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KA9MOT
06-13-2012, 12:34 PM
I built my Ten-Tec Model 1202 Dual Band (HF/VHF) SWR/Power meter. It looks great and works well, on Forward Power...... On Reverse and on the SWR setting it reads very high (almost as much as forward power).

I've checked all of my solder joints, and I can find nothing wrong so I suspect I may have a bad component. Would anybody have any idea where to start?

There is a very poor scan of the schematic here: http://74.220.205.254/files/1202%20Manual.PDF It is located on page 5.

Thanks in advance.

K7SGJ
06-13-2012, 12:53 PM
My first gut hunch would be to check the polarity of the diodes, and then make sure you read the resistor colors right. Some times, the orange and red look close, as well as the blue and green. Of course the obligatory solder bridges should be checked for. Just a quick guess without looking at the schematic as I'm on the way out. Please post what you find, and good luck.

XE1/N5AL
06-13-2012, 01:43 PM
I'm assuming you have the device connected to a reasonable load, or antenna, and you aren't really getting almost 100% reflected power. :)

Do you get the same odd results on both the HF and VHF sections of the device? The HF and VHF sections of the schematic look to be fairly independent. If one section is working properly, you can narrow down the problem considerably.

KA9MOT
06-13-2012, 03:40 PM
I have triple dog checked the polarity of the diodes. Double checked them before I soldered them. It is connected to my dummy load. I have not checked the VHF side as I do not have a 2M rig...... maybe I can get my buddy Scott KC9SIW to bring his by. And they are separated on the main board, but combines on the switch board.

KA9MOT
06-13-2012, 03:45 PM
If I wound the transformer wrong, would it cause this problem? I'm certain I wound it correctly and almost certain I soldered it to the mainboard correctly (INPUT vs. OUTPUT)

N8YX
06-13-2012, 04:27 PM
Did you check the diodes before you soldered them in? Not for polarity, but for open/shorts/voltage drop from anode to cathode?

KG4CGC
06-13-2012, 04:37 PM
I have had the diode issue in an older antenna tuner.

KA9MOT
06-13-2012, 05:38 PM
Did you check the diodes before you soldered them in? Not for polarity, but for open/shorts/voltage drop from anode to cathode?

No.

XE1/N5AL
06-13-2012, 06:22 PM
Do you have a digital voltmeter (or another high-impediance measuring instrument, like a VTVM) to take some DC voltage readings?

HF Forward Power measuring circuit
With the SWR/Power meter running and while transmitting:
1. What is the DC voltage at the cathode end (the banded side) of diode D3?
2. What is the DC voltage at pin 7 of U2a? (it should be about 1/2 the voltage measured in Step 1.)

HF Reverse Power measuring circuit
With the SWR/Power meter running and while transmitting at the same power level as above:
3. What is the DC voltage at the cathode end (the banded side) of diode D4?
4. What is the DC voltage at pin 1 of U2b? (it should be about 1/2 the voltage measured in Step 3.)

Ideally, the values from the reverse power DC readings should be much less than the values from the forward power DC readings if you are transmitting into a 50 Ohm load.

KA9MOT
06-14-2012, 01:21 AM
Do you have a digital voltmeter (or another high-impediance measuring instrument, like a VTVM) to take some DC voltage readings?

HF Forward Power measuring circuit
With the SWR/Power meter running and while transmitting:
1. What is the DC voltage at the cathode end (the banded side) of diode D3?
2. What is the DC voltage at pin 7 of U2a? (it should be about 1/2 the voltage measured in Step 1.)

HF Reverse Power measuring circuit
With the SWR/Power meter running and while transmitting at the same power level as above:
3. What is the DC voltage at the cathode end (the banded side) of diode D4?
4. What is the DC voltage at pin 1 of U2b? (it should be about 1/2 the voltage measured in Step 3.)

Ideally, the values from the reverse power DC readings should be much less than the values from the forward power DC readings if you are transmitting into a 50 Ohm load.

I'll check these items when I wake up. I got tied up today.

NQ6U
06-14-2012, 08:58 AM
I got tied up today.

Was she wearing her stiletto-heeled boots?

K7SGJ
06-14-2012, 11:24 AM
Was she wearing her stiletto-heeled boots?

I know her. We met in one of those hanging Asian sex basket thingies.

KA9MOT
06-15-2012, 02:20 AM
Do you have a digital voltmeter (or another high-impediance measuring instrument, like a VTVM) to take some DC voltage readings?

HF Forward Power measuring circuit
With the SWR/Power meter running and while transmitting:
1. What is the DC voltage at the cathode end (the banded side) of diode D3?
2. What is the DC voltage at pin 7 of U2a? (it should be about 1/2 the voltage measured in Step 1.)

HF Reverse Power measuring circuit
With the SWR/Power meter running and while transmitting at the same power level as above:
3. What is the DC voltage at the cathode end (the banded side) of diode D4?
4. What is the DC voltage at pin 1 of U2b? (it should be about 1/2 the voltage measured in Step 3.)

Ideally, the values from the reverse power DC readings should be much less than the values from the forward power DC readings if you are transmitting into a 50 Ohm load.

OK, got 'er done!

Cathode of D3 = 1.6V
Pin 7 = .88V

Cathode of D4 = .88V
Pin 1 = Battery Voltage (10V) TX or RX.

The trace for Pin 1 on U2 goes directly to V+.

X-Ray circuit board here: https://www.tentec.com/downloads/manuals/1202%20x.pdf

I think maybe the schematic is wrong?

KA9MOT
06-15-2012, 02:21 AM
Was she wearing her stiletto-heeled boots?

Ahhh! She's been bragging about me again! :rofl:

I knew somebody was gonna jump on that...... :lol: I've been doing a lot of doctoring the last few days. Been getting some issues resolved and learning allot of stuff. I'm off for the weekend now though. WOO-HOO!!!

XE1/N5AL
06-15-2012, 12:02 PM
Hi Steve,

The x-ray circuit board view shows U2, Pin 8 going to the V+, like in the schematic. Pins 1 & 2 go to the pad labeled "REV" and pins 6 & 7 go to the pad labeled "FWD".

IC with Pin 1 indication:
_______
1|O.......|8
2|O.......|7
3|O.......|6
4|O.......|5

Circuit board x-ray with U2 pins numbered:
6052

KA9MOT
06-15-2012, 12:13 PM
DOH! Give me a minute, and I'll see what the numbers are.

OK.


Cathode end of D3 = 1.6V
Pin 7 of U2 = .83V

Cathode end of D4 = .88V
Pin 1 of U2 = .83V

XE1/N5AL
06-15-2012, 03:02 PM
Hi Steve,
One more favor: Could you please measure the DC voltages at Pin 3 and at Pin 5 of U2?

KA9MOT
06-15-2012, 03:23 PM
On Pin 5 while TX and in FWD and REV, I have .86V
On Pin 3 TX/FWD = 0V
On Pin 3 TX/REV = 0V

XE1/N5AL
06-15-2012, 08:33 PM
Sorry, I had to disappear for a few hours to attend a Father's Day show that was presented by my granddaughter's daycare school. My granddaughter is almost three years-old and has been taking ballet lessons for a while. So, it was neat that they let her open the show with a dance. She loves to get on stage and perform for audiences -- what a little show-off!

The forward power measurment circuit seems to be working correctly.

The DC voltage representing the forward power measurement, at the cathode of diode D3, is 1.6 Volts. This voltage is divided in half, to 0.86 Volts DC, by the R7/R13 resistor voltage divider and applied to Pin 5, of U2a. U2a is configured as an Op Amp voltage follower circuit (voltage gain = 1). The output on Pin 7, of U2a, is 0.83 Volts DC; which is about the same as the input voltage on Pin 5, of U2a, but with a low impedance and sufficient current to drive the SWR/Power meter movement.

There is something strange going on in the (almost identical) reverse power measurement circuit.

The DC voltage representing the reverse power measurement, at the cathode of diode D4, is 0.88 Volts. This voltage should be divided in half by the R12/R14 resistor voltage divider and applied to Pin 3, of U2b. (Note the schematic error, which incorrectly calls R14 as R24.) Rather than seeing 0.88/2 = 0.44 Volts DC on Pin 3, of U2b, we see 0 VDC. This looks like either R12 isn't soldered in well, or Pin 3, of U2b, isn't soldered in.

Also, this really puzzles me: Under the conditions of 0 Volts DC on the Pin 3, of U2b, I would have expected to see 0 VDC on the output Pin 1, since it is configured as a voltage follower circuit (voltage gain = 1). Instead, we see 0.83 Volts DC, which is the same as the output of U2a. Normally, U2a and U2b should operate independently. My first thought was that the two outputs, on Pins 1 (U2b) and 7 (U2a), were somehow shorted together. But, the condition might be caused by an open circuit on Pin 3, as discussed in the previous paragraph, which is causing U2b to misbehave.

Next Step: based on your measurements, could you check if the 0.88 VDC you measured on the cathode of D4 is appearing on one side of R12, and if 0.44 VDC (i.e., half of 0.88 ) appears on the other side of R12. And, If the 0.44 VDC appears on R12, why doesn't it get to Pin 3, of U2b.

KA9MOT
06-25-2012, 08:45 PM
UDATE: I removed the main board to check again for bad, missed, bridged solder joints and discovered that the wire lead for C15 (3pf) that goes to the board had broken. I repaired that and went over every solder joint with a jewelers loop. I did find a few solder joints that weren't perfect so I resoldered them. No bad joints or bridges were found. I put it all together and VIOLA! IT WORKS! So I added a couple of White LEDs for back lighting. I need to replace the 10K pot because the one supplied is a cheap piece of junk and is hard to turn, but that is easy.

Her's some pictures!

6205620662076208

KC2UGV
06-25-2012, 08:47 PM
Right on man! The LED backlighting looks pretty snazzy.

XE1/N5AL
06-25-2012, 11:19 PM
Cool look with the LEDs!

What kind of LEDs did you use? Did you have to do anything to them to get the light to diffuse and illuminate the meter face? I have a couple of old Yaesu FT-736R transceivers that I'd like to upgrade from incandescent to LED backlighting. On the FT-736R, even when both of the meter lamps are functioning correctly, the meter is somewhat dim. Nice, bright LEDs would be a big improvement.

KG4CGC
06-25-2012, 11:28 PM
Cool look with the LEDs!

What kind of LEDs did you use? Did you have to do anything to them to get the light to diffuse and illuminate the meter face? I have a couple of old Yaesu FT-736R transceivers that I'd like to upgrade from incandescent to LED backlighting. On the FT-736R, even when both of the meter lamps are functioning correctly, the meter is somewhat dim. Nice, bright LEDs would be a big improvement.

I can say this much, make sure whatever you use does not have a focusing lens. I used a couple those once and it only illuminated a spot.

KA9MOT
06-26-2012, 12:28 AM
Cool look with the LEDs!

What kind of LEDs did you use? Did you have to do anything to them to get the light to diffuse and illuminate the meter face? I have a couple of old Yaesu FT-736R transceivers that I'd like to upgrade from incandescent to LED backlighting. On the FT-736R, even when both of the meter lamps are functioning correctly, the meter is somewhat dim. Nice, bright LEDs would be a big improvement.

Just a plain White superbright 5MM LED. One on each side pointing toward center. These are eBay LED that come with the proper resistor for 9-15V. I purchased 100 for a penny and waited a few weeks for them to come from China. If you'd like, tell me how many you need and I'll send ya some. I also have 3MM ones.

Oh Yeah, I also have red, green, blue, and yellow.