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Hey Y'all,
My QMX has been doing well for a few days and quite a bit of use after fixing some solder joints, but now I notice something that bothers me.
The power will stay up for a while until it gets really warm. Then power will reduce somewhat, I expect hot finals will lose some power, that's normal in regular rigs in my experience, however after a while it will lose even more, up to a watt and a half, sometimes more. Cool things off and it's back up.
Measuring the drive to the finals I get 2.505v on one pair and a 2.534v on the other pair. This isn't at the maximum heat, but was showing low power when I shut it down to test.
Obviously the drive should be the same on both sides, and it has other times. Could the issue be the driver IC or one set of BS170s?
Maybe some before the driver? I'm wondering if this is a clue to my issue of blowing finals far too often.
I can change both the IC and the finals, but before I do I wanted to get opinions from the experts in case we can find the "real" issue.
Thanks all for your comments.
73,
Cliff, AE5ZA
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I would replace all final transistors.
If you routinely experience very hot finals, you might want to consider inserting a bit of thermally conductive foam between the board and the aluminum case. Good ones are about 15 W/mK if I believe the catalog spec. Those good ones are loaded with heavy minerals and it's quite heavy and cool to touch.
Which transformer configuration did you use? What's your supply voltage?
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Ryuji,
I probably will change all the finals, but just wondered if there was some testing that could be done to help an on going problem. That idea of the foam might help also.
I was using 10V on a 12V build to see if I could get more life out of the BS170s. Transformer is the original design. Unit was build nearly 5 months ago now. Worked great for a long time until I stressed it with no antenna attached and transmitting several times. Driver IC and finals have been changed multiple times.
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On Sep 29, 2023, at 20:01, Ryuji Suzuki AB1WX < ab1wx@...> wrote:
I would replace all final transistors.
If you routinely experience very hot finals, you might want to consider inserting a bit of thermally conductive foam between the board and the aluminum case. Good ones are about 15 W/mK if I believe the catalog spec. Those good ones are loaded with heavy minerals and it's quite heavy and cool to touch. Which transformer configuration did you use? What's your supply voltage?
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There are several mechanisms for MOSFETs to deteriorate, temporary deterioration, permanent deterioration and complete failure. Temporary deterioration tends to be fluctuation of Vth and/or Ron. Both of these deterioration can be stable or somewhat random. These could lead to some strange phenomena.
I wish I had an easy testing method. I have been looking into every relevant piece of the schematic and really hoping to find something fixable that is leading to strange phenomenon. One of two suspects is the transformer. I think the new so-called "transmission line" type is a bit tough on the final transistors although the older conventional type is also not strain-free. I'll be building a different transformer and test with a fresh set of final transistors when I have time.
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Could it have something to do with heating in the final's output
transformer?
On 9/29/23 17:30, Cliff wrote:
toggle quoted message
Show quoted text
Hey Y'all,
My QMX has been doing well for a few days and quite a bit of use after fixing some solder joints, but now I notice something that bothers me.
The power will stay up for a while until it gets really warm. Then power will reduce somewhat, I expect hot finals will lose some power, that's normal in regular rigs in my experience, however after a while it will lose even more, up to a watt and a half, sometimes more. Cool things off and it's back up.
Measuring the drive to the finals I get 2.505v on one pair and a 2.534v on the other pair. This isn't at the maximum heat, but was showing low power when I shut it down to test.
Obviously the drive should be the same on both sides, and it has other times. Could the issue be the driver IC or one set of BS170s?
Maybe some before the driver? I'm wondering if this is a clue to my issue of blowing finals far too often.
I can change both the IC and the finals, but before I do I wanted to get opinions from the experts in case we can find the "real" issue.
Thanks all for your comments.
73,
Cliff, AE5ZA
|
Paul,
Could be. It gets pretty hot, but I've read that is normal, but maybe not.
As a desperate move I've thought about winding the new type.
Let's see now, new finals, drive IC and output transformer. Hmmmm... If it'll fix it I'll do it. I like building things, but don't like undoing things if there's any way around it.
toggle quoted message
Show quoted text
Could it have something to do with heating in the final's output
transformer?
On 9/29/23 17:30, Cliff wrote:
Hey Y'all,
My QMX has been doing well for a few days and quite a bit of use after fixing some solder joints, but now I notice something that bothers me.
The power will stay up for a while until it gets really warm. Then power will reduce somewhat, I expect hot finals will lose some power, that's normal in regular rigs in my experience, however after a while it will lose even more, up to a watt and a half, sometimes more. Cool things off and it's back up.
Measuring the drive to the finals I get 2.505v on one pair and a 2.534v on the other pair. This isn't at the maximum heat, but was showing low power when I shut it down to test.
Obviously the drive should be the same on both sides, and it has other times. Could the issue be the driver IC or one set of BS170s?
Maybe some before the driver? I'm wondering if this is a clue to my issue of blowing finals far too often.
I can change both the IC and the finals, but before I do I wanted to get opinions from the experts in case we can find the "real" issue.
Thanks all for your comments.
73,
Cliff, AE5ZA
|
If it'll fix it I'll do it. I like building things, but don't
like undoing things if there's any way around it.
Copy that! I managed to melt my CPU
while doing intial testing on my QMX (I think some clippings got
where they didn't belong), so I ordered a second kit.
Built it this last week, except that my
ADHD wouldn't tolerate going step by step through the instructions
in the assembly manual. I think I got all the right parts
in the right places (yet to be seen...), but I exchanged the male
and female connectors for JP304/JP206 and JP303/JP205. And in the
midst of it all, somehow I knocked C107 off the board (and I can't
find it anywhere!)
I thought building a second time would
be a snap, though winding the torroids would be tedious. I WAS
WRONG!
Good luck with that transformer-- Could
you spray it with cold when it's hot, to see if that's whats
causing the power decrease?
Just a thought!
73, Paul -- AI7JR
On 9/29/23 18:39, Cliff wrote:
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Show quoted text
Paul,
Could be. It gets pretty hot, but I've read that is
normal, but maybe not.
As a desperate move I've thought about winding the
new type.
Let's see now, new finals, drive IC and output
transformer. Hmmmm... If it'll fix it I'll do it. I like
building things, but don't like undoing things if there's any
way around it.
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I wouldn't change the transformer unless it's broken. A new transformer of the same type wouldn't change much. (I'm talking about a different design in my previous post.)
Same for the driver IC. It's probably ok if you see the output coming.
The Curie temperature of Amidon 43 ferrite is about 150C. I wouldn't worry about it. (I would worry more about the loss in the transformer. BN43-202 should be able to handle 20W easily but it gets this hot with just a couple of Watts.)
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Isn't whatever is heating the transformer, output power lost?
On 9/29/23 18:57, Ryuji Suzuki AB1WX
wrote:
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Show quoted text
I wouldn't change the transformer unless it's broken. A new
transformer of the same type wouldn't change much. (I'm talking
about a different design in my previous post.)
Same for the driver IC. It's probably ok if you see the output
coming.
The Curie temperature of Amidon 43 ferrite is about 150C. I
wouldn't worry about it. (I would worry more about the loss in
the transformer. BN43-202 should be able to handle 20W easily
but it gets this hot with just a couple of Watts.)
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I'll have to find some freeze spray. Would love to use it to identify what the heat is affecting.
toggle quoted message
Show quoted text
If it'll fix it I'll do it. I like building things, but don't
like undoing things if there's any way around it.
Copy that! I managed to melt my CPU
while doing intial testing on my QMX (I think some clippings got
where they didn't belong), so I ordered a second kit.
Built it this last week, except that my
ADHD wouldn't tolerate going step by step through the instructions
in the assembly manual. I think I got all the right parts
in the right places (yet to be seen...), but I exchanged the male
and female connectors for JP304/JP206 and JP303/JP205. And in the
midst of it all, somehow I knocked C107 off the board (and I can't
find it anywhere!)
I thought building a second time would
be a snap, though winding the torroids would be tedious. I WAS
WRONG!
Good luck with that transformer-- Could
you spray it with cold when it's hot, to see if that's whats
causing the power decrease?
Just a thought!
73, Paul -- AI7JR
On 9/29/23 18:39, Cliff wrote:
Paul,
Could be. It gets pretty hot, but I've read that is
normal, but maybe not.
As a desperate move I've thought about winding the
new type.
Let's see now, new finals, drive IC and output
transformer. Hmmmm... If it'll fix it I'll do it. I like
building things, but don't like undoing things if there's any
way around it.
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Yes, loss in the transformer turns into heat. But that's a different mechanism than what I think is stressing the finals.
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If the surface temperature is up to about 80C or so, I wouldn't worry about it. It's best to keep at 70C or below, though that alone doesn't kill the transistors in such a short period of time.
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Really? I thought this was the opening topic:
The power will stay up for a while until it gets really warm.
:-)
On 9/29/23 19:08, Ryuji Suzuki AB1WX
wrote:
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Show quoted text
Yes, loss in the transformer turns into heat. But that's a
different mechanism than what I think is stressing the finals.
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Different story. Unless the ferrite core reaches about 150C the transformer will not lose performance. One exception is if the temperature melts the insulator on the wire.
