[Elecraft] KPA-500 270V ERR

[Fred Jensen]

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