🚀 go-pugleaf

Sylvia Else wrote:

> Phil Allison wrote:
> 
>> "Sylvia Else"
>>
>>>> The main switching transistor appears to be intact. I haven't 
>>>> removed it from the circuit, but the voltage/current plot given by a 
>>>> component tester feature on my oscilloscope gives the expected 
>>>> traces for the base collector and base emitter junctions, allowing 
>>>> for the presence of the diode across the base emitter junction.
>>>>
>>> I further surmise that the failure of Q1 doesn't explain the failure 
>>> of the 8.2 Ohm resistor, because even with its specified maximum beta 
>>> of 40, the switching transistor wouldn't pass enough current to burn 
>>> out the resistor.
>>>
>>> The implication is that some other event has done for the both of 
>>> them, but surprisingly not destroyed the switching transistor.
>>>
>>> <sigh> I thought I'd understood the sequence of events, but clearly 
>>> not :(
>>
>>
>>
>> **  In an earlier post you state the PCB had been subjected to water 
>> ingress and insect attack -  so almost anything is possible.
>>
>> Odds are, the switching transistor was forced hard on by the above, 
>> taking out the 8.2 ohms and Q1 in quick succession.
>>
>> Relace whatever parts you find are damaged, clean the PCB carefully 
>> with detergent and a brush (as you would washing glass ware etc in the 
>> sink ) rinse with clean water and dry thoroughly with lotsa hot air ( 
>> ie a hair dryer).
>>
>> Then cross you fingers and try it again.
>>
>> If all is well, coat the PCB is clear acrylic lacquer to help it survive.
>>
> 
> It's true that I mentioned brushing away a dead spider.
> 
> I wish I'd noted exactly where the spider was. It conceivably was around 
> the 200K resistor, which could explain both the failures, and the demise 
> of the spider.
> 
> Anyone know the resistance of a small spider before it dies from shock?
> 
> Sylvia.
To me it looks like a safety circuit that is designed that requires you 
to  pull the plug , so that Q1 being a thyristor in my case of thinking 
will clamp down on the circuit from an over voltage, and remain that way
  until you pull the plug and wait. The 8.2R could just be burnt out or
  it maybe located in a thermo area intentionally to burn out (thermo Fuse)
   in which case, Q1 would also clamp.

  Either scenario will prevent the coil to be energized, if that is what
  T1 is?

  Since you haven't supplied any component part numbers, it's hard to say
really, if that is what's going on.

-- 
"I'd rather have a bottle in front of me than a frontal lobotomy"

http://webpages.charter.net/jamie_5"