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Sunday, 1 January 2012

Elecraft T1 for £10 a 2N3906 and 1/4W 3K3

I picked up a T1 that someone built at a rally a while back but was stated to be not working cost me £10. If really was dead I could use the L match network.
I didn't find a troubleshooting guide to figure out what the problem is but his is what I did...
All the values, and components 'appeared' to be in the right place etc Resistance checks on page 15 and 22 of the manual seem fine…
Apply power (with PIC removed) and the regulators appear to be applying the correct voltages etc..
The section reads:
Use your DMM to make the following resistance checks. If the board fails any of the following checks,
carefully check the position and orientation of all parts and inspect the board with a magnifier for solder
bridges or missed solder joints.
Resistance across capacitor C19: between 137 K-ohms and 148 K-ohms. Press S2 and confirm reading
drops to between 117 K-ohms and 135 K-ohms.
Resistance between D3 anode (end without the band) and the “ –“ pad near D7 (ground) where the
black wire is attached: > 100 K-ohms (may show open or infinite on some DMMs). Press S1 and confirm
the reading drops to between 117 K-ohms and 130 K-ohms. If the resistance is higher, try reversing your
DMM leads.
Set your DMM to diode test. Connect the negative probe to either end of resistor R9. Touch the
positive probe to the following pins on J5 and verify that the diode tester shows approximately 1.6 volts
forward drop across each LED. J5 is the connector at the opposite end of the control board from R9. Pin 1
is the round pin at the end near S2. Each LED may also light up when the test voltage is applied (not all
diode testers supply sufficient current to produce light):
__ Pin 1: Red LED ___ Pin 2: Yellow LED __ Pin 5: Green LED
The LED do not light up. And the diode tests fail.
Humm ... scratched head a bit and had a chat with Elecraft and this extra info helped and I include it here in case anyone else have a problem:

Also for starters I had removed the switch bord from the uPC and relay board underneath for the first set of tests.

Make sure the red lead from the battery goes to the + connection near the unbanded end of the 1N5817 diode at D3. The smaller round positive connector on the 9V battery goes to the battery terminal for this red wire. (That was fine)

The black lead from the battery goes to the - connections between the yellow and red LEDs. (That was fine too)

J4 is the connector on the left side of the T1 control board.

J5 is the connector on the right side of the T1 control board.

Verify the MCU has no bent pins and is fully pressed all the way down in its IC socket. (OK)

Do you see 6V on pin 1 of the U1 processor when the PWR button is tapped? (use the thumbscrew or BNC jack for ground) (Yes)

You can test this at J4 pin 3, which is the pin just above and between the green and yellow LED, and it is the 3rd pin when counting beginning with the round pin 1 of J4. U1 pin 1 and J4 pin 3 are directly connected together. Remember that J4 is on the left side of the control board.

Also, J5 pin 3 should show 9V to ground  when the unit is off and S1 has not been pressed. Remember, J5 is on the right side of the control board as you would normally face the unit. (OK)

When PWR button S1 is pressed and HELD down, J5 pin 3 should be 0VDC. (OK)

If the MCU comes ON and is working, when the S1 button is released, after a few seconds - J5 pin 3 will rise back to 9V . This is when the MCU times out and returns to "sleep mode", and releases the /HOLD_ON line at U1 pin 5. (I will test later... and it was fine, after I fixed some things but it did not work as it should initially)

This change in voltage at J5 pin 3 and U1 pin 1 and the 6V appearing at U1 pin 1 must occur, or something is wrong with the power up circuit of D3, R7, C20, Q1, R14, S1, D4, C19, U2, D4. Check all of those parts and their soldering very closely. Both U2 (78L06) and Q1 (2N3906) should be installed with their flat side facing up.  (Problem #1 Q1 was inserted backwards so chopped it out and replaced it with a new component the right way around this time)

Be sure U2 and Q1 are not swapped with each other. Be sure R7 is 120K and R14 is 3.3K.
(Problem #2 1K resistor in place, replaced with 1/4W 3.3K)
Verify all of the parts are in the correct locations, and are not damaged or unsolder-ed. (OK on parts spent some time going over the underneath solder connections)

Be sure D3 and D4 are not installed in reverse. D3's banded end goes toward R14, and D4's banded end goes toward switch S2. (Both OK)

MCU U1 must be installed with the notched end closest to the J3 remote 1/8" phone jack, or to the left as you face the main board. (Problem # 3 the uPC socket and uP were in reverse, so I flipped the uPC and T1 worked fine)

You can use an ohmmeter to check for any shorts between the connector pins and ground with the battery removed, and between any pins of the parts and a nearby connection that is not at ground. Note some connections are intentionally grounded. Use the schematic as a reference for these tests. You can find an accidental short circuit or solder bridge this way.

Examine both sides of both PCBs very closely using a bright light and a magnifier. Look for missed solder connections, shorts or solder bridges or splashes, etc. Remove any excess solder and clean up any poor connections as needed, using Soder Wik and a Q-Tip moistened with acetone or alcohol to clean the PCB. (The board was cleaned up a bit)

Do you ever see any LEDs light up when the PWR button is tapped (yellow LED),  or if it is held down for more than 1 second (green LED)? (Operating as should now)

Did you verify the LEDs are not installed backwards? You can check them for correct orientation by using the diode test function on most DMMs. (Diodes fine)

First remove the 9V battery.

Then place the positive test probe on the anode connections for each LED at pins 1, 2, or 5 of the J5 connector, and the negative lead on the common cathode connection at either end of R9. 

J5 is the connector on the right hand side of the tuner as you would normally face the top and front of the PCB (near R21). Pin 1 is the round pin near the battery compartment. R9 is near the left top edge of the T1 control board.

Each of the LEDs should light enough to be seen in a dimly lit room as you move the positive probe to J5 pin 1, 2, or 5 and hold the negative probe on R9.

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