QCX 40 NO POWER OUTPUT #problem #40m #qcx40


Jim Allyn - N7JA
 

On 3/7/20 3:16 AM, Greg Walters via Groups.Io wrote:
It turns out an individual as offered to check it out for me. If he has no luck, and you are still interested, I'll let you know. 


     Still interested.  Please let me know if it becomes available.  Thanks.


Greg Walters
 

Thanks Jim,

It turns out an individual as offered to check it out for me. If he has no luck, and you are still interested, I'll let you know. 

Thanks again.

This thread can be put on hold for now. 

Thanks,
--
73,
Greg
KY4GW


Jim Allyn - N7JA
 

On 3/6/20 4:19 AM, Greg Walters via Groups.Io wrote:
If anyone would be interested in buying my broken QCX 40, I'd sell it cheap, you pay shipping. Maybe $20?

     I'm  interested.  You can email me off list, or whatever.

                                              Jim Allyn, N7JA


Greg Walters
 

Dave,

I tried to switch it with practice mode on and off. No difference.

I think the issue is way before the output areas. My voltages are off all over the board, as noted above. I can't even trust the on board test equipment because it gives me false readings. 

I don't have any fancy equipment to troubleshoot this better. I don't have a lot of time either. 

I'm half tempted to sell this broken thing to someone who has the time and tools to troubleshoot and fix it. I'll gladly buy and build another one as I love building these radios. This was the first one I built and has been running the longest. I think I have built 3 maybe 4 others since then. 

If anyone would be interested in buying my broken QCX 40, I'd sell it cheap, you pay shipping. Maybe $20? It is mounted in a custom box, but I'd pull it out of that so I could put the new 40 in there. The switches are all mounted both on and off board. The key input, and audio jack are mounted off board. The RF out is also off board. And the display is off board. I've attached a photo for anyone interested. 


--
73,
Greg
KY4GW


_Dave_AD0B
 

Is the radio in practice mode?

--
73
Dave
AD0B
Ham_Made_Keys


Greg Walters
 

Thanks Alan,

I should clarify that this rig worked perfectly until I let a friend borrow it. He plugged it in and tuned his antenna, but discovered it didn't have any power output. He tried my 20 meter rig also, and the same thing happened there. I did a "factory reset" on the 20 meter QCX and went back through the alignment of it. Not much changed, and it started putting power out. 5.3 watts or so with 13 volts. 

Since that worked on the 20 meter, I tried the same on this 40. I needed a lot of adjustment with the alignment. But still doesn't have any power out. 

I just checked receive, tunes appropriately, and receives nicely as before. I found a great very strong signal running 15-20 wpm and the decoder only put Ts on the screen for each dit or dah. 

Just out of curiosity, I tried checking out the RF while connected to the antenna. When I did, and keyed up, I lost receive. I cycled the power and receive came back. I keyed while not in test equipment, and it kept on with the receive. When I went to the menu and selected RF, without even checking, as soon as I keyed, the receive went out. 

This is a very interesting issue. 
--
73,
Greg
KY4GW


James Daldry W4JED
 

Hi, John

The voltage chart was written using the on-board "voltmeter". Since it has a relatively low input impedance it will pull down any voltage that has a high impedance source. Trust me - the actual voltage on pin 3 of IC8, as with any op amp wired as a voltage follower, is within a few microvolts of the voltage on pin 2. If you were to put a second voltmeter on IC8 pin 1 or 2 (they are connected together) while checking pin 3 with the on-board voltmeter you would find that all 3 pins would be at the same voltage - within microvolts. The reason the on-board meter is used is that that is the meter Hans knows that every QCX builder has on hand.

These op amps used in these radios have a DC open-loop gain of 140 db. That's more than the path loss between the 50000 watt FM radio station you are listening to and your radio antenna. Any difference in DC voltage between pin 2 and pin 3 is magnified by 140 DB.

73

Jim W4JED

On 2/26/20 8:27 AM, John Brock wrote:
It seems to me the voltage measurement table in the instruction manual is off in a  few instances. I am  looking through the receiver function on my 20M QCX. It seems too quiet to me. Don't get enough volume. Hear a few faint signals. I will admit my Icom isn't hearing a lot on 20M either..

So What confuses me on the voltage measurement table is the expected readings on the differential amps in the RCV chain. Like IC6, IC7, IC8 pins 2 and 3 are inputs to the amp. I think they should be equal. Same with pins 5 and 6. The manual says IC8 pin 2=2.46 while pin 3=0.65 for example.

Can someone set me straight on this?

Thanks
John
WA8US


Alan G4ZFQ
 

. Like IC6, IC7, IC8 pins 2 and 3 are inputs to the amp. I think they should be equal. Same with pins 5 and 6. The manual says IC8 pin 2=2.46 while pin 3=0.65 for
John,

They are equal.
The manual also says that readings were taken using the internal meter of the QCX that loads voltage sources and shows lower readings. Look at the schematic, IC8 pin 2 connects to IC8 pin 7 through 2 47K resistors. Therefore the simple built-in meter reads low because it's input resistance is only about 13K.
Ohm's Law my be used to confirm this.
A modern DVM has 10M input impedance giving readings that are very very close to actual voltage.

