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Yep. ?On QCX if it’s not broken not ‘fixing’ it seems the best plan. ? ?

And good point on the zeners probably requiring more changes and a re-tune which may cause other issues?

As I said running on a lowish voltage seems to work for many months of beacon TX ?at a time so that will do …?

Thanks for the great insight? Bruce and Evan. Ive had a few "oh crap" moments hooking up the rigs where while tuning I noticed the antenna switch was off. A simple protection circuit seemed inviting. So far no BS170s have been murdered. The silver bullet for protection, then, is for the loose nut behind the key to pay attention.?
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regards,
Bryan, N0LUF

On Mon, Apr 8, 2024 at 04:39 AM, Bryan Curl wrote:

Thanks for the great insight? Bruce and Evan. Ive had a few "oh crap" moments hooking up the rigs where while tuning I noticed the antenna switch was off. A simple protection circuit seemed inviting. So far no BS170s have been murdered. The silver bullet for protection, then, is for the loose nut behind the key to pay attention.?

I may not have been as lucky as you, Bryan. I am using an automatic tuner so the propensity for my High Band QDX wandering into a dangerous overvoltage situation is greater. In any event, I may have been bitten today. After operating on 20m through 15m I noticed a sudden drop in output power. My casual glances at the inline wattmeter showed the little beast humming along nicely at 4-5 watts when, sudden upon switching bands, there was a drop? from 4.5w to about 2.5 watts. After dinking around, I got serious and lashed the rig up the wattmeter and a dummy load and confirmed same. ?

Then, in my fumbling around, I bumped the radio a bit and the output power re-assumed the 4.5w range. However, upon close sniffing the radio emitted that familiar odor -- most strongly in theDBS170 area.

Now my question is, aside from the output power, is there a way to determine that there may be [problems or should I just replace the four finals? Should I find four closely matched transistors? How closely a match? Should I put the 47V Zener across L14? Will there be other problems to took for?

..etc.

TIA.
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William, k6whp
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"Cheer up, things could get worse. So I cheered up and things got worse."

On Thu, Apr 11, 2024 at 08:40 PM, k6whp wrote:

I bumped the radio a bit and the output power re-assumed the 4.5w range.

This sounds a lot more like a poor solder joint or other loose connection than a damaged FET.? Semiconductors typically do not recover from bowing up.
73, Don N2VGU?

Bears a solid investigation, Don..

Thanks!?

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William, k6whp
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"Cheer up, things could get worse. So I cheered up and things got worse."

Hi William,

Did you measure the current draw when it is receiving?? A high current when in receive indicates that at least one of the BS170s failed.

It also helps you get the best advice by listing the model,? board, and firmware you use.??
Example:? QDX Rev 5 with firmware 1_10

One last point: it may also help to start a new topic rather than tack onto this topic.

73
Evan
AC9TU

Thanks. I toyed with the idea of a new topiic but had been researching this one thoroughly and thought it best to append my questions here lest I be accused of not searching other threads.?

I'll monitor the current as well as examine the solder joints. If the intermittent power loss occurs, I will start another thread and provide details suggested along with comprehensive symptoms.?

One exit question: why would receive current increase due to a bad transmit final transistor??
William, k6whp
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"Cheer up, things could get worse. So I cheered up and things got worse."

On Fri, Apr 12, 2024 at 10:08 AM, k6whp wrote:

One exit question: why would receive current increase due to a bad transmit final transistor??

In the QDX, the BS170s are always connected to the input power through L14.? Since they are MOSFETS, when they are working, current will not flow through them until the gate voltage turns them on when the transmitter is activated.? If they are damaged, they can conduct current all the time, which will show up as a high current when not transmitting.



You are correct that this message thread has wandered far from the original topic.? Unfortunately, there is no welcome email when you sign up for the group that lays out the recommended use of the system.? It's not your fault; most definitely, the "common" practice has become to respond with new questions, even if not on topic.? The recommendation is more for your benefit, as often I will skim by a topic that I no longer have an interest in following.? Starting a new topic would cause people like me to read the post and decide to comment if they have something to add.

Either way, it is better to ask than not to ask.

73
Evan
AC9TU

Thank you for the explanation, Evan. The matter is moot re solder joint or whatever. Was working 24m with the unit this AM and it belched smoke and fire..well smoke anyway. No question one or more of the finals gave up the ghost.?

Also no question that it did not survive in an ATU set-up. Now I am in the middle of the massive 105-message thread about when, where, and how folks should put the 47V Zener diodes across the finals.?

The controversy rages and I have questions I will put up on a separate thread.?

Again, thank you.?
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William, k6whp
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"Cheer up, things could get worse. So I cheered up and things got worse."

On Fri, Apr 12, 2024 at 11:50 AM, Evan Hand wrote:

You are correct that this message thread has wandered far from the original topic.? Unfortunately, there is no welcome email when you sign up for the group that lays out the recommended use of the system.? It's not your fault; most definitely, the "common" practice has become to respond with new questions, even if not on topic.? The recommendation is more for your benefit, as often I will skim by a topic that I no longer have an interest in following.? Starting a new topic would cause people like me to read the post and decide to comment if they have something to add.

WELL SAID!
?I tell users on my groups.io forums the same thing.
There are 2 main reasons for starting a new topic, rather than posting new question inside old topics:
1. It is much easier to scan subjects when doing a search for something your "need to know"
2. The BEST users who give advice may have stopped following the current subject before you post a new topic within it.

To me, the second point is most important!
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Robert Giuliano
KB8RCO