[Test-Equipment] Wavetek Rockland 5120a

[Alan Melia]

Hi all, I made an enquiry about the possibility of obtaining some manuals or
any information on this beast some time back. It is obviously an odd one,
because I was deafened by the silence. The only Google hits seem to be
others looking for information. I started a topic on a discussion group and
got 256 visits but only one reply !! This leads me to believe that there are
lots of these around and no information !!

To try to start off somewhere here is some info I have found on my unit :-
Of 3 machines discussed with owners so far none has an internal reference
osc. and 2 have a faulty 23v power supply. The 23v PSU is a split phase
full-wave rectifier with a 1000uF 50volt wkg cap across it. I had  9volts of
100Hz "ripple"....... a 1000uF tacked across the motherboard connection pads
(in front of the transformer) makes this better (the supply is not
regulated) but doesnt fix the fault.

The synthasis seems to be done in too parts, 100kHz and up is handled in the
long screened boxes, easy to remove but could be difficult to repair. The
control BCD codes go to J3, J4 and the plug-on links to the box near the
side-wall. My unit works correctly above 100kHz provided all the lower
decades are set to zero. As soon a any lower decade switch is set above
zero, the output count is incorrect and random, and the spectrum analyser
display looks like wideband noise around the programmed frequency.

The lower decades seem to be synthasised on the two unscreened pcbs  (one
with SMAs 10MHz IN and 10MHz OUT ) There is no sign of phase-look loop type
chips in this area, the majority of the chips are 4-bit full adders
(74LS283) and registers/buffers. There is at the rear of one board an area
that looks like a discrete DAC. I wonder if this could be a form of TTL
built DDS ??  I doubt that Rockland only used this design in only one
instrument, so has anyone any information on a Rockland (or Wavetek , who
bought them later) unit with a low frequency (1Hz to 99.9kHz)  synthasiser
with a similar architecture??  I just want to get a feeling for how it
should work, to plan a fault-finding strategy.

Thanks for indulging me, I hope what little information I have found is
useful to someone.

Best Wishes
Alan  (G3NYK)