A few issues and questions - T1/T2 & Low RF output

[G0UJA]

My kit was setup and working well on CW with good reports and a couple of known issues but has now developed a low output power fault.

I would appreciate any advice on the following...

Issue 1:
PWR ~13w / SWR 9.9 / EFF 99% readings were all nonsense pointing to the T1/T2 coils but I checked these multiple times and reworked the connections and I am quite sure they are built correctly and connected well;

Is there anything else known that may cure this issue other than remaking T1 & T2?

Issue 2:
After using the kit on CW for a couple of days the power suddenly dropped to around 0.1W but the OLED was still reporting PWR ~13w / SWR 9.9 / EFF 99% readings. I suspect that the BS170s may need changing so I have ordered some genuine Fairchild units but I am not sure how they are damaged as the VSWR is <1.2 but they may just be duff;

Could the 'T1/T2 reading' issue have damaged the FETs?

How is the PWR measurement on the OLED calculated - is this input power because it is not a realtime measurement of RF output power because even with very low RF output it is reporting the same values?

I am yet to tune the filters with my nanoVNA but otherwise everything seemed to be working well and I am a little perplexed as to why the power suddenly dropped off.

[Iw2fpe]

Hi

Look this!
viewtopic.php?t=395

[wa2t]

Hi James,

Read this thread (from the top): viewtopic.php?p=2126

73,

Robert, WA2T

[G0UJA]

Many thanks for the feedback and Robert WA2T the topic in link you provide looks identical to my issue - even down to the other kits within my group buy working perfectly.

I noticed that touching the capacitors and or resistors seems to bring the readings in to the normal ballpark. I also noticed that when taking voltage readings on the FWD/RVS pins also brings the readings in to line.

Did you ever get to the bottom of what was causing the strange readings?

There seems to be very few components that could be the issue other then the main ATmega328 being at fault.

[wa2t]

Many thanks for the feedback and Robert WA2T the topic in link you provide looks identical to my issue - even down to the other kits within my group buy working perfectly.

I noticed that touching the capacitors and or resistors seems to bring the readings in to the normal ballpark. I also noticed that when taking voltage readings on the FWD/RVS pins also brings the readings in to line.

Did you ever get to the bottom of what was causing the strange readings?

There seems to be very few components that could be the issue other then the main ATmega328 being at fault.

Hi James,

Yes, I changed the components mentioned in one of the posts I made in that thread. The results are power and SWR track LP-100A measurements pretty well (so that problem is solved), but (tr)uSDX measured/displayed efficiency is 10-11% worse. That is as far I went with the issue other than reporting it all to Manuel.

Changing the ATmega328 may indeed fix the problem, but I do not think it is the fault of the ATmega. I think it is poor choice of application circuit components/values (see the datasheet quote in my post) that cause the issue to occur with some ATmega328 parts.

73,

Robert, WA2T

[G0UJA]

Good news - FETs replaced and up and running again... No idea why they failed but interesting reading this topic which appeared today:

viewtopic.php?p=3230#p3230

Issue 2 solved.

Issue 1 to work on...

[G0UJA]

UPDATE:

Tonight my club had a construction evening for the group buy and I manged to do the following to try to identify and solve the issue with my PWR/SWR/EFF readings:

1) The ATmega328p on the main board was replaced with a brand new chip to rule out any issues with a faulty microcontroller. Bootloader and firmware reloaded fine.

2) My RF board was replaced with a known working RF board. The PWR/SWR/EFF readings were still displayed incorrectly on my original main board with a new microcontroller.

3) My RF board was then tested with a known working main board. The PWR/SWR/EFF readings were still displayed incorrectly on the substitute main board.

When the substitute RF board and substitute main board were put back together they work perfectly.

Both my boards were checked under a microscope and look visually fine.

No other boards in this group buy share this issue that I am aware of.

Multiple club members verified this behaviour and nobody could understand how this is even possible.

