🚀 go-pugleaf

Phil Allison wrote:
>  "Sylvia Else"
>> Phil Allison wrote:
>>> "Sylvia Else"
>>>>>> As for whether I could substitute a 6.8, maybe I could, though I'd 
>>>>>> have trouble getting one that has a 350 volt rating.
>>>>>  **   Huh   ??????????
>>>>>
>>>>> No need for that whatsoever.
>>>>>
>>>>> In operation, the resistor is not subjected to more than a few volts.
>>>> As I commented earlier, if the switching transistor fails by shorting 
>>>> out, then the resistor will blow. After it's blown it'll have 340V 
>>>> across it.
>>> ** Irrelevant.
>>>
>>> Once it has fused, the resistor  will be OPEN circuit.
>> Which just means it won't conduct unless the voltage across it exceeds its 
>> insulating properties.
> 
> 
> ** No,  it  WILL  be open circuit to the voltage that caused it to fuse.
> 
> Cos the fusing behaviour will not cease until the part becomes open circuit 
> in the given situation.

That just begs the question of whether it will fuse in its designed way, 
or whether the excess voltage will cause it to fuse in an unintended, 
and possibly damaging, way.
> 
> 
>>> The voltage across the break can be thousands of volts.
>> So you say, but where's the evidence?
> 
> 
> ** You came here for the advice of folk with experience of electronics,  cos 
> you have none.
> 
> That advice is based on many decades of ACTUAL experience, in my case.
> 
> If you simply replace the fusible resistor in the PSU with a similar part, 
> then it will work as well as the original one did.

How do you know the original wasn't rated to 350V? The issue is not 
whether it will work, but whether it will fail safe.

Sylvia.