Hi Andy, you know so much it's frightening and I know so little. So, can I hopefully remove D90 and D92 the 1N4148 and replace each with a 5.6V zener and in the polarity shown in the schematic (not the way they are now)? With any luck will that fix the problem? Adam
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Galaxy DX-2547 suddenly virtually no output
- Thread starter Adamf
- Start date
As shown sir.
MOSFET Final and Driver?
Zeners? Band to the LEFT when you're facing the front of that IRF520 - GATE to BANDED end/side/leg
Diodes? SAME THING - only request that you provide some protection for the Gate in some fashion.
For BIPOLAR?
Zeners are not used - Diode is installed (singularly) with Band to the RIGHT - EMITTER of Bipolar (1969/2078 e&c)
Only way to know if if you recheck the ability to adjust Trimmers and get BIAS to 50~55mA NO MORE than that...
I'll explain why - just do this - get BIAS working right first, then I'll take it from there...
MOSFET Final and Driver?
Zeners? Band to the LEFT when you're facing the front of that IRF520 - GATE to BANDED end/side/leg
Diodes? SAME THING - only request that you provide some protection for the Gate in some fashion.
For BIPOLAR?
Zeners are not used - Diode is installed (singularly) with Band to the RIGHT - EMITTER of Bipolar (1969/2078 e&c)
Only way to know if if you recheck the ability to adjust Trimmers and get BIAS to 50~55mA NO MORE than that...
I'll explain why - just do this - get BIAS working right first, then I'll take it from there...
Don't go there, you should have seen my earlier works...
This is why I posting this message, to clarify yours.
And since some people, someday, may come across this thread - looking for answers...
You mentioned it quite well...
I did this up for others to help their Galaxy radios survive...
Hmmm...well, what would you LIKE to do?
Each option suggested does work, ONLY one works per what the FACTORY does.
The other options have dangers embedded in their use.
Right now? Fix your Bias - you have the schematic - follow it and verify you can CHANGE the VOLTAGE being applied to the GATE.
You can remove the Final and Driver to do this, you can check Gate voltage individually, start with the controls in one direction of turn complete stop - and turn the trimmers and measure at the GATE foil pad (or BAND end of the DIODE used, to see where it takes the voltage (this is a leaning step I know - been there ) , then turn the trimmers to the LOWEST voltage setting (turned all the way down) and leave them down so you can complete the repair and finish the next step in the install.
Leaving out the Big Stuff Makes it easier and less likely to make a mistake if you save the power parts to be put in last.
So for BEST results, try your best to get the radio back to STOCK - follow FACTORY guidelines and schematic if you want FACTORY results.
By what you're telling me, as found earlier, this radio has had work done to it, Zener's, no matter what, on a MOSFET final and driver are used - that is factory(SIC) - even I had to rework boards in for repair to fix that - you're not alone in this.
It seems that many of todays boards are NOT following the schematic - for if they did - they wouldn't be performing or at least being kept by their owners - and being those stellar performers at Bird watts as others tend to expect.
So to help - yes, ORDINARY STANDARD Diodes work, So does Schottky types, but in any event, their PIV rated voltages are TOO HIGH to be considered safe for Standard RF boards using MOSFET.
Notice the wording above. I said "Standard RF Boards" - meaning for type acceptance - they follow schematic.
But not all do...at least in latter production runs, anything goes when you have to use up all the parts in the bins, leftover rolls and still on the Shop Floor as cuttings.
It's is done to use up what's left - to Amortize off the inventory and make the best ROI (Return On Investment) for that site. Because that factory may never get a second chance to obtain an order from that Holdings Company ever again...
Seems tedious, but the above saves you from a major failure later.
When you get to here, and want to know about Cx - get the radio working first...
Each option suggested does work, ONLY one works per what the FACTORY does.
The other options have dangers embedded in their use.
Right now? Fix your Bias - you have the schematic - follow it and verify you can CHANGE the VOLTAGE being applied to the GATE.
You can remove the Final and Driver to do this, you can check Gate voltage individually, start with the controls in one direction of turn complete stop - and turn the trimmers and measure at the GATE foil pad (or BAND end of the DIODE used, to see where it takes the voltage (this is a leaning step I know - been there ) , then turn the trimmers to the LOWEST voltage setting (turned all the way down) and leave them down so you can complete the repair and finish the next step in the install.
