Problem with setting the PA bias current

[HB9TZU]

Good evening

I have not found a post about my problem in the group yet. Now I hope the group can help me.

I have a Hermes Lite 2 from Makerfabs with all options and it works in reception.

Problem no. 1
LAN connection, the right LED (LNK) does not light up. Is it possible that the LED is defective?

Problem no. 2
I want to set the BIAS current using the HL2Setup programme.
When I click on the Test PA BIAS button, for a moment I see the value 1975 ma, which changes very quickly.

When I try to set the PA BIAS current in QUISK (V4.2.26 according to the YouTube video) it also shows 2070 ma.

What could be wrong?

73 de HB9TZU
Christof

[brhl...@gmail.com]

Have a look at the heatshim if there is a short.

[HB9TZU]

Hi all

I have removed the heatshim. The bias current is still too high (same values as in my email).

HB9TZU

[HB9TZU]

Hello all

Today I measured (again) the resistance values according to the power supply shorts.

As they are all > 500 ohms, I assume that there is no problem here.

+3V3 and GND 584 Ohm            
+2V5 and GND 788 Ohm
+1V2 and GND 509 Ohm
Vbias and GND 56 kOhm
Vsupply and GND 0.89 MOhm
Vop and GND 1.6 kOhm
Vpa and GND 17 kOhm
+3V3 and 2V5 1.73 kOhm
+3V3 and 1V2 1.2 kOhm
+2V5 and 1V2 1.1 kOhm

I then measured the voltages according to No Transmit point 4 with the following values
Vpa GND 7.93V
Vop GND 10.14 V
Vvias GND 10 V

These values seem fine to me.

What else can I measure? As the bias current is too high when I go to transmit (Quisk button PTT),

I assume that I have a problem in the TX branch.

I received the HL2 in November, but was unable to use it for a few weeks for health reasons.

Then came Christmas and again almost no time. I am concerned about the 60 day period with Makerfab.

73 de HB9TZU

[Steve Haynal]

Hi HB9TZU,

Regarding your problem 1, perhaps there LED is bad or one of the resistor associated with that LED is not installed well. Please visually inspect R131, R132, R133 and R134. You can also post high resolution phone photographs of the front and back PCB where the ethernet jack is located. See the schematic at www.hermeslite.com

Regarding your problem 2, first, it is not necessary to adjust the bias as it comes set from the factory. Second, we have seen high current issues like you describe when a component around the heat shim or the nut and bolt near the PA have damaged a nearby component. In particular B106 or J30. Please visually inspect B106 and J30. You can also post high resolution phone photographs of the front and back PCB near the PA heat shim and bolt. Please see this thread for more details:

https://groups.google.com/g/hermes-lite/c/EpyX0eOXYrk/m/KF4OT0GxAAAJ

Are you capable or interested in doing these repairs yourself? If not, please contact Makerfabs regarding a warranty exchange. It will matter if you damaged B106 or J30 during installation or if the board arrived with the damage.

73,

Steve

kf7o

[HB9TZU]

Hi Steve

Thanks for your message.

Firstly, I would like to solve problem 2.
I will check B106 and J30 tonight and take a high resolution photo if necessary.

I can replace B106 (0.1 uF) and J30 (0 Ohm). I may have to order B106 if I can't find one in my SMD box.

A piece of wire would do for J30, at least for a test.

If the BIAS current is OK, I'll have a look at the LED on the LAN connector.

I'll write again...

73 de HB9TZU
Christof

[HB9TZU]

Hi there

Attached are three photos. B106 and J30 look fine to me.

But on J31 the solder joint does not look the same as on J30 or B106.

73 de HB9TZU
Christof

[Steve Haynal]

Hi Christof,

Thanks for the photos. J31 does look like it may have a poor solder joint. If you have an Ohm meter, you should measure 0 Ohms from the B104 pad nearest J31 to the via just left of the J in J31. If you don't measure 0 Ohms, then I'd try reheating the right terminal of J31 with a soldering iron.

We should determine if nearly 2A is really being drawn when you engage TX even with no signal. Can you measure the current that your power supply supplies the HL2? If so, what does it measure when you briefly engage TX with no signal?

It is okay to briefly (2 to 3 seconds) engage TX with the board outside of the enclosure. After you do that, do any of the components, in particular either of the LDMOS PA transistors, feel hot to the touch?

73,

Steve

kf7o

[HB9TZU]

Hello all

The first thing I did this evening was to re-solder J31 on the right side.

Then I measured the resistance with the ohmmeter as you described.

The meter read 0.5 ohms, which I think is ok.

The power meter on the power supply showed 0.24 amps when I was not transmitting.

Then I started QUISK. When I pressed PTT, the power supply showed 0.6 amps.

The PA current reads about 450mA, and the value increases if I transmit for a long time.

I then started HL2 Setup and briefly clicked on the Test PA Bias button.

The power supply showed only 0.41 A. Finally I clicked on the Set PA Bias button

and after a short time the values 79 and 77 were written.

The LMOS PA transistors did not get hot.
I will put the HL2 back in the case tomorrow evening and check again.

I don't know if the problem is solved.

Is there any explanation for the difference between the Quisk and the HL2 setup?

73 de HB9TZU
Christof

[Steve Haynal]

Hi Christof,

It sounds like you've made some progress. Please let us know if your HL2 is now transmitting. There shouldn't be a different between hl2setup and Quisk. Which version of hl2setup were you using?

73,

Steve

kf7o

[HB9TZU]

Hi all.

Two days ago I updated QUISK to the latest SW (V4.2.26) and I have hl2setup version 1.3 from 2019.

After a few attempts I can set the same BIAS current of 100mA in QUISK and hl2setup, hl2setup does it automatically (value 83 is written).

Yesterday evening I experienced some minor setbacks during the test. With Qusik I was able to transmit, but only reached about 1 watt. With Thetis I had no output power at all. As a result, I had to read the instructions more carefully today. The document "Hermes Lite 2 Thetis Installation and 3rd Party Apps" was a great help. Thanks to the author N8SDR.

I reinstalled the Thetis SW and did the basic configuration according to the document. And now my HL2 is transmitting at a good 5 watts.

Thanks for the help (Steve) here in this group.

73 de HB9TZU

[Steve Haynal]

Hi Christof,

I am happy to hear you see 5W with Thetis. My guess is that you have the band limits low or the TX drive not all the way up in Quisk.

73,

Steve

kf7o