This is every combination of my boards with known working boards and does not narrow down which board actually has an issue (if any) unless there is a fault on each board causing the exact same issue which is difficult to understand.

Very confused.

[N6YWU]

Here's one more thing to check:

If you have a sensitive Ohm-meter, and can find pairs of test points, one on the RF board and one on the digital board, that should be connected via the header, check the connector connection path resistance. Do this for every pin in the header. An unusual resistance could throw off lots of things between the digital board and the RF board. The *Rxxxx*.com's kit problems might be related to something like this as well (wonky connectors, or soldering, or vias)

73, Ron, N6YWU

[G0UJA]

Thanks for the suggestions Ron, I am going to look in more detail at the full tracks tonight - I did try bridging the top to bottom FWD & RVS pins without any changes but I suspect the issue may be on an inner track.

I've put a topic up to see if there is some form or layout for the internal layers.

[G0UJA]

All inner tracks seem to be within spec.

Can anyone confirm, with NO RF BOARD connected, if you try to TX what PWR/SWR/EFF readings do you get displayed?

Mine are totally the same even if the RF board is connected or not.

[selfhood]

ADC5E423-6259-4205-BCE8-5D64E186A3A2.jpeg (227.3 KiB) Viewed 3816 times

I don't think it's a problem with the main board. Does the relay has click sound when the knob is double clicked? If not, it is a U1 or U7 issue on the RF board. If the relay works properly, try replacing the PA Fet (BS170) on the RF board. If that doesn't work, Connect the output power meter and measure whether the output actually comes out. If there is no output, try soldering the output terminal again.
The problem of S-meter not being displayed properly can be solved by removing the enamel at the ends of T1 and T2 and sufficiently soldering.

[G0UJA]

Thank you selfhood for the images - I think there is an issue with both my main board and the Rf board though because I am not getting the same readings as you.

I may also add though that this unit works perfectly and within spec other than the strange readings, I have also fully aligned the coils with a VNA using the method in this forum without any issues.

This is my main board without the RF board attached:

2022-05-30 10.15.39.jpg (105.4 KiB) Viewed 3749 times

This is my main board with the RF board attached:

2022-05-30 10.20.14.jpg (90.57 KiB) Viewed 3749 times

I'm really not sure what direction to go, microcontroller and FETs all replaced, all coils reworked, PCB inner tracks checked for continuity, every connection on the header pin fully tested from start to end path. The thing will just not read properly?

[dl6sez]

Hello James,

have you done a power cycle when you added your RF board? Relays have to be reset and set according to band because they are bistable relays keeping the setting without power....
and than have you checked RX first? If RX works there should be the possibility to get RF out to the antenna/dummy load.
If you still have a problem with SWR and power reading go and check T1 and T2: does winding direction match pcb holes for wire and is enameled wire really stripped of coating at the solder joints?
My 2 Cents

73 de Chris DL6SEZ

[G0UJA]

Thanks Chris, yes I fully remove power before taking the boards apart and putting the boards back together. The power output and RX are no problem at all, the kit works exactly as it should and I have made lots of contacts on CW without any issue - the only problem I have are the strange PWR/SWR/EFF readings.

I have remade the T1/T2 coils 3 times without any change at all and I have run out of wire but I have ordered some more and I will give it one final attempt before I give up.

I will wrap the ferrite with a layer of electrical tape this time in case the wire I was using was scratching on the edges - this still would not explain why the main board on it's own is giving strange readings.

[dl6sez]

Hello James,

oh i see you have very well done it...
Maybe you have a chinese copy Atmega328P wich has a problem on ADC.
Have you read on the other thread wa2t suggested to reduce the capacitance in the circuit after the bridge rectifiers 1N4148 and lower the serious resistances to get the ADC working? He succeded
Probably you both wa2t and you have a Atmega328P copy which draws higher current when sampling at the input.... You could also remove the 1N4148s and check during TX with a voltage applied from outside if the ADC works. ....Maybe when the diodes are short by themself this could lead to strange reading also....