Leaving out the Big Stuff Makes it easier and less likely to make a mistake if you save the power parts to be put in last.
- - BEFORE you install those MOSFET's
- Find the LOWEST Voltage setting This PREVENTS you from applying power and blowing the FINAL and OR DRIVER from too much ON (Trigger) voltage.
- Why? Because the BIAS voltage is capable of making them turn on by themselves
- - you don't want that,
- turn it down when you're done checking - verify they STAY down - not climb up - prove that they hold steady - Yes, you can remove the Mirror board, but as a Safety precaution - keep a Dummy load on the Antenna Connector - so if you accidentally key up the radio, cause a short or other type of accident - the board stands a better chance of surviving the mess if you let some of the power flow into a load somewhere - antenna connector is about the best spot.
- If you removed the Mirror Board - and checked the BIAS for adjustment - DID YOU ALSO REMEMBER TO DO THIS WITH THE MIRROR BOARD INSTALLED TO VERIFY YOU DO NOT HAVE A SHORT TO BIAS CAUSED BY AN ERROR?
- This would show up as a RISE in voltage to the GATE - a BIG JUMP several volts you can't turn down or adjust - then you know you have other issues - STOP and recheck - repair any work necessary to fix your BIAS properly.
- Turn off the Power when you're done checking - unplug if you need to...
- Why? Because the BIAS voltage is capable of making them turn on by themselves
- Install the Driver and Final - Mounting it PROPERLY using the Heat spreader insulator pad, Hardware - all the Jazz needed to make the part properly mounted - and NOT SHORTING to Back panel or anywhere else.
- Verify parts are mounted (including Your Mirror Board jumper), are in their correct spots and their LEADS are soldered to the CORRECT pads. use your Ohmmeter to verify this if you're not sure
- Once soldered in, close up any panels except the cover (as needed to obtain access) and remount all the hardware.
- Reapply power - check for "smoke" - if you did your job right, this "smoke" stays in the parts.
- Start the tune up process - remembering that you do have a Dummy Load mounted on the antenna connector to protect you and your stuff from each other.
- Follow the steps needed - so you can check BIAS using the MIRROR BOARD JUMPER Removed
- - then set the trimmers for mA BIAS as said earlier.
I Fixed it - this is the CORRECTED graphic of your board
with the TEST POINTs properly labeled...Ahemn...Sorry about that...
with the TEST POINTs properly labeled...Ahemn...Sorry about that...
So for BEST results, try your best to get the radio back to STOCK - follow FACTORY guidelines and schematic if you want FACTORY results.
By what you're telling me, as found earlier, this radio has had work done to it, Zener's, no matter what, on a MOSFET final and driver are used - that is factory(SIC) - even I had to rework boards in for repair to fix that - you're not alone in this.
It seems that many of todays boards are NOT following the schematic - for if they did - they wouldn't be performing or at least being kept by their owners - and being those stellar performers at Bird watts as others tend to expect.
So to help - yes, ORDINARY STANDARD Diodes work, So does Schottky types, but in any event, their PIV rated voltages are TOO HIGH to be considered safe for Standard RF boards using MOSFET.
Notice the wording above. I said "Standard RF Boards" - meaning for type acceptance - they follow schematic.
But not all do...at least in latter production runs, anything goes when you have to use up all the parts in the bins, leftover rolls and still on the Shop Floor as cuttings.
It's is done to use up what's left - to Amortize off the inventory and make the best ROI (Return On Investment) for that site. Because that factory may never get a second chance to obtain an order from that Holdings Company ever again...
- So, remember to fix BIAS and make it adjustable - first...
- Install your Diodes Zener or Standard - both have to have their BANDED end to the LEFT or GATE side of the MOSFET.
- Verify you can adjust the GATE voltage BEFORE and AFTER you install the MOSFET's Mirror Board in to verify no shorts to Drain or SOURCE issues
- - turn them to the LOWEST setting before you leave to go onto the next step of your repair.
- THEN Install your MOSFET's with the MIRROR BOARD Removed.
