[Elecraft] KPA500 T/R Switch Board – D8 Identification

[Brian D]

D10 S/c gave me the same problem. several years later it has recurred but is
intermittent this time. I'm about to investigate suspect heat has affected a
dry joint this time.

If yours is an early amp then there are modifications to bring it up to
current spec. I seem to have lost teh details of that.



"Earl via groups.io" <earl.ab9tx=gmail.com at groups.io> wrote:

> Oliver it looks like D10 is cooked not D8?
> 
> On Sat, Jun 6, 2026, 06:32 Oliver Bross via groups.io <oliver=
> bross.eu at groups.io> wrote:
> 
> > Hi all,
> >
> > I’m troubleshooting an Elecraft KPA500 that has the following symptom:
> >
> >    - TX output is normal (500+ W)
> >    - In STBY, receive is normal
> >    - In OPER, receive is attenuated significantly on all bands
> >    - Elecraft support suggested an internal T/R switching issue
> >
> > While inspecting the T/R Switch Board, I found D8 appears damaged and
> > may need replacement.
> >
> > From the KPA500 schematic I have, D8 on the T/R Switch Board is labelled
> > *S1M*. D7 and D9 in the same area are also shown as S1M.
> >
> > Before I replace it, can anyone confirm:
> >
> >    1. Is D8 indeed an *S1M (1A, 1000 V SMA rectifier)*?
> >    2. Were there any board revisions that used a different diode?
> >    3. Has anyone seen a failed D8 cause receive attenuation in OPER mode
> >    while TX remains normal?
> >    4. Are there other components on the T/R Switch Board I should check
> >    at the same time (relay contacts, PIN diodes, switching network,
etc.)?
> >
> > I’ve attached a close-up photo of D8 and can provide the relevant
> > schematic section if needed.
> >
> > Thanks and 73,
> >
> > OliverOM0RX
> > 
> >
> 
> 
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-- 
Brian D 
G3VGZ G8AOE G3T
IO94im