Michael,
I have an AT-10 and love it.? My AT also had tuning issues until I resoldered the relay pads.? There is a utility on the GitHub webpage that will help. You can read my experience and see the link here.
Bob? ?W7DIT
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Hi all,
I have purchased a preassembled ATU-10 at AliExpress (HamRadioShop Store). Build quality looks decent, but tuning results are poor especially on 60m and 80m. E.g. tuning stops at SWR 3.0 (measured at IC-705) similar to the SWR without tuner. In this case the ATU-10 displays SWR 2.6. In seldom cases a second tuning cycle improves SWR to a reading of SWR <1.20 at the ATU-10. Changing operating frequency by a few kHz frequently helps in getting a better tuning result.
Is this common to the ATU-10 or did I get a faulty one?
I have tried firmware versions 1.5 and 1.6 without difference. With the relay test program I checked all capacitor relays are switching correctly and the values of the capacitors are roughly ok. Not so easy to test this with the inductors.
Any further suggestions for checks?
73 de Michael, DB7MM
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I'll have a look. Thanks!
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A VERY nice example from the aviation industry with 12VDC across relays at 3 cases - no diode, reverse diode at coil, reverse diode at switch
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The back-emf of the relay coil has to be addressed at the relay coil. The reverse body diode of the transistor is irrelevant for this overvoltage, as it is not imposed on it directly, but trough the nearest PS capacitor and God knows how much tracks, and appears even in reverse to it, keeping it shut. Why is there such push to avoid a cheap component to address a local and well known issue, that might otherwise mitigate trough the circuit and cause who knows what and where? There are 15 relays, and while tuning they are switched over multiple times and will generate overvoltages at the coil level. The diode will solve this issue locally and any possible problems will be avoided. Otherwise, the moment 2-3-4 relays get switched at the same time, the cumulative back-emf might surprise the CPU...
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Why do you want to add an additional diode, given that the 2N7002 used for switching has already that diode integrated?  73, Joerg
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Hi, Yes, agreed. There is a diode drop from the supply pin, so at 13.8V the relays will have around 13.1V. The relays specified on the schematic have a maximum application voltage of 15.60V. 73, Dave 
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BTW , there is change of damaging the relays if using with the transceiver power 14v ... or so ...
the PIC will work fine , but the relays are getting power directly ...
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Hi David,
You just need to be careful that the maximum VDSS for the 2N7002 of 60V is no exceeded, otherwise the FET could be damaged.
73, Dave
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Hi?
You can use 0.1uF with diodes in parallel or 1uF with no diodes .
In the original design the EMF were measured on the 12V power line. What is happening in the relay's line is not so important.?
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hi Tim,
as I made the translation of the manual, I've left over the description of the EEPROM content in English and German.
Look the appended pdf.
73, Immo
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Is it wise to place a capacitor as well as a diode in case one has rectification issues with the diodes?
I check the schematic of my ICOM AH-4 and it has both diodes and a 0.01uF capacitor.
Mike N2MS
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On 03/06/2023 5:41 AM 9H5BM <jmcservv@...> wrote:
Hi Dave .
Yes you can put 4148 diodes across the relay coil, observing polarity.
I purchased the full kit with bare pcb just the cpu and a diode was soldered and each part was tested before installing it.
73's
Jason
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Greetings
I bought a pre-assembled tuner off ebay last summer, and LOVE it. Works great.
On the screen on power up, it says BH8TZB firmware 3.2.
I inadvertently got into the setup, and I fear, may have changed some settings.
My question is this, is there a way to put this back to 'default,'....or if not default, at least what the values *SHOULD be? Such as "fider," etc.
Thanks!
Tim?
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Hi Dave .
Yes you can put 4148 diodes across the relay coil, observing polarity.?
I purchased the full kit with bare pcb? just the cpu and a diode was soldered and each part was tested before installing it.?
73's Jason?
On Mon, Mar 6, 2023 at 11:37?AM < g8ptn@...> wrote: Hi Jason,
The board was supplied with all SMD's fitted. My preferred solution is to have diodes across the relay coils to suppress the back EMF. Also to be noted, the relays have a lower rating than those specified by the original design but I shall only be using the ATU for QRP, with the Stockton bridge wound with a 5:1 ratio and the configuration registers updated accordingly.
73, Dave?
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Hi Jason,
The board was supplied with all SMD's fitted. My preferred solution is to have diodes across the relay coils to suppress the back EMF. Also to be noted, the relays have a lower rating than those specified by the original design but I shall only be using the ATU for QRP, with the Stockton bridge wound with a 5:1 ratio and the configuration registers updated accordingly.
73, Dave?
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Hi?
i too ordered a kit from China , best bet is to check every component before you solder it ! this way you know its real value and it's ok. and replace that 0.1uf with 1uf 100v.?
73's jason?
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Well spotted,you never know what your going to get from china,fake parts covid the list goes on!,simple just dont trust anything chineese,i think thats the best bet!.
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Hi Shirley, I have not measured the capacitor value, but it is physically different to the others and since the back EMF is greater, its value is smaller. I will probably just fit a 1uF in parallel or fit diodes across all coils for good measure !!
73, Dave
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That's an error on the silkscreen. That capacitor is supposed to be a 1uF like all the others. I'm in the process of building one from a kit, and if you put a 0.1uF part at that spot there aren't enough for the other places they're supposed to go. If you have an assembled one, you could try putting a capacitance meter across that part to see if it actually is 0.1uF or a 1uF.
On Sun, Mar 5, 2023 at 4:17?PM < g8ptn@...> wrote: A minor observation on the ATU-100 that I received from China. Although the schematic shows 1uF capacitors across each of the relay coils (to provide some smoothing of the back EMF), one of the relays has a 0.1uF capacitor fitted as shown on the silk screen.
With a supply voltage of 13.8V, the peak back EMF is 20V with 1uF capacitors and 40V with 0.1uF.
The maximum VDSS for the 2N7002 is 60V, so it should be okay.
I may increase the capacitor to 1uF or fit diodes across each coil, although my understanding is that the original design did not have diodes to avoid any issues with rectified RF.
73, Dave
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A minor observation on the ATU-100 that I received from China. Although the schematic shows 1uF capacitors across each of the relay coils (to provide some smoothing of the back EMF), one of the relays has a 0.1uF capacitor fitted as shown on the silk screen.
With a supply voltage of 13.8V, the peak back EMF is 20V with 1uF capacitors and 40V with 0.1uF.
The maximum VDSS for the 2N7002 is 60V, so it should be okay.
I may increase the capacitor to 1uF or fit diodes across each coil, although my understanding is that the original design did not have diodes to avoid any issues with rectified RF.
73, Dave
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Billian Marinov
Immo, DL5KB
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Shirley Dulcey KE1L