Hi Ed I have a 5120A with a non-workinf DDS board. I cant remember the model
but I did find a generic ''circuit'' for how the DDS worked in one of the
later PTS manuals. I'm guessing you have already gone beyond that in your
circuit tracing. The 5120A has two boards and the only information given is
to determine which board the is failing. My unit will go wild if any digit
other than zero is set.
Good luck with it
Alan
G3NYK
----- Original Message -----
From: "ed breya" <e...@telight.com>
To: <time-nuts@lists.febo.com>
Sent: Sunday, September 16, 2018 9:25 PM
Subject: [time-nuts] 8 kHz problem in Wavetek/Rockland 5135A synthesizer
My (formerly) trusty 5135A crapped out a while back, and I've been trying
to fix it recently. I have tried in vain to find some particular details
on the remaining problem circuit. I haven't found any kind of manual for
it, but found one for the 5120A, an apparently similar, older model.
The initial problem was a blown main filter cap in the +5V supply, readily
fixed to restore operation. However, there is now a persistent 8 kHz step
in the output - a 10.000... MHz setting puts out 10.00800... and so forth.
There is also some interaction with the 10 kHz decade settings. I suspect
that the +5V PS failure has damaged something in the large LSTTL DDS
circuitry.
I have narrowed it down to the "DB1" board, which handles the 1 and 10 kHz
digits, and the output end of the DDS system. The 5120A seems to have
exactly the same guts as the 5135A here, but there is no detail of the
circuitry. It's stated as a "send it to the factory for repair" type deal,
with no schematics or parts info at all, unlike the other sections and
modules, which are well documented. I suspect that even if I find the
proper 5135A manual, it will be the same story - no info on the DB1 or its
associated DB2.
I have shotgunned a few of the parts most closely associated with these
two digits, and have been trying to trace out the actual circuits. Still
no change in operation. The DB1 does the top two digits of BCD to binary
conversions, and somehow the counting, sine ROM, and DAC, while the DB2
does all the lower digits, all using mostly trees of 74LS283 adders - lots
and lots of them.
So anyway, does anyone know of more info on the 5135A, or of how the guts
may have been implemented in detail? Is there a repository of info on
various synthesizers here somewhere? I thought I had seen in the past some
listings, comparisons, and maybe documents about them here, but nothing
popped up in my recent searching.
Ed
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