[time-nuts] 5370B Question / help needed

[Thomas Allgeier]

Hello Folks,

I'm coming back to this after a few days of prodding etc. and there has
been some progress. The fault has been tracked down to the A3 input board
and it points at a crack in the board or a joint. Here is the sketch:
After a good clean of the switches and re-seating all boards etc. the 5370
sprung back into life with almost-in-spec performance of 102.xx ns with
it's own 10 MHz. Trouble is it didn't last - after a while and triggered by
sliding some switches around it went back to the 14 ns. Fiddling with the
BNC's may have the same effect, i.e. there is a mechanical element to it
all.
Turns out that running it with the front panel removed I can make it go
from 14 to 102 ns by slightly bending the A3 board, certainly while it is
cold. After a while this trick doesn't work anymore, my suspicion is
whatever crack/gap is causing the trouble has expanded too far to close it
tight. After cool-down we're back to square one.
I notice there are a few SMD components on that board, right in the middle
where it would bend most - basically on the reverse side of the switches.
Capacitors and resistors I expect. I wonder if it is worth going over the
solder joints of all these carefully.
What has stopped me so far are 2 questions:
Am I the only one with this observation or has anybody come across this
before?
Secondly the solder on these SMD's is coated with a black substance.
Clearly this could be removed somehow but it is probably there for a
reason. Has anybody re-touched joints like these before?
On an instrument like this it is very much a case of "proceed with care"
and I'd hate to do more damage by rushing in.

On a related subject: last year there was a discussion over redesigning the
input board(s) for the 5370 / 5345. Did this get off the ground? If my A3
packs up completely...

Thanks in advance for any suggestions,

Thomas.


Date: Wed, 5 Jul 2017 11:00:35 +0100
From: "Thomas Allgeier" <th.allgeier at gmail.com>
To: <time-nuts at febo.com>
Subject: Re: [time-nuts] 5370B Question / help needed
Message-ID: <F2C3025C50DF4411A8EC836C55B8E061 at flintec.uk>
Content-Type: text/plain; format=flowed; charset="UTF-8";
        reply-type=original

Thanks all for your help and suggestions - I've been off grid for the last
few days.
I will look into the dust/contacts issue first, and sweat up on the manual
and archive posts in relation to the adjustment procedure.
Then I will try to see how far this gets me and report back - watch this
space as they say.

I may well need the extender cards but since I am based in the UK shipment
would have to be considered. Probably worth checking all other options
first.

Best regards,
Thomas.