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bitx40 display flashes and audio clicks when powered on.
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I just recently wired up the bitx40 and when I turn on the power the display flashes and the speaker clicks but that it all. When I remove power from the PA socket, the radio resets itself and it begins to receive just fine (the display gets bright and the contrast is too high) but I can tune around and receive just fine. As soon as I plug the power back in to the PA socket, it display begins to flash again and the speaker clicks with the flash. I have searched for obvious signs of shorts etc.. however everything looks fine. I also noticed "by touch" that the final mosfet gets very hot. I checked to make sure nothing was shorted out against this and it is not touching ground. I would assume at this point that the output mosfet is toasted, or am I missing something?? |
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Try to measure and reduce the? IRF bias to manage the recommended Idrain under idle condition(without any signal input) On Wed, Feb 15, 2017 at 10:32 AM, Mparnell <barakuda318@...> wrote:
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Regards
Sarma ? |
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Thank you, I just gave that a shot and there was no change. I measured the voltage at the DC jack and noticed that it reads 0 volts until the unit flashes and clicks then it jumps to between 2 and just over 3 volts and goes back to 0 between flashes/clicks. This is a 12 volt 1.5A power supply, which I am only using to receive and test with as I do not have an antenna tuned for 40 meters yet. I may need to try a different power supply. Thank you for your input Mvs Sarma. On Tue, Feb 14, 2017 at 11:42 PM, Mvs Sarma <mvssarma@...> wrote:
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You are not transmitting, so there should be no bias voltage to the gate of the IRF510, and thus no drain current into the IRF510. ?Definitely something wrong here, not just an adjustment. ?Without power to the PA socket, check the gate of the IRF510 with a voltmeter, should be zero volts when not transmitting. ?If that's true and if the IRF510 is drawing so much current when you do apply PA power, you likely do have a blown IRF510. ?? There is a contrast control somewhere in there for the display, but it's between the two boards and hard to get at. On Tue, Feb 14, 2017 at 09:02 pm, Mparnell wrote: When I remove power from the PA socket, the radio resets itself and it begins to receive just fine ? |
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I understand the practical difficulty with the display pot location. ?But if i recollect , you indicated the IRF getting too hot. and now the current? is not there on the drain circuit?On Wed, Feb 15, 2017 at 11:45 AM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
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Regards
Sarma ? |
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I think he was saying that he was not transmitting, but the IRF510 was still getting hot when he put power to the PA connector. ?When receiving, the LM78L05 does not get power, and thus there is no gate bias voltage, and Vgs on the IRF510 is zero. ?So my understanding is that the IRF510 was drawing lots of current, but should have been drawing no current at all. On Tue, Feb 14, 2017 at 11:38 pm, Mvs Sarma wrote:
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I get your point., Jerry. ?I fear whether the fet did not give up by a possible leakage between drain and gate.?Let us see. regards ?sarma ?vu3zmv On Wed, Feb 15, 2017 at 9:12 PM, Ion Petroianu <ion.petroianu@...> wrote:
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Regards
Sarma ? |
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I get your point., Jerry. ?I fear whether the fet did not give up by a possible leakage between drain and gate.?Let us see. regards ?sarma ?vu3zmv On Wed, Feb 15, 2017 at 10:16 PM, Mvs Sarma <mvssarma@...> wrote:
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Regards
Sarma ? |
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Regarding the IRF510:
There is no power on the gate on RX, but there is power on the drain, whether the connected PA is to the to the Vcc source or another power source (though it is possible to have a second, switched source for PA). This sounds like a classic avalanche situation. Since he is feeding the rig with 1.5A max, it is probably shutting down the regulator in that supply. That resets and begins the cycle all over again with each TX power-up. First, set RV1 to zero volts on the gate on transmit. If it still happens (which it probably will) then the IRF510 is bad and should be replaced. Note that when this is done, start the TX alignment with RV1 at the zero level. You may also have to adjust R136. As above, the display problem is probably a contrast adjustment since RX appears to be ok. john AD5YE |
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Guys thanks for all the input. I'm going to be doing some more troubleshooting tonight and we shall see what we come up with. I've ordered some irf510's just I case but I am highly suspecting that is the issue.? I'll post here what I find. 73's KE0AJP On Feb 15, 2017 4:42 PM, "John Backo via Groups.Io" <iam74=[email protected]> wrote: Regarding the IRF510: |
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Near as I can tell, he never hits the PTT switch to transmit. ?And the IRF510 is still heating up. I did tell him that the gate to the IRF510 should be zero volts during receive. ? If it isn't then the next step would be to figure out why. ?The 12v TX rail that powers the LM78L05 should also be zero volts during receive. ?If that is not zero volts, I suppose there could be some sort of relay fault or a short that keeps the TX rail at 12v during receive.? But if the gate voltage is zero and the IRF510 is heating up, then this is just a blown IRF510. ?I'd remove the IRF510, then power up the board (including the PA +12v supply into the board) and see if everything works as it should, including pressing PTT to transmit (even though it won't transmit due to the missing IRF510). ?Then adjust RV1 on the main board for zero volts on the IRF510 gate, I believe that will be fully clockwise (and thus fully counterintuitive). ?Power down, install the new IRF510, and carefully adjust RV1 for 100ma into the PA 12v connector as per the wire-up instructions on hfsignals. ?Note that the RV1 setting is very touchy, and advancing it too far could blow the new IRF510. ?The correct RV1 setting for the new IRF510 (for 100ma of drain current) could be significantly different than it was for the old IRF510. |
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True, Jerry.