(I melt some feedline transformers but that was using polyethylene jacketed wire and running 100W. I use teflon jacketed wires so that won't happen again!)
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I'd still try cooling it to see what happens. Sometimes my view
of what's significant needs to be "adjusted" by experience! ;-)
On 9/29/23 19:31, Ryuji Suzuki AB1WX
wrote:
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Show quoted text
Different story. Unless the ferrite core reaches about 150C the
transformer will not lose performance. One exception is if the
temperature melts the insulator on the wire.
(I melt some feedline transformers but that was using
polyethylene jacketed wire and running 100W. I use teflon
jacketed wires so that won't happen again!)
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If you must cool something, cool the transistors and the driver instead. They would like that. Transformer performance actually increases until it suddenly breaks so it won't be very useful trying to cool it unless the temp is above 100C.
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I had one of the PA (BS170s) fail, became a resistor - possibly due to a transient high swr.? The output power had dropped substantially (5W to 2.5W). With the current firmware Q507 is turned on, even though in the receive mode until after the first transmit, this caused the initial current to be high until until after the first transmit (~100mA higher). You can find the bad BS170 since it is warmer. Need to check it after power on before a transmit.??
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Chris,
I've seen the same thing in the past, but not this time.
Thanks.
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Show quoted text
On Sep 30, 2023, at 07:58, Chris KB1NLW via < chrisrey1@...> wrote:
I had one of the PA (BS170s) fail, became a resistor - possibly due to a transient high swr.? The output power had dropped substantially (5W to 2.5W). With the current firmware Q507 is turned on, even though in the receive mode until after the first transmit, this caused the initial current to be high until until after the first transmit (~100mA higher). You can find the bad BS170 since it is warmer. Need to check it after power on before a transmit.??
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Paul,
Sorry to hear of your grief with your new one. I also was thinking a second build would be easier. Guess not, but at least you had learned some lessons on the first one that would help on the second.
toggle quoted message
Show quoted text
If it'll fix it I'll do it. I like building things, but don't
like undoing things if there's any way around it.
Copy that! I managed to melt my CPU
while doing intial testing on my QMX (I think some clippings got
where they didn't belong), so I ordered a second kit.
Built it this last week, except that my
ADHD wouldn't tolerate going step by step through the instructions
in the assembly manual. I think I got all the right parts
in the right places (yet to be seen...), but I exchanged the male
and female connectors for JP304/JP206 and JP303/JP205. And in the
midst of it all, somehow I knocked C107 off the board (and I can't
find it anywhere!)
I thought building a second time would
be a snap, though winding the torroids would be tedious. I WAS
WRONG!
Good luck with that transformer-- Could
you spray it with cold when it's hot, to see if that's whats
causing the power decrease?
Just a thought!
73, Paul -- AI7JR
On 9/29/23 18:39, Cliff wrote:
Paul,
Could be. It gets pretty hot, but I've read that is
normal, but maybe not.
As a desperate move I've thought about winding the
new type.
Let's see now, new finals, drive IC and output
transformer. Hmmmm... If it'll fix it I'll do it. I like
building things, but don't like undoing things if there's any
way around it.
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Just pulled the finals planning to change them all, but decided to test the voltage on the gates with them out. The voltages are different, slightly and I noticed that one side the drive voltage increased slightly when the finals were pulled and the other side not. 2.523 vs 2.546 with the finals out.
Am I making a big deal out of nothing here? Only 0.023v different. I don't remember looking that closely before so maybe they always have been that way, but my recollection is that they were much closer.?
I hate to change the driver IC for nothing, but if it'll make a difference, I have the chip to do it.
BTW, with the board cool power out is back up to normal.
toggle quoted message
Show quoted text
Ryuji,
I probably will change all the finals, but just wondered if there was some testing that could be done to help an on going problem. That idea of the foam might help also.
I was using 10V on a 12V build to see if I could get more life out of the BS170s. Transformer is the original design. Unit was build nearly 5 months ago now. Worked great for a long time until I stressed it with no antenna attached and transmitting several times. Driver IC and finals have been changed multiple times.
On Sep 29, 2023, at 20:01, Ryuji Suzuki AB1WX < ab1wx@...> wrote:
I would replace all final transistors.
If you routinely experience very hot finals, you might want to consider inserting a bit of thermally conductive foam between the board and the aluminum case. Good ones are about 15 W/mK if I believe the catalog spec. Those good ones are loaded with heavy minerals and it's quite heavy and cool to touch. Which transformer configuration did you use? What's your supply voltage?
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Ryuji Suzuki AB1WX
Paul - AI7JR