- Finish up and clean up so you can get radio set to finish the tune-up repair.
Seems tedious, but the above saves you from a major failure later.
When you get to here, and want to know about Cx - get the radio working first...
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Because, if you have not learned already...
There's info in the sheets you'll need to know when it comes to setting the BIAS levels.
Really all you need to do is set the "TP" to draw to 55mA...
But, do you know the EXACT Voltage?
No, you don't...
Here's why...
See where the RED arrow points to?
GATE THRESHOLD VOLTAGE...
Ok, a bolder - more focused look...
And that is set on 250 uA (Micro - NOT Mili - 1/1000 of a Mili - even smaller)
Gate Threshold Voltage - by Definition...
Why the concern?
Because we're dealing with a simple process - with a complex nature of thickness variables - even using the precise processes we can in making these - we still have over 2 volts of "adjustment" that is needed by the end user (you me, the rest of the world) to make the part trigger on and work properly.
Trigger - Work Properly?
MOSFET's are FIELD EFFECT Devices - they don't need a "direct connection" like their Bipolar cousins do, the Bipolar is a physical Electrical Mono-Directional JUNCTION - device that works under specific conditions linearly and can also act as a switch MOSFET or any FET - is a device that simply takes a doped seeded Silicon sand Grain and applies a Gate using an oxide-layer in between to insulate the Gate - forming a DEPLETION or ENHANCEMENT mode device.
So why does this matter?
Why did your radio quit working?
Think about that before sending off a snarky reply - because it is not your fault you didn't know this - or even if you did - did you even know that OEM radios use ZENER diodes - not Standard PN junction Diodes?
Zener's are designed to withstand being reverse biased to a specific voltage they conduct only one way until that reverse voltage threshold is reached - then they collapse - breakdown - without being damaged (if the circuit is done right). They are there to keep the GATE voltage from exceeding another rating buried in those sheets...
Another one...
Gate to Source Voltage...
I posted the above for FET, Has a simple diagram - and is similar to that which MOSFET is a part of that family of Semiconductors, in a very basic sense - it is the maximum voltage you can APPLY to the GATE - before the INSULATOR that Gate sets upon, gets perforated by the voltage wanting to jump or arc across - for when that happens the Gate SHORTS to the same layer the SOURCE and DRAIN used and the device is destroyed.
These things also generate heat, meaning it has thermal profile - which then means heat produced in the part can DISTORT the part internals and damage the part due to excessive power being placed across the leads and thereby damaging - destroying the part in the process.
That is a layer of "oxide" meant to keep the Gate's Voltage from arcing across, but it's not a perfect insulator - heat affects the ability of the Oxide layer sandwiched in there - to remain stable - meaning it can deform from the heat - it can literally crack and form a tear - and allow the Gate voltage a means to jump across.
So you know, you can't just adjust voltage directly and expect the IRF520N to work as expected - you are dealing with RF - in a Small Signal application to a Gate - to generate a larger output across the Drain to Source - The Driver does part of the Work - The Final takes the ball and runs with it from there.
But you have to set the right "on" voltage to make the MOSFET turn on - at the right time and Stay on - for only that amount of time needed to form the signal.
That is why you set BIAS using Current - you're making the MOSFET VERY SENSITIVE to changes in Power.
What can happen is the DRIVER generates too much power for the GATE of the FINAL to withstand.
POOF.
There's the problem - then use Zener's instead of regular STANDARD Diodes - to solve that.
So how does this work?
Think of this like a Carburetor, or even a simple Engine.
To perform work you have to start the engine first - get it moving.
I mention Carburetor - because it can make more sense if you're into cars - at least while they still make them with Reciprocating engines using fossil fuels.
The engine starts and runs, and you can vary the engines speed by changing the way the Carburetor applies fuel and air to mix together in a given VOLUME of space - Stoichiometry
It works if you get the Balance right...
That's why the MOSFET is similar to an Engine - doesn't perform very well unless you have Voltage to Current ratios or your Air to Fuel Mixture going thru the Carburetor in the right ratios to mix.