73 Alan G4ZFQ


John Brock
 

It seems to me the voltage measurement table in the instruction manual is off in a  few instances. I am  looking through the receiver function on my 20M QCX. It seems too quiet to me. Don't get enough volume. Hear a few faint signals. I will admit my Icom isn't hearing a lot on 20M either..

So What confuses me on the voltage measurement table is the expected readings on the differential amps in the RCV chain. Like IC6, IC7, IC8 pins 2 and 3 are inputs to the amp. I think they should be equal. Same with pins 5 and 6. The manual says IC8 pin 2=2.46 while pin 3=0.65 for example.

Can someone set me straight on this?

Thanks
John
WA8US


Alan G4ZFQ
 

With the Fluke, after keying up without using the on board first, the voltage stayed steady at 1.7, but if I checked it with the on board, it would read 0 just the same after keying.
Greg,

That appears to suggest the on board meter is wrong, maybe a bad soldered joint.

others were wildly off. Particularly IC7, 8, 9, and 10.
? You mean pins 5, 6, 7?
If so this is not possible, you say pin 1, 2, 3 are correct, look at the schematic, that section of the IC is fed from pin 7.

Then the LCD is off oddly, but still works fine.
I'm not sure, 2 of those connections are not used. Recheck, check soldering.

There is no RF at Q1, Q2, or Q3.
Check voltages on Q1, 2, 3, 6, RX and TX.

Is the radio dead?
Does the RX work? Have you gone through the alignment?

Do I need to scrap it and buy/build another one? (I don't mind, I love building these things.)
I'm sometimes a little upset if something I've built works with no problems! Part of the fun is finding the faults and learning in the process.
Nothing you can build is beyond repair.

One thing that many find is bad soldered joints, go over any that might look bad.

73 Alan G4ZFQ


Greg Walters
 

I don't know why that sent already...


OK. I posted this once with a few measurements using the on board test equipment the other day. 

Tonight, I began to go over it again taking all measurements, again with the on board test equipment. I began to get weird readings, so I broke out my Fluke 77III and checked those voltages again. They were definitely off. I checked Clk1 and with the on board it was varying, but went to 0 after I keyed up. It wouldn't show voltage again until I turned the radio off then back on again. With the Fluke, after keying up without using the on board first, the voltage stayed steady at 1.7, but if I checked it with the on board, it would read 0 just the same after keying. 

For example, Clk 0 on the on board, was varying between 1.53 and 1.81. On the Fluke, it was rock steady at 1.70. So, I used my Fluke to take all the measurements listed below. 

I will list them as they are on pages 128 and 129 of the manual. 
Here are all the measurements. This is with a power supply at 12.72 volts. 

Clk0--1.70
Clk1--1.70
C2--3.40
D2--4.95
T1 pins 1,2.3, & 4--0
T1 pin 5--2.53 
T1 pin 6--2.52
T1 pin 7--2.52
T1 pin 8--2.516
C43--2.516
C44--2.521
C45--2.521
C46--2.518

IC5
1--2.554
2--2.523
3--2.52
4--0
5--2.521
6--2.525
7--2.597
8--12.30

IC 6
1--2.594
2--2.593
3--2.593
4--0
5--2.594
6--2.596
7--2.596
8--12.30

IC7
1--2.549
2--2.550
3--2.551
4--0
5--1.552
6--1.553
7--1.553
8--12.30

IC8
1--2.527
2--2.527
3--2.506
4--0
5--2.537
6--2.552
7--2.552
8--12.30

IC9
1--4.74
2--4.74
3--4.71
4--0
5--2.493
6--2.508
7--2.509
8--12.30

IC10
1--6.17
2--6.17
3--6.17
4--0
5--6.13
6--6.13
7--6.17
8--12.30

LCD
1--0
2--4.89
3--0.78
4--4.85
5--0
6--0
7--4.88
8--0
9--4.88
10--0
11--0
12--4.87
13--0
14--0
15--4.96
16--0

Some measurements are dead on, some were slightly off and others were wildly off. Particularly IC7, 8, 9, and 10. Then the LCD is off oddly, but still works fine. 

There is no RF at Q1, Q2, or Q3. 

Is the radio dead? Do I need to scrap it and buy/build another one? (I don't mind, I love building these things.)

Any help to revive the radio would be greatly appreciated, if it isn't dead. 
--
73,
Greg
KY4GW


Greg Walters
 

OK. I posted this once with a few measurements using the on board test equipment. 

Tonight, I began to go over it again taking all measurements, again with the on board test equipment. I began to get weird readings, so I broke out my Fluke 77III and checked those voltages again. They were definitely off. I checked Clk1 and with the on board it was varying, but went to 0 after I keyed up. It wouldn't show voltage again until I turned the radio off then back on again. With the Fluke, after keying up without using the on board first, the voltage stayed steady at 1.7, but if I checked it with the on board, it would read 0 just the same after keying. 

For example, Clk 0 on the on board, was varying between 1.53 and 1.81. On the Fluke, it was rock steady at 1.70. So, I used my Fluke to take all the measurements listed below. 

I will list them as they are on pages 128 and 129 of the manual. 

Clk0--1.70
Clk1--1.70
C2--3.40
D2--4.95
T1 pins 1,2.3, & 4--0
T1 pin 5--2.53 
T1 pin 6--2.52
T1 pin 7--2.52
--
73,
Greg
KY4GW