COBRA 200 GTL DX, RF DRIVER MOSFET REPLACEMENT - RD16HHF1

[TRANZMATCH]

hi i find with cobra mike modulation to low and flat what type of power mike would you recomend for this rig thanks.

[weazle66]

@TRANZMATCH Most people i know moan about the flat audio on these radios, i think any decent power mic would be a improvement over the original.

[TRANZMATCH]

hi thanks for your help ordred  one with knights electrocom 73 derek g0omf.

[TRANZMATCH]

ware  can i buy rd16hhf1 in uk.

[weazle66]

@TRANZMATCH Try Knight's Electrocom, they normally stock them.

[xtranaut]

Is this driver replacement common in all radios in the series? I have a 3rd generation Cobra and all but one of the suggested cobra fixes to inherent problems was necessary so they must have corrected some shortcomings as they learned.

[DIESELDOG956]

Can you use other up grades on the driver

[weazle66]

@DIESELDOG956 I have never tried as i have a good supply of RD16HHF1's and they are quite cheap, the IRF520/ERF2030 is not the same as a RD16HHF1 so would not work as a direct replacement - i think others may have all ready tried this without much success.

[DIESELDOG956]

Can you use a 2030 or a 520 for the driver

[norseleague]

How do you tune up the modulation? I haven't any-I got it used. I knew something would be wrong so would i change the mosfet?

[weazle66]

@norseleague If the radio has good output power but just no modulation then i doubt that the MOSFET driver is the problem.

I would recommend having someone who knows these radios well check it over for you to find the problem.

[Blazerman6789]

I have a question, what is your reference point for the bias voltage, is your negative lead of your voltmeter going to chassis ground? Thanks a lot for your help, great video and info, look forward to resurrecting the old cobra!

[weazle66]

@Blazerman6789 The reference point for the GATE voltage is the PCB track to the GATE, i always set the voltage before installing the new FET just in case the voltage is set too high. use the PCB chassis ground for the negative lead.

[Blazerman6789]

@Blazerman6789 so i have the cobra 200gtl open on my bench and have removed the mosfet driver, when i measure from chassis ground to gate trace, i measure 0.1volts, should i not be going to chassis ground and then the gate trace?

[weazle66]

@Blazerman6789 Measure with the positive probe at GATE trace and negative probe on negative chassis ground.

[weazle66]

@Blazerman6789 Remember you measure the voltage while in TX, the voltage to the GATE is only applied while in TX.

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[digiglen]

130ma is best setting to keep RD16HHF1 lasting.. So many people try to peak this stage an end up blowing the RD16HHF1.. The radio works best around 50 watts. in qso`s.. I find that the radio can drift slightly when hot...But saying that a fan near the heatsink is handy.... I find the cobra 200 excellent on RX.

[TonyTheWizard]

Thanks for the video :)

what needs adjusting to lower the volage as you havent indicated in this video ?

[weazle66]

@TonyTheWizard Your quite right, what a plonker i am - i will add it to the text so people know.

The Gate voltage should be set to 3.2v using VR21 which is close to the MOSFET, this is what Mitsubishi recommend - i always set the voltage before installing the new device.

If you don't have a service manual then you can find it at CB-Tricks- in the service manual it says the bias current should be 1.3A which is too high if you ask me, probably should say 130Ma!!!

[yaesu101e]

Yes, The two I've had , won't track with the clairifier when transmiting above 27.4050. I was told that the clairifier was not linear. ????

[vicmeuk]

Trimmer resistors (variable) I find them a little too sensitive and can go open circuit at points..Pulse switched channel selector is not that robust..I took your advice on the correct votage setting using one of your RD16HHF1 transistors. Radio performs well.. Fixed four of these radios now.... I`d like to widen the Audio response on this radio as it`s a bit narrow..Overall I like the cobra 200 as I find it has SUPERB RX!.... Great video again.from you.weazle.

[HC5CA]

Thanks for the video. I've got one of these units on the shelf, and the MOSFET driver is likely the problem. I might get around to fixing it this weekend. Thanks again and 73!

[weazle66]

I have repaired a few of these radios now and it's always been the same fault.

Most people think it's always the main outputs when they have no output but in all the radios i get to repair only about 50% actually need new finals the others have other output related problems.