[time-nuts] 8 kHz problem in Wavetek/Rockland 5135A synthesizer

Alan Melia alan.melia at btinternet.com
Tue Sep 18 17:42:18 EDT 2018

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

----- Original Message ----- 
From: "ed breya" <eb at telight.com>
To: <time-nuts at 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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