Hello all,

I have an issue with my BITX40 that started earlier this week, and am unable to figure it out.?

Symptom: No RF output, and initially, no current draw. Later, 2A current draw, still no output.

Troubleshooting: I powered down the radio and started tracing the RF path back from the BNC center connector. It shorted dead to ground. I went back to the TX/RX relay (next to the BPF) and found continuity on both poles to the center pole. After cycling PTT, there is only continuity in the NC pole, not the NO pole. Now, the RF out is not grounded out. I powered up the radio and tested transmit, and immediately got about 2A of power draw (total, not just the PA) but with no RF output.?

I think I have a sticky relay, although I'm not sure how it could fail and have both poles conduct to the center pole at the same time. This leads me to believe it might be the other relay (by the LPF) being sticky, but I don't understand the circuit well enough, as I am having a hard time understanding the schematic as it relates to the tx/rx relays.?

I've inspected the board under magnification, and have found no obviously burned components. All the resistors in the PA circuit show proper resistance. No capacitors are shorted or burned. I tested the voltage to Q13 and Q15 during transmit and they are all correct, and the bias voltage regulator is fine too. I have no problem setting PA bias to 100ma, so RV1 seems fine.?

So at this point... HELP! I'm lost. Thanks a ton, I appreciate the help immensely.

--
Ryan Flowers W7RLF

?

?<-- Learn how to go digital on the BITX40

The thought that the relays might be the problem is probably a good one, but there have been no complaints on
the list of this problem, so...first things first.

Think physically of the relays as being like 16 pin IC's. The schematic shows which pins connect to what. Use a DVM and feed the
appropriate pins with about 6v. Engage the relay and measure the expected voltage out in each condition. Is it right?

You say that the total current draw is about 2A. Is this also on receive? Does the RX work OK? The total receive
draw should be about 150ma to 200ma. More indicates a problem (which may be traceable to the relays).

Is your power supply limited to about 2A? Is this why you experience a 2A current draw no matter what the condition?
If more is available, then something is limiting the current draw to 2A.

If the IRF510 drain is disconnected, what is the total current draw on both RX and TX? The total draw should not exceed
the RX value on RX. and would be about 2A on TX. But with the drain of the IRF510 disconnected, the total draw should
be about the same on RX and TX.

Check the output of U3 on TX. Is it 5v? Is there no more than 3.5-4v on the gate of the IRF510? Is there 0v on the gate in RX?

The main criteria is: does RX work or not? If it does, probably you should look at the relays (for erratic operation), and also
Q13 which has been reported as blowing up in some cases (assuming all the adjustments are correct). It is hard to determine
whether or not the relays are good if the operation is erratic, but it would probably be a good idea to replace them if you suspect
they are. There are good panasonic (and other) units available which should do the job. The important criteria are the coil
voltage and the pinouts.

It is also possible (maybe even probable) that the IRF510 has given up and needs to be replaced. Ordinarily, these blow out and
open the drain/source, but it is possible that one could be shorted...but that would no show up at the antenna connection with
no power applied. If it is shorted with no power applied, almost certainly, the relay contact has not released. and pins 12 and 16 on K1
are still connected, which grounds the RX connection to the antenna on TX. Normally, on RX pins 12 and 14 are connected.

Hope this helps.

john
AD5YE

Hello John,

Thanks a lot for the reply. I had similar thoughts about the relays: suspect, but not a common problem. I use digital modes almost 100%, and with FT8 I toggle the relays?a lot. Perhaps I just wore them out. So to run through your questions: 1) It receives beautifully, but I have had to toggle PTT in the past to get it to receive after a TX cycle. 2) Power is a 30A supply. 3) IRF510 has been replaced, that was my first thought too. 4) Q13 has good voltages on it on TX. 5) RX current draw is normal, not 2A. ?I will check the things you said to check in the next day or so. Thanks again!

--
Ryan Flowers W7RLF

?

?<-- Learn how to go digital on the BITX40

I looked up the relay, and it's a?vrs2h. It is wired differently than I was expecting, and so I retested both relays for continuity with and without PTT pressed. The relay by the LPF acted normally, but the relay by the PTT relay itself acted odd. Pin 4 is switched between pins 6 and 8 on the diagram, but 6 and 8 instead conduct to each other (which seems WAY off to me), and pin 4 conducts to neither of them. I am going to pull the relay and test it out of the circuit tonight. Will report back.?

--
Ryan Flowers W7RLF

?

?<-- Learn how to go digital on the BITX40

开云体育

I bought relays for a project, they look like the ones in BitX?

About $1 each?

The ones I have used on the project worked great, have not tried them in BitX

Mike, WA6ISP

I looked up the relay, and it's a?vrs2h. It is wired differently than I was expecting, and so I retested both relays for continuity with and without PTT pressed. The relay by the LPF acted normally, but the relay by the PTT relay itself acted odd. Pin 4 is switched between pins 6 and 8 on the diagram, but 6 and 8 instead conduct to each other (which seems WAY off to me), and pin 4 conducts to neither of them. I am going to pull the relay and test it out of the circuit tonight. Will report back.?

--
Ryan Flowers W7RLF

?

?<-- Learn how to go digital on the BITX40

-- 
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID  "MotDog@..."
Mike@...

The BITX40 relay is a Virtual VRS2H-S.

