TRX2A Main Board short diagnostic

[DG4FCO]

Hi all!

Now I am done with all parts and did checks as mentioned.
Optical check seems ok, Check of DDS Board with own power supply works.
Unfortunately there must be a short-circuit, so I disassemble it and check board by board.
There must be a short-circuit at the main board, somewhere in the 5V Area (too much current need ).

Now I test the main board without attachments and without inserted boards.
I feed the power to C63 (Output of Reg1, LP2951) and measure current.
After many searches I found a problem at Transmit/Receive Control, which drain(? suck) all the current.
So I first remove IC4 (carefully with my hot-air-smd equipment), which seems to remove the short-circuit.

After that 5V keeps stable with 100mA current. I re-enable Reg1 and feed it carefully with power (C65,C66) up
to 5V and check current, then slowly up to 14V and check current. Still 100mA.

But: If the 5V is charged with 100mA, then Reg1 must burn about 0,1Ax9V => 900mW?
Also https://cdn-reichelt.de/documents/daten ... 50_NAT.pdf told, it only "Guaranteed 100mA output current"?
So there must be another problem on my board? Or is 100mA / 5V the "normal" need of the main-Board?

Also I can't find a shortage at Transmit/Receive Control. If there is a grounded output (Pin 6,8,3,11), will this explain
the high current need like a short-circuit?

Hope someone can lead my mind in a proper direction.

72/3 de Frank, DG4FCO

[5B4AIY]

Hi, Frank,

You still have a problem. The major current consumption is by Q1 and Q2 on the receiver section if you have recent (Revision C) main board, or the Spur Elimination module if an older version. These two transistors consume about 13mA to 15mA each. the rest of the integrated circuits fed from the +5V supply in the quiescent state draw no more than about 10ma - 15mA at the very most, so the total current drawn from the +5V regulator should be less than 50mA. You could simply remove R113 (I am assuming you have a recent Revision C main board) to eliminate the current drawn by Q1/Q2, and then re-check to see how much current is being drawn from the other integrated circuits.

73, Adrian, 5B4AIY

[DG4FCO]

Hello Adrian,

thanks for the values! I tried to find out, how to separate some modules to test them, but
maybe it was too late in the evening for my brain.

Do you have some more hints like "remove R113" to seperately test the main board?
I didn't found such information in your document you send me.

Thanks in advance

72/3 de Frank, DG4FCO

[5B4AIY]

Hi, Frank,

You are right, there is no mention of this in the constructional notes I sent you, and indeed, to try and write a document to diagnose every fault is clearly impossible, there are just far too many variables to deal with.

In this case you will have to try and discover what is drawing the excessive current. Bear in mind that the idle current of the main board's ICs is very low, no more than about 5mA to 10mA, so, something must be getting warm. In the 6 years that I have being providing assistance the vast majority of faults have been caused by faulty assembly, or connections/joints that were not soldered. In my own case, my transceiver did not work first time, and it was as a result of missing two solder joints, all too easy.

So, carefully examine the board and verify that all the connections to all the components are good. An open circuit on the input of a CMOS IC can easily cause the chip to draw an excessive current. Similarly, a short on the output pins can also cause excessive current to be drawn. Carefully use a needle and gently scrape between the leads of the ICs to make sure that there are no whiskers of solder - I had this occur on the display board and give rise to a short on the +5V bus.

Make certain that all the ICs are correctly oriented and that you have not inadvertently put one in backwards. With power applied, touch each chip and make sure it is not getting warm, the power consumption is low, so nothing should be warm to the touch.

73, Adrian, 5B4AIY

[DG4FCO]

OK, I will do so. Unfortunately this weekend is Grandchild-Weekend OK, this is not un-fortunately but funny
So it will take some days, maybe weeks until I can spend enough time for this.

I swear, I will give report!

72/3 de Frank, DG4FCO

[DG4FCO]

I did some high-res-fotos , so I can inspect my "Art" at a big Screen instead of looking through the magnifier.
So I may can start earlier, as I saved them on my web-site as usuall.

Please don't look, they are ugly


72/3 de Frank, DG4FCO