[NLRS] Amp Driving Me NUTS...

[Dr. Gerald N. Johnson]

On 5/11/2011 10:25 AM, w0zq at aol.com wrote:
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> Wow Scott, that's a good one !   My suggestions -
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> 1. The replacement MRF648's were bad even before you installed them .... are they pulls from an old amplifier or are they brand new, never installed parts?  Are you confident that the new replacement parts are good?
> 2.  Do a very close inspection of the RF (copper) traces on the PCB looking for anything funny .... especially a hairline crack. You might play with a continuity checker to make sure that all PCB traces are good and not open.
> 3.  While doing that very close inspection, look very close for shorts and cold solder joints.
> 4.  Can you measure Vcc right at the devices? Make sure that when you transmit that Vcc is staying at 13 vdc and not diving ... if it dives it may indicate a high series resistance someplace on the Vcc line, for example a bad fuse. I have had a high resistance fuse, or fuse holder. Make sure there is no significant voltage drop across the fusing system on transmit (during high current demand).  Is your power supply capable of providing 25 amps and are your connects to it good?
> 5.   I have also seen bad relays. Both the input and the output relays can be a problem, usually caused by pitting. Many brick users use RF sensing, not PTT.   RF sensing in these bricks can lead to pitted relays - a pitted relay will often show up as an open.
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Yes RF keyed means the relays switch RF power and its hard on them. It 
might be possible to clean the relays up with a thin flat file or a 
fingernail sandpaper board or a bit of one. It could be handy to trace 
signal with a wide band scope or RF probe on a meter, but most meter 
probes won't survive 150 watts RF.

All that Jon says is good and say's he's been there and seen these 
problems before.

73, Jerry, K0CQ

> Good luck !
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> 73, Jon
> W0ZQ
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