RF getting into cheap LED meters?


I have just finished putting together a 23cm amplifier based on a PE1RKI 150w amp.
In my case I now have switch mode PSU's for 28v DC (amplifier)  and 12v DC (relays, sequencer and fans).

All works well as an amplifier.  Except I fitted some cheap LED dual A / V meters from a rally. These meters work fine out of the confines of the case but in the case their display on Amps only  reduces (rather than rises) as the amplifiers output wattage increases. At levels beyond 50watts the meters effectively start going 'backwards' until by 100watts they read zero. (volts readings remain stable / true).

I assume RF is getting where it shouldn't,  the meters are not screened, the PCB's are held in a plastic frame. I tried decoupling caps at the meters with some effect, but not enough.  A mixture of clip on ferrites on the LED meter leads seems to have tamed this issue and today I will fabricate some screening boxes for the meters.

Is there anything else I should look at (other than buying better meters).

Thanks Andy GD1MIP 

PS a link to my meters.... https://drive.google.com/folderview?id=1YBujeGcEnsWeOeAZxSjfBZWJMp00yydh

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