Galaxy dx959 mosfet final and driver bias voltage?

[Handy Andy]

​

There are several variants of the same thing - adjusting Gate voltage to make the Radio key up right...

VR 10 - FINAL
VR 12 - Driver

There are points you can check VOLTAGES on, that help you - and there are two spots to check and use the one that works for you - but either way, DO NOT SET BIAS ABOVE 3.3V - these will LATCH ON and blow up if you go too high...

• The FOREMENTIONED is what will happen if you set VR12 or VR10 too high - EACH MOSFET IS DIFFERENT - EVEN IN SAME BATCH - SO USE TP "TAB" for mA ON SEPARATE METER TO CHECK CURRENT DRAW AS YOU SET VOLTAGE! VOLTAGES ARE CHECKED TO FOIL GROUND NOT CASE GROUND!
• AMMETER = CURRENT DRAW - TP 7 to +POSITIVE of AMMETER and -NEGATIVE to TP you wish to check - and NO MORE THAN 35mA until you are comfortable with results.
• DONE ON TX INTO DUMMY LOAD TP 7, 8, 9 JUMPER BOARD REMOVED WITH AMMETER INSTALLED - READ ABOVE
• One - Use TOP LEAD OF L33 or L37.
• Two - Check Voltage on BANDED leg of D90 or D92

L33 and L37 - I highly recommend that you use - REORIENT - L37 and L33 opposite of what is shown - for you can then set your TEST LEAD POSITIVE (+) to the top lead of the resistor if you need to verify gate or tap for RF signal thru Scope Probe - to see RF or Voltage.

The ZENER 7.5V recommendation is arbitrary - buy you may need to swap that 5.6 or even 5.1V Zener to a higher voltage to obtain any gain or if you wish to have swing. The 5.6 or 5.1V Zeners used may limit your ability to obtain the Drive peak you want.

 

[Ridgerunner0788]

Ya this is a 2547 with the 959 inside trying to figure it out it's werid to have receive and not transmit .

 

[loosecannon]

LOL ridgerunner, i can't argue with that logic...

I guess we need to be more specific.

here's what you need to do. go to google, and search for a datasheet for the IRF520.
this will show you the pinout of the transistor so you can tell us which leg reads what.
one leg will be the gate, give us that voltage in RX and in TX.
next will be the drain leg, do the same.
next will be the source leg, again, measure RX and TX voltages and post them.

do this for the driver (Q49) and then do it for the final (Q47).

now google the 2SB827 datasheet and get the pinout for that one (Q54).
now you can tell us what the voltages are on the Base, Collector, and Emitter legs in both RX and TX.

take your time and post back the results making sure that there is no room for confusion.

also, make sure you only have a 4 amp fuse on the power cord in case you have a short it will blow the fuse hopefully before blowing up any more parts.
LC

 

[Handy Andy]

BLUE = BASE
RED = Collector
AMBER = EMITTER​

 

[Ridgerunner0788]

Ok sorry to get back so late I finally got the 2547 to work with the mouser irf520s pbf , I see a dk of 10 swing 25 30 watts I am trying to lower the dk down to about 2 dk swing 10 to 15 I ve done the normal pot adjust on CBC tricks and copper talk but the dk won’t come down for some reason does any one know

 

[loosecannon]

How did you finally get it to work?
LC

 

[Ridgerunner0788]

I tried a different batch out of the package I got from mouser and it worked , it swings good talks good now thanks for all the help guys

 

[loosecannon]

there are two trimmers on the board that control the AM deadkey.
one is for low and one is for high.
turn the external RF power knob all the way down, and set the low trimmer to the lowest deadkey you want available.
now turn the external knob all the way up and adjust the high trimmer for the highest deadkey you want available. (best not to go over 6 watts with this)

these two trimmers work together to set the range of your RF power knob, and adjusting one will affect the other, so you will have to go back and forth a bit to get them set right.

if you can't get the low trimmer to go low enough, turn the RF power knob all the way up, and then lower the high trimmer a bit, then turn the RF power knob all the way down and check again. the low power should be lower now.

I like to set them to do 1 watt to 5 watts.
LC

 

[Ridgerunner0788]

I left the oringal mosfet setting s alone and put the new mosfet irf520pbf in place and it work started putting out watts right around and then adjust the ref power , I rebuilt this radio , for a guy new finals new audio chip did the mod max regulator witch works flawless great performance unlock clearfier 10k bump extra channels this radio was a dead radio when I got it from him also put knew power supply in it , I made the Super Bowl channel 6 with this radio talk to slow Motion , I have a YouTube video on on this highly modified 2547

 

[Tallman]

The IRF520N means it is the N "Enhanced Mode" meaning it has a magnetizing current that continues even after it is shut off. As long as your signal is going through a capacitor and does not affect any bias circuits it should work fine. Or so they say.

 

[Cobra999]

Do you need to key up to take voltages? When I measure without key, I get 1.48V on driver, and if I key, it goes to 0V. When I measure final, I get 0.8V and 0 on key. V12 and V10 only give it a few 0.1’s.. so I can’t seem to get anywhere near the numbers your suggesting. Any ideas?

Sure.

1) Keep that mirrored bias board in place; do not remove it. AM or SSB mode can be used.

2) Place the "+" lead of the voltmeter on the top lead of L37* and the "-" voltmeter lead on the solid ground wire between the large metal xtal filter can and the 10.240mhz xtal. The driver voltage can be set to 3.6v using vr-12.

3) Next, place the "+" lead of the voltmeter on the top lead of L33* keeping the "-" lead of the voltmeter on the solid ground wire between the large metal xtal filter can and the 10.240mhz xtal as you did for the driver. Adjust the final transistor vr-10 for 3.5v.

4) Done.

NOT RESPONSIBLE FOR WORK DONE INCORRECTLY.

NOTE:
* = the board is marked at these locations for a choke; but they are actually resistors in the MOSFET radios at these locations. Don't let that throw you off - Robb

 

[Handy Andy]

Do you need to key up to take voltages? When I measure without key, I get 1.48V on driver, and if I key, it goes to 0V. When I measure final, I get 0.8V and 0 on key. V12 and V10 only give it a few 0.1’s.. so I can’t seem to get anywhere near the numbers your suggesting. Any ideas?

Tells me you've lost TX voltage power to this section - might have a blown resistor feeding Bias voltage into this section...or shorts - when voltage drops - check your TX feeder line - locate L41 or L39 - make sure you're sending power to feed the BIAS trimmers of Driver and Final.

Locate this post...open it in a separate window if you can ...
https://www.worldwidedx.com/threads...driver-bias-voltage.155425/page-3#post-656260

Locate L41, even L39 - make sure when you TX, you are seeing 8 Volts in TX - if you do something towards those "blue" trace highlited pads is not getting voltage to power the Gates properly.