Re: Something has been blown

Arv Evans
 

Ceasar

It might be worthwhile to make up a little test jig for evaluating IRF510 devices. 
Maybe just a pot to vary the gate bias and a 1K resistor in the drain lead.  Ground
the source lead.  Monitor drain voltage as you vary the gate bias.  At between 3
and 4 volts on the gate you should see drain voltage decrease indicating that the
device is drawing current.  If this current is not adjustable it might indicate a defective
device.  Of course this is just a DC test and not fully representative of RF performance.




In BJT (Bipolar Junction Transistors) we are used to seeing the base draw current
to forward bias the device, but with MOSFETs there is no gate current.  They are
only affected by voltage at the gate.  Once we accept that it is easier to troubleshoot
circuits that have these devices.

An oscilloscope or RF Detector Probe could be used to measure RF at various points
around the IRF510 devices.  You should have at least a couple of volts RF on the
gate lead, and more RF volts on the drain lead.  If nothing on the gate then you could
use the probe or scope to verify presence or absence of RF voltage in the drive section.

Arv
_._


On Fri, Jan 26, 2018 at 9:23 AM, César EA3IAV <Cesarleon@...> wrote:
Thank you Arv

It is weird. I was adjusting the pa with the blue squares and the fuse blew. I changed the fuse and it happened again. It was like that until i changed the transistors... i have quite a few.
now still no power out visible through power meter even in lowest selectir (2w mode)
0,5amps while ppt but as i speak there is no increase on that 
i can hear myself in a close receiver  though...
i feel like these fets are bad

what else could br the reason to not output power?
what is that round blue trimmer for?

i do receive fine btw

i am going tonmy local electrinic shop to buy more fets and fuses 😟


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