After assembly I used a standard 9V battery to start my 12V QMX.? The computer found it and I was able to load the software.? After resoldering a couple of solder joints everything came up fine and I had good RX but no TX.? Thinking maybe 12V would help I tried a 12V PS and had nothing.? No LCD lit, not recognized by the computer, etc.? Tried again with 9V same thing.? There was no smoke at any time and all compnents look OK to me under magnification.? I am guessing that one or both of the PS boards may be bad now.? How can I go about checking them out?? Please explain this to me as if I'm 5 years old because that's about the level my tech ability is at!

73, Bill NZ0T

A useful start is to work out what you did as that will predict the problem/damage

Was the 12v power supply 12.0 V. ?Or 13.6V ?

On Mon, Aug 21, 2023 at 10:49 AM, <nz0tham@...> wrote:

Please explain this to me as if I'm 5 years old

both of us taken together: we are 10 years old dear friend! So let us hold hands ;-)

Somewhere in this posting group with such a weird search function, there is a splendid thread that might be of use for you. It is valuable for me (vy tnx!!!) so I took the pain of copy-and-pasting it to a text file where I can get hold of it myself:
QUOTE:
"
Chris
Aug 6 #106787
It might help to check the PSU boards independently of the main board and each other. This will give confidence that these are working and if they aren't help to isolate the problem to a smaller area..
"

It might help if you search for the # number. Maybe.?

But let us think further (me just thinking loud)!

At the time I placed the early order for this rig, I was far, very far of being in need of yet another qrp toy... My spouse will sure confirm this statement after she finishes treating me with the large wooden spoon for buying yet another kit ;-)

I could not resist the buy because of two reasons:

1° I find the wealth and freshness of ideas behind this rig (like for most of other qrp-Lab's developments)? so refreshing and inspiring that I would vote for it as being the finest advance in ham - radio since Sako drunk a Saki to celebrate JA1MP implementation of SSB. To this appreciation belong the two PS boards inside the QMX and the qrm-stealth drive that makes them so ingenious.

2° I find that such fresh ideas need support. Trustfully buying was my modest part to say: I appreciate what you do, both you Hans out there, you yl and xyl team, you junior thech supporters!

But now, I somehow got scared of my own courage and wish there would be a less adventurous way to pass trough the smoke test. I wish, there would be a way to replace these inovative power supplies with plain (LDO?) linear voltage regulatos,

either for a test, or just for the initial "smoke test", or ... for diferent other adventurous voltage hikes that might prove offending towards the main 3,3V professor.

I understand that there is a 78M33 3,3V linear regulator needed for the miraculous "Münchhausen powerUp maneuver". So all I would dream of would be a semi-official way to disable the "handover" from the 78M33 to the smart buck converter.

This would be a help of some sorts.

Efficiency would be another issue. Because of being driven from the main suppy (which might be 12V) I reckon that the efficiency of the linear regulator is poor. But if instead of that other buck converter, the one who brings the 5V needed for the audio, if instead of this other one buck converter a linear regulator would come into use....

well, in this case the 3,3V regulator could just be daisy-chained to the 5V rail and work under a lesser burden.

As I stated above: just thinking loud. The QMX is a splendid rig and I would hate smoking it's unreplaceable professor by one of my careless maneuvers in the dark. After all, I bought this kit as a playground to build myself and get some learning by doing so. As my spouse would put it, I do not need yet another rig, otherwise I would have bought myself one that is ready-to-fly. I wanted one to be able to tinker with.

Being able to avoid the shallows of those?ingenious?qrm-stealth buck converters by using plain?ingenuous?linear regulators would bring some peace to my mind.

I can go this way all by myself, but would be glad of any company: a critical one would be most welcome! Yes!?

yours friendly, Razvan dl2arl

Bruce, yes it was a18.8V MFJ switcher turned down to 12V, actually about 11.8V on my meter.

Make that a 13.8V switcher!

开云体育

If you have a dead QMX then the first thing is to check if the USB COM port is visible on your PC.? If it is use PuTTY to diagnose what is happening.

If it isn't then check a few voltages:

Does the display light up while you have the power button pressed?? It it does but goes off when you release the button then the problem may be in the Q104 or Q105 area.

Remove the board from the box and remove the display.

Use one of the connector outers as ground for your volt meter..

There's a row of holes on the top left of the main board, these are connectors JP205, JP303 and JP208.

The third hole from the left is VDD.? this should be more than 2.5V, ideally 3.3V.? If it isn't there's a power supply problem, look on the PSU boards.

First, check for the +12V on PSU #1? Pulling PWR_ON low or PWR_HOLD should provide volts on +12V.

Then check PSU #2, supplying power to +12V should give about 3V on VDD.

You need a voltage AND current limited power supply for this. If you don't have one, get one. EBay do this sort of DC to DC converter for not very much.

Getting a bigger hammer is seldom effective.

Chris, G5CTH

Please tell me what to look for on Ebay to find this DC to DC converter.

73, Bill NZ0T