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QDX Rev 4: Q11 (BS-170) blown, replacement gets instantly very hot. Elevated current draw on RX.
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I supply 8.8 volts to my QDX which I built for 9 volts.
-- 73, Dan - W2DLC |
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Adam
Daniel Conklin <danconklin2@...> wrote:
What do you consider to be long key down? I accidentally had a key downWhat voltage did you supply to the QDX? |
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Ryan Flowers
Indeed, I'm aware that 14V is pushing it. I believe Hans has run his at similar voltages without issues. With the Rev4 regulators etc it seems like a fairly safe bet. But... I think I'm going to turn down my PSU to 12 V! Or run a separate one for the QDX. It's going to take me a week or two to get time to work on it, but I'll report back.
-- Ryan Flowers - W7RLF MiscDotGeek - QRP and More (Website) QDX Revision 3 Full Build Series (YouTube) |
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Cliff
Ryan,
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The Build Manual recommends that it not be run above 12V so 14V is really pushing it. 73,
Cliff, AE5ZA
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Ryan Flowers
Thanks for the guidance, folks. Much appreciated. The very first thing I did was check SWR, and it was fine. No idea why it blew up. Maybe because I'm running it a bit hot a 14 V? I dunno.
Also, in my case, there's always RF in the shack. (Get it. My initials. They are "RF". I very nearly called my YT channel "RF In The Shack") -- Ryan Flowers - W7RLF MiscDotGeek - QRP and More (Website) QDX Revision 3 Full Build Series (YouTube) |
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The fact that RF was getting into the shack indicates something. Anyway, in general, I'm not having the heating issues others are having. Maybe it's luck as you put it. Maybe my luck will run out. Maybe there's something else involved that builders have not yet discovered that's making the difference.
-- 73, Dan - W2DLC |
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William Smith
Unfortunately, reflections from complex impedances, combined with the length of your feed line, can result in any number of combinations of voltages and currents seen at the QDX. If you get lucky, and those voltages/currents never exceed the ratings on your output transistors, then nothing happens. Unfortunately, as others have seen, even a brief instant at “the wrong VSWR“ can almost immediately blow up your finals (and possibly even the driver IC)
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The fact that you got lucky doesn’t mean that someone else didn’t get unlucky. This also says that there is not a single number for VSWR that is “bad“ and another number that is “good“. It’s more complex than that, if you see what I did there.😁 73, Willie N1JBJ
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What do you consider to be long key down? I accidentally had a key down time of about 3 minutes into a more than 50:1 SWR with my QDX (both needles on the meter were nearly straight up), the case didn't get warm and I didn't blow up any parts. This was caused by a change in my antenna (weather related) that caused RF getting into the laptop and affecting the touchpad so I wasn't able to click the tune button to turn off the transmitter. After trying for that length of time I finally pulled the power plug out. The QDX is still working fine.
-- 73, Dan - W2DLC |
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Replacing BS-170's is like a "Right of Passage" for QDX as they are not tolerant to a bad VSWR or Long Key-Down while Tuning.
I have replace minne (all) twice (maybe only one failed but easier to pull 'em all! Some folks have added Sockets for ease of replacement but to me that just tempts fate! Elsewhere on here I offered up my solution (others have similar) and then you will be okay! In a nutshell: 1 Add a Heatsink 2.Add Thermal Tape to between the fins of the heatsink and the top cover. 3 wedge some thermal-Tape underside the PA to leech heat to the bottom cover. Mine run cool to very slightly warm after 2hrs use! Also, A resistive Tuner like Emtech ZM-2 i)or similar with (TUNE / TX sw) is better than most, especially auto-tuners (Noooo) 73 Terry |
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Evan Hand
Ryan,
The best way to tackle this issue is to remove all 4 BS170 transistors. Closely look at IC5 for a dimple on the surface. The dimple is a good indicator that IC5 had blown when Q11 failed. The other check is to measure the gate pads of the 4 BS170 and verify that a 5-volt square wave is present with all 4 BS170 removed. Best done with an oscilloscope, but a DMM can be used. The DMM should read 2.5 volts DC when transmitting and 0 volts when receiving. Before installing the BS170s, check to verify that all are OK. I use a transistor tester to verify them. A simple breadboard circuit can be made to do a simple test:  Located Here: https://www.homemade-circuits.com/how-to-check-mosfet-using-digital/ 73 Evan AC9TU |
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Alan G4ZFQ
On 29/11/2022 07:04, Ryan Flowers wrote:
inactive QDX, due to Q11 blowing up. I powered it off, replaced Q11 and then powered it up. The QDX boots up fine (lots of flashing, then solid LED) but I noticed that Q11, within seconds, got VERY hot again.At the least remove Q9. Better them all. Check the voltages on the gate pads. Looks like Q11 is turned on either by a faulty Q9 or faulty IC5. 73 Alan G4ZFQ |
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Ryan Flowers
Hi eveyrone,
I tried to keep it as simple as possible in the subject. Bad Smells and an inactive QDX, due to Q11 blowing up. I powered it off, replaced Q11 and then powered it up. The QDX boots up fine (lots of flashing, then solid LED) but I noticed that Q11, within seconds, got VERY hot again. I powered it off and haven't had time to or energy to touch it since. I'm tempted to replace Q9 also but I know better than to just throw parts at things. I'm sure others have run into the same type of thing... but I'm not even sure what to search. Any help or guidance or suggestions and even well intentioned and light hearted jesting, mocking, and pointing in my direction and giggling are appreciated. 73! -- Ryan Flowers - W7RLF MiscDotGeek - QRP and More (Website) QDX Revision 3 Full Build Series (YouTube) |
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