73 de Chris DL6SEZ

[G0UJA]

Thanks for the advice, I checked all the diodes and capacitors in the circuit and they are fine so I did a quick and simple version of the modification by WA2T without removing any of the original components, simply piggybacking 2 x 1M resistors on to the header of the RF board:

2022-05-30 19.58.28.jpg (98.9 KiB) Viewed 3686 times

This seems to work and although not really a 'fix' it tracks the real measurements much closer than without it with the exception of the efficiency which is reading low.

2022-05-30 20.08.42.jpg (13.88 KiB) Viewed 3686 times

2022-05-30 20.10.29.jpg (15.12 KiB) Viewed 3686 times

Hopefully one day somebody will find the real reason that some boards have this issue - until then I've spent too much time trying to get this to work properly and I'm leaving mine as is

[dl6sez]

Nice to see it works, nearly as it should do
In the beta firmware Manuel has on his download page, one can adjust the "R shunt" in menue and therefore the efficiency....

73 and hope to copy you once on the bands
Chris DL6SEZ

[DL2MAN]

Could you affected ones please post a closeup picture of your AtMega, so we can determine if it is a certain type that is affected ?
The mod is just a workaround in my opinion, and the original schematic works for most of the people, considering, we have a few thousand units in the wild and only a handful complaints about this.

73 Manuel; DL2MAN

[G0UJA]

Thanks Manuel, I will post a close up image of the microcontroller later this evening but as a side note, none of the other kits in my group buy have this same problem and they all have an ATmega from the same batch - in fact mine has now had 2 tested with the same result.

Is it worth removing/replacing C31 & C39 on the main board and testing without the RF board attached to see if it makes a difference in case they are leaking or not within spec?

[DL2MAN]

I have no clue where this issue could come from.
This is why I didn´t give too much input on it.
When I experienced it once ->my own fault, by plugging together both boards under current it fried the ADCs
I changed the ATMega and the Issue was gone.

What I know from the DIP28 Times: ATMegas have Differences in Quality.
It was simple to determine, as you could just remove them from the Socket and plug in another one.
While one was not usable with an OLED, another one showed no sign of Noise.
The "Sensitive to OLED Noise" One however performed perfectly in a Rig with LCD.
Both of course with the same software.
So there´s (quality) differences, I don´t have a clue about.

73 Manuel; DL2MAN

[G0UJA]

Excuse the mess, this was the microcontroller I removed and replaced with another identical one from the same batch, however, all the other boards produced using the same batch of chips work fine and do not exhibit the same issue:

2022-05-31 23.08.31.jpg (87.13 KiB) Viewed 3577 times

[dl6sez]

Hello Manuel and James,

my guess: think there are chinese copys of the Atmega328P in the original supply chain.
I worked in semiconductor development many years and can't believe that in these days the manufacturing tolerances of the silicon fabs have become so worse. Looks more like with shortages money can be made with cheap not 100% functioning copys. You can find copys with different specs of Atmega328, just think about the Si5351 and MS5351....
Search in Goolge for Atmega328P copys, you will find many chinese offers

73 de Chris DL6SEZ

[selfhood]

I looking at your picture, it seems to be a problem with the main board. If ATmega328p is not a problem, try replacing U1 (74ACT00) and U2 (78L05). Please use the flux together to avoid short circuits as U2 has high pin density.

[G0UJA]

The 78L05 appears to be fully working within spec even under full load so I am hesitant to change this, I have already changed the ATmega328P and this is from a known working batch so could you explain your thinking behind changing the 74ACT00?

Are the readings calculated from the drive level part of the circuit which includes U1 in addition, or are they just calculated from the values presented at the FWD/RVS ADC pins on the ATmega328P?

[sv5fri]

Dear OM's

Because I have the same problem and after a few minutes of operation the Watt & SWR are back to normal.
My personal opinion has to do with the non-linear output ADC Atmega328p (quality, whether the component is genuine or not).