[Elecraft] KPA-500 270V ERR

[David Gilbert]

Pedantic?  If those were truly PIN diodes like you called them the 270v 
bias wouldn't have been used there.

Dave   AB7E


On 8/26/2021 2:56 PM, Fred Jensen wrote:
> This morphed into a pedantic discussion of solid state diodes.  
> Chuck's original question was about the 270 V error.  I'm fairly sure 
> the only purpose for the 270 V in a KPA500 is bias for the T-R 
> switch.  He asked for suggestions.  The T-R switch and the source for 
> the 270 V might be a good place to start troubleshooting.
>
> 73,
>
> Fred ["Skip"] K6DGW
> Sparks NV DM09dn
> Washoe County
>
> On 8/26/2021 2:23 PM, David Gilbert wrote:
>>
>> High voltage rectifier diodes would have very low doped N-regions, 
>> which means fairly long carrier lifetimes so no doubt they work 
>> somewhat like a PIN diode if properly biased.  But they aren't really 
>> the same thing, and I still say that a PIN diode has performance 
>> advantages in many situations.  They are more difficult and costly to 
>> build, though.
>>
>> I used to manage a large semiconductor entity that manufactured these 
>> things.
>>
>> 73,
>> Dave   AB7E
>>
>> On 8/26/2021 2:05 PM, jerry wrote:
>>> Using 1N4007's and 1N5208's ( I could have the last # wrong ) as 
>>> "Poor Man PIN
>>> diodes" is pretty established practice in the amateur community. 
>>> Look up
>>> W6JL on QRZ.com.  He has an extensive article about it on his page 
>>> there.
>>>
>>> Also Hans Summers of qrp-labs uses them in his 50W QSK amplifier.
>>>
>>>   Apparently, these kilovolt rectifiers behave very much like PIN 
>>> diodes,
>>> at speed.
>>>
>>>                - Jerry KF6VB
>>>
>>> On 2021-08-26 11:46, David Gilbert wrote:
>>>> That sounds odd to me.  True PIN diodes are current actuated devices.
>>>> The carrier lifetimes are long enough that the devices are "on" even
>>>> if the signal peaks exceed the voltage of the control current ... as
>>>> long, of course, as the control current exceeds the signal current.
>>>>
>>>> On the other hand, I've heard that Elecraft has sometimes used regular
>>>> switching diodes instead of PINs, and for those you need a voltage
>>>> that exceeds the peak voltage of whatever you're switching.
>>>>
>>>> Both types of diodes have their place ... using one where the other
>>>> works better is not good practice.
>>>>
>>>> 73,
>>>> Dave   AB7E
>>>>
>>>> On 8/26/2021 11:33 AM, Fred Jensen wrote:
>>>>> I think the 270 V circuit is DC bias for the PIN diodes in the 
>>>>> TR-switch.
>>>>>
>>>>> 73,
>>>>>
>>>>> Fred ["Skip"] K6DGW
>>>>> Sparks NV DM09dn
>>>>> Washoe County
>>>>>
>>>>> On 8/26/2021 10:32 AM, Chuck Chandler wrote:
>>>>>> My KPA-500 has been running great for several years.  Recently I 
>>>>>> noticed it
>>>>>> was making the occasional extra "click" or "thunk" upon powering 
>>>>>> up or
>>>>>> down.  Usually it would "click" when powered up and again when 
>>>>>> powered
>>>>>> down, but recently a few seconds after the first click there 
>>>>>> would be
>>>>>> another one, maybe more of a thunk sound.
>>>>>>
>>>>>> This afternoon I turned it on and when I pushed the 
>>>>>> Operate/Standby button
>>>>>> I got a fault light and the 270V ERR message on the display. The 
>>>>>> menu HV
>>>>>> option shows 68.4V, varying a bit, on my 240V line.  I put it on 
>>>>>> the bench
>>>>>> and opened up the top cover.  There is a smell of overheated 
>>>>>> components,
>>>>>> maybe burnt but more like too hot.
>>>>>>
>>>>>> I've submitted the contact form on the Elecraft support page. Any
>>>>>> suggestions?  For now, I'm running barefoot...
>>>>>>
>>>>>> 73 de Chuck, WS1L
>
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