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Author Topic: SB-200 meter dose not work  (Read 5431 times)
KD0GES
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Posts: 28




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« on: December 01, 2012, 04:46:02 PM »

I have a sb-200 that the meter does not work.
I deoxit the meter selector switch and it didn't help.
I can get movement of the meter by putting my ohm meter across the terminals.
Any help of what to look for will be appreciated.
Also can I run the amp using an external power meter to tune it for max output?
Thanks
Dale (KD0GES)
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W1QJ
Member

Posts: 1444




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« Reply #1 on: December 01, 2012, 09:35:34 PM »

if the meter shows no indication on any selection then chances are you have a bad connetion or broken wire or some sort of mechanical problem.  If the meter moves with an ohm meter then the meter itself is probably good.  Check the meter for back to back safety diodes, remove them and see if the meter works.  Maybe have a shorted diode there.   I think you will find a bad connection or even a corroded  terminal on the meter.  Remove the nuts and clean the terminals.
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KD0GES
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Posts: 28




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« Reply #2 on: December 02, 2012, 07:42:54 AM »

Thanks for the help.
Does radio shack hove the diodes to put across the meter?
And what type of diode should I use?
Thanks
Dale
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RFDOG
Member

Posts: 18




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« Reply #3 on: December 02, 2012, 08:12:16 AM »

With all due respect, if you don't know the answers to those questions you should not be fooling around in there. Electrocution is permanent.  At least download the manual and read it.
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KD0GES
Member

Posts: 28




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« Reply #4 on: December 02, 2012, 09:46:59 AM »

My electronics is a little rusty.
I had 2 years of votech training 25 years ago and never got a job.
If I remember correctly diodes have .7 volts before current will floe
Dale
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K7KBN
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Posts: 2784




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« Reply #5 on: December 02, 2012, 09:57:25 AM »

Depends on the diode material (whether germanium or silicon).  0.7v is about right for germanium, but silicon is maybe half of that, like around 0.2v.
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73
Pat K7KBN
CWO4 USNR Ret.
G3RZP
Member

Posts: 4464




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« Reply #6 on: December 02, 2012, 10:30:03 AM »

Wrong way round, Pat!

about 0.7volts for silicon, around 0.2 to 0.3 for germanium, around 0.2 for Schottky.
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KA5N
Member

Posts: 4380




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« Reply #7 on: December 02, 2012, 11:03:33 AM »

The meter on the SB200 didn't come with protection diodes across the meter, so if it
has diodes, then someone added them.  Who knows what they may have used.  If
either diode is shorted then the meter won't indicate and probably wouldn't indicate
even with the current from a multimeter.  It is simple enough to check the diodes
(if indeed they are there) with a multimeter.  Remove them and check resistance
a short will give about zero ohms.  A good diode with indicate zero in one direction
and very high resistance in the other (maybe no indication).  It is a BAD idea to try
and operate the amp without a working meter, particularly if you are no well versed
in the operation of the amp.  Do you know a local tech who can help?  An SB200
is a simple and easy to repair amp, since you seem unsure as how to proceed, then
please get help before you damage the amp farther or injure yourself.
Allen KA5N









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K7KBN
Member

Posts: 2784




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« Reply #8 on: December 02, 2012, 03:54:33 PM »

Wrong way round, Pat!
about 0.7volts for silicon, around 0.2 to 0.3 for germanium, around 0.2 for Schottky.

D'oh!  Back to "read before posting" again....  Grin
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73
Pat K7KBN
CWO4 USNR Ret.
KD0GES
Member

Posts: 28




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« Reply #9 on: December 03, 2012, 02:52:50 AM »

Upon further investigation I found some wires that have gotten hot enough to melt the coating.
When I turned it on before the tubes would light up.
I am now replacing the bad wiring and while I am at it I probably will put in new capacitors in the power supply.
My guess is the rectifier diodes are bad.
I did find the diodes for the meter protection at radio shack.
I am assuming the transformed is OK if the tubed light up.
Thanks for the help.
Dale (KD0GES)
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KD0GES
Member

Posts: 28




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« Reply #10 on: December 03, 2012, 07:54:36 AM »

Is there a good way to test the HV side of the transformer?
Dale
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KA9CCH
Member

Posts: 87




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« Reply #11 on: December 03, 2012, 09:18:13 AM »

Here is some good info for getting your sb200 on he air

http://www.w6kan.com/sb200.htm

Remember High voltage will kill...

GL
KA9CCH
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KD0GES
Member

Posts: 28




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« Reply #12 on: December 03, 2012, 03:44:39 PM »

I removed the high voltage output wires from the power supply board for the transformer and checked the resistance and got 13.2 ohms.
My guess is it should read 0 ohms on the secondary side of the transformer with an ohm meter.
Would this indicate the transformer is bad?
Thanks
Dale (KD0GES)
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AA4PB
Member

Posts: 12779




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« Reply #13 on: December 03, 2012, 03:56:20 PM »

No, the secondary should read higher than 0 Ohms so 13 Ohms is probably okay.
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KD0GES
Member

Posts: 28




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« Reply #14 on: December 03, 2012, 03:58:25 PM »

Good
Thanks
Dale
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