It is an ordinary DPDT, Form Factor 2C relay, sized 20mmx10mm.
Virtual is the name of the manufacturer.

It is similar to the AXICOM MT2 C93418 and the Hasco 212.
There are others. The Avala project uses some, so Sunil should have a few.

They are all over e-bay and ali express. Most of them seem to come from China.

I was thinking further, Ryan, and I thought "What if the PTT switch was sticking?"
It may be a more likely candidate than the relay and would produce the same result...
except that the 12v TX would stay engaged at all times during a fault condition.
Hmmm...


john
AD5YE

Mike, check the pins against those in the BITX on the BOTTOM of the board.

If they match, this relay will work. It has the same specs as the Virtual relay.
The 2 end pins are the coil. The two pair of 3 pins are the contacts, with the common
in the middle (But that would have to be verified -- there are variances).

john
AD5YE

Thanks for the help guys. I do have doubts about my vox controller that I built, so I did testing with the regular mic used for voice SSB (not digital) and got the same results. I pulled the relay, but I think I broke it while desoldering it. Desoldering braid stinks, as does removing relays from boards. I think I pulled one of the coil contacts out of it, so I can't test it :/ time for at least?one new relay.?

Now that it's out, I have a bit more testing to do, but for now my bitx40 is out of commission. Time to grab the icom and get soldering for the time being until I get more parts in.
--
Ryan Flowers W7RLF

?

?<-- Learn how to go digital on the BITX40

I added? a RCA jack from? the Ptt connector? going? to Amertron 811.? Output of the Bitx40 7 walts . Amp peak at 100 walts. Found that? when you add a amp the bitx40 driver modulation is over? driven. So i add 10k pot? to adjust? mic gain at the? mic input.? It did? cut out? the? distortion and clean audio? at 100 walts. Addition features 4 pin mic input with? icom hm36 microphone.? Addtional i added ANL audio filter to cut out? noise on the? receive.? A 3 amp circuit? breaker instead of a 2 amp at transmit near the? 2 amp drawn .? Other modifications 330k and 47k across? the? 10k VFO to slow? the tunning? from? running to fast. Not bad? for a girl?
Francesca W7LTG NV

Friday, 25 August 2017, 08:47PM -07:00 from Ryan Flowers geocrasher@...:

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I have ?bitx40 ?and completely wired up. get nice hiss when the volume up. display lights up only showing Raduino V1.01. ?frequency never shown, anyone have that problem? ?i think the software is not in the chip.
Francesca W7LTG ? NV?

Ryan W7RLF wrote...

I pulled the relay, but I think I broke it while
desoldering it. Desoldering braid stinks, as does
removing relays from boards.

I'm a newbie with a hot air soldering station, but I
think you would find it a lot easier to remove relays
using one compared to a soldering iron and wick. With
the hot air tool, you can wave it around and heat all
of the pins up at the same time. You can go back after
with the iron and some wick to remove excess solder
to get it ready for the replacement. I think wick
does do a good job of soaking up solder when the part
has been removed, but it just doesn't seem to get 100%
of it while the part is still in place.

I didn't have the hot air tool when I replaced Q14
and Q13 (probably not needed!) but did have it when
I removed C91 & C92 with it (still only outputting 2W
though) and was a cinch, but they were SMD parts
and not a relay! I did remove some through-hole
parts from a board for a friend and I think it
would have been all but impossible to do a good job
without the hot air tool.

On the SMD practice board that I have, I made a mess
of installing some tiny LEDs. I think they are 0402
size but the pads are 0805. The biggest problem was
that I probably put too much solder paste on the board
and the LEDs floated up to the top when the solder melted.
It was a real confidence builder later when the 8 and
16 pin ICs and the transistors (same size as on the BITX)
were easy to install.

Good luck with the rest of your troubleshooting!

--
73 Keith VE7GDH

Thanks everyone for helping me out with this. I was able to do more troubleshooting, and could find no circuit faults that stood out to me. I didn't have the correct relay, so I wired up another 12v dpdp relay that I had, and?made it work lol. Immediately, the bitx40 started transmitting again. I'm quite happy! Attached is a picture of the repair with the relay I had on hand. 72!



--
Ryan Flowers W7RLF

?

?<-- Learn how to go digital on the BITX40

开云体育

Good Evening!

What is the nomenclature on the Q13—need to try that replacement to see if the power picks up...only ~100mw now, if that.

73, John/N6VTS

Q13 is an mmbt3904. ?
It runs hot, a 2n3904 would be a better choice if replacing it as the leaded version can dissipate more heat.

But there's a hundred different parts that might reduce power on you like that,
you won't do much good just shotgunning every part in the transmit path.
I suggest you check all the DC values around Q13, and not rip that transistor off the board
unless the base and emitter voltages look wrong when pressing the PTT switch:
? ? /g/BITX20/files/K7AGE/BITX40%20Voltage%20Measurments.pdf

Here's another thread on debugging the transmitter.: ?
? ? /g/BITX20/message/31352

Jerry

Before measuring DC voltages unplug the Raduino.

Q10 voltages in the chart are not correct. Short the 12Mhz xtal and then measure the voltages. The Base-emitter should
be 0.6-0.7v normally.

If the BFO Q10 is oscillating then the readings will be haywire depending on the meter used.

Raj

At 05-11-2017, you wrote: