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DX959 No mA draw on tp's

J

jerry110

Member
Apr 2, 2010
7
1
13
Hello And Thanks for the help in advance!
Here is a little background:
One day i powered up the radio and had no carrier 4w swing on AM, 8w sb audio reports are my audio was pinched.

I thought it was the final and or driver. (IRF520) Replaced both of them and now i have no mA draw on either TP9 or TP8 i do however have 12 volts on TP7 on Tx . I have checked many diodes on the schematic going back to IC9 all test good.
Any Ideas?
 

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They are both IRF520s.... i have 2.50V on the gate on key no mA draw on the TP 8 and 9
I just noticed that gate voltage drops as soon as i key up
 
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I just looked at the schematic. Yes; it does use two MOSFET IRF520N's for the driver and final (Q49 & Q47). The adjustments on the board won't be used for adjusting mA, like a DX-959 bipolar driver/final radio will. They will need to have gate voltages adjusted on both of them instead. A MOSFET is a voltage controlled device; not amperage controlled IIRC.

Did you check the two zener diodes ('5V6') D90 & D92?
 
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yes checked both zeners and most of the diodes i could get my hands on all check a-ok.....so both gate voltages should be 3.65?
 
jerry110 said:
yes checked both zeners and most of the diodes i could get my hands on all check a-ok.....so both gate voltages should be 3.65?
Click to expand...

Not positive about that voltage number. Best way that I know of is to turn the variable for the driver up until it turns on; then do the same with the final. They will have a threshold voltage. When it turns on; then just a smidge higher. They should get fairly warm under load; but letting them get hot is right out. Running too much voltage on them can toast them fast.

Set it for 4w DK and 16w PEP. On SSB, set the ALC for 20. Don't remember the VR's for those ATM. You can run it higher (<30w); but not unless you put a heat sink on the radio first.

Exitthirteen and a few others have far more experience than I do with MOSFETS.
 
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Stop the press's 2SC2314 location Q51 must have an internal problem i wiggle it around and everything comes up nice... wiggle it more no love... i checked the solder side looks good... waiting for parts.... I'll let you know if that fix's it... Thanks!!!
 
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Yes Sir i tapped on it and wiggled it my carrier came back and it swings to 10w then nothing i tap on it some more same thing... i re flowed the trace side to verify not a bad joint didnt help must be an internal thing weird
 

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