Anyone out there with some SB-610 experience?

[Steve]

Larry, thanks for the advice. I have replacement caps for C604, C605 and
C606 on the way. When I install the replacments I'll take a look at the
resistors you mention.

I'll let you know how it works out.

Thanks everyone!

Steve
K8JQ

Larry Knapp wrote:
> 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
>
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