Anyone out there with some SB-610 experience?

Wed Jul 30 18:03:14 EDT 2003

Steve - Thanks for the opportunity to reply.  Most issues with these scopes
(SB-610, HO-10) are in and around the high voltage area; many of these
components are underrated and/or are operated at the extreme of their ratings
…very seldom are there issues in the low voltage or bias.  Not to say there are
not ever any issues, just the messages regarding issues of the monitor scopes,
on this reflector, do not seem to point to these areas.  The CRT (3RP1) is very
rugged and though there are some that have failed, many including mine in my
two scopes, are the original ones that came with the unit.  As you mentioned
transformer failure is also common.  I wonder if it’s really the transformer or
the components that are failing after the transformer that cause the
transformer to fail?  Maybe some one else can comment on this….I am just
suggesting something here, not insinuating anything.

Regarding the first issue of concern…the display is most likely dim because of
component failure in the high voltage area; those specific components that feed
voltage to pins 1, 2, 3 and 4 of the CRT.  The first two capacitors in the 600V
circuit are prone to failure (C604 and C605).  I would replace these with newer
capacitors…you may have to parallel/series them to gain the rated voltage and
capacitance.  These are not electrolytics so just regular orange drops should
do fine.  The next capacitor in the line, C606 is also a prime suspect…I would
change this one also; again, it’s not an electrolytic.  Again finding one
capacitor with a 1600V rating is not easy, so some parallel/series caps may be
necessary here also (I’ll let you do the math).  Increasing the capacitance is
not a real problem either….if you cannot come up directly with .15 mfd.  R605,
the 330K resistor which is from lug 4 to lug 2 of terminal strip B should be
checked and replaced if it’s out of tolerance.  There are a total of six of
these resistor values (330K) in the SB-610…this one is too low a rating…it’s at
½ watt…I would replace it with at least a one watt or higher.  The next
culprits are resistors R508 and R510…these are 1/2 watt also.  These are found
on the control lugs of AL and AK and should be replaced with 1 or 2 watt
resistors of the same resistance.  Next, take a look at R506…it’s a 330K also
(last of the three to replace)…replace this with a higher wattage…1 or 2 watt
is fine….if necessary.  Lastly, replace R505, 100K, if it’s out of tolerance.
PLEASE NOTE:  If you do any initial measurements or after changing components
do measurements, these are dangerous voltages you are dealing with here….take
all proper precautions.

Regarding your second issue…my SB-610 sweep frequency is at about 1/2 to 2/3rds
of full control, when it’s fully operating.  Adjusting this just sets the
correct parameters of using the scope trace.  What your seeing is just normal
to any scope.  Maybe someone else can do a better explanation of this for you
if you still have issues.

Hope this helps you Steve.  These are not hard to fix or work on.  If you have
problems, I’m sure there are many on this reflector willing to assist (me
included).

73, Larry KC8JX
--- Steve <steveac at CHARTER.NET> wrote:
> Hi Pete and Larry and Jim,
>
> Thanks guys. Here's the situation.
>
> I bought and built an SB-610 in the early '70's. In the late '80's it
> quit working and I found the power transformer's 600 volt secondary to
> be open. So I put the unit aside with the intention of getting back to
> it. So, fifteen years later, I'm getting back to it :)  I did some
> trading recently to acquire another monitor scope that I could use for
> parts and whose transformer was good.
>
> I installed the working transformer in my unit and now I have a trace on
> the screen.
>
> First issue: If the unit's been turned off for a while and cools, when
> it's turned on there's a trace. It isn't very bright, but it's a solid
> line across the screen with the SWEEP FREQ set at full CCW. I know it's
> been a while since I last saw the screen, but as best I remember from
> years ago, the trace was bright and keying waveforms and voice patterns
> were readily viewed in a room with normal lighting. Now, the room has to
> be darkened a good bit to see the patterns. Why is the display so dim?
>
> Second issue: After it's been on for about ten minutes, the trace
> becomes choppy. By that I mean that the horizontal trace line has gaps
> in it. With the sweep frequency at minimum (full CCW), the trace has
> four or five gaps in it, the length of each gap is about a quarter of
> one of the divisions on the face of the scope, the gaps are spaced about
> two divisions apart and they move from right to left across the screen.
> If I turn the sweep frequency toward max, the gaps synchronize and stay
> still when the SWEEP FREQ control is at about 1 o'clock. Any idea what
> causes those gaps?
> Thanks. Steve K8JQ

=====
May your days be full of sunshine and good thoughts fill your head.
From: Larry Knapp, KC8JX, St. Joseph, Mi  49085
  Best 73's

__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free, easy-to-use web site design software
http://sitebuilder.yahoo.com

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.asp?list=HEATH
To post - HEATH at LISTSERV.TEMPE.GOV
Archives - http://interactive.tempe.gov/archives/HEATH.html