How I broke (and repaired) my HR500

[Geert Jan PE1HZG]

Hi folks,

Just a note to advise people not to make the same error I made.

The HR500 typically needs 5W MAX input power.
When the HR500 is not online (set to MODE == OFF) then the HR500 does not switches the PA inline when one starts a transmission. One would think that more than 5W power is allowed then, it would destroy the MOSFETs but as long as the amplifier is online, more power "should" be OK.

I found out that is not the case. The RF level input detector is always in-circuit (even when the PA is MODE == OFF) and I managed to blow up the input RF detector.

The PA then still works and full output is available, however the input drive indicator barely moves (whether  MODE is PTT or OFF) and hence the input limit protection also doesn't work.

In my case, I managed to damage D1 (1N5711W) on the Rear Panel board. I obtained a replacement via Digikey (you need the SOD123 casing, 1N5711W-FDICT-ND), replaced it, and all is well again.

Doing what I did is definitely dangerous because a high input power is a sure way to kill the MOSFETs but during experimentation, one does what one does and I did not expect this defect to happen.

At least, when it happens, or when one prepares a digikey order, perhaps ordering some spare 1N5711 diodes may not be a bad idea.

73, Geert Jan PE1HZG

[N1IG - Anthony]

How much power were you using?