalum capacitor? Do you 
> or any of the group have any thoughts on this or can help with some data 
> on the preselector option?
>
> Les Layton
>
>
>
> ---- L D Ritta <ufp at optusnet.com.au> wrote:
>> Hello All
>>
>> I have been looking at the preselector option used in the WJ8718A and 
>> noticed they used a chip.
>> A   841009 but my google search found nothing usefull. What is it, do you 
>> have a datasheet.
>>
>>
>>
>>
>>
>> 73 Lee
>