[Amps] AL-1200 Grid Current - negative?

[R.Measures]

>Continuing this thread...
>
>In addition to the bad resister inside the meter, the two 1.5 ohm grid 
>resistors were open (thanks to W1QJ for encouraging me to check those too).
>
**  A suddenly open grid-current meter shunt resistor indicates a burst 
of grid current.  Are there glitch-protection diodes across the meter 
movements?  Have you measured the full scale meter I-sensitivity?

>Several weeks back I posted my AL-1200 story - I was using it on 40meters 
>during a contest when it arced.  The IC756ProII connected to it went south - 
>  the transmitter no longer put out any RF.  ICOM has it, they say some 
>protective diodes were taken out.
>
>Earlier, I discovered that the resistor in the parasitic suppresser came 
>unsoldered.  Is it a reasonable theory that the parasitic suppresser failed 
>causing some self-oscillation and excessive grid current that took out the 
>grid resistors (and my 756proII)?  Or should I be looking for a different 
>underlaying cause?

**   What is the measured resistance of the suppressor resistor that 
became unsoldered?
>
>I'll be picking up some new grid resistors and taking it from there.
>
>   Dana
>
>
>
>Dana Roode wrote:
>> Amps folks -
>> 
>> Ok, I removed the tube and the meter still went negative.  I checked the 
>> filament connections with the tube out, nothing is shorted to ground.
>> 
>> I was suspect of the metering circuit itself.  The left multi-function 
>> meter measured 300 ohms across the terminals, the right grid meter 
>> measured 15k. The parts list indicates both meters are 300 ohm 1ma.
>> 
>> I took the grid meter apart, it has a component (a precision resister, I 
>> assume) in series with each internal meter movement lead.  One measured 
>> 100 ohms, the other about 15k.
>> 
>> I am pretty clueless about this, and Im at a loss as to why a 100ohm 
>> resister would become 15k, but perhaps this is my problem.
>> 
>>   Dana
>> 
>> 
>> Dana Roode wrote:
>> 
>>> What does it mean when you power up an AL-1200 and the grid current 
>>> meter pins negative (no drive power supplied)?
>>>
>>>   Dana
>>>
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>> 
>> 
>
>
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