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Hello fellow hams,

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I started my QMX build today. I followed all the steps and I did all the checks mentioned in the instructions.

Also checked every solder joint before proceeding to the next one.

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After building, checking and soldering T501, I checked the continuity between the A and B points as per manual.. and there is continuity.

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Any advice on how to troubleshoot? Any probable suspects?

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Thank you!

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Pedro F4JAW

Wind toroids using the chopstick method others have recommended.

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Only wind toroids over carpet floors.? Inevitably, you and everyone else will drop them.

They are ceramic and will shatter if you drop them on a tile floor.? Hans buys them in? the thousands, you will not find replacements easily.

If you have a reason to make an extra order from qrp-labs.com buy some extra from the spar parts section.

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Those 47uh axial are more delicate then similar sized resistors -bend leads without applying pressure to body.

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Everybody including me have been fixated with heat dissipation of the bs170.? Don't bother with extra heat sinks.

Some of the problems with? damaging the bs170 was from very early software versions.? Newer software versions

have high SWR protection.? Just do not disable the SWR protection.? ?The heat is dissipated thru the leads and not the plastic.

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Some of the assembly has to be done in the exact order.? Solder has both an electrical, and mechanical purpose.

If you solder before everything is aligned? it will not end well.? I am referring to the connectors on the two power boards,?

and the connectors that extend thru the optional case.? ?

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You have one chance to bend the leads of the encoder in the correct direction- which is probably opposite of what you would think.

I think I just soldered scrap wire to make the connection?

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stan ag5vh

If you do make another order from qrp-labs.com,

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In addition to a few extra bs170 and toroids, buy the

$8.50?

50-ohm 20W QRP HF Dummy Load

Remove T501 and check again. If there is no continuity, you most likely have a short between the windings of T501 or it may be incorrectly made.

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Al, K2ZN

A short between A & B means that either a) somehow the primary and secondary wires of T501 are shorted together, or b) there was a short on the board before you put T501 in.? Most likely a) but check both.

A short between primary & secondary is easy to accidentally do if you scrape too much of the lacquer off the ends of the wires.? Also, sometimes the core itself has some sharp edges just inside the holes on either end - these can scrape the insulation off the wires as you pull them through the core, potentially causing shorts.? You can use a craft knife or a small conical grinding stone from a Dremel tool to carefully 'sand' those edges of the core to make them smooth, so they don't scrape the wires.

Hello Stan,

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- No cont between any of the A and B points in the PCB (same letter or between letters)

- T501 exhibits no cont between P and S

- T501 all P have cont to each other

- T501 all S have cont to each other

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So what’s next? Put T501 in again and pray? What am I missing?

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Thanks for your help!

I'd be tempted to try two things.

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1) With T501 still removed, bend the wire ends down as if they were soldered into the PCB and make the continuity checks for the primary and secondaries again. Look closely at the ends near the binocular core edges to see if the insulation got cleared away a little too far up the legs and are possibly touching the core, or between the primaries and secondaries.?

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2) Rewind T501 being sure to follow the winding instructions exactly.?

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Greg

Very good progress.

Greg's suggestion #1 is a good one.? Maybe also take a close-up photo of your T501 and post it so we can see what you did and maybe help.

If both the board and the coil test good separately, all that is left is an assembly issue - very likely something shorting when you have the leads all in place before soldering.

Or maybe accidentally soldering the leads in the wrong holes, crossing the primary/secondary so they cause the short.

Which winding instructions did you follow (from the T501 document)?

So after some mechanical difficulties I have new elements for this investigation:

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- T501 is built to spec

- after desoldering only the 2 wires side of T501 (A circuit) from the PCB I discovered that the Q505 side of circuit A is shorted to ground. The Q506 side is not shorted to ground.

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All my BS170s are installed flat side against PCB.

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Any suggestions on how to proceed?

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Thank you very much!

On Fri, Oct 4, 2024 at 07:12 AM, <ptsmonteiro@...> wrote:

Q505 side of circuit A is shorted to ground.

This doesn't make sense to me, Q505 and Q506 are on circuit B (3 wire side). Presuming that was a typo.??

I would check carefully the holes for D503 (empty, optional part).? These are adjacent to the holes you just unsoldered.? If somehow a solder bridge got between them (either side of board), it would short Q505 to ground.

The 3 side of the schematics is not the 3 wire side of the PCB. The double wire is (the coil tap) is installed on the opposite side on the PCB layout.

This happened to me, and it turned out to be one of the finals was DOA or killed by heat when soldering the transformer (internally shorted) and caused that continuity. Just another item to check.

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Greg N1TR?

After a lot of time troubleshooting I found I had exactly the same problem. One of the BS170 was conducting between the 2 opposite pins causing the short.

Had to order Bs170s to replace this one and found that they die easily with too much heat. This should be advertised on the manual to avoid frustration (to test them before soldering and to apply minimum heat).

I am having a similar problem. Points “B” have continuity.?

Point “A” on the right has continuity to point “A” at the top. The bottom point “A” is not showing conductivity.?

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I checked the lower row three pins to the left of the faulty A and have no continuity.?

any ideas what the issue could be?

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Thank you!

If you only lack continuity on the lower left A pin, then there are two possible issues:

1) the T501 connection closest to that A has a bad solder joint: most common issue here is incomplete removal of the enamel on the wire.? See red circle in photo.

2) the T501 winding was done incorrectly - most likely problem is that the two primary wires wound together for the center tap are not contacting each other, e.g. the enamel on one of the wires prevents its connection to the other wire where they are twisted.

Another way of saying this is that the 'lower' half of the primary winding either isn't conducting where it is soldered into the board at the blue circle, or it isn't conducting with the top half of the primary winding through the twisted wires at the purple circle.? The 'upper' half of this pair of twisted wires IS conducting properly, which gives the continuity between the upper two A points.

There are other winding problems on this transformer that could cause the problem, like getting the wires crossed (or not) in the wrong places, so check its construction carefully.

Hope that helps -

Stan

Here's the photo I referenced...

You’re right! It was a bad solder. Once fixed, I have continuity. Incredible. Thank you! This is my first kit and the instructions and support are first rate.?