[Premium-Rx] RA1792 Problems. Help Please!

[Stuart Lamb]

Group,

Thanks to everyone for your suggestions. I'm going to have to clear the
shack up a bit before I can again access to the 1792, but I'll let you know
how I get on.

Meanwhile, I have another problem: I can't find my service manual! Please
would anyone have an electronic copy they could share with me?

Thanks again,


Stuart

-----Original Message-----
From: premium-rx-bounces at mailman.qth.net
[mailto:premium-rx-bounces at mailman.qth.net] On Behalf Of
davesc50 at tiscali.co.uk
Sent: 30 April 2008 18:32
To: danrae at verizon.net; premium-rx at mailman.qth.net
Subject: Re: [Premium-Rx] RA1792 Problems. Help Please!


Hi,

As Dan points out my description of the faults may have been a little 
over simplistic.
I am aware that the later Mk5 and Mk6 receivers have a different 
manufacturers Tantalum capacitors fitted and that they are not as prone 
to faliure.
Blue Tantalum capacitors are much more prone to faliure than the later 
yellow ones.
Stuart does however mention his is an early receiver although does not 
specify the exact revision. 

Dan is the acknowledged expert on these receivers and I would go with 
anything he says over my statement.

I did however, all be it fleetingly, mention the battery problems on 
the processor PCB as another possible cause.

I would never jump in and replace all the caps lightly and my comment 
was ment to be a little tongue in cheek.

If the supply rail to the processor is comromised by a failing 
capacitor the same data coruption faults can appear.

Hope this clears things up a bit,

Dave.S.
>----Original Message---
>From: danrae at verizon.net
>Date: 30/04/2008 16:01 
>To: <premium-rx at mailman.qth.net>
>Subj: Re: [Premium-Rx] RA1792 Problems. Help Please!
>
>David Schofield wrote:
>
>> Hi Stuart,
>>
>> The short answer to your question is YES. There are very well 
known 
>> faults on the RA1792. Basically suspect "every" tantalum capacitor 
in 
>> the unit.
>> The easy way to fix the unit is to replace all the tants. 
>
>
>Hold on there!
>
>It isn't easy; there are a LOT of them.  I did it once and it took a 
>week of intermittent work to complete.   I forget the count, but it 
is 
>up in the fifty plus range, and in particular the ones on the double 
>thickness A4 board are a pig to remove since the plated through 
holes 
>have no heat relief.
>
>I will not disagree that in some of them, but not all, the tantalums 
are 
>prone to failure, but the symptoms are sudden death, after being 
>powered  off.  I only did the one I referred to above because it had 
a 
>total of five dead ones when I got it, and I thought the message was 
>clear enough and I could spare the time!
>
>It isn't a bad idea however to replace all the aluminium 
electrolytics, 
>as in any 25 plus year old radio.
>
>In Stuart's case the symptoms he describes, a gradual failure, is 
almost 
>certainly down to battery damage to the A6A2 card.   In both designs 
of 
>cpu board the components that link the cpu board to the rest of the 
>radio are adjacent to the battery and any leakage will give the sort 
of 
>data bus problems he describes. 
>
>"What we have here is a failure to communicate!"
>
>Exactly what damage has been done varies.  I have often had to remove 
IC 
>sockets where fitted, since the corrosion destroys the contacts 
inside.  
>Also the VIAs on the board in that area are prone to go open 
circuit, 
>since the alkali from the nicad gets under the resist layer and 
destroys 
>the trace at the edge of the hole.  I have had to remove the 34 way 
edge 
>connector a couple of times as well.  
>
>And a plea to any 1792 or 6790/GM owner who has not already done so: 
>change the battery for a new NiMH one!
>
>73
>
>Dan
>ac6ao / g3ncr
>
>
>
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>Email Help: paul at premium-rx.org
>
>




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