Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
Shorts and hot PAs
|
Jess Gypin
Seems there have been several kits that have a similar problem to the one that I still have a problem with. Initially hot PA transistor on first power up and then something involving Q5, Q6 and the nand gate. I replaced a shorted Q6 and then only the same problem on trying to transmit the first time. Now I have a so so receiver that has no real peaks on the IQ balance and lo and hi adjustments. There is some peaking of the band pass filter. I have also looked all over the PA tx/rx path with nothing conclusive. My next step was going to be another good look at the band pass and dc measurements in the static state. From what I remember the last time I had it on, the receiver seemed so so and a couple of quick transmit tries via the onboard micro switch, all three of the PA transistors got warm very quickly and the regulator on the left edge of the board seems hotter when in receive than it should be. I have not checked dc voltages yet as I just have put it aside for now. I get the impression that if and when the problem with my 40 meter kit is found, it will be something simple and stupid that I did wrong or just another bad part. Jess AE0CW |
|
Jess
I think you may be reading too much, and assuming that you would have the same issues as I had (which are rather small in the big picture).? I suggest concentrating on the receiver.? check continuity of each winding - to make sure the wire is really soldered to the pad - yes don't touch the wire in making this measurement.? the peaking of the trimmer on a 40m unit is rather soft.? if you have continuity in the receiver transformer, and all is assembled correct in the receiver -- it will then calibrate!? follow the instructions carefully, and see if you can get favorable nulling from the resisitive trimmers -- it will slowly decrease on the LCD and eventually jump scale - the number will diminish by 1 each time.? If this isn't working - my guess its a coil disconnection issue -- as even if you were a few turns off it would still have SOME null activity.? Let's avoid jumping to conclusions yet on transmit -- let's work the receiver.? Warm is hard to measure subjectively.? I will give you clue that the PNP tends to warm up more than the MOSFETs -- under normal CW it is less pronounced.? I would not fret if it gets quite warm if you are willing to key down for a few seconds!? I plan to major on CW with this rig.? Before you take too much of my advice, I could tell you about my troubleshooting fits fixing my K2 - but these are on the web someplace - and that rig is alive and well.? Hang in there and enjoy the journey -- especially as I presume you have other rig(s) to operate.? you are welcome also to email me direct.? Curt |
I suggest concentrating on the receiver.Curt, Maybe, but what if a BS170 in the PA is shorted? That will certainly reduce the RX sensitivity, will it also affect the nulling? 73 Alan G4ZFQ Let's avoid jumping to conclusions yet on transmit -- let's work the receiver.? Warm is hard to measure subjectively.? I will give you clue that the PNP tends to warm up more than the MOSFETs -- under normal CW it is less pronounced.? I would not fret if it gets quite warm if you are willing to key down for a few seconds!? I plan to major on CW with this rig. |
|
Jess Gypin
Curt,
toggle quoted message
Show quoted text
Thanks for the input. And I have checked and rechecked and rechecked and reheated and resoldered and rechecked and reheated the toroids. I have built quite a few kits over the years and have had more than my fair share of toroid problems to the point where I am confident that they have been checked out very thoroughly. I am really only saying this. There have been several people that have had hot PA transistors in power up and/ or not transmitting. And a few that have had to replace some of the Q1-Q3 and/or Q4,5,6 transistors. Just looking at how they might have something in common. And no, I don¡¯t read too much. Just spotting a small occurrence trend. But, having said that, I am on here talking about the ¡°journey¡± as are several people. And I do appreciate all the input from people like you and others that are smarter than me. It¡¯s been a while since I worked on analog electronics and as I said, I am very poorly equipped living in an RV and caring for ailing parents. So, thanks for the input. Jess AE0CW Sent from my iPhone On Jan 8, 2018, at 7:29 AM, Alan G4ZFQ <alan4alan@...> wrote:
I suggest concentrating on the receiver.Curt, |
|
Jess Gypin
And if and when I find a toroid problem I will gladly eat my words and hat!?
toggle quoted message
Show quoted text
Sent from my iPhone On Jan 8, 2018, at 7:56 AM, Jess Gypin <ontarget1911@...> wrote: |
|
Jess
of course insure the rig is not in transmit mode while trying to receive !? I assume that rig isn't transmitting and receiving at the same time.? (my bad if it really is) a classic test is to put your finger on the input of the audio chain, and hear a buzz.? if audio is okay - this only leaves the mixer and PLL as active parts.? I was able to use the built-in test source to check out my receiver (after it no longer worked) and using my fingers found a loose resistor.? in my case the only issue with those transmit parts was operator error.? I had not read the full manual to discover that plugging in GPS can cause the rig to go into transmit.? I damaged only the PNP.? some have wondered if this PNP is strong enough to handle the current load -- I believe (as does Hans) that it is adequate unless there is a circuit problem (or someone like me transmits too long into an open circuit).? as you and I know, it only takes one missing connection to make something not work.? Yes I won't rule out a problem none of us have thought of.? troubleshoot what you can - including verifying you can hear the LO in a sniffing receiver.? to show I am mortal (again) - the regen receiver which once worked is now receiving weakly (its a Paraset 80) - something to work on when I find time between work days.? CUL Curt PS - I discovered something - my regen is receiving just as well with antenna disconnected!? so something is not attached .... it happens |
|
I have been reading this thread on PAs and their woes and in general testing. For as long as i can remember when i test something for the very first time ( this includes the 4 U3S i have for various beacons) I first say a little prayer (Aretha mode), but what i do next would help a lot of people i get a 22 Ohm resistor and put it into the supply line and even if there is a short the max current is controlled to some extent. You smell a carbon resistor burning before BS170s. These days a current limited PSU would be the job but to be honest the resistor does the job just as well. Of course the choice of resistor depends on the job, obviously 22R? would be of no use testing a 100 Watt PA so the sizing depends on the supply voltage and anticipated normal current drain.Lastly don't forget to remove said resistor to achieve full output. cheers Geoff GI0GDP On Tuesday, 9 January 2018, 2:33, wb8yyy via Groups.Io <wb8yyy@...> wrote: Jess of course insure the rig is not in transmit mode while trying to receive !? I assume that rig isn't transmitting and receiving at the same time.? (my bad if it really is) a classic test is to put your finger on the input of the audio chain, and hear a buzz.? if audio is okay - this only leaves the mixer and PLL as active parts.? I was able to use the built-in test source to check out my receiver (after it no longer worked) and using my fingers found a loose resistor.? in my case the only issue with those transmit parts was operator error.? I had not read the full manual to discover that plugging in GPS can cause the rig to go into transmit.? I damaged only the PNP.? some have wondered if this PNP is strong enough to handle the current load -- I believe (as does Hans) that it is adequate unless there is a circuit problem (or someone like me transmits too long into an open circuit).? as you and I know, it only takes one missing connection to make something not work.? Yes I won't rule out a problem none of us have thought of.? troubleshoot what you can - including verifying you can hear the LO in a sniffing receiver.? to show I am mortal (again) - the regen receiver which once worked is now receiving weakly (its a Paraset 80) - something to work on when I find time between work days.? CUL Curt PS - I discovered something - my regen is receiving just as well with antenna disconnected!? so something is not attached .... it happens |
to navigate to use esc to dismiss