He turns on power, the rig clicks and turns off, and after REMOVING the PA power, RX is ok when power is applied. This is almost certainly the output transistor going into avalanche. What is amazing is that it didn't blow up. I suspect that is because the IRF510 can take about 4.5A continuous current, but he is only feeding it 1.5A. The regulated voltage shuts down before heating can destroy it completely. In any event, that is not a proper way for any decent MOSFET to act. Hi. There still might be another problem. Hmm...maybe a solder bridge drain to gate? Or VHF oscillation? How interesting... I am beginning to think that it might all come back to RV1. Mine happens to have the slot aligned with the "B" of Bourns. One wonders where his is? john AD5YE |
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John, you are absolutely right in How/when it happens. as for RV1 mine was cranked almost all the way up (turned almost all the way counter-clockwise) I am going to try and pull the mosfet tonight and see if the problem persists with the PA power hooked up to the board. I've got a proper power supply (adjustable) to use on it now as well.? On a side note, I shorted the two PTT pins "as if pushing the ptt button" and the relay clicks, right when the unit flashes on for a second but of course clicks off when the unit powers itself down. so I'm assuming the relay is ok. I have found no solder bridges or other shorts to mention, I even checked with a magnifying glass so that I wouldn't miss those pesky little solder balls that are notorious for "unknowns" I'll post my findings tonight when I get a chance to troubleshoot further. 73's KE0AJP On Wed, Feb 15, 2017 at 5:38 PM, John Backo via Groups.Io <iam74@...> wrote: True, Jerry. |
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Ok, I pulled the IRF510 and hooked up power to PA. The receiver functions just fine now. I went ahead and did some voltage checks while the mosfet was out. Voltages on the board where Gate would be I adjusted to 0 volts on tx. on the board where drain would be was equal to the power supply. on the board where source would be was zero volts. This was while in tx. I will wait now for the new 510's to arrive so I can hopefully get this on the air.?
Thanks gain everyone for the input. 73's KE0AJP |
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Important!? Before you install the new PA turn RV1 fully clockwise and do the same with R136, the silver trimmer near the corner on the same side of the board. You might need to have it turned up a little if you don't get 100mA with RV1. Turn up RV1 counter clockwise until your PA current reading with a amp meter reads .100 mA while holding down PTT. Then turn R136 counter clockwise until the meter reads 1 Amp while speaking long aahhh. Like when the doctor says "Now open and say aahhh". Yours is what mine did when I changed the PA and it was still adjusted for the old one at a higher Bias setting. And it took a long time to find out what R136 does. It's like a driver gain adjustment. It's what you'll need if the current isn't reading 1 Amp when saying aahhh in the mic. You should never have to yell to be heard on the radio, or to get a wattage output reading. |
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Thanks very much for this, John. For the record and/or posterity, I was unable to get a full 1A from HF Sigs' board #869. I turned both R136 and RV1 fully clockwise, then opened RV1 until the Fluke 87 showed 100mA. ?(Amp input; meter on the A/mA setting) R136 had to rotate almost fully CCW to get a solid 7W output power on the WM-2 Wattmeter. ?The PA was only drawing about 740mA at that point. The IRF510's heatsink was warm to the touch, and the resting current draw was up to about 150mA. ?I turned RV1 a bit CW so the 'warm' current was 100 mA. ?Current with a strong 'ahhh' and a solid 7W out still shows about 740mA draw by the PA. I'll have a CARE package from Mouser tomorrow - I'll get the signal on the o-scope on the dummy load and check the output signal then. ?In the mean time, I have a solid, intelligible signal on the SDR receiver now - thanks for that! |
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Just thought I would let everyone know that the problem was indeed the Mosfet. I replaced with a new one, did a crude alignment and now I have a working Bitx40. I will need to do a better alignment to get the tx just right but we're in business. I just need to wire up the microphone now. Thanks a lot for all the help guys. On Wed, Feb 15, 2017 at 5:47 PM, Mparnell <barakuda318@...> wrote:
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Ion Petroianu, VA3NOI