So that is where Idle and Idle Mixture comes into play - the settings have to be right so the engine can perform work and idle smoothly so that power delivery at all speeds and Engine loads can be performed and remain optimized (in the Radio sense - perform work by producing signal effectively and as efficiently as possible to provide power levels for the Modes it is operated in)
So in a way - Idle Mixture setting is a lot like Idle Current setting in Bipolar - only now, we're in the newer technology of MOSFET - and it still needs to "idle" - awaiting the moment to turn on and produce work - efficiently and effectively as possible - so that is why you Trim the IDLE CURRENT - you're setting a Mixture ratio of "OFF State" to "ON Threshold" - engine at idle - once you touch / apply / mash the accelerator pedal - the Carburetor responds by applying Fuel and Air in a specific volume expressed by your throw of pressure onto the pedal and making the Throttle plate of the Carburetor moves to an angle - (conduction) and generates power.
The Zener is a lot like a Restriction - only done to protect the Engine from Over revving - a condition that can destroy the motor the Carburetor supplies the Mixture for..
So you set BIAS to Idle the parts so they turn on when they should - you set the Idle Current (idle speed) using the Air to Fuel Mixture as the "Gauge" to set the engines ability to run smoothly in Stoichiometry - you can't set the idle speed with only air, or only fuel - needs both as a mix of the two to work right and you set the balance between both by setting the Trimmer to set the MOSFET's Gate Threshold Voltage (the ON voltage) to form a current draw - that current draw is the amount of voltage needed to maintain Idle.
To make sure you have the right Threshold voltage being applied - you check the Current
You cannot just set the idle speed screw and expect the thing is going to run - Because - it won't.
There's info in the sheets you'll need to know when it comes to setting the BIAS levels.
Really all you need to do is set the "TP" to draw to 55mA...
But, do you know the EXACT Voltage?
No, you don't...
Here's why...
GATE THRESHOLD VOLTAGE...
Ok, a bolder - more focused look...
And that is set on 250 uA (Micro - NOT Mili - 1/1000 of a Mili - even smaller)
Gate Threshold Voltage - by Definition...
Why the concern?
Because we're dealing with a simple process - with a complex nature of thickness variables - even using the precise processes we can in making these - we still have over 2 volts of "adjustment" that is needed by the end user (you me, the rest of the world) to make the part trigger on and work properly.
Trigger - Work Properly?
MOSFET's are FIELD EFFECT Devices - they don't need a "direct connection" like their Bipolar cousins do, the Bipolar is a physical Electrical Mono-Directional JUNCTION - device that works under specific conditions linearly and can also act as a switch MOSFET or any FET - is a device that simply takes a doped seeded Silicon sand Grain and applies a Gate using an oxide-layer in between to insulate the Gate - forming a DEPLETION or ENHANCEMENT mode device.
So why does this matter?
Why did your radio quit working?
Think about that before sending off a snarky reply - because it is not your fault you didn't know this - or even if you did - did you even know that OEM radios use ZENER diodes - not Standard PN junction Diodes?
Zener's are designed to withstand being reverse biased to a specific voltage they conduct only one way until that reverse voltage threshold is reached - then they collapse - breakdown - without being damaged (if the circuit is done right). They are there to keep the GATE voltage from exceeding another rating buried in those sheets...
Another one...
Gate to Source Voltage...
I posted the above for FET, Has a simple diagram - and is similar to that which MOSFET is a part of that family of Semiconductors, in a very basic sense - it is the maximum voltage you can APPLY to the GATE - before the INSULATOR that Gate sets upon, gets perforated by the voltage wanting to jump or arc across - for when that happens the Gate SHORTS to the same layer the SOURCE and DRAIN used and the device is destroyed.
These things also generate heat, meaning it has thermal profile - which then means heat produced in the part can DISTORT the part internals and damage the part due to excessive power being placed across the leads and thereby damaging - destroying the part in the process.
That is a layer of "oxide" meant to keep the Gate's Voltage from arcing across, but it's not a perfect insulator - heat affects the ability of the Oxide layer sandwiched in there - to remain stable - meaning it can deform from the heat - it can literally crack and form a tear - and allow the Gate voltage a means to jump across.
