I have been wondering why I have not made a single QSO on my uBITX V6. I just assumed that it was bad band conditions, poor antenna, low power a number of things. I never really tried hard to get QSO's I just tried a little bit every now and then. This afternoon I hooked up a watt meter to it and sadly found out that it isn't transmitting at all. I checked the wattmeter on other rigs and it worked just fine. I put it back on the uBITX and nothing. So does this mean that I need to replace my finals before I get my first QSO on it??
I can't think of anything else, I hope that you guys have some ideas.?
--
'72

Aaron,
First, don’t get discouraged.
Have you tried putting the uBITX in CW mode and pushing the PTT button on the microphone with the watt meter connected? Start out on the 80 or 40 meter bands first. Does the TX light come on? Can you heard a relay click?
Have you tried another microphone yet? I replaced mine with a CB microphone having a built-in preamplifier. It made a tremendous difference in power output for the phone mode.
I’ll let other folks chime in with more technical troubleshooting advice now.
Stephen

Yeah I had it in CW mode when I was testing it with the wattmeter. I do see the TX come on the screen when I push the PTT on the mic. I also hear the relay clicking when I push the PTT button. I do have a nicer mic, I don't know if it has a preamp or not built-in but I want to make sure that the rig works before I do any mods to it.?
--
'72

开云体育

Aaron,
Verify that you do not have the "skewed pot" issue pictured in the following message:
/g/BITX20/message/73189

If that is the problem, then most likely you will have to replace one of the finals.? IRF510s are relatively cheap and readily available.

After the visual inspection, I would validate that the Bias regulator is delivering 5volts when the PTT is pressed and that there is a gate bias on each of the IRF510 output transistors.? All of this should be done into a good 50ohm dummy load rated for at least 10 watts.? The 20watt QRP-Labs dummy load is a good low-cost dummy load for up to 20 watts at only $8.50 plus shipping


The last test would be to readjust the bias on the finals to verify operation.? REMEMBER that the pots are REVERSED.? Minimum bias (current) is fully CLOCKWISE? You turn them counterclockwise to increase the current, being VERY careful not to exceed 150ma for each device.? Here is the HF Signals bias settings page:


If you can adjust the bias, then most likely the finals are OK.? The next most vulnerable device in the chain is then Q90.? This transistor has been know to be blown by nearby high power transmitters.? There is a recommended back to back diodes (1n4148 as an example) from the switched antenna lead on K1 pin 12 for the receive section to ground.? This will not affect receive sensitivity, yet protect when a high power transmitter keys up when in receive or powered down.

The above are just suggestions.? You should review the schematic and do the measurements to validate before making the mods.

Good luck hunting down the issues.
73
Evan
AC9TU

Hello Aaron,

I would check the following in order:

1. That both the red and brown wires of the power supply connector are connected to the positive of the power supply. To double check i would measure the voltage on the tabs/ heatsinks of the finals (+ of power supply should be present).

2. The current consumption when pressing the PTT in SSB mode, no modulation, should go up to about 450mA indicating that the finals are most likely ok.?

73, John

Juan,
If your audio reports are coming back OK, then no problem, do not change anything.? However, the most impact for voice communication is in the mid audio range: 500 to 2500 hertz.? You might have the BFO set too low such that the SSB filter is allowing some of the carrier through and then cutting off the high audio frequencies.? Here is a video on the Calibration of the v6 uBITX.?


If you were to leave the BFO setup as in the first step, you would get more carrier bleed than when centered as it is designed in the 3rd step.? The first calibration of the BFO is to ensure that you get the low-frequency beat tones when doing the frequency calibration.? After setting the calibration frequency, you then adjust the BFO to bring the filter back centered on the 300 to 3000 hertz range for the maximum punch of the audio.

FWIW
73
Evan
AC9TU

John,
The v6 has the 3 pin connector, however, the power is coming directly onto the mainboard.? This is different than all of the prior version, where you comment is right on.? Not sure why they left the 3 pin connector, as the pins are jumpered together on the board.

FWIW
73
Evan
AC9TU

Ok I'm still learning this stuff and a lot of what you guys are saying has gone over my head. So please be patient with me.?
Evan: My pots are straight. Where would I find the Bias Regulator??
John: I don't have any red and brown wires at the power supply

--
'72

Aaron,
On the schematic, we are looking to verify that U2 is being supplied 12votls on TX, and regulating that down to 5volts on TX.


On the actual board, I believe it is where the P1 CONN 01X03 lower right corner, next to the blue pot (I do not have av6, I do have a v4 and a v5).


While you are at it, you can verify that you have 12volts on the drains of the two IRF510 PA MOSFETs.

Let us know what you find.
73
Evan
AC9TU

You are right Evan I was thinking V5. Your comments are spot on.

Aaron, please disregard and follow Evan questions about the 12v on the finals.

