SB 220 problem

[ray mack]

Larry:
        Try to remember what state it was in the last time you used
it.  Was everything OK back then?  If so, then it is unlikely that
something drastic has happened just from being unused.

        First turn off the power and remove the power cord from the
wall.  Let the power supply discharge for 10 minutes.

        To test the meter, remove both of the nuts and wires.  I would
use a 1K resistor in series with an ohm meter.  touch the ohm
meter/resistor pair across the meter.  IF you read a couple of K Ohm
then the meter is OK.  You will probably see the needle move.  (I'm
usually more of a daredevil and put the ohm meter directly across the
unknown meter, but that is probably not a good idea in this case.
Meters would be nigh on impossible to replace.)

        The likely problem is dirty contacts on the switch since none
of the functions works correctly.

        If it is anything like the meter circuit on the SB200, the
resistors used for HV may be cooked and way off value.  The problem is
that 1W carbon comps are only rated to about 350VDC.  The ones in the
SB200 have about 600VDC across each resistor in the string.  The other
problem is that they used 20% resistors and all the ones in our unit
were at the top of the tolerance.  If there are 3 resistors in the
string you might want to use 6 equal value resistors to get the same
value but that lowers the voltage across them.

        Let us know what you find.

Ray Mack
WD5IFS
mack at mails.imed.com


______________________________ Reply Separator _________________________________
Subject: SB 220 problem
Author:  lalbert Main mail <lalbert at RICONNECT.COM> at mails
Date:    5/29/98 6:10 AM


I'm getting back into ham radio. I fired up my SB 220. The output seems ok
(the finals seem a little bright). My multimeter is not functioning.(HV,rel
power and grid current). The plate current meter seems ok. I removed
the.02cap across the the meter, it's not shorted. where do I go from here?
How do I check the meter itself? I would appreciate some input. Thanks.
Larry   W1GSH

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