So you know, you can't just adjust voltage directly and expect the IRF520N to work as expected - you are dealing with RF - in a Small Signal application to a Gate - to generate a larger output across the Drain to Source - The Driver does part of the Work - The Final takes the ball and runs with it from there.
But you have to set the right "on" voltage to make the MOSFET turn on - at the right time and Stay on - for only that amount of time needed to form the signal.
That is why you set BIAS using Current - you're making the MOSFET VERY SENSITIVE to changes in Power.
What can happen is the DRIVER generates too much power for the GATE of the FINAL to withstand.
POOF.
There's the problem - then use Zener's instead of regular STANDARD Diodes - to solve that.
So how does this work?
Think of this like a Carburetor, or even a simple Engine.
To perform work you have to start the engine first - get it moving.
I mention Carburetor - because it can make more sense if you're into cars - at least while they still make them with Reciprocating engines using fossil fuels.
The engine starts and runs, and you can vary the engines speed by changing the way the Carburetor applies fuel and air to mix together in a given VOLUME of space - Stoichiometry
It works if you get the Balance right...
That's why the MOSFET is similar to an Engine - doesn't perform very well unless you have Voltage to Current ratios or your Air to Fuel Mixture going thru the Carburetor in the right ratios to mix.
So in a way - Idle Mixture setting is a lot like Idle Current setting in Bipolar - only now, we're in the newer technology of MOSFET - and it still needs to "idle" - awaiting the moment to turn on and produce work - efficiently and effectively as possible - so that is why you Trim the IDLE CURRENT - you're setting a Mixture ratio of "OFF State" to "ON Threshold" - engine at idle - once you touch / apply / mash the accelerator pedal - the Carburetor responds by applying Fuel and Air in a specific volume expressed by your throw of pressure onto the pedal and making the Throttle plate of the Carburetor moves to an angle - (conduction) and generates power.
The Zener is a lot like a Restriction - only done to protect the Engine from Over revving - a condition that can destroy the motor the Carburetor supplies the Mixture for..
So you set BIAS to Idle the parts so they turn on when they should - you set the Idle Current (idle speed) using the Air to Fuel Mixture as the "Gauge" to set the engines ability to run smoothly in Stoichiometry - you can't set the idle speed with only air, or only fuel - needs both as a mix of the two to work right and you set the balance between both by setting the Trimmer to set the MOSFET's Gate Threshold Voltage (the ON voltage) to form a current draw - that current draw is the amount of voltage needed to maintain Idle.
To make sure you have the right Threshold voltage being applied - you check the Current
- The Trimmers allow you to:
- Adjust the Voltage - thru BIAS, so you can make the Gate of the MOSFET turn on at the right time
- Then to make sure you have the RIGHT Voltage to meet the THRESHOLD level needed
- The MOSFET will begin to turn on and draw a small current.
- You Adjust the BIAS Voltage to SET the Current to 55mA
- - so always check and adjust for CURRENT
- You simply cannot SET the MOSFET Gate to a Known Voltage
- - each MOSFET will see this "Threshold" (Quantum State from High Impedance TO Low-Impedance transition region - Conduction) level differently by as little as 1/100th of a change in voltage being applied to the Gate
- Devices by Manufacture and or Same Brand is also affected by these simple differences on the ATOMIC scale - the change in the thickness of the Oxide layer not only changes the capacitive values but also the THRESHOLD level of conduction.
- You simply cannot SET the MOSFET Gate to a Known Voltage
You cannot just set the idle speed screw and expect the thing is going to run - Because - it won't.
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I know this is an old post, but I just had the same exact problem with a DX 2547 I picked up on FleaBay. It was working as it should for the first 2 days I had it. Day 3, turned it on and nothing on the meters no matter what knob was turned. Turns out it was the “claw clamps” the hold the ground bar I believe it’s called in place. From right to left, one was spread open more than the next. It must’ve been touching enough to make contact all these years but then shipping shook it up enough to where it wasn’t making solid contact. I can see how with oxidation, this could become an issue with age. Carefully squeezed the claws just enough to lightly pinch the ground bar and poof! Problem solved. Again, I am late to the party, but I hope this helps.
73s
73s
Hi, thanks for trying to help but that was not the problem. Thanks again, Adam