73, John

Here are the measurements that I have.?
INPUT: 7.87
OUTPUT: 12.85
That may be backward as to what you were wanting, I determined the pins from the datasheet that I found here:?
I could not test the IRF510 PA MOSFETs because it was this time that gravity decided to ruthlessly attack my multimeter and hurled it to the floor and breaking it. I hope to have a new meter by the end of the day and I will test the IR510 PA MOSFETs then.?
--
'72

I will assume that you have the input and output measurements reversed. Even with that modification, the output pin of U2 (the 78Lo5ACZ) should be 5volts +/- 0.15volt.? There is something wrong with either your measurement, the regulator is bad, or there is something else pulling the voltage higher than it should be.? It is a surface mount device, so tricky to replace without a hot air surface mount rework station.

As far as I can tell, the input is to the right of U2, and the output is to the left as shown in the board picture I sent before.? The center pin is at ground, 0volts.

You can measure the drains of the IRF510s on the large tab connected to the heatsinks.? The 12volts is there all of the time.? You do not need to key the PTT switch to take the measurement.? Switching the gate bias off puts them in a high resistance mode, such that only a few milliamps of current is drawn for both of the devices.

Double-check the U2 voltages.? If you are truly getting almost 8 volts on the output of the regulator there is something really wrong with the circuit.? My only suggestion is to order a replacement before you try to remove it for testing.? When ordering get the IRF510s as well.? I believe that you will need to pull them to verify that they do not have a drain to gate short that is pulling the regulator output up.? Do this before you try to remove U2.? If that is the cause of the U2 output voltage being over 5volts, then with both IRF510s removed you should get 5volts on the outpput of the U2 regulator.? Replace the IRF510s if that is the case.

There are others on this board who will do the repair that have the proper tools and experience.? I have done this type of replacement once (I thought I had an issue with one of the BAT54SL used in the product detector, that is the only removal experience. I had 4 transistors to install in a filter kit that were surface mount that went well), however I am not confident on my capabilities to work on someone else's uBITX, even at no charge and the owner taking all of the risk.? The best option would be to find a nearby ham or club that could help with the measurement and problem solution.

Hope the above helps, and good luck in finding and fixing the issue.
73
Evan
AC9TU

Evan, Aaron,

Since the unit is described as working and we know that 7.87V on the output of the regulator would mean death to the Raduino it must be the reference point of the measurement.?

Is it a coincidence that 12.85 - 7.87 is virtually 5Vdc, or was the measurement done from the positive as reference instead of the negative?

73? John (VK2ETA)

John,
Actually there are two 7805 types of regulators in the uBITX design.? One as you pointed out supplies the Raduino.? The other is an SMD version soldered on the mainboard for the bias voltage on the finals (in the blue box of the screen shot of a section of the uBITX schematic).? That one is the one that I asked for the measurements.??

Still, I agree that it is a strange coincedence that the difference is 5Vdc.

Aaron,
The voltage measurements should be made in refference to the supply negative, any of the ground points on the connectors like the shiled of the BNC RF connector.? Another point would be pin 3 of the P1 power connector that is not used.

73
Evan
AC9TU

I redid the measurements, the picture above shows the pin names and the measurements that I obtained.?
Input to Ground 4.97 volts
Output to Ground 12.85 volts

I measured both IRF510's and I got 13.10 volts off each one.?
--
'72

Sorry, Aaron, I had given you the incorrect pin assignments before.? What you have labeled as Output is the Input, and the input is the output (I double-checked the datasheet).? With that understanding, all looks good.

So the next step is to try setting the PA bias adjustments per the HF Signals instructions given here:


!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!CAUTION!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The bias controls are backwards from what most designs would implement.? That is CLOCKWISE is minimum bias, and counter=clockwise is maximum.? You do not want to overdrive the IRF510s, our you will cook them.? They are sensitive, so take it easy when increasing the bias.??

If you can set the bias for an increase of 100 ma for the first, then another 100 ma for the other IRF510, then both should be good.? The problem then is with the drivers.

Quick question, do you have the uBITX connected to an antenna when another rig was transmitting nearby?? It did not need to be turned on.? If so, then the next area to check is Q90, first for DC voltages in TX, then measuring the output with a scope or RF probe.

Let us know what you find.

73
Evan
AC9TU

Ok I'm sorry but I'm going to be a bit grouchy. As some of you know I have been having one problem after another with my uBitX V6 since day one. It has been aggravating me badly. I am at the end of the line with this radio. I believe now that it will be regulated to being a $200 dust collector.??
I tried for a couple of months to make at least one QSO with it. But it wasn't transmitting so I brought it to this thread. I tried all of the suggestions of the wonderful people in this group. (I'm not aggravated or upset with anyone in this group or this group). I tried different power supplies, different coax cables, antennas and such with no luck. For the past two weeks, I have been fighting tooth and nail to get it set up to operate digital modes. That finally happened (Note: I switched over to Reeds sketch and it works, the radio control is great). This morning I spent the day running WSPR thinking that at least it may be transmitting even a few milliwatts, but absolutely nothing on 20, 30, 40. When I bought this rig I wasn't expecting a 7300 or a KX3, but I was expecting something a little better than a Michigan Mighty Might. I'm not saying that the uBitX is bad, I'm just saying that I got a rare bad unit.?
Perhaps I will have better luck homebrewing one.?
I don't have the funds to send it off to get fixed or to order a new one. I took the gamble and lost $200 and now I'm out of the game.?
Thank you guys for all of the help and advice that you have given me.?

--
'72