On Sep 18, 2005, at 4:41 PM, David Kirkby wrote:
> jon s wrote:
>> Thanks to everyone so far for their thoughts
>>
>> The 87A was completely "OFF" - not in standby. I understand that
>> there is still some power running some some of the circuits as the
>> meters indicate exciter power levels even when powered down.
>>
>> Upon power up the amp goes into it's warm-up mode - the Wait LED
>> lights; no Hard Fault Codes are indicated; after warm-up mode - upon
>> pressing a Band segment button on the Amplifier there is motor
>> movement in the amp as it does it's "thing". However the amplifier
>> does not sense the RF from the exciter to change bands automatically.
>> Also no "amplification" is indicated. Th amp does not shut down by
>> itself and powers down without issue when turning it off.
>>
>> We removed the top cover looking for a component, (based on the "bang
>> and flash" described by my father I expected to see something blown
>> (capacitor?). Nothing was immediately evident however.
>>
>
> I can't help feel you have not looked hard enough. For something to
> flash like that, it must leave some indication of where it happened.
Agreed. The mystery of where a SB-220 flashes when it makes a big-bang
took many moons to solve. Turns out it is from an anode-cooler's
top-screw - usually V2 - upward to the bottom side of the perforated
cover. Thus, the damage was hard to see.
- The source of the arc is an intermittent parasitic oscillation at c.
110MHz, which happens to be the resonant frequency of the circuitry
that is in series with the 220's DC blocking C. The feedback path that
supports the oscillation is the anode-cathode C of 0.3pF, which has an
Xc of 5000-ohms at 110MHz,
end
>
>
>> I tried to talk to the amplifier using a comm program as described in
>> the manual - I was unsuccessful in this however. I guess my Father
>> will call Alpha power Monday and ultimately probably box it up and
>> ship it back for diagnoses and repair.
>
>> Previously to this problem the amp has performed without issue for 4
>> 1/2 years - my Father just chases DX - I occasionally go to his
>> station and operate contests with it.
>
> From what others have said here many times, there can be problems
> moving heavy packages (damage etc). It must be worth spending some
> serious time looking.
>
> My Compaq UPS (6 kW) decided to blow itself up on Friday. That made
> quite a bang, but there is evidence of smoke on the front, so the fault
> should be easy to find. It took out a 32A breaker in the process - it
> is
> the only item on that breaker.
> --
> David Kirkby,
> G8WRB
>
> Please check out http://www.g8wrb.org/
> of if you live in Essex http://www.southminster-branch-line.org.uk/
>
